myBailey07

Help me debug a steering wheel vibration/shimmy, please.

I have a steering wheel shimmy that shows up right between 55-70mph and have been having a super hard time trying to figure out what it can be. It is not super heavy and if you hold the wheel firmly it does not shake, however, if you hold the wheel lightly or let it go it is noticeable. It does not shake under braking and above 70mph either goes away, or becomes so light that you barely notice it. Annoying as heck though.

Sounds like a wheel balance issue? However, it seems to be not the case and I need some forum wisdom to figure out where to go from here…

Background and what has been done already:

For a recent track weekend at COTA I replaced tires, front brake rotor rings (AP Racing) and pads the day before. I do not recall the shimmy on track and I also did not go off or hit anything. However, after the track weekend I noticed it.

So, here is what has already been done:

I have three weelsets and it showed up consistently on all three sets. Each set was then re-balanced – no improvement.

We then mounted new tires on two of the sets and had them carefully road force balanced at the dealer – no improvement. Shimmy still continues across both sets of wheels. All the wheels were also checked to make sure they are straight. At this point I concluded it is likely not a wheel balance issue.

As a next step I mounted new rotor rings (AP Racing) to make sure I did not maybe have a rotor that was out of balance. I also made sure that each hub and all the mounting surfaces were flat and clean – No improvement. Ugh!

I also visually inspected all the suspension bolts and can’t visibly see anything lose or bent. (I have RSS Tie rods and Tarett caster bushings up front in order to get -3 camber and zero toe)

So, that said, what would be the next things, in order of sequence, to inspect and/or replace in order to figure out what the heck is going on?

Mech33

This can be common with tires slightly out of balance. Maybe you rotated a tire on the wheel under heavy braking at the track? I'd take the wheels and tires in to get re-road force balanced and see if it goes away.

myBailey07

As I said in the original post, I had two sets of wheels freshly mounted with new tires and both sets road force balanced and checked for being straight. Shimmy persists across both sets of wheels.

ShakeNBake

That is ahead scratcher. What surfaces does it happen on (ie. Crowned, worn/tram railed, smooth, textured, etc?) A bad shock can occilate at certain frequencies, causing a vibration through the steering. If it varies with road surface, could be it. Does it happen in stiff mode? On sweepers?

t-design

From my experience - it's always balance issue. Yes, I've read your text. If you tried 3 set of wheels, may be it's rotors? Did you try completely new rotors?

Coming up at certain speed is bullet proof evidence. It means it directly linked to rotational speed, and wheels and rotors are the only suspects...

myBailey07

I did replace the outer ring on the AP Racing rotor as it started around the same time as the first ring was replaced (I cannot definitively remember) but the problem continues. Maybe the hat is bent or something. I have a set of new oem rotors on order to replace and see.

I am stumped and in trial and error mode now, and so is the dealer...

myBailey07

Yep, head scratcher it is. Been chasing it for over 4 weeks now and spent over $700 in balancing alone, with no success

I can't feel it around sweepers as I need to keep a firmer grip on the wheel and the lateral load will "overpower" it. So, pretty much driving in a straight line with no lateral load. Stiff and soft makes no difference, I tried. Road surface makes it more or less pronounced, but it is still there.

I'm about to tow it to SoulSpeed or ATX and just drop it off and tell them to "make it go away" and not call me before they figured it out...:-(

Jamie140

Did you try try a road force balance. That's certainly what it sounds like.

Good luck.

4carl

The true test of wheel balance is after they zero the wheel have them rotate it in the machine spindle and spin it again. If its still zero the balance is perfect. If not either the machine isn't calibrated or they are not placing the weights properly.

The wheel should show zero no matter how many times it is re-positioned on the machine spindle. Ive had tons of wheel balance issues over the years that's how i figured out this way to test , it works. If your wheels pass the test then rotors? Good luck carl

neanicu

Tires out of balance is my bet.

trebien

Doesn't sound like wheel balance across all the sets, unless the original balance machine made the same problem across all 3 sets.

Another option is slight toe out on the fronts, or somehow a loose bushing/bolt allowing a little wiggle in the toe. This would also explain it going away under a sweeper, with a little turn to the wheel.

Double checked the alignment?

myBailey07

Yeah, I guess the next step after I remounted new oem rotors is to take car to shop that knows what they're doing to recheck wheel balance (again...3rd time) check bolts, bushings, alignment and shocks.

4carl

The SmartMoney says it's something that Rotates. Not alignment ect.

electron mike

Rotors/pads is my guess. I have AP rotors and DS1.1 pads and after my last track day I had some vibrations. Mine is slight pad deposits and/or rotor variation that causes the rotor to hit the pad slightly in the front when the brake pedal is not applied.

Same as you, no shimmy under braking. Mine is a bit better after a round of rebedding, but not completely gone. I didn't have this issue with stock rotors.

It could also be a caliper piston not fully disengaging, causing the pad to hit the rotor, but I looked at mine and they are releasing.

Veloce Raptor

Rear rotors