My Experience with Steering Shimmy, ADUS 207 Poly Rack Bushings, and Wheel Balancing
HI folks, I'm writing this to share a recent experience with my 2001 GS430 in the hopes that it may potentially help some of you figure out your own car problems.
First, many of us 2GS owners have been plagued with the annoying steering wheel shimmy/vibration at highway speeds. If you do a search on this forum, there are hundreds of posts with people complaining about this problem and desperately hunting for solutions.
My 2001 GS430 was no different and I have dedicated a huge amount of time and money chasing this problem over the past two years. If you do a search for some of my posts you will see that I tried a lot of different things like new ball-joints, tie rod ends, shocks, poly caster arm bushings, different wheels, new tires, road force balancing, hubcentric rings, brake rotors, etc etc etc. All these things helped to various degrees but I never was able to get rid of the steering wheel vibration completely.
I finally took the car down to one of the most respected suspension shops in Nor Cal... Custom Alignment in Mountain View, CA to have a look (mind you this is after taking it to at least a half dozen other shops over the past two years who weren't able to solve it). Custom Alignment found several things:
1.) My car was equipped with the ADUS poly rack bushings that I installed last year. Multiple alignment shops informed me that my car was not maintaining an alignment for some reason. In other words they would align it to spec, take if for a drive, put it back on the rack only to find that the alignment changed while the car was being driven. These ADUS rack bushings were the culprit due to poor design, explained below:
First, if you look at the outside perimeter of the ADUS poly rack bushings you will see that it's not a perfect circle. Instead it has 4 "bumps" around the perimeter. What happens is that under extreme stress, the bushings can rotate causing the steering wheel to go off center.
Secondly, the steel cylinder that slides into the rack bushings were identified as too long in length. When the rack bolts were tightened down, there was no compression on the bushing which promoted the bushing rotation under stress.
Thirdly, the tolerance between the outer diameter of the steel rod and the inner diameter of the rack bushing is wrong. In fact you could wiggle the steel cylinder while it is inserted into the bushing. The tolerance is way way way out of the ballpark.
IF YOU ARE IN THE MARKET FOR RACK BUSHINGS, AVOID ADUS 207. INSTEAD BY FIGS. THE FIGS BUSHINGS WERE ROUND, HAD THE APPROPRIATE TOLERANCES, AND THE CORRECT LENGTH STEEL CYLINDER. IF YOU HAVE ADUS 207 BUSHINGS INSTALLED NOW, GET THEM OUT OF THERE AS I AM CERTAIN THAT YOUR ALIGNMENT IS CHANGING IN REAL TIME AS YOU DRIVE, EVEN IF IT ISN'T OBVIOUS TO YOU.
2.) Although it didn't contribute to any vibes or steering wheel shimmy, we installed a rear camber kit and adjustable front upper control arms so that the car could be aligned to spec to cure the inner tire wear issue. Both were SPC brand
3.) I purchased new front tires and had them road force balanced at Custom Alignment. After installing all the parts above and performing a road force balance, Joe Silva (the owner) took the car for a spin but he still felt a little shimmy. He brought the car back into the shop and put the wheels back on the road force balancer while adjusting the balancer settings for additional sensitivity. That made ALL the difference. For the first time since I've owned the car, it is 100% shimmy/vibration free. Big thanks to Custom Alignment for spending time identifying and fixing all the issues.
In conclusion, if you have steering shimmy problems, I highly recommend you take the car over to Joe Silva at Custom Alignment for a diagnostic. He's an honest guy with lots of suspension experience and his shop has all the latest and greatest equipment. They really took the time to figure out what was going on and what needed to be done.
And avoid the ADUS 207 poly rack bushings. Use Figs Engineering poly rack bushings as they are superior in design.
I hope this is helpful and here she is, 100% problem free for the first time
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2001 GS430 Crystal White on Redrilled BMW Style-95 Wheels
Good to know, I have those same bushings and am getting a bit of shimmy recently - everything else is brand new OEM or high quality FIGS stuff, so imagine this is probably the culprit! Have ordered a set of the FIGS rack bushings now.