Millions of semi-tractors hit the road every single year to keep America running with everything from the mail and Amazon packages to gasoline and milk. Truckers are often unsung heroes, and our lives wouldn’t be the same without them. But they couldn’t do that work without the tool of their trade, and if you look closely, you’ll discover semi-tractors are brilliant pieces of engineering. Trucks pretty much do everything for a specific reason that helps them perform the jobs they’re tasked with, and you may have wondered why some trucks make a sort of rapid-fire staccato noise when they need to slow down? The answer is the compression release engine brake, most commonly known as the Jake Brake. This system allows the truck’s engine to do the deceleration rather than the service brakes, and there’s some great history behind it.
It was during a recent Autopian staff meeting that I learned that some car enthusiasts aren’t necessarily trucking enthusiasts. Many of my colleagues have been car junkies and auto writers for decades. They can identify cars through just a picture of a taillight and explain the principles of a four-stroke engine in detail. However, while semi-tractors are road-going vehicles that share the highway with cars, there’s quite a bit that they do differently from your everyday Ford. As such, my colleagues wonder why semi-tractors do some things a certain way differently than cars do. If my auto writer co-workers have such a curiosity, I have to imagine that a lot of other drivers do, too!
Some folks describe the sound of a compression release engine brake as that of “machine gun fire.” You might have also noticed that many communities in America have banned the use of these types of brakes. If you’ve ever driven around suburbia, there’s a chance you’ve seen white signs saying “No Engine Brake.” These signs aren’t saying that you cannot use your car’s engine to slow down. Instead, they’re telling truckers to use a form of braking that isn’t a Jake Brake due to the noise. Take a listen for yourself:
But why do trucks using a compression release engine brake sound so loud in the first place? It comes down to the process utilized to briefly use the engine’s strokes as an air compressor.
The original compression release engine brake was officially called the Jacobs Engine Brake Retarder from the Jacobs Manufacturing Company. The system’s slang nickname, the Jake Brake, would also become a registered mark of Jacobs. The Jake Brake would become such an influential device that all compression release engine brake systems, regardless of their maker, would be called a “Jake Brake.” It’s like how people call just about any facial tissue a “Kleenex” even if it’s from a different brand.
From The Father Of The Modern American Diesel
The inventor of the Jake Brake was not the Jacobs Manufacturing Company, but the man often considered to be the father of the modern American diesel engine, Clessie Lyle Cummins. Here’s what I wrote about Clessie in the past:
By the 1910s, Cummins was involved in a number of exciting developments. In 1911, He was on the pit crew for the Marmon Wasp, the racecar driven by Ray Harroun to win the inaugural Indianapolis 500. During this time, Cummins also went to work for banker William G. Irwin, acting as his chauffeur and mechanic. Irwin would aid Cummins in his future exploits, including opening a machine shop in 1915. By 1918, the Cummins machine shop was busy enough to justify purchasing an old cereal mill to expand. Cummins Machine Works spanned 5,000 square feet of space.
Just a year later, Cummins would open and become the president of the Cummins Engine Company. It was that same year when Cummins began to see a future in diesel. The first diesels in America arrived in 1911 when Busch-Sulzer began building engines. Still, when Cummins arrived on the scene in 1919, the diesel was still a niche in America. Anyway, in 1919, Cummins began building his first diesel engines based on a license from R.M. Hvid Co. These were small diesels, good for just 6 HP, which was enough for agricultural use.
It wouldn’t take long for Cummins to create a diesel of his own design. Cummins earned a patent for a direct-injection diesel design in 1921 and in 1924, that engine was put into production as the Model F. 1929 marked a major shift for Cummins. Until then, the brand put its engines to work in the agriculture and marine industries. However, the economy had crashed and with it was demand for engines to put into yachts.
The company that Clessie built was in danger of failing, and Clessie used the threat of closure to make what would become a historic shift. Cummins planted a Model U into a 1925 Packard limousine and decided to show America that diesel had a place in cars. That car would drive some 800 miles from Indiana to the 1930 New York Auto Show, consuming only $1.38 ($26.37 in 2026) in diesel fuel to get there.
That alone proved that diesel was not to be overlooked, but Cummins decided to double down on proving diesel’s worth in automotive applications. The company followed up its shenanigans in 1930 by entering a diesel-powered racecar into the 1931 Indianapolis 500. Cummins didn’t care about winning. It just wanted to prove that a diesel car could complete an entire race without stopping for fuel. Amazingly, the company’s bet paid off and the car never stopped. By the end of the race, it even placed in a respectable 13th out of 33 entrants. Not bad when Cummins wasn’t even trying to win.
The Race That Changed Clessie
That race wasn’t the only motorsport that Clessie entered his company into that year. As a paper from Clessie’s son, Lyle, and published by the American Society of Mechanical Engineers (ASME) writes, Clessie Cummins would join forces with Ford Moyer and Dave Evans to drive a Cummins-powered truck from New York to Los Angeles to set a new truck speed record. Like many of Cummins’ bombastic activities back then, the drive was just as much of a test as it was a publicity stunt. The truck was loaded up with the Cummins Indy 500 racer and dispatched on its drive across America.
Something that the Cummins team learned in the early days of equipping cars with diesel engines was that diesels don’t have natural engine braking that’s as strong as a gasoline engine.
Generally, engine braking in a gasoline engine in a car works by lifting off the throttle. This closes the throttle body. When the pistons enter their intake strokes, instead of getting a large charge of fresh air, the highly restricted airflow causes the piston to pull a vacuum. Now, the pistons have to work against that vacuum. You can then downshift to produce more drag within the drivetrain. When used well, engine braking can reduce your car’s dependency on its brakes during a long downgrade.
Basic diesel engines work on a different principle. In a common gasoline engine, the throttle body helps the engine inject just the right amount of air for an optimal air-fuel ratio for engine speed and power. In a basic diesel, the engine can gulp down as much air as it wants, and throttle control is achieved through the metering of fuel. Thus, a throttle body isn’t needed. The flipside of this is that there isn’t a throttle body that can be closed to facilitate engine braking.
