a43656

Hundreds of threads on this topic, and I think I've read them all. I've covered the obvious things those threads mention (rotors, wheel balance, control arm bushings, lugnut torque), a few things none of those threads mention (intermediate axle bearing, running it on the lift without wheels and tires), and a couple things left to check that those threads mention (checking runout with a dial indicator, trying different pads, and some talk about steering columns that I don't understand why it would be a factor in my case). A few threads seem to hint that the OEM pads have a habit of putting deposits on the rotors.

Here is my story:
-2008 SS, manual trans, non-Brembo, ~125K miles
-All front end parts are GM OEM FE5 parts, some newer, some original, including OEM rotors and OEM pads (i.e. Ferodo HP1000)
-Lugnuts always torqued - nobody has worked on this car but me for 25K+ miles.
-Suddenly started getting a brake pulse and steering wheel shake between 40 and 20 mph, only when moderately braking.
-Shake is the same cold, warm, or hot
-Very light braking - no shake.
-Heavy braking - no shake.
-Moderate braking - shake starts about 40, gets worst in the middle, and starts to end around 20 mph.
-Just driving along, no shake or wheel imbalance feel at all.


Went under car - found completely blown out intermediate axle bearing. Figured I had found the problem - WRONG. Replaced entire intermediate axle and right side CV. Still shook per above.

Put on new aftermarket rotors and rebalanced wheels. SEEMED FIXED. Took a 1000 mile highway trip, and the shake came back halfway through the trip, but getting worse and worse as we went along. (Rotor deposits from highway driving?)

Calipers look great, pins not worn, not bent, lubed with Sil-Glyde, sliding freely. Pads look great - plenty thick, all 4 about the same thickness, very little taper on any of them.

Replaced slightly torn lower control arm bushings (the rear doughnut looking one). Used MOOGs. FIXED ABOUT 25% OF THE SHAKE. Torque steer and steering feel improved, though.

BIG CLUE:
Ran car on the lift. (Gotta turn off ESC to do this or traction control kicks in). The shake is worst at 34 mph with the brakes on. Doesn't matter what gear - the clue is 34 mph. But the wheels were shaking and appearing "imbalanced" even without the brakes on.

Took wheels off, snugged down the rotors, ran again on the lift - it fixes a lot of the shake by still there at 34 mph. So the whole drivetrain shakes at 34 mph? Do they all do that? I wish I had another car to check this way!

So it seems like it is a driveline vibration that happens right around there? But the extra weight of the wheels and tires makes it worse, and then adding braking makes it bad enough to go all the way up the steering wheel shaft?

Of course I'm going to try rotors again (turn them down) because doing so DID make the problem go away - for all of 600 miles. It just seems very suspicious that the whole drivetrain has a vibration at the same speed. Motor mounts? Original CV on the left side?

If anyone has bothered reading this far, do you have any thoughts? Hoping I might stumble onto someone who has gone as far down this path as I have.

Thanks in advance!

donbrew

Why not consider the obvious? Wheel hubs.

donbrew

Don't run it up on a lift anymore; you will damage the CVs.

a43656

Sorry, I should have added that - they are also fairly new ACDelco parts and I'm not finding any slop or typical bearing failure noise from them. Any time I have lost hubs, the symptoms have been wider reaching than this.

donbrew

Rear hubs? when the car is jacked up grab the wheels top and bottom and wiggle. I suspect that you will be able to feel a tiny bit of movement, almost none is allowable.

Yes, rear hubs can affect the steering wheel, along with rear drums and brakes.

a43656

The peak of my shake happens at 34 mph, both on the road and on the lift, so I'm interpreting that as ruling out the rears.

I agree with you that I should take it easy on the lift on account of the CVs!

donbrew

If you run the trans with the wheels up, you will get a rumble. That is the CV and slip joint telling you they are being torn apart, because that is way beyond their design angle.

I didn't even have my turban on and I knew your reply would be "I'm not going to look into that because..."

If you find a solution, please come back and post it.

a43656

There is no reason to believe that a 34 mph vibration at ANY ride height, including on the lift, not only with brakes applied but amplified when the brakes are applied, is related to the rear wheels that aren't spinning when on the lift - especially when the front rotors "fixed" it for 700 miles. The CVs are not the wheel travel limit in either jounce or droop, especially not on the (lowered) SS.

Good luck with your turban!

whopper

I think what Don is trying to tell you is that if you are getting rumble from the CV joints, that rumble may be different that the one you are experiencing with the car on the ground. ie: two different rumbles - no matter if you don't think they hang down low enough.

Have you checked all the ball joints?

Oldblue

So then according to your test results it's the axle cv joints causing the shake at 34 mph.