Having the infamous shimmy at 70mph *Part 2*

[giannid]

Like the title says I haven't been able to trace/eliminate my shimmy since I bought my Rora two months ago.

I have noticed that my shimmy slightly improves after I clean the rims with a brush. I clean the inside of the rims as much as I can. My rims don't get really dirty and I don't have a lot of tar stuck to them (but I do get the occasional tar here and there)

Can the cleaning be helping the wheel balance? Or the water is actually getting inside the bearings or brake calipers?

Any suggestions/comments?

G

[aldrichd]

You have what is referred to as a "Speed Vibration" (that's what it was called when I used to be a mechanic many years ago). The shimmy/vibration comes and goes as you reach a certain speed then drive out of it. In your case the 70 mph range.

Here's something to try...remove a wheel then rotate it 180 degrees and put it back on the car. Take it for a drive and see how that works. Repeat as necessary with the other wheels. Also rotating the wheels front to back may help also.

Here's why:
Brake rotors are supposed to be factory balanced. If you look at the vanes on a rotor you might see a small pieces of metal wedged in there. That's a weight to balance the rotor. (On drum brakes you will see a piece of metal welded to the outside of the drum) You may have lost a rotor weight and the rotor is out of balance causing your shimmy. Rotating the wheels 180 degrees may balance out the brake rotor AND wheel/tire assembly.

The tires and wheels could be perfectly balance but if the rotors are out of balance you will never get rid of the shimmy.

My point is you may have to work the rotor and wheel combinations to hopefully get the shimmy to a manageable level.

[centennialman]

There's lots written about this problem on the forum. Assuming that you have quality tires, and they don't have any warped belts or uneven spots, and, if nothing is worn, or having extra bits stuck on, here's a quickie on what you might do:

1) Remove each wheel in turn, and remove all rust / corrosion from the mating surfaces of the hub and wheel. I use a flat backed sanding pad to carefully clean up the wheel mating surface.

2) Reinstall the wheels, torquing to 100 ft/lbs (important!!). Road test. If the problem is not cured, then,

3) Take the car to a shop that has a Hunter Road Force balancer - many GM stealerships have them. This is the only type of balance that you should do if you have the shakes. It simulates the force on the wheel as if it was still on the car, under load. The shop is unlikely to clean the mating surfaces, so make sure that you did step 1) prior to getting the balance.

4) When you get the car back, re-torque the lug nuts to 100 ft/lbs. This is the manufacturer spec, and I'm convinced that most shops don't really care what it is. I never see them adjusting their air wrenches.

All of the above matters. These cars are documented to be extremely sensitive to wheel balance.

[giannid]

Thanks for all the good info ...

I recently purchased Yoko Avid's and had them force-balanced with a Hunter machine. One tire came out-of-round from factory, so TireRack replaced it without any questions. I still had the shimmy after that. All my tires have low force balance numbers (I think the highest is like 10), which leads me to believe that I have rotors that are not "true". I had my suspension checked over several times and the only thing that was replaced was my stabilizer links. These were replaced with GM OEM ones, so I don't think my problem lies there. I did have my pads changed in the front and the rotors were resurfaced. My mechanic said that they looked fairly new, so he didn't bother changing them. I confirmed that they were 20k old from the VIS check that aurorabrain sent me (thanks again). These rotors were replaced under warranty some time ago and I am aware of all the ACDelco rotors issues.
It just feels weird that my vibration comes and goes whenever it wants to, but I do understand that the road surface plays an important part, specially when my tires are fairly new.

I will keep you guys posted when I decide to change my rotors ... hopefully I won't keep dumping money on a problem that I might never solve.

Thanks,
G

[majoraurora]

Check your 6 cradle and 4 swing arm bushings carefully.....

[giannid]

I had all my rotors replaced this past weekend ... my shimmy is almost gone!!! I think I gotta tighten the stabilizer links more (recently replaced), but I don't know how or where they should be tightened ...

I need guidance from the experts ...

G

[austinator]

You just hold them on top with a wrench and turn the bottom with a wrench or socket wrench. They should be tightened until you run out of threads. Don't try to crank them too tight when you run out though. I assume you know where they are located?

[giannid]

austinator said:

You just hold them on top with a wrench and turn the bottom with a wrench or socket wrench. They should be tightened until you run out of threads. Don't try to crank them too tight when you run out though. I assume you know where they are located?

I don't know exactly ... could someone post a pic for me??

thanks,
g

[centennialman]

giannid said:

austinator said:

You just hold them on top with a wrench and turn the bottom with a wrench or socket wrench. They should be tightened until you run out of threads. Don't try to crank them too tight when you run out though. I assume you know where they are located?

I don't know exactly ... could someone post a pic for me??

thanks,
g

The driver's side is just visible in this pic. They attach the sway bar to the control arm. The red bushings are just visible in this pic.

[giannid]

Thanks for the pic, but I don't have the garage space, time, and equipment to inspect those. I'll take it to my mechanic as soon as I can ...

Thanks for the help though

G

[97 Aurora 32V Northstar]

Man I wish my suspension was that clean. I have the shimmy too but am in dire need of some new tires, we'll see how it goes after that.

[martindaman]

i too have that shimmy in my aurora but mines starts when i hit 40mph and hit the brakes, when that happens i lift my foot off the brake and it does goes away or until i come to a stop, i have a feel for my car and ive learned how to avoid getting the shimmy but yea it is a bother when you have people in your ride, what else can i do t get rid of this

[centennialman]

martindaman said:

i too have that shimmy in my aurora but mines starts when i hit 40mph and hit the brakes, when that happens i lift my foot off the brake and it does goes away or until i come to a stop, i have a feel for my car and ive learned how to avoid getting the shimmy but yea it is a bother when you have people in your ride, what else can i do t get rid of this

In all likelyhood, you have a warped front rotor. It's not worth machining them. Get a new set; RockAuto, eBay, etc. You need to 'bed in' the new rotors gently at first. No panic or high speed stops. Sometimes, a rotor will warp if you have been driving at high speeds for several hours, and then do a panic stop. The sudden heat rise will cause a swelling on one spot of the rotor, and you will feel it pulse everytime it goes past the pads.

[aurora2001tan]

I have recently replaced my rotors after I warped them with too hot of a break in on the break pads. I found one side with .0015" thousands the other about 10 thou. Ordered new ac delco rotors from rock auto for 130 bucks. They come painted black in the ribs and outside. Made in China though! Put those on and caught one with 4 thousands runout. I corrected that with a shim from BRAKEALIGN.COM My rotors are like new recently replaced so all I had to order was the conical washers for 17 and the shims at 8 bucks a piece. I got 2 .003 shims and 2 .006 shims
.002 or .001 is within gm spec as a true and strait rotor runout. I got one down to 1 and the passenger side was .002 so I left it alone. The massive brake pulsation is gone but I do have this shimmy at around 70mph. It goes away but a quick turn of the steering wheel will cause a pulse in the steering wheel, not really from the road but in the steering wheel!!! Position strait and everything is smooth!! Maybe hard to explain.

SO with new hubs, new rotors and brakes and a VERIFIED IN SPEC runout the problem has to be somewhere else. Its due for an alignment. If that doesnt work I suspect the ISS Steer wheel shaft that is. My strut evidently were replaced some miles ago and they are sweet. My front tires have like new tread on them. Rear tires need replaced. All tires have PERFECT even wear. So for me, it has to be an alignment thing.

The rims have been swithced around and appear strait on the balancer.