In the early days of diesel trucks, this meant leaning on the vehicle’s service brakes to slow down on steep mountain grades. Of course, friction brakes generate heat over time and can fade or fail when overheated. This was the unfortunate reality for Clessie and his crew driving their truck across America. Yet, the men held it together most of the way across America until they found themselves on Cajon Pass on U.S. Route 66 heading into San Bernardino, California. The pass had a long section of gravel road that was steep and windy, a nightmare scenario for a vehicle relying only on service brakes. Even worse? The road was bisected by a railroad grade crossing.
From Clessie Cummins, via ASME:
“About dusk on the fifth day, we reached the top of Cajon Pass west of Barstow, California. Before retiring to the sleeping compartment, Dave had warned me against this thirty-five mile stretch of mountainous downgrade. ‘Wake up Ford and me when you get to Kayhone Pass,’ I had understood him to say, ‘I don’t want to be in this box when you start down that twister with the kind of brakes we’ve got.’ I had heard but not seen, my Spanish being nonexistent, the word Cajon failed to register when the sign appeared. Soon, however, I realized my error. The brakes wouldn’t hold. Now running in third gear, I tried desperately to get into a lower speed. Nothing doing. I saw I would just have to ride it out.
Well down the long grade by now, I suddenly saw something moving across the road ahead. There was a long dark shadow and then a red glow flared in the sky. I realized with new alarm that a freight train was cutting across our path. The truck roared on. Dave and Ford screamed bloody murder in the compartment behind me. And I clung to that steering wheel like a madman. Had Mack Sennett been on hand with a movie camera, he would have gotten enough footage for one of his famous Keystone Kops features.
As we raced inexorably toward the crossing and doom, the train’s caboose loomed out of the darkness. Its red lights cleared the highway just as we reached the tracks. We had escaped certain death by inches.”
The men would set a new coast-to-coast truck speed record of 97 hours and 20 minutes over 3,214 miles. The gas engines in the race were faster, but had to stop more often. It was an impressive accomplishment, but the thought of nearly dying in a crash followed Clessie. He thought that there had to be some way to make diesel engines as effective at stopping as they are at going.
Getting Diesels To Slow Down
Clessie would discover the answer 24 years later, after he retired from his namesake company. From the ASME:
It was also in 1955 that Clessie enticed his youngest son, Lyle, a graduate mechanical engineer, to join forces and form the large concern which he named Centco (short for Cummins Enterprises Company), a name chosen to keep the household accounts separate from Clessie’s ventures in the basement. The basement was actually an area that included an office with a view, a soon to be equipped machine shop with the usual lathes, milling machine, etc. and a four-car garage. Another member of the Centco team, added in 1957, was Ray Hansen. Hansen was an able machinist, welder, and sheet metal bender whose hobby was building and racing sports cars.
Lyle’s initial effort was expended on thermodynamic analyses to prove Clessie’s idea of turning the engine into a compressor really would provide sufficient retarding potential. The answer was an unqualified “yes,” but how to do it? One scheme was to clutch-in a high pressure pump and a timed distributor to carry hydraulic force to a slave piston, which in turn would act on the exhaust valve to open it at the proper point on the compression stroke. A second method considered was to use a multi-plunger pump hydraulically timed to act on the slave piston. While both of these methods could be made to work, neither was considered a best solution.
An idea for a practical method, emphasizing the heat of the invention, came to Clessie in 1957 during a sleepless night in a Phoenix, Arizona hotel room. The idea that hit Clessie revolved around taking advantage of perfectly timed motion already built into Cummins and Detroit Diesel engines; these engines have a third cam on the main camshaft that activates the fuel injector of each cylinder. A simple retrofit mechanism should be able to transfer this motion to open the exhaust valve. The idea was jotted down on a bed-side scratch pad and was telephoned back to son Lyle in Sausalito early the next morning. By the time the vacationing Stella and Clessie Cummins returned home, layouts of possible design solutions were waiting, albeit in retrospect, they were more complicated than proved to be necessary.
While researching if anyone else had done this before, Clessie did find patents going back to 1918 for different designs that opened a valve near the end of the compression stroke of the engine. Some of those designs were to slow the engine down, while others were to make starting easier. However, none of them were commercially viable because they required heavy modifications to existing engines. What made Clessie’s idea different was that his device would be added to the motions that the engine already made.
The ASME continues:
How best to transfer the injector cam motion was developed during the next two years. The simplest method was to tie together mechanically the injector and exhaust rocker levers with a one-way locking connection so that the injector cam could open the exhaust valve, but the exhaust cam could not actuate the injector plunger. The experimental construction consisted of blocks welded to standard rocker levers over the rocker shaft bosses. The injector rocker block had a deep curved slot open to the rear. Engine oil pressure, controlled by a threeway solenoid valve and acting through a hydraulic piston, forced the pin into the exhaust rocker lever slot. Engagement occurred during the exhaust, intake, and part of the compression strokes on a catch-as-catch-can basis.
Because the Cummins fuel system at the time tended to inject some fuel into the cylinder, even during coasting conditions, it was necessary to add another hydraulically-operated piston to hold the injector plunger seated whenever the locking pin was engaged. This piston had a wedge-shaped outer end acting against an extension to the injector plunger spring retainer and bridging around the injector rocker level.
Clessie’s Invention Worked
The test rig for Cummins’ engine brake was a 1955 Chevrolet Suburban wagon. In 1956, the GM engine was tossed out for a Cummins JN-6, 401 cubic-inch straight-six diesel good for 125 HP. Apparently, this engine was so big and heavy that the Suburban needed heavier springs up front in addition to a front clip elongated by 11 inches just to house the beast. The modification work was handled by a Rolls-Royce dealer who was a friend of Clessie. The completed rig weighed 6,500 pounds.
