When it comes to suspension maintenance, people often overlook the humble bump stop. Effectively a second rubber spring that prevents your car’s shocks and/or struts from bottoming out, these things take a lot of abuse and wear over the years. Let’s just say that you’re going to want to change your bump stops out before they’re in a sorry state.
My Boxster is reasonably youthful in human years but positively old in car years. It’s a 1999 model, turning 27 years old in Spring. You know what was 27 years old in 1999? A 1972 914. Still, it’s been practically coddled. Alright, maybe coddled isn’t the right word considering it’s had some paintwork and seen some dents, but quite well-maintained and kept out of the winter salt. It’s lived a largely indoor existence having covered the equivalent of 71,500 miles, and all the rubber parts are surprisingly mint. The bushings look good, the top hats and spring insulators aren’t dry-rotted, the end links were done recently, that sort of stuff.
However, I did notice that body control has been getting a little bit imprecise over freeway expansion joints, so I figured I’d change out the dampers for fresh ones while it’s parked up for the winter. Instead of the factory Bilsteins, I’m going with direct-replacement Koni Special Active dampers because they’re reasonably priced, work with the stock springs, and have a pretty trick piece of tech going on in each of them.
Most dampers, um, damp by controlling oil flow through a piston with a certain number and diameter of holes in it. That’s an oversimplification, but it means that the damping is essentially fixed to one set of compression values and one set of rebound values. The Koni Special Active dampers augment this with a special valve controlling a parallel flow of oil to the piston, increasing damping almost in time with piston movement. This means you get less damping when the damper shaft moves quickly (for example, over bumps on city streets) to keep the ride comfortable, and more damping when the damper shaft moves slowly – such as under hard braking and while cornering, to increase body control.
A wide variety of automakers use this tech, including Fiat on the 500 Abarth and Lamborghini on the Gallardo, partly because it’s sort of like fully mechanical adaptive damping. Considering Toronto’s road surfaces are generally awful, the fancy Konis sounded like just the ticket, even if I had to make a little modification. They all come in red, I drive a yellow car, and the last time I check, my driver’s licence doesn’t say Ronald McDonald. Bit of masking, bit of black spray paint, and good enough.
However, this story isn’t about dampers, it’s about bump stops, the little chunks of rubber or foam rubber that prevent the piston in a damper from simply slamming into the bottom of the damper body when you hit a really big bump. As I proceeded with the ever-sketchy use of spring compressors on the right front spring, removed the nut holding the strut mount on, and pulled off the boot, a certain horror awaited me. That aged, red bump stop looks a whole lot worse than it looked a couple of years ago, mostly because part of it is just gone.
No wonder the right front corner felt crashy over potholes this past year. Not only was the remaining bump stop substantially shorter than it should’ve been, time had also hardened it to the point where it was harder than expired Weetabix. Just look at the new bump stop on the right. Pliable, tall, complete.
While the old dampers definitely weren’t blown, the new dampers just damp more than the aged originals. Plus, I now have new bump stops, strut bearings, and strut mounts up front. While I’ll have to wait until Spring to see how they feel, the really challenging part is yet to come. See, doing the front dampers on these cars is fairly easy, but the rears demand five hours of book labor, including disconnecting the CV axles. Still, probably worth it.
So, if you drive an older car and haven’t checked your bump stops in a while, check them soon. New ones cost just a few dollars each, and might really help how your machine rides over heavily potholed roads, train tracks that are a little more severe than they look, that sort of stuff. They can also just age out quicker than your bushings, so even if you shake the wheel and everything seems fine, have a gander and see how those bump stops are doing.
Top graphic images: Thomas Hundal
Correction: Isn’t the proper Autopian name for these is Gummipuffers?
Thanks to 15 years in TX and FL, the front bump stops on my ’11 128i are *gone* – as in completely departed the car. Struts themselves are still perfectly fine, but it doesn’t make sense to take it all apart and not replace everything at this point. I have all the bits, just haven’t gotten the ’round tuit’. Kind of waiting for my new garage to be finished, but now that the weather here in SW FL is nice, will probably just do it in my current driveway. Not too much of an emergency here in FL where the roads are baby-butt smooth, and my car doesn’t have runflats. I am sure those things contribute to the bump stops (and everything else) getting blown out on BMWs.
