Bushing Longevity?

[wyatth]

I'm wondering how long different suspension bushings and components are expected to last. I know it varies by driving style and road conditions, but there can be a range, and some components simply wear faster/earlier.
My new-to-me E90 ZCP has 48K and I've now pushed it over a variety of conditions to get a deep feel for it. Shocks, springs, subframe bushings, powertrain mounts, etc. all feel fresh and great. But there's a serious steering wheel shimmy under heavy breaking. Is it normal for FTABs to wear this fast? Or is this normal even on fresh OE bushings and monoballs are the answer? Any other components that I should keep an eye on? I am coming from an E46 M3 which goes through FCABs/RTABs in <50K.

[MSY]

Probably not FCAB. If it's never been tracked then bushings on this car are good until 75k to 100k. I've had 3 e92 m3s. All got near 100k.

[slicer]

Front Caster Rod Bushings are notoriously weak on the E92. I would change them to monoball; especially for someone living in CA. The other bushings that are nice to replace are the sub frame and diff bushings. It's beneficial to firm things up in those areas.

[wyatth]

I’ve never heard of the “front caster rod bushings.” Is this a/k/a the front tension/brake arm? Monoballs are a common swap here. The Rogue black bushings also looks appealing.

I don’t want diff whine, so I’ll stick with OE diff mounts. But I’ll probably go with aluminum subframe mounts when the stocks are worn. I don’t see the need to replace them preventively, given the labor involved and my application.

[EricSMG]

Wyatt - at 33k I have no shimmy under hard braking, so either you've got worn FTABs or warped/deposited front rotors (the latter would also be noticeable under very light braking, though).

I would be weary of monoball FTABs on this chassis as I find the stock front suspension to be borderline too harsh over sharp hits like deep manhole covers - considerably more so than the 46M over the same hits. This is even after new PS4S tires. I'd imagine the solid tension arm bushings to increase this sharpness dramatically just as poly/solid FCABs do on the 46M.... could be wrong though.

[wyatth]

Brakes are good.
That’s why the Rogue blacks look appealing. Most people report no NVH from monoballs here, so the blacks should be stealth while still limiting deflection under load.

[EricSMG]

Originally Posted by wyatth

Brakes are good.
That’s why the Rogue blacks look appealing. Most people report no NVH from monoballs here, so the blacks should be stealth while still limiting deflection under load.

Worth a shot, sure, it's just that I'm not getting any shimmy with stock parts so food for thought.

These cars sure do handle good, though, eh? Damn good. The amount of front grip is impressive and the chassis is supremely balanced.

Looking up the RE blacks now....

Edit: ah yes, these aren't monoballs (my assumption until now) at all but urethane insert/aluminum housing bushings. Very nice and good price, too. These could be very nice for a street car.

[slicer]

Originally Posted by wyatth

I've never heard of the "front caster rod bushings." Is this a/k/a the front tension/brake arm? Monoballs are a common swap here. The Rogue black bushings also looks appealing.

I don't want diff whine, so I'll stick with OE diff mounts. But I'll probably go with aluminum subframe mounts when the stocks are worn. I don't see the need to replace them preventively, given the labor involved and my application.

Correct.

http://www.splparts.com/products/spl...x-f8x-bmw.html

Diff whine is minimal with Poweflex Purple.

[slicer]

Originally Posted by EricSMG

Wyatt - at 33k I have no shimmy under hard braking, so either you've got worn FTABs or warped/deposited front rotors (the latter would also be noticeable under very light braking, though).

I would be weary of monoball FTABs on this chassis as I find the stock front suspension to be borderline too harsh over sharp hits like deep manhole covers - considerably more so than the 46M over the same hits. This is even after new PS4S tires. I'd imagine the solid tension arm bushings to increase this sharpness dramatically just as poly/solid FCABs do on the 46M.... could be wrong though.

Front monoball change resulted in zero NVH increase on the e92 in my experience. I installed Delrin FCAB on my e46 and it was noisey. Not the case on the e92 as it's a different suspension design.