The test mule had shown that Clessie’s invention had merit. If the truck was forced down a 30 percent grade in second gear with the engine running at its governed RPM limit, the compression brake got the engine down to idle in less than 200 yards. Later, Cummins would put guests in the truck and then send it down San Francisco’s famously steep hills. The passengers would be terrified, and then impressed when the truck came to a safe crawl without Clessie touching the friction brakes.
After the tests in the Suburban were a smashing success, Clessie scaled the system up and installed it into a Cummins NHRS, a 855 cubic-inch straight-six supercharged diesel making 300 HP. Clessie had a couple of these engines in his yacht, which made testing his ideas cheaper than having a proper research and development facility. Later, Clessie’s design would be modified by upgrading to hydraulically transferring the injector motion rather than mechanically.
Once Clessie had a design locked in, he put it into semi-trucks on the road, starting in 1959 with rigs operated by the Sheldon Oil Company of California. On the initial test run, a Sheldon Oil truck descended down the Sierras on U.S. Highway 50 near Lake Tahoe. Usually, the drivers coming down this grade would have to miss the turn into the asphaltic oil plant on the road because the brakes were heavily faded, hot, and ineffective.
This time, however, by using Clessie’s invention, the truck slowed down so well using the engine alone that the driver touched the brakes only twice. The turn into the plant was made easily, and the truck’s brake drums were only warm to the touch. After enough testing, it was clear that Clessie had invented something that not only made trucking easier but also significantly safer.
Clessie began marketing his idea, and as ASME writes, he was contractually obligated to give his namesake company the first dibs on the tech. Yet, Cummins, as well as two other diesel engine manufacturers, were not convinced about the reliability of the device or its commercial viability and rejected Clessie. Yep, the company that Clessie founded shut the door on him.
Jacobs, which was then the world’s largest manufacturer of drill chucks, eventually caught wind of the Clessie engine brake and cut a deal with Clessie in December 1959. The design was refined further, put into more trucks, and tested. By 1961, the Jacobs Engine Brake Retarder hit the market, eventually becoming a staple of American trucking.
How A Modern Jake Brake Works
The Jacobs Engine Brake, as it’s marketed today, is now housed under the Cummins umbrella. Cummins offers a simplified explanation of how it works if the above sounded a bit too consuming.
Cummins says that, when the driver in the cab flicks a switch or pulls a lever to activate the Jake brake, the engine works normally through its intake cycle. Then, during the compression cycle, the exhaust valves are closed at first. Then the Jake Brake opens the exhaust valves when the piston gets near the top of its compression stroke. Check out this handy video:
Instead of compressing and then combusting an air-fuel mixture, the compressed air now fires out of the exhaust system. Meanwhile, the tons of energy in the truck continue to push the engine to compress more air. The engine is not fueled during this process. As the cycle continues over and over, the energy of the moving truck decays, slowing it down.
Cummins says that a Jacobs Engine Brake or Jacobs Compression Release Brake can provide up to 85 percent of a truck’s braking needs and can slow a modern truck from 55 mph to 43 mph, 30 percent faster than service brakes alone. Of course, the benefits aren’t just in slowing trucks down fast, but also in reducing service brake wear and fade. You’ll still need to use your service brakes to come to a complete stop, but now you don’t have to tackle a mountain pass with your service brakes alone.
This graphic illustrates what happens during the compression cycle when the Jake Brake is on versus off:
While the Jake Brake and its many variations are the most famous devices for slowing a commercial vehicle down, there are other ways to get the job done. Some diesel engines have an exhaust brake, which consists of a butterfly valve in the exhaust to restrict exhaust flow and create heavy backpressure, slowing the engine down. Exhaust brakes are less effective than Jake Brakes, but are quieter. Some manufacturers use exhaust brakes, some use Jake Brakes, and some use combinations of both.
There are also hydraulic or electric retarders that you can find inside of commercial transmissions or drivelines that slow the vehicle by using the driveline or transmission as a brake. The five-speed ZF 5HP592C housed within my 2002 Nova Bus RTS-06 has a transmission retarder, and I found it amazingly effective at slowing the bus down through the Ozarks without me needing to touch the service brakes at all.
Semi-tractors aren’t the only vehicles with Jake Brakes, either, as you can find them in other vehicles utilizing heavy diesel engines like motorhomes.
Why Jake Brakes Can Be Loud
Alright, so you know what Jake Brakes are, how they came to be, and why they’re used. But why are they so loud? Admittedly, the sound of a Jake Brake is an acquired taste, like the sound of a two-stroke gas engine, a two-stroke diesel, or a V-twin. Jake Brakes can sound rather satisfying, though the subject of when they get used can be controversial.
In the past, Jacobs Compression Release Brakes were known for being extraordinarily loud and giving off machine gun-like sounds. This was a byproduct of the Jake Brake effectively temporarily converting the engine into an air compressor. The sudden rush of highly compressed air thunders into the exhaust manifold, carrying shockwaves with it. Some air-powered construction tools, like jackhammers, have a similar phenomenon. Here’s another sound clip:
Cummins says that, since 1978, the federal government has required that the vehicles that reach customers meet strict noise level requirements. Likewise, Cummins says, modern emissions equipment has made Jake Brakes far quieter. Perhaps so quiet that a typical driver might not even realize that a truck is using its Jake Brake on a downgrade.
However, some owner-operators delete their mufflers and straight-pipe their rigs. The consequence is that when they fire the Jake Brake, the characteristic pops of the system can be heard by motorists and people at home. Sometimes you’ll even hear a Jake Brake in situations where you’d think it might not be that necessary, such as trucks driving around truck stops or rest areas. You’ll also hear them when some trucks trim speed for lower in-town speed limits, places where there might not be a hill in sight. This is, at least in part, why many local jurisdictions ban the use of semi-truck engine brake devices.
This also pisses off some other truckers, too, because a lot of them are trying to sleep while someone’s just cruising through the truck stop with their Jake Brake on. As a result, there is a sort of a push among some truckers and companies to convince others to either stop making their trucks loud, or to at least refrain from using Jake Brakes around town or other places where people want some quiet time.