Oddly, both rear struts blew out over the summer two years ago as the car was sitting parked in the garage while I was in Maine. Got back to FL, went for a drive and “woah” – this thing is riding like a Buick! Took a look and they were covered in oil. So blown that when I changed them and set them down on the driveway, all the oil just poured out of them. Weird. Bump stops were in chunks as pictured. Cheap and easy to fix though. Fronts not quite as cheap, definitely waaay more work. I just went with Sachs as fitted at the factory. I am perfectly fine with the stock ride/handling balance.
The bumpstops look like they might be the very same part as for the Boxster too.
Thomas I’m very interested in hearing how the Koni reds perform. We’ve got a high mileage C6 in our household that is new to us and desperately needs new shocks. The local club says Koni Yellow adjustable ones is the move, but they are nearly 2x the cost. If Koni Reds are good enough for Porsche, they are probably good enough for a high miles Vette.
If lowered bump stops are a routine maitenance item
“Most dampers, um, damp by controlling oil flow through a piston with a certain number and diameter of holes in it.”
Dampers gon’ damp.
Meh, bump stops are just a bandaid for under sprung / under damped suspension…
I thought so too, but once I got an NC Miata I realized after reading up on their suspension that the bumpstops are tall and are tuned to be a functioning part of the suspension when driving at the limit. These cars lean and then settle in. The bumpstops work in harmony with the springs.
On German cars, they are an integral part of the design of the suspension. It’s a way to add more progressive spring rates. And since Ze Germans are really good at the ride/handling balance thing, I figure they know what they are doing.
I put the Koni Special Actives on my ND Miata Club last year and I love them. The stock Bilstiens were a bit crashy over bumps, the car rides so much better now.
I kind of wish I had gone for those on my 128i. But I was only doing one end at that time, and between not wanting them mismatched and the added cost to do all four at once, my Inner Yankee Cheapskate directed me to go for the factory-spec OEM Sachs parts. it doesn’t have the sport suspension, so it’s not like it rides harshly to start with. When the time comes on my wagon though, it’s getting them. That car gets the best.
Konis are magic in general, if you can stomach the price. My Spitfire has Koni reds on it.
PSA one the same subject. Oftentimes when you install aftermarket springs on a car, the manufacturer will tell you to trim some of the bump stops off. Be careful if you do this – any jagged cutting will lead to the bump stop splitting and becoming useless much more quickly.
This is one of those things that you only have to think about on a car that is 20+ years old.
And it’s stuff like this that makes me biased toward getting a newer vehicle vs an older vehicle.
I noticed they were disintegrated on my 2014 T&C when the wheels were off for new tires to be installed, so I wonder if these are more of a “check every 5 years or so” inspection.
I’m actually surprised the brake shop didn’t try to sell me some when I was in there three years ago.
Meh, they are cheap and easy to replace. I wouldn’t let a $20 set of these stop you, and if you’re replacing the damper anyway then you would be pulling the one off the old damper to put on the new, even if they weren’t completely shot, I would just replace them if I were replacing my struts.
You can do a HELL of a lot of fettling of a car for what ONE payment is on a decent new one. I’ve owned my ’11 128i for 5.5 years now, it’s approaching 16 years old (built June ’10), and I have yet to spend a single grand on it including a new set of tires, in repairs and maintenance. That’s ONE car payment on a median priced car today. In *5.5* years. I paid cash for it in 2020, just shy of $17K with 46K on it from the BMW dealer in Wichita – all the money for a base 128i convertible then, but it’s been worth every penny. I have all the service records for the car, from new the PO put brakes on it and had the oil pan gasket done. It had a valve cover gasket and plugs and coils done under warranty. And a set of tires. Which I replaced because I hate runflats, I actually sold them on to a neighbor. They might have spent $3K at the dealer on that stuff – it was all done at the BMW dealer in Austin TX. They traded it in at the dealer in Wichita on a MINI. No idea why Wichita, that’s kind of a haul from Austin, but it was serviced in Austin just before it was traded in. All I have had to do is struts all around (rears let go, fronts only because the bump stops are gone), a windshield washer pump, HVAC blower (probably could have just lubed it, but it’s cheap and easy), and one radiator hose that I managed to break. Plus I replaced the sidemarkers, 3rd brake light, and radio ariel due to sun damage last year. Did the serp belt and tensioner preemptively when I bought the car, along with a battery. Otherwise, just fluids and filters in 5.5 years.