[EricSMG]

Originally Posted by slicer

Front monoball change resulted in zero NVH increase on the e92 in my experience. I installed Delrin FCAB on my e46 and it was noisey. Not the case on the e92 as it's a different suspension design.

Yep, I understand it's a different design. However, the FTABs complete control the fore/aft movement of the wheels and thus take 100% of the initial impact load just as the FCABs do on the 46M.

As such, any reduction in fore/aft compliance of the wheel will increase impact harshness (not noise) over sharp hits. There is simply no way around this. It may be a non-issue for some people but will be or others.

The question is not if they will increase harshness but rather how much.

[wyatth]

These things handle fabulously in stock form, I am just fine tuning to match my preferences, style, and roads.

I will inspect my current bushings soon and go from there (along with an alignment). Perhaps they're worn, in which case I will just replace with OE and see how fresh stuff feels. If they look fine, maybe I give the RE blacks a go. A lot of people say the monoballs feel like stock under normal driving. I did like the Dinan monoballs RTABs on the 46, but did not want to repeat the TCK plates up front. Threading the needle on this one.
Was just hoping people would chime in with their experience on general suspension wear.

[slicer]

Originally Posted by EricSMG

Yep, I understand it's a different design. However, the FTABs complete control the fore/aft movement of the wheels and thus take 100% of the initial impact load just as the FCABs do on the 46M.

As such, any reduction in fore/aft compliance of the wheel will increase impact harshness (not noise) over sharp hits. There is simply no way around this. It may be a non-issue for some people but will be or others.

The question is not if they will increase harshness but rather how much.

I don't agree. The e46 design is significantly different and that bushing design on the e46 makes it more susceptible to NVH. I have had both, ran Delrin on e46 and monoball on e92. I immediately detected more NVH with e46. Immediately detected nothing with the e92 monoball.

Try it out and report back. It's certainly possible that you are more sensitive and will disagree with me. I'm surprised you have a strong opinion considering you have never experimented with the monoball bushing change. I should clarify that changing that one single bushing did not increase NVH. I did detect an increase in NVH when I went to full monoball on the entire front and rear suspension. In other words I agree that rubber bushings are more compliant in general. However, converting that one bushing to monoball did not cause a detectable increase in NVH in my experience.

[ebisu8]

I'll have to concur with Slicer here. When I ran my Fall Line Monoballs, I experienced zero increase in NVH. Even when I moved to my full front SPL Arm conversion, there wasn't even an increase in NV. There was an increase in H but it wasn't truly harsh, it more so made it tight/responsive feel.

[EricSMG]

Originally Posted by slicer

I don't agree. The e46 design is significantly different and that bushing design on the e46 makes it more susceptible to NVH. I have had both, ran Delrin on e46 and monoball on e92. I immediately detected more NVH with e46. Immediately detected nothing with the e92 monoball.

Try it out and report back. It's certainly possible that you are more sensitive and will disagree with me. I'm surprised you have a strong opinion considering you have never experimented with the monoball bushing change. I should clarify that changing that one single bushing did not increase NVH. I did detect an increase in NVH when I went to full monoball on the entire front and rear suspension. In other words I agree that rubber bushings are more compliant in general. However, converting that one bushing to monoball did not cause a detectable increase in NVH in my experience.

Again, the designs may be different but the two bushings share the same single purpose in life - to control 100% of the fore/aft movement of the front wheels. When you hit a bump the wheel gets thrust backwards with immense force - this force is absorbed by the FTAB/FCAB bushing.

To be clear, I'm not saying you're wrong but I think we have different definitions of what NVH is. Are you really saying that there was "zero" difference over sharp edges, lane dots, etc.? I'm not talking about noise, I'm talking about energy transfer to the cabin over sharp hits.

My angle is simply that any time you replace rubber with a solid bushing where the bushing is in the direct load path of impacts, there will be a comfort tradeoff.

Even changing tires affects NVH. I just replaced worn RE71s with new PS4S' and noticed a dramatic decrease in harshness over sharp edges. Both the tires and the FTABs are 'front line' items - nothing else takes the initial hit. The dampers are secondary and come after the initial spike.