An Invention That Changed Trucking
All of that aside, the Jake Brake was perhaps one of the greatest innovations in trucking. Now, truckers who have an engine braking system don’t have to rely entirely on their brakes, which can overheat and fade on long downgrades. Instead, they can flip a lever, depress the clutch, and let the Jake Brake do most of the work.
While there haven’t been published safety statistics about Jake Brakes that I could find, it’s not hard to find a trucker who swears by their system. I got to experience the value of slowing down without the use of service brakes in my own bus and can attest that it’s amazing, at least to someone who spends most of their time in cars and motorcycles.
It’s all the more incredible that the impetus of the Jake Brake was what could have been a fatal truck accident. If it hadn’t been for Clessie Cummins nearly smashing into a train while racing a truck across the country, I wonder how trucking could have been different. At any rate, the next time you’re coasting your car down a mountain and hear a truck firing off tons of pops, now you know why. That trucker is getting safely down the grade without relying entirely on their brakes!
Top graphic image: Kenworth
I did a stint at Detroit Diesel’s engineering and manufacturing center in Detroit for about a year and it was fascinating. they make the DD15 and DD16 liter engines there. Connecting rods as long as your arm, mechanics need a crane to move heads around since they are over 4 feet long. The plant is super old, and they have an engine dyno room that was grandfathered in as it wouldn’t meet modern standards. A large room with over 30 engine dynos, maybe half are running at any given time, with 15-16 liter engines going through the paces. Its super hot and loud, they have bullet proof glass panels on rollers in case you need to work next to a running engine.
One thing that blew me away is they’d do durability tests at 100% load at an RPM above redline. They’d set it where the engine is basically screaming and walk away for lunch and the engine would take it like a champ. I asked one of the engineers how this can happen (who worked on the mercedes s500 engine at daimler) he said a typical car engine spends less than 1% of its time at redline. While in places like Mexico, a truck is typically overloaded then has to drive into the mountains. The driver is basically flooring it the entire time. It would be like bouncing your car off the rev limiter for hours. Different use cases, these huge engines are just built to live at the extremes of their operating conditions.
I had a few-month-long stint at the Cummins Tech Center, running the cold temp test trailer. We had weekly test result reviews, and I was amused to see one based on a Boston bus drive cycle…it was a square wave of throttle input from 0-100-0-100 over and over again.
Seems they’re lot like aircraft engines that way.
Yes. Diesel engines are most efficient when kept at a steady RPM for long periods, rather than lots of RPM changes.
Piston aircraft engines and stationary engines (and related power equipment engines) are sort of specialties in gasoline engine designs, since gas engines are typically best at handling frequent and wide RPM changes.
I mean, beyond the rich fueling on spool-up with diesels, that’s true for spark-ignition as well since you can tune intake/exhaust for a narrow range.
I was thinking more of engines designed to operate mostly near peak rated power, rather than mostly at a small fraction. I guess it’s that way across the spectrum when you compare industrial and consumer goods. That $5000 Hobart stand mixer can mix batch after batch of dough while a $50 Target countertop model is going to melt its plastic gears if you do your second batch too soon after the first.
A lifetime ago I worked at a research facility. While I was there, the engineer lab had a Mack Diesel on a dyno, screaming away at full load for days. I really don’t know how many hours it ran, but it seemed like more than a week. The only time it stopped was for oil changes.
Huh, I’ve just been zigging away from the flame spurts in the Fire Swamp.
They are a marvel of engineering and a boon to safely navigate mountain passes. They are also a huge creator of noise pollution and their overuse makes the world a worse place.
I love the deep dive, but I cannot stand Jake Brakes. I know they serve a purpose, but the fact some truckers choose to use them in cities is a class A jackass move. I feel so bad for the poor saps who live near interstates.
Mercedes, maybe you can do a piece on a Telma electromagnetic brake sometime – that seems like a much better solution for the modern era.
Retired Fireman here. Most of our Fire Engines now have Jake Brakes, with a switch that the driver controls: Off, Low, Medium and High. We use these settings based on the road conditions, etc. No Jake Brake is needed on slippery roads, etc.
The cool things is that on our ladder truck there is no Jake Brake. There is a large magnet on the drive shaft that works like a Jake Brake, but without the noise. It is so much smoother when letting off of the gas that the Jake Brake.
That’s a clever use of magnets.
That’s an electromagnetic retarder — something that’s been a lot more common and popular in Europe for a while.
Jake brakes are the bane of my existence.
I live in Brooklyn about 2 blocks from the bqe, which is the local highway. Jake brakes are ABSOLUTELY prohibited as there are apartments that abut the highway (we’re talking windows 10’ from the road surface for a few miles) for almost half of the entire length of the bqe.
And all day and night, I hear the burble of Jake brakes. 2 blocks away. In 14 years, ive never even bothered opening my windows, as they’re loud enough with the windows closed to interrupt a conversation with anyone that isn’t used to them. Half of my building (25 units) uses noise cancelling headphones. And we’re 2 blocks away. Back of the napkin, I’d easily day 50-100k people hear them at a db level that is illegal in an urban environment.
When I lived 4 blocks away from the bqe, they were a small nuisance. I can’t imagine what it’s like for people who live directly next to the highway.
Elected officials have come and gone that have claimed that they’d ticket. No dice.
There’s a reason why signs say NO JAKE BRAKES in every small town off 80 between Reno and Omaha: one truck can wake up an entire hamlet.
You’re hearing Dump Trucks. IN the Tri-State area dump truck fleets are a point of pride and as such are mostly extensively modified, straight pipes being a huge one. I knew several drivers that wore earplugs rather than quiet the pipes. As an aside, in the NYC area,the more modded and chromed out the truck (dump, RoRo, Mixer, sanitation), the more likely it is owned and operated by an organization that is most assuredly “NOT the Boy Scouts”
I’m guessing you’re looking forward to EV trucks becoming widespread, can’t hear regen braking.
You should hear the sounds that my diesel chainsaw makes when I let the engine brake on it rip.
