Steering Wheel Shake (not brake related)

[Ximian]

During a recent track day, I started getting a bad steering wheel shake from high speeds. On the way home from the track, it would even shake when lifting off from the throttle.

After inspecting the rotor and brake pads, they looked fine. I then checked and control arms and quite a few of them could be easily moved. I've replaced just about all of them in the front and the one pair that was loose in the rear.

Replaced -
Front: tie rods and bellows, tension struts, wishbones, sway bar link
Rear: toe arm

After replacing those and getting an alignment, the steering wheel shake is better but still there. Currently at speeds 70 MPH and above, when braking the wheel shakes. At 65 MPH, nothing. At 60 MPH, even the hardest of braking, nothing. Never had pulsating from the pedals while braking, they're firm. Letting go of the steering wheel while braking, the car itself wasn't shaking noticeably either.

So what else could it be?

[gtenedio]

either your rotors are warped from over heating, or you need a wheel balance. if you dont have heat marks on your rotors, just go for a rebalance..often times the wheel weights come off during sessions from heat.

[Ximian]

Originally Posted by gtenedio

either your rotors are warped from over heating, or you need a wheel balance. if you dont have heat marks on your rotors, just go for a rebalance..often times the wheel weights come off during sessions from heat.

Two separate sets of wheels and tires, still shakes.

It's pretty difficult to warp rotors, especially since I have a pretty good cooldown procedure. Warped rotors and brake pad deposits wouldn't speed below 70 MPH for causing steering wheel shaking and you should be able to feel it through the brake pedal. Not brake related.

[jradon]

Have you tried checking the steering rack and bushings?

[Ximian]

Originally Posted by jradon

Have you tried checking the steering rack and bushings?

Not yet, still trying to find a diagram on it so I know what and where to check it. I ordered the sway bar upper and lower bushings so when I replace those, I'll look over the steering rack.

When I replaced the tie rods, I noticed the left/driver's side had a lot of grease on it while the right/passenger's side had no grease. Thought it was odd since I've read that the grease shouldn't be needed, but I didn't clean it up.

[Ximian]

Replaced the sway bar bushings and the steering wheel shake that happens when lifting off the throttle quicker after accelerating (above 70) is done. I did go a higher speed this time and there is a very slight steering while shake at those high speeds without braking.

Also noticed that EDC on high and the steering wheel shaking isn't as hard. Not sure what that tells me yet since the EDC and spring still look like they're in good shape.

I don't think the steering rack has any bushings. A cursory view of the rack didn't show any problems so I'm not sure what the next step should be.

[Ximian]

I think I mostly have it have it figured out. Maybe.

I took it to a shop, they diagnosed it as warped rotors. I replaced the rotors, got new brake pads and it's all pretty good.

I was able to find a place that would turn the warped slotted rotors, for fun. Took them a while to get to it and they didn't turn it, but used a grinder or sanded the rotors. I also recently replaced wheel hubs so I put one on the ground and took turns spinning the rotors looking for any runout. Since they both looked great, I put them back onto the car with old track pads. Predictably, still had a steering wheel shake but this time at all speeds above 15 MPH. That's an interesting difference.

Since the rotor surface is fine and can't have pad deposits and I also replaced all of the front control arms and bushings, I decided to take a closer look at the brake pads. The pad surface looks fine, not including a bit of build up in the slot down the middle. Then I got the bright idea this evening to take out a caliper and measure the pad thickness in various places.

After measuring the pads is when I realized that the pad thickness on the leading edge (against the spin of the rotor) is thinner than at the trailing edge. Sometimes by as much as .8 mm. After swapping between the street pads and track pads, I reinstall the track pads in no specific orientation. That means sometimes I was using the thicker side on the leading edge.

Using the very precise and professional method of "rub the brake pad against the concrete floor," I was able to reduce the difference in thickness to no more than .4 mm. Once I reinstalled the pads with the thinner side on the leading edge, I took the car out for another test drive and this time it was much smoother. There is still a bit of pulsing under braking, but it's improved drastically. After bedding in the pads, heavy braking from 100 MPH had no steering wheel shaking. But there is still a shake at lower speeds meaning I could do a better job of evening out the brake pad.

My goal now is to -

• Reduce the difference in thickness no more than .1 mm from the leading edge to the trailing edge on each pad.
  
• Reduce to thickness difference to no more than .3 mm between the four pads.
  
• Reinstall with the thinner side on the leading edge.