All that said, I am open to the idea that I'm wrong in this case (hoping, actually)... it's just that experience has taught me that there's no free lunch with hard bushings. The problem here is that harshness is very subjective - some people hate it and others call it "more responsive" and the truth is always somewhere in the middle. My only goal in conversations like these is to get at the real truth.

[Richbot]

Shimmy under braking could also be a tire issue. Check your wear on the fronts. Won't necessary come up on a balancer, as a tire belt failure etc. will often only show a symptom when it's loaded

I have not seen any evidence on here that there are any bushings that are weak links other than the front tension arms. Maybe somebody can show me a post-mortem on some of the other bushes, particularly the rear trailing arm bushings attached to the stamped steel piece, those things I could see deciding to call it quits after a while

So if the tires are ok, and you're sure you don't have a pad deposit issue on the front rotors, I'd look at the tension rod. But only after eliminating those possibilities

I chased a noise/vibration on the front end for a bit at about 65k miles, even changed front hubs, until I realized the tires were where the noise was coming from (I had eliminated tires because both my sets of tires made about the same noise, silly me). I have 109,000 on the car now and the bushings are all original and there is no measurable "prybar test" slop in any of them as of the last check a few thousand ago

[slicer]

Originally Posted by EricSMG

Again, the designs may be different but the two bushings share the same single purpose in life - to control 100% of the fore/aft movement of the front wheels. When you hit a bump the wheel gets thrust backwards with immense force - this force is absorbed by the FTAB/FCAB bushing.

To be clear, I'm not saying you're wrong but I think we have different definitions of what NVH is. Are you really saying that there was "zero" difference over sharp edges, lane dots, etc.? I'm not talking about noise, I'm talking about energy transfer to the cabin over sharp hits.

My angle is simply that any time you replace rubber with a solid bushing where the bushing is in the direct load path of impacts, there will be a comfort tradeoff.

Even changing tires affects NVH. I just replaced worn RE71s with new PS4S' and noticed a dramatic decrease in harshness over sharp edges. Both the tires and the FTABs are 'front line' items - nothing else takes the initial hit. The dampers are secondary and come after the initial spike.

All that said, I am open to the idea that I'm wrong in this case (hoping, actually)... it's just that experience has taught me that there's no free lunch with hard bushings. The problem here is that harshness is very subjective - some people hate it and others call it "more responsive" and the truth is always somewhere in the middle. My only goal in conversations like these is to get at the real truth.

First of all - please don't take my responses in the wrong way. No negativity intended. I enjoy a healthy discussion about geeky car things.

I have not detected extra harshness (the "H" in NVH). The other variable that I should add is that I have a high quality coil-over that nicely controls movement. Conceptually rubber bushings are used in order to keep NVH down. When you go to monoball you are asking the shocks and springs to control all of the movement since the suspension joints are now allowed to move more freely and precisely. At the extreme (100% monoball bushings throughout) this allows you to obtain a more precise and consistent alignment because you don't have the suspension moving around under load. Plus you are able to tune your suspension behavior more precisely utilizing your shocks / springs because you don't have the variable of sloppy rubber bushings. I would imagine (but can't confirm as I did not experiment with this) that a stock shock would not control movement as well as a high quality shock such as the Ohlins TTX that I'm using. Especially that initial punch from an abrupt bump or dip. Therefore that could be a variable that is allowing me avoid experiencing a change in NVH.

In the example of the E46 that main bushing isn't even available as a monoball because the design doesn't allow for it. At least that's my understanding. The e92 design moves more freely in it's design. Plus the e46 arm itself has multiple loads on it. It is a C-shaped arm with 3 bushings attached to it. The E92 arm in question has one bushing on each end and likely doesn't have as much work to do.

Picture of the E46 bushing and control arm:

[wyatth]

Eric, have you tried monoball RTABs on the 46? I am hoping these are like that. Those added precision (kept toe in line) without NV or much H. I support these even on softer, DD cars, and loved mine. But for FCABs I stayed stock on that car. I am hoping that the FTABs on the E9x are like the 46's RTABs.