Great article as always Mercedes!
I’ve been vaguely aware of how Jake Brakes work for a while, but another explainer is always appreciated.
However, one sentence towards the end confuses me; “Instead, they can flip a lever, depress the clutch, and let the Jake Brake do most of the work.”
I think you ideally need a truck in gear to get any benefit of engine braking?
Correct. Per the embedded Jacobs video, you select the Jake Braking intensity, release the clutch, and let off the throttle.
I didn’t watch the video but maybe they misspoke and meant to say “releasing” the clutch. In real life, you can flip on the rocker switch at any time and the jakes work whenever you’re off the throttle. EXCEPT when the clutch pedal is depressed, because then the engine isn’t connected to the rest of the drivetrain.
Mercedes, I drove truck for years and I’ve never fully understood how the Jake worked. I put the noise down to “the energy has to go somewhere”. Now I understand it, thanks to your informative and entertaining post. Thank you.
One can even put a Jake on a Cummins Ram, at least the first year model – if it has three pedals. 😉 I try to be nice to the neighbors, but everyone knew when I first arrived, nursing the 11,000 pound trailer downhill to the stop at the bottom. She’s real fine, my 409.
I loved engine braking on my 1953 Ariel Red Hunter 500cc one cylinder motorcycle: Pops to start off car alarms and 1 foot flames from the exhaust at night.
OK, now cover the sliding sleeve system on the Holset turbo of the Cummins B-series 6.7L diesel. It’s a variable nozzle (VNT) boost control device AND an exhaust brake – all in one!
You know, the first time I saw the headline I didn’t click because I went “yeah, I know what a Jake brake is.” But I’m so glad I clicked because I learned:
1) Somewhere along the line I was told it was “Jacobson” and it’s actually “Jacobs.”
2) It’s the damn drill chuck company! Whose name is still stamped on all my chucks.
3) I never knew diesels didn’t have a throttle body. Now all those runaway motor videos make a lot more sense.
Thanks!
I believe most modern diesels do now have a throttle body, but it’s normally open rather than normally closed like on gassers. It’s there both for emissions-related duty and to reduce NVH at shutdown.
“However, some owner-operators delete their mufflers and straight-pipe their rigs.”
… because they’re assholes.
Seriously… Jake Brake noise as well as the use of illegal straight unmuffled pipes (with the police rarely enforce the laws surrounding the excess noise) is yet another reason why I look forward to battery electric vehicles replacing ICEs.
You would not be fond of my fleet, however I respect your opinion sir. However until we’re on a more formal basis, I prefer you to refer to me as Jacob Brakington the III
If your fleet consists of muffler deletes and straight pipes The Sandwich wouldn’t be the only one not fond of it.
Hey I get it different strokes for different folks. It is noteworthy however that a turbocharger makes for a pretty decent muffler, even without a cat in many cases.
The issue is one person’s harmless fun is another’s public menace. Volume, location, time of day, tolerance level, weather, reflective surfaces, etc, all that weigh in. Opening up a loud car on an isolated dry lakebed or even a freeway is very different from doing the same in a crowded urban setting or in a suburban neighborhood in the middle of the night. By modifying an exhaust and/or blasting noise in inappropriate settings that person assumes all the responsibility and liability for whatever comes of those choices. If that means torches, pitchforks, exhaust pipe potatoes, penalties and tickets they’ve only themselves to blame. They should expect no sympathy either. I’d say the vast majority of people despise modified exhausts, especially other peoples modified exhausts.
The easiest solution for noise enthusiasts is of course to revert to a stock exhaust with a pre muffler bleed pipe resonator to duct the excess noise into the cabin instead. Then those enthusiasts can crank up the windows and play that noise till their own ears bleed while disturbing no-one else.
I agree. The BMW pop tune squad, the VQ Bros, and Harley brotherhood guys seem to be the worst offenders of what u laid out above.
Last couple times I was pulled over for speeding both cops were complimenting the sound of the V.
One asked me to rev it up loud which was cool. He then proceeded to show me pictures of his cammed Pontiac G8 GT.
Im a fan of the loud stuff but time and place is key.
Ugh… Somebody in my neighborhood has a BMW with a pop tune. It sounds like ass. And my house is on a sweeping corner, so it’s always decelerating/accelerating as it passes by. And my home office workspace is on the second floor facing the road, so I get the full “benefit” of it every time.
I don’t mind the sound of high-performance engines and exhausts; a little exhaust crackle on lift-off is fine. But this thing just sounds like it’s just got a serious ignition timing problem.
Interestingly, enough, I have a similar office set up. Facing the street , 2nd floor, on a bend in the road, so lots of deceleration.
Regardless of the exhaust, etc.… The amount of bad ass fast performance vehicles available to the younger set these days is quite amazing.
Yeah, these are the same jerks who run straight-piped Harleys and other unnecessarily loud garbage…because their mothers never loved them. The joke is on these guys though: they’ll have significant hearing loss by age 40.
I insist on having quality mufflers on my old IH iron for many reasons, one of which is that I don’t want to be a dick, and another for the hearing loss issue. I’ve already got some serious tinnitus from live music and machinery in my youth, and I don’t want to lose anymore.
I had an exhaust leak on one side in the Scout for a month or so last year and I could not get it fixed fast enough.
I’m not sure what rank I’d put these in but my least favorite 3 straight piped engines I hear regularly would be: Uncorked 4 bangers, Nissan VQ bros, and Harleys. The bikes might be #1 as I hear them all summer and fall here in MKE area.
Thank you Mercedes for this great article! about 25 years ago I was in Greece for a college study abroad kinda thingy, and we took a large coach bus (I think it was Iveco or Mann or Volvo, but can’t recall) to tour the country. I sat in the first couple rows as the stadium seating gave us great views of the road ahead, and I kept noticing the driver operating a lever on the curves. We asked him what that was, he said it was a supplemental braking system. I’d never seen it on American busses before or after that time, but after reading this it must have been a Jake Brake.
