Shimmy while braking. Yes, another thread.

[aom7]

This has been posted numerous times, but I figured I'd just add to the mix in case it helps someone out.

About 50k miles ago (9 years) I paid an indy to replace my front upper control arms (aka traction strut), Front Struts (oem BMW M-Sport), Idle Arm Bushing, Center/L/R Tie rods. Rotors (ATE and BMW OEM Pads) were replaced by me about 5 years/12,500 miles ago.

Car drove smoothly for years. I rarely drive it much nowadays, but took it for a drive 2 years ago and randomly it had that 45-55 shimmy, but only while braking. It was very smooth otherwise. But the rotors were only <10k miles so figured it wasn't that. I didn't mind it much since I've driven it around 1k a year since then. But during COVID, I have no where to go, so I figured it'd be a good time to track it down.

Looking at my repair logs, I noticed the front lower control arms were not replaced during my ownership. So I decided to try that first. It was Meyle branded unit, so I guess the previous owner replaced it. The bushings looked somewhat OK and the ball joints were I'd say 75% as tight as the new ones. After replacing them, it didn't really make much of a difference, the front end seemed tighter but the shake was still there while braking between 45-55.

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So I decided to replace the front upper control arms (aka Traction Strut) again (I figured 10 years and 50k miles of use were probably enough use) and when I pulled them off, I noticed the bushings were indeed cracked and the ball joints were slightly loose, but not a crazy amount. I also replaced the strut tower bearings on both side since I had the part anyway and with everything off, I was like 90% there.

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I also replaced the front sway bar endlinks and bushings, one end link boot was torn open, but even so, in general, it all seemed tight.

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Buttoned it all back up and now, the car had a brake shimmy at 65-55 mph! But the shimmy went away under 55 and didn't occur over 65. Slightly more intense too than the brake shimmy at 55-45.

[aom7]

So after pulling and prodding at all remaining parts (testing wheel bearings, idler arms) I decided to swap out the rotors and pads.

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Put in Zimmerman Coat-Z Rotors with OEM pads (which still had a lot of meat left on them, but I figured I didn't want to do this again by reusing the old pads in case there was something going on there). Took it for a drive... braking was smooth at all speeds and smooth as glass otherwise, yay!

Could it have been the rotors all along? Possibly, but not entirely, because of the cracks in the upper control arm bushings. I think the rotors may have amplified the problem, but it would have always been there due to the condition of the traction strut/upper control arm.

The carnage: (I also found a leak in my HCV pump, turns out it was the Oring... so I ordered a used one and rebuilt the whole thing. I also noticed my brake booster hose was a bit hard and flattened, so I replaced that as well)

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It's been an expensive week, but now I can take it up to speed and brake at any intensity and it's back to being smooth again! And it drives so tight (like pretty much zero play and immediate response). Coupled with my Servotronic Hack, it now has a tight/heavy German tank kind of feel, that I really like. It's dead straight on the freeway and S curves are much more precise and better weighted.

Maybe I'll drive it more now, lol! The only thing left is to tackle the TCG, which haven't been done (I'm at 140k miles), but I do have a leaking TC cover, so it's tempting to get it all done at the same time (there are no symptoms otherwise though and with the average 2-3k miles year, I'd have to weigh that carefully, if I do it, then I'm definitely never selling it).

Some observations: my "trusted" indy used aftermarket parts, Meyle, TRW, which is fine, but in reviewing my past invoices, he charged me what would have been the BMW full price part cost. So not too happy about that.

I used Lemforder and BMW parts for this. It was a bit pricey after all was said and done, but the money saved by doing it myself helps. I also prefer Lemforder over Meyle.

Of course, when tightening the control arm bushings, you have to jack up the suspension to put it at "ride height" and always follow proper brake bedding in procedures.

Time to go for a drive!

[purplecty]

Alot of good work here! Glad the issue was resolved fully when replacing the rotors. Those upper arms needed replacements regardless. The upper arms removed were Meyle, TRW or Lemforder? I prefer the Meyle specifically for their HD Upper control arm bushings...

[aom7]

Alot of good work here! Glad the issue was resolved fully when replacing the rotors. Those upper arms needed replacements regardless. The upper arms removed were Meyle, TRW or Lemforder? I prefer the Meyle specifically for their HD Upper control arm bushings...

Glad you concur, yeah sometimes I do this work and wonder did I go overboard and maybe replaced something that didn't even need to be changed? Yes, I think the Upper arms were due regardless. I went through every piece I replaced and noted the upper arms were TRW.

Still bummed about the pricing vs. aftermarket use by my indy. I've had a 10 year relationship with him and his family too.. Like back in 2011 he charged me $177 per side for the upper control arms, which turned out to be TRW, not sure what they were 10 years ago, but TRWs today are $66 a piece. BMW OEM are $204 today. My Lemforders were around $120. I don't see anything on the paperwork that says they'll use aftermarket parts either. I haven't used him in a few years since I've started doing all repairs and maintenance myself. So it's sort of a moot point. I guess, really, if you want something done right, gotta do it yourself!

I was eyeing Meyle HDs, but was worried as others have said they are a bit "harsher" since the bushings are a different type (bonded?). I wanted to keep a bit more OEM/compliant ride for this car. Funnily, now that the whole front end has been redone, I've been reminded how bad most of the roads in SoCal are. I'm feeling a lot of "road imperfections" LOL. The tightness is incredible though, I might actually start driving it a bit more now, lol.

[timothytimmons]

I had the shimmies. I replaced the front rotors and it went away. I used BMW rotors. I tried others rotors and it didn't go away.

[racer2086]

Glad you got that figured out. Arms and rotors. It's the chicken or the egg argument. Replacing them together means you should have good luck for a long time.

In regards to the TRW arms, at one point, TRW made suspension parts for BMW. I remember the centerlinks were TRW.

[aom7]

I'd like to add, if you happen to get any grease or other lubricants/dirt on the rotors after working on it, use some brakleen. I had a shimmy again a few weeks later, but had forgotten that I did some work around the area and must have grabbed the rotors without thinking. I was about to think I needed to just go with BMW rotors and do the job all over again.

But after using the brakleen, the braking was fine again.

[Mark3377]

Just been through that myself. Rotors are the main culprit when shimmy...ing. NEVER BUY CHEAP ROTORS. I almost crashed with bad shimmy going downhill on curves from Flagstaff, AZ towards Phoenix. The front end of the car seemed to jump up and down when braking. Never again.
Did Meyle HD for tension struts and ATE for rotors and pads. If shimmy ever comes back, it's gonna be Genuine rotors from then on.

[kotik]

i had an issue with shimmy when braking. the car had new 750 calipers that were purchased at autozone (or something). I was able to diagnose the problem to the calipers sticking and warping the rotor. I replaced the calipers with a set from a high end re-manufacturer, cut the rotors, and the problem went away. So crappy caliper rebuilds could be an issue.