GC Shims with OEM RTAB - passenger side rtab keeps sliding out of the arm??? HELP

[Daydream M3]

Hi guys,

Ive recently had a problem with my passenger side rtab in that the rubber bushing keeps sliding (partially) out of the rear trailing arm. This inadvertently causes a "knocking/ thumping" noise when I turn corners rather hard (usually leftward turns). Also, the noise manifests itself when accelerating hard through first and then switching to second ... thats when the noise appears as if the rear trailing arm is shifting and hitting the mounting point where it bolts in to.

Ive had the OEM bushing replaced several times and it still backs out usually after a hard track event or lapping day. Id imagine under normal street driving I wouldnt have the problem.

I have the GC shims in there as well and thought it would be a remedy for the rta moving in the mounting point.

IS IT POSSIBLE, for the rear trailing arm (where the bushing goes) to wear down and cause the oem bushing to not seat correctly? Also, what stops the oem bushing from staying in the rear trailing arm? or is it merely just hammered into the rear trailing arm hard?

Wondering if anyone has had the same experience? Someone said switch to powerflex poly rtab because they have a lip on either end that would prevent the rtab from sliding out of the rta although.... i dont think the lip would stop the bushing from coming out under such hard loads anyways..... there has to be something else that is holding the rtab in place that my tech is not doing correctly.

Any advice would help
Thanks in advance

[Goofynick6]

Sounds like you need a new bracket the rtab goes into..

[Daydream M3]

thanks for the reply goofy nick

so its the black piece that typically bolts into the rear subframe of the car?

[vmwerks]

Yes... actually it sounds like you need a new trailing arm since that is where the bushing is pressed. Try a set of Powerflex rtab's, they float and will not slide out since they have the spacers built in.

[4ZPN]

A trailing arm is about $500 last time I checked, so I would suggest getting the Powerflex RTABs cuz it's a lot cheaper.

[Daydream M3]

thanks for the reply guys

So once I get the polyurethane powerflex bushings, I shouldnt have my rear trailing arm shifting anymore because of the built in lips on the bushings?

Two more questions then

1) if the poly rear trailing arm bushings are lubed up very well.... will they squeak? I drive my car through the winter. Are ireland engineering rear trailing arm bushings better in the sense that you can take each side apart when putting the rtab into the rta?

2) do you need to do another aligment when the rear trailing arm bushings are put in.... i just got an alignment before the bushings started to shift.

Thanks

[zrozof]

I've got a suggestion, not sure if it's idiotic but, get a new thru bolt and nut. I would assume that for the bushing to come out, that nut has to first back out a little bit to make the extra room (You are torquing that thru bolt to 81 ft/lbs?). Just something to try before replacing the entire arm. Also, there's a forum sponsor that sells used parts (?) Bavarian Engine Exchange (?). If necessary you could probably get an arm for a lot cheaper.

[Goofynick6]

Yeah, the bracket that the 3 large bolts go through that mount to the frame, I'd check to see if it needs replacing..

[vmwerks]

1) if the poly rear trailing arm bushings are lubed up very well.... will they squeak? I drive my car through the winter. Are ireland engineering rear trailing arm bushings better in the sense that you can take each side apart when putting the rtab into the rta?

The RTAB's use a metal center support, use never seize and they will not squeek. A little comes with the bushings but I always add more. The IE and the pflex are the same design.


2) do you need to do another aligment when the rear trailing arm bushings are put in.... i just got an alignment before the bushings started to shift.

You SHOULD get one... your rear toe will be off... prob not by much as long as you put the carrier back in the same place. The alignment should be less $$ since they are ONLY setting rear toe.

Walter Ford
President
Valley Motorwerks

[madspeed]

its your bracket thats worn. get a new bracket and also you definitly need to get an alignment once its replaced.

[JamesM3M5]

How can it be that the bracket gets "worn"?

I'm betting the RTAB rubber has separated completely from the aluminum outer sleeve. I've seen it before. It is not the bracket, it is not the trailing arm, and Powerflex bushings get sloppy enough to slip around in the trailing arm as well.

[Daydream M3]

i know its not the rubber coming out of the bushing because it is 3 weeks old and I have done 2 lapping days on it..... I also have the shims.

Perhaps the lapping days are enough to shred the oem bushing but Im guessing it isnt?

Does that mean I need a new trailing arm. I hope not :(

[zrozof]

Are you the guy that posted about this same problem about a week or two ago and provided a couple pictures? Could you repost those pictures?

EDIT: No it wasn't. Have you seen this thread:

http://forums.bimmerforums.com/forum/showthread.php?t=53375&highlight=rtab

[vmwerks]

How can it be that the bracket gets "worn"?

I'm betting the RTAB rubber has separated completely from the aluminum outer sleeve. I've seen it before. It is not the bracket, it is not the trailing arm, and Powerflex bushings get sloppy enough to slip around in the trailing arm as well.

My point exactly.. the bracket doesn't "wear".

[ScotcH]

I had the same issue on my car ... 2 weeks after install, it slid out. I just said screw it and installed IE poly bushings. I'm guessing the tolorence for machining the trailing arm is not that great, and it's a crap shoot to get a bushing that stays in.

[erobinson]

How can it be that the bracket gets "worn"?

I'm betting the RTAB rubber has separated completely from the aluminum outer sleeve. I've seen it before. It is not the bracket, it is not the trailing arm, and Powerflex bushings get sloppy enough to slip around in the trailing arm as well.
How would Pflex bushings slip around at all? Unless you mean rotating? They're nearly solid.