For my ordered-new ’11 BMW wagon, in the 55K miles from new my sole out-of-pocket actual repair has been a new battery. Otherwise just scheduled maintenance and tires, plus a couple of pre-emptive maintenance things. And a new windshield insurance paid for. I haven’t even had to do the brakes, there were done under maintenance warranty when it was 3.5yrs old due to the rotors rusting up while it was parked seaside for a week at a conference I was attending. The rust didn’t come off evenly and caused vibration. I was shocked BMW covered it, but they did. The good old days of the only thing you paid for the first four years was gas and tires. Even got wiper blades at every annual service. Big difference between the two cars is location. The poor 128i has been baking in the TX then FL sun and heat from new, the 328i has been in cold Maine from new. Sleeping away the winters in the garage other than the first one.
Oh I agree with what you say. But I’m not talking about buying new and having car payments. I’m talking about buying used and having a choice between a newer used car vs an older used car.
Nearly new used cars aren’t enough cheaper than actually new cars. To me it only makes sense to buy properly discounted new or buy 8-10 years old but low miles minty fresh like my convertible. You pay a premium for that, but you still save a ton of money.
FWIW my 2019 BMW’s bump stops are looking pretty haggard. 250k km on the odometer…I’d imagine there’s some combination of Number of Bumps Stopped + Age that ultimately determines lifespan.
I got mine 3D printed. Working a treat.
Hard to beat new bump stops to smooth out bumps while you’re bumping beats. I’ll be sure to bump up bump stop priority on my old beater.
Feels as good a time as any to throw this out there.
Very good point and always relevant. How’s life treating you? New car looks like a fun project.
Thanks for asking, pretty good overall! It’ll be a fun little flip, hopefully I can get it fixed and sold pretty quickly, a friend has an NC in need of some work for dirt cheap and I need to make some space for it. The desire for projects always outweighs the available space, but that’s probably for the good of my sanity.
How are you the Eunos doing these days?
Oh man keep me posted on that NC… My wife has started getting very nervous with me driving the kids around in the Eunos so it has me looking for a slightly safer daily, and I have spent far too many hours this week looking at everything out there, and the NC is very high on the list right now.
But the Eunos is fantastic, the cool weather lately has me falling more in love with it every day since I can leave the top down 90% of the time.
The Autopian discord will absolutely be flooded with NC content if it happens. I need to get more specific details but it’s a black over black NC1 base with a 6-speed swap, not sure on mileage. He got rear ended and the guy cut him a check for what he bought it for since he wanted to avoid getting dropped by insurance, so if I want it it’s mine for $1500, running and driving. If all goes well it’s just a rear quarter panel replacement at a body shop and used bumper away from being a usable Miata I can beat on absolutely guilt free, and if my dad ever wants to sell me his ND2, then I can find a new home for the NC. The project car cycle truly never ends.
I absolutely get where your wife is coming from on the Eunos, being in the mountains with tons of trucks I got very sketched out with my NA6 back when I had it. Driving at night was agony with being constantly blinded, and I was acutely aware that any accident would be deeply painful. It was so great to drive and I miss it, but I enjoy the relative security of newer Miata’s.
I look forward to it! If you do pass on it or decide against it, please shoot me pics, I might be interested.
Yeah the old cars provide about as much safety as wet toilet paper so I get it. But I have to convince her that an NC is safe enough…. I’m also looking at the IS250C, but manuals in those are hard to come by, and man they are heavy. Going from 2200lbs to nearly 4k would be a big change! There’s always the 996…