It probably wasn’t a Jake Brake, but a transmission retarder (unless the transmission was a manual) and or you heard the stattico exhaust note. I rode in the front passenger seat in a National Park Service bus at Mesa Verde. The driver would operate a lever on the downhills and he told me it was a retarder built into the transmission.
If it was a bus on a European chassis, it would have been a retarder, not a Jake brake. They’re always operated with that separate little lever either on the column, like an additional stalk, or mounted on the dash.
Depending on the engine manufacturer, some will engage an exhaust brake (also not a true Jake) in addition to the hydraulic or electromagnetic transmission or driveshaft retarder — at all or only some levels of the retarder lever’s settings.
A few of the buses I drove in university had actual Jake Brakes fitted, none had transmission retarders – but these were older buses 30-odd years ago, transmission retarders may not even have been a thing then. With proper mufflers on the engine you don’t really hear them. But as the article says, there are a number of ways to get the same end result.
One thing to note – you can’t leave the Jakes engaged on a manual – if you do, they kick in when you lift the throttle to shift, crashing the engine to idle and making it impossible to shift the non-syncro transmissions US trucks and buses typically have. BTDT, oops. If you can’t find ’em, grind ’em, and if that doesn’t work, well, stop and try again from scratch.
Interesting. This was 2001 maybe, just before 9/11. haven’t had as much fun as I did flying to Greece out of Philly…just a nonstop party where I was actually handed a jug of wine by a passenger I did know, exhorting me to chug it in a language I did not understand. But I digress…
The bus was one of those large tour buses with the large, hanging body toned (in this case white) full length external mirrors on both sides. Transmission was automatic, and the lever he kept pulling on just before hitting the hairpins and down-grades reminded me of the Ferrari 360 reverse lever. The bus made no appreciable extra noise when he pulled the lever. Inside it was plush and had 2×2 seating. And I remember that the bus was new! Our driver was very possessive and careful with it, and he lost his shit when another car scraped the side of it at a service station.
Good times!
Either a transmission retarder or exhaust brake – most, if not all, Japanese & Hyundai trucks use exhaust brakes and they are much, much quieter.
In NZ, lots of towns have the “No Engine Braking” sign on the outskirts, which covers both Jake brakes and exhaust brakes, seeing as we have a mix of Japanese, Korean, European and US trucks (also some Chinese, but they’re large confined to coaches and city BEV commuter buses – truckers are wary of unproven Chinese truck brands, so not a big demand).
LOL – I’ve had a few flights like that.
Never had a bus new enough to care that much about though. I drove for my university (best work study job EVER), and it was quite a collection of misfit toys picked up on the cheap. But well maintained by the university motor pool guys.
If it was silent, then it was definitely a hydraulic or electromagnetic retarder.
An exhaust brake is a lot quieter than a Jake brake, but there’s still some noise and vibration inside the vehicle when it kicks in.
I remember the coaches I rode in Spain in the 80s (usually Spanish-licensed Setra bodies with Spanish Pegaso engines) had retarders. The exhaust brake would kick in at the last one or two notches on the retarder intensity lever — which you’d feel if some car driver brake-checked on a curve or descent.
Thanks! I guess Mercedes needs to to a piece on these braking apparatus now 🙂
In Europe today Scania have an automated non-synchro gearbox that uses the Jake Brake system to slow down the engine on changing up gears allowing lightning fast gear changes. Even in the late 70’s we had Cummins engines with Jake Brakes and Fuller 9 or 13 speed non synchro gears that we could do super fast up-changes because we didn’t have to wait for the engine revs to drop.
Detroit Diesel basically owned the coach industry in the US in the 70s and 80s – I never drove a bus with anything else in it. My fleet was a mix of automatics and 5spd Spicer manuals (first was really only for climbing trees, normally start in second). I have seen Eagle buses with 10 and up speed boxes, but more than five was unusual. Only a few had Jakes – this was the nearly dead-flat midwest so nice to have but not a necessity. The couple that did originated out West where they were a lot more important! My favorite, a beast of an MCI with an 8v92TA and 5spd had them. Always tried to get that one for the football team trips. Those boys were HEAVY, LOL.
The other side of the fleet was a motley mix of ancient GM Fishbowl transit busses. With every mix and match of engine and automatic transmission those things were ever sold with, from “no speeds” and 6-71s to three speeds with 8v71s. One lonely 4spd manual 8v71 too, but that had coach seats so didn’t do the transit routes normally. Thank God for that, and that I only very rarely had to drive the transit busses as a fill-in driver. Booooooooring. Right after I graduated and was gone from school the whole fleet had to be retired due to ADA accessibility requirements – none of them had wheelchair lifts or anything. They had a grant coming to do it my last semester.
yeah It was def a euro brand, come to think of likely a Scania…i might have to dig out some old photos and see if i’ve got the bus in them!
Hino – Toyota’s commercial truck builders – had tranny retarders in the late 90’s. To one used to Jakes, they seemed useless.
To be fair, although I’m far from a Toyota fan a Hino is a good truck to drive. I drove out of Maine, so the washer fluid reservoir next to the heater core was a wonderful feature, and one I wish would become universal.
A friend had a Hino tilt-bed wrecker. He liked it, but parts were spendy. Amusingly my Mercedes has a coolant coil in the windshield washer tank – not really all that useful in Florida, but a nice touch.
I can stab a downshift with the jakes on just fine, but yeah, upshifting is no bueno.
Some truckers will leave the jakes on while cruising, so in case of an unexpected emergency stop, it’s already slowing down before they even hit the whoa pedal.
I always did that too when I had them. I think Detroits have even less engine braking than 4-stroke diesels do. Every little bit helps!
Amazing coverage of one of my favourite features of a semi truck! I still argue that Cat has the best sounding one.
Ooh, is this my queue to write an article on transmission retarders? They’re a damn slick piece of tech.
Yes!
Yes please!
That sounds awesome! Email Matt or David, however, because I cannot approve of such things.