[Richbot]

They take loads in pretty much the same way and same directions as an RTAB, just, you know, on the front

[EricSMG]

Originally Posted by slicer

First of all - please don't take my responses in the wrong way. No negativity intended. I enjoy a healthy discussion about geeky car things.

I have not detected extra harshness (the "H" in NVH). The other variable that I should add is that I have a high quality coil-over that nicely controls movement. Conceptually rubber bushings are used in order to keep NVH down. When you go to monoball you are asking the shocks and springs to control all of the movement since the suspension joints are now allowed to move more freely and precisely. At the extreme (100% monoball bushings throughout) this allows you to obtain a more precise and consistent alignment because you don't have the suspension moving around under load. Plus you are able to tune your suspension behavior more precisely utilizing your shocks / springs because you don't have the variable of sloppy rubber bushings. I would imagine (but can't confirm as I did not experiment with this) that a stock shock would not control movement as well as a high quality shock such as the Ohlins TTX that I'm using. Especially that initial punch from an abrupt bump or dip. Therefore that could be a variable that is allowing me avoid experiencing a change in NVH.

In the example of the E46 that main bushing isn't even available as a monoball because the design doesn't allow for it. At least that's my understanding. The e92 design moves more freely in it's design. Plus the e46 arm itself has multiple loads on it. It is a C-shaped arm with 3 bushings attached to it. The E92 arm in question has one bushing on each end and likely doesn't have as much work to do.

Well, I'll take your word for it albeit cautiously optimistic Fyi - Turner now makes a true monoball FCAB for the 46M and it's been getting rave reviews about the precision it adds with a fair amount of NVH tradeoff.

And, yes - great discussion and no intent to debate or argue. It's just that after all these years I tend to take "no NVH" comments pretty lightly unless the person is able to intelligently justify the claim, which you've done well.

Good stuff.

Originally Posted by wyatth

Eric, have you tried monoball RTABs on the 46? I am hoping these are like that. Those added precision (kept toe in line) without NV or much H. I support these even on softer, DD cars, and loved mine. But for FCABs I stayed stock on that car. I am hoping that the FTABs on the E9x are like the 46's RTABs.

I haven't. That said, I'd bet they're similar to poly RTABs in terms of NVH = not bad. Notable, but nothing major.

At the front of the car, though.... things seems to be amplified greatly as we learned with poly FCABS. Lane dots make the dashboard sounds like it's going to explode, ha!

[slicer]

Originally Posted by EricSMG

Well, I'll take your word for it albeit cautiously optimistic Fyi - Turner now makes a true monoball FCAB for the 46M and it's been getting rave reviews about the precision it adds with a fair amount of NVH tradeoff.

And, yes - great discussion and no intent to debate or argue. It's just that after all these years I tend to take "no NVH" comments pretty lightly unless the person is able to intelligently justify the claim, which you've done well.

Good stuff.

Good point; I share your skepticism of forum opinions. I do my best to leave some room for error in what I say for that reason. I acknowledge that I might be less sensitive to NVH than others. My car is not a daily and I have accumulated a number of compromises with the changes made to the car (full monoball, no cats, no resonators, low ride height, lots of camber, race seats, cage, etc). It's to the point that it would drive me crazy as daily in its current form. However the front monoball conversion was one of my first modifications.

[SYT_Shadow]

I have the BW front brake bushings. Different people call them different things but I think we're all talking about the same thing
I noticed zero or close to zero change in both M3s.

I tracked each car at least one season with the stock bushing and never had shimmies or weird things happen, but still swapped them out.

The purple diff bushings are a completely different story. Do not do that on a pure street car.
I was convinced by the forum to move to solid subframe bushings and purple diff bushings and holy moly, thank God i only did that on the track car because it would drive me completely bananas on the street one

[wyatth]

^ Why'd you swap if no shimmy on stock bushings?
I don't want to go looking for things to swap or ways to make the car firmer, and did not plan on these. It was only after I felt the shimmy ...
I'm sure it's not the brakes and I would be surprised if it's the tires. I will inspect the stock bushings closer, get an alignment, and will go from there.