First you won’t sell me the MGF, now you won’t approve my articles. I can only take so much heartbreak!
You’re lucky you cover my favourite subjects nearly exclusively.
Cruising around Iowa, there were always “No Engine Braking” signs when you’d come to a town. I would respect them, even in my Dodge Ram Diesel (Exhaust brake, but still loud).
I designed the engine brake for the Mack and Volvo 11 liter and 16 liter engines sold in North America. They’re thermodynamically interesting things – I wrote my undergrad thesis on the topic. AMA!
Wow that is cool 🙂
I fucking love this community.
My question: Why the christ is your injector torque down process so complicated?
Hah! My glib answer is that it is originally a European designed engine, not an American one. More seriously, I’m pretty sure it is an artifact of work that was done to cure injector cup leaks from the early days of these engines when they were running the cam driven EUI injectors at high injection pressures to keep smoke down in the 2006-7 model year range. The injector hold down clamps are a bit dainty because of packaging constraints, so we couldn’t just brute force holding the injector down. Ultimately switching to conical seat injector cups fixed it, but not before writing several PhDs on installation procedures that would produce the most consistent clamping forces.
As someone who worked at International during the Maxxforce years, you don’t have to elaborate on Euro engines in North American markets. “Oh, we don’t need DEF, we’ll just run EIGHTY PERCENT DUTY CYCLE on the EGR.”
EGR cooler replacements helped buy my house.
Those EGR coolers/filters got Dan Ustian a fancy golden parachute also. And I had to get a new job.
Were you in Indy? There’s a little mini-museum in the basement of the Bona Thompson Memorial Center in Irvington. There are a few fridges and lawn mowers, plus some engines, cranks, and mementos from the plant. It’s pretty sad.
I sent some photos to my boss at the time – I work for Cummins and we’ve had several International transplants.
International Harvester – Irvington Historical Society
Nah, I just worked for a dealership up here in Canada, eh.
Top-feed injectors take all the fun out of a side-feed torque procedure! It feels like cheating.
What makes them thermodynamically interesting as opposed to just kinda neat mechanically?
Well, when I first started learning about how they work, I had a hard time believing that releasing cylinder pressure at the top of the compression stroke would slow down a truck. After all, a lawnmower engine uses compression release to make pull starting them easier! The fallacy in that logic is actually caused by the pull rope; when you compress air in the cylinder on the compression stroke, the (rigidly attached) crank gets almost all that energy back again on the expansion stroke – it basically acts as an air spring. But pulling a pull starter doesn’t act the same, since the rope goes slack rather than pushing your arm back, if that makes sense. Jake brakes work by absorbing all that compression work then blowing it out the stack rather than recovering it on the expansion stroke.
There are more interesting details (like the fact that hot air absorbs more energy than cold air, even if both cases compress to the same final pressure, or that raising the initial pressure by turbocharging will absorb more energy, even if you are still only compressing to the same final pressure…) that are all implied by the ideal gas law, but you’d never think of it without putting pen to paper and working them out. At least they weren’t obvious to me at the beginning.
Using an engine as a compressor was well known since mono block air compressors using the front of a Model A Ford had been around since the 20s. Cummins’ genius was doing it dynamically where mono block compressors permanently modified part of the engine.
There are quieter alternatives that are often used in Europe like the Telma electric retarded that uses magnets around the driveshaft to feed a resistor bank like the dynamic brake on a locomotive. Some automatic transmissions incorporate a hydraulic retarder
The main reason Jakes are loud is the same reason so many Harleys are loud – people fit loud exhausts on them. They really don’t need to be much louder than the engine itself is. Of course, those straight piped diesels are loud as hell under load too.
The Telma magnetic retarder was very heavy, around 1000 lbs and would get so hot on long downgrades that they glowed red at night and dimmed your headlights by draining your batteries. I had a 25 seat school-bus with one fitted. In Spain they even fitted à rear drive axle on their semi trailers with a Telma on the diff so that they got double the safety.
I know I’ve seen signs that specifically say “No Jake Brakes” but only rarely. I just checked Wikipedia, and it cites an article from 2000 that said Jacobs filed trademark infringement claims against anyone use “Jake Brake” instead of more generic language.
I’m guessing governments got the message, but there are still independent places like campgrounds where the owners use whatever language they feel like.
Were I a commercial operation, I would not tempt Jacob’s lawyers.
Thanks for the article! I had always thought Jake Brakes were just some kind of flap you’d slap over the exhaust to start creating massive backpressure in the exhaust. The reality is a lot cooler!
Those exist, as a butterfly valve in the tail pipe but are just called exhaust brakes.
Ok right, that was mentioned in the article! Glad to hear that my idea wasn’t entirely wrong, but also glad to hear about a different system!
I live on the side of a ridge in West Virginia, and I heat by wood stove as much as I can. I keep my wood on the porch, so I can add some to the stove in the night, when it’s coldest. I can hear some trucker using his Jake brake at 4:30 in the morning all the time, and it’s extremely loud and obnoxious, and he is on a small dirt road, not on the highway. I can truthfully say that I hate Jake brakes! Obviously, it’s hilly around where I live, and you can hear them for miles away. I understand the usefulness, but either these locals have removed most or all of their mufflers, or they just love the sound and love being assholes!
I definitely understand why there are noise complaints near major urban/suburban areas…
Three years ago I was at a Holiday Inn Express near a major airport in Mexico with my family including a 1 year old. Never heard a single plane coming or going but all night I heard semis decelerating by using their Jake Brakes as if the windows were wide open. Not a fun night.
I cannot imaging hearing them on a constant basis and can only hope they become background noise.
Reasonable. Were I your neighbor you’d hear me at 4:30pm but not am. Shame people can’t think of others.
My uncle was a trucker. I’ve known what Jake Brakes were ever since I was 13 years old and he let me pull the lever. It was like the damn thing dropped an anchor.
And you know those signs you see entering a small town that say “NO ENGINE BRAKING”? Yeah, they mean Jake Brakes.
We talk about best car chase movies all of the time, but never discuss trucking movies. If you’ve never watched Convoy, you are doing a disservice to your brain.
Let them truckers roll, 10-4!
Convoy is good but I am partial to Smokey and the Bandit as I always wanted to be the Snowman more than the Bandit.
The opening theme song from Smokey and the Bandit (Jerry Reed – The legend) is still one of best trucker songs I ever heard.
https://www.youtube.com/watch?v=L0OflL0INck
Need Mercedes to next do a deep dive on a “Georgia overdrive” as described in the classic “Six Days on the Road” by Dave Dudley
Indeed. You can tell by my profile pic that this is my favorite movie by a long shot, and it has bugged me for years how everybody is all “East Bound And Down,” while I’m over here like, hello, “The Legend”?
Well he got to the bottom safe and sound
Everybody asked Bandit how he made it down
He said, “Folks, when the truck picked up too much speed
I just run alongside it and drug my feet”
That is, as the kids call it these days, to the best of my limited modern day pop culture knowledge, a “bar.”
Agreed on this being a trucker movie, but SatB is all about that Screaming Chicken and it’s really the main character, not Snowman. The Duel and Maximum Overdrive are a couple others where the tractors are the main characters even if they are the antagonists and more anti-trucker.
Point of order: There was no trucker in “Maximum Overdrive,” only the truck.
Ha, very true. Appreciate your correction:)
When discussing trucking films you can’t forget the ’98 classic Black Dog, starring Patrick Swayzee, Randy Travis, and Meatloaf.
https://www.youtube.com/watch?v=LJDyr3xiDrE
Yes! Black Dog is fantastic!
I hear big trucks on the highway 1/3 mile from me engaging these regularly. The sound travels.
EV drive systems solve this, but at great cost. For long-haul trucking, I think a PHEV diesel with a smaller 300-ish horsepower 4-cylinder diesel acting as a generator in a series-hybrid configuration would be the ideal. EV tractor-trailers have massive range reductions in mountainous areas because they are already efficient, and cannot take advantage of thermal efficiency increasing with load as gasoline or diesel rigs can. Do this in an aerodynamically efficient package, ala Luigi Colani’s designs, and we might be able to get 20 mpg fully-loaded big rigs, at least when and where they need to use liquid fuels at all.
You are right on the ball.
Welcome to what Edison Motors is trying to do.
Fun fact on regenerative braking in heavy vehicles, our buses often have to disable it when the SoC is too high, as the batteries don’t yet have the capacity to absorb the braking current.
Also, because we exclusively use permanent magnet motors (efficiency and power output), you can’t tow or push them more than about 500 feet without pulling the axles or driveshaft.
Permanent magnet motors create current when they rotate, no matter what. So they’re super good at making fires out of the wires if you try to tow them.
I have PMDC motors in my electric velomobiles, and that translates to eddy current losses, heat buildup, and a whirring noise when I pedal them with the motor(s) disabled. You can run a small amount of current to cancel these losses out as long as your control system can do Field Oriented Control, but that requires energy from the battery pack. A motor with narrow laminations, say around 0.2-0.25mm, would be the most cost-effective means to minimize those losses. You can go thinner, but you’ll see greatly increased costs, diminished reductions in losses, and potentially a loss in torque density as the laminations get thinner and take up more volume.
We really need inexpensive switched reluctance motor designs. The control systems are expensive to develop, but there are no cogging torque losses, and the potential for efficiency is arguably greater than the standard PMDC systems.
The 2026 Subaru Solterra EV will give an advisory in the dash about reduced regenerative braking effectiveness if you drive it with a fully charged traction battery. My old Chevy Bolt EV had a setting – sometimes called hilltop mode – in which charging would stop at 90% SOC. This way, if you lived at the top of a long, steep hill, regen braking would still work immediately after an overnight charge.
Edison Motors in Canada is working on the trucks of your dreams. Though they specialize in logging trucks (and other vocational uses), not so much highway trucks – great application because you get lots of regenerative braking going down the mountain, and then can use that battery stored energy going back up, and it’s almost always loads down, empties up in the logging industy in the Western Canada mountains. Also designing their trucks for extreme repairability and simplicity. They have a great YouTube channel.
Fun fact, they’re not just used in trucks. Many RVs use semi chassis and have them as well. I had a 40ft RV Class A based on a Kenworth chassis with a Detroit Diesel power plant. The Jake brakes were incredibly useful for the mountains in Arizona.
Oh snap, I knew that but didn’t add it. A few thoughts get lost in a 4,000-word saga! I’ll add that in, too. 🙂
Correction: it was a Freightliner chassis. I had a Kenworth previously
Very few RVs are on semi chassis (basically just the handful that are front engine and have semi cabs). Most Class A pushers are on a couple of generic chassis specifically for RVs from Freightliner, International and a couple other makes, a couple higher-end ones make their own, and the REALLY high-end are based on monocoque coach buses from Prevost, etc. All of them that are diesels can optionally have Jakes or the sundry transmission retarders. The ones on actual semi chassis or are buses have actual inline six HD truck engines, the rest typically have the same smaller engines as diesel pickups or medium-duty truck engines, various Cummins or GM/ Ford engines. LOTS cheaper than the real thing.
One oddity of the RV industry is that currently nobody makes a gas engine pusher chassis, AFAIK. But I expect that to change as diesels get less popular due to the expense of meeting emissions regs. A pusher with one of the big, modern relatively efficient gas V8s would be a nice compromise, especially if the price of diesel stays high. Cheaper up front, much cheaper to maintain, and the cheaper fuel would largely offset the increased consumption of it – and most RVs don’t hammer on miles the way a semi does anyway. Having the engine 40ft behind you is a lot nicer than having it next to you, no matter what fuel it uses. For those reasons, gas school buses are making a major comeback after decades of them being nearly universally diesels.
Sounds like a nice rig you had! All the coaches I drove back in the day but one were Detroits – love them!
The upcoming Cummins B7.2L will have them available, as well.