Steering Wheel Rock

Paulporsche · 05-01-2008, 02:50 PM

I've been getting a steering wheel rocking back and forth @ low speed as I come to a stop, say for a stop sign. The column isn't moving, and I don't have any vibration on the road @ speed.

The rear shocks are new, as are the tires, but the front shocks could have as much as 90,000 mi on them(!) I don't feel any movement side to side or top to bottom on the wheels. I had this before and after switching wheels and tires.

I have a lot of front neg camber and I'm wondering if that's the cause.

The look and feel are as if the road is undulating and taking the wheels, and the steering wheel, along with it, and yet the road itself seems fairly even. It seems to vary in intensity from one road surface to another.

What do you think?

porsche930dude · porsche930dude's Garage

i get that sometimes too. In my case i see it as being because the front is diving with weight on it plus the tires get more or less traction and follow the bumps in the road. That and it has no power steering. It could be somthing different for you i dont know

Howard M · 05-01-2008, 04:21 PM

Slightly warped front rotor? Mistorqued wheel lugs?

rusnak · 05-01-2008, 04:57 PM

I'd say warped rotor or hub. If you overtighten or don't use a torque wrench, you can warp the aluminum hubs.

gtihop · gtihop's Garage

I used to get a slow steering rock at slow speeds when turning- installed bump steer kit and replaced the front tires that were 20 years old- so far no more rock.

Paulporsche · 05-02-2008, 07:25 AM

Thanks, everyone.

I already have the bump steer kit.

I wouldn't be surprised if the rotors are warped. I think they've seen a lot of miles. Although I'm surprised I don't feel any pulsing in the pedal while stopping.

Fast Corners · 10:10 AM

Check the alignment of the front end. Even with a bump steer adjusted for a lowered car you can have the car pull left or right and back again during braking. If the surface is bumpy or irregular and you have very little toe the car can feel unstable. Flexing in the suspension bushings can cause changes in toe setting that may push you to a slightly toe out condition.

I would check your toe, caster and camber settings to see if they are in spec and I would also check the condition of the front suspension bushings. If the shocks have 90K on them then I would imagine that the bushings would have atleast that kind of mileage on them.

In reading you post again, I noticed that it varies based upon the road surface. This leads me to believe that it is the front end alignment or bad bushings. If your rotors were the culpret it wouldn't make any difference on what the road surface was like. Additionally, with a lot of neg camber you are reducing the contact patch when going straight. This can have significant affect on braking on a bumpy surface. With smaller contact patches it is easier for the tire to be unloaded when it goes over a bump. In effect a momentary loss of traction on one side will cause the car to pull to the side which does have traction. When the tire regains traction it will tend to pull the car back that direction.

How stiff is the car sprung? What shocks are you running?

cgarr · cgarr's Garage

Jack up the front end and spin your wheels and see how straight the tread runs.. Hit any pot holes lately?

Paulporsche · 05-02-2008, 02:12 PM

FC, thanks.

The car is rather softly sprung w/ stock 77 torsion bars, but Bilstein HDs.

I know my rear bushings are ready for replacement. I wouldn't be surprised if the fronts are ready too.

I'm wondering about the alignment settings. I agree re the neg camber. I'll have to research camber and caster symptoms.

Craig, I'll check that, although (I forgot to mention) when I changed tires I also changed wheels w/ the same symptom. No recent pothole hits.

ManaMan · 05-02-2008, 02:21 PM

I took a slantnose out for a test drive, and noticed that the steering wheel would shudder/rock on braking, but the brake pedal felt smooth (no pulsing). I passed on buying the car, and met the guy who bought it at the local AX. He told me he had found the front suspension pan was rusted and that he bought the part to replace it. He still has to take the front end apart, and R&R the front pan, more work than the price of the car justified. Check there.

rusnak · 05-02-2008, 02:38 PM

Paul,

come to think of it, we had a "wheel shimmy" in the 911SC way back in 1984 that turned out to be caused by a bad left front strut cartridge. We ended up changing the entire strut, ball joint everything to make sure we got it. Problem went away. It could be worn struts, or a loose nut, or worn strut bushings.

Paulporsche · 05-05-2008, 03:25 PM

OK. I'm leaning towards rotors now. Had it on the highway today and applied lots of braking force, and got lots of steering wheel vibration in return. Accelerating and steady running produce no shimmy.

tcar · 05-05-2008, 04:31 PM

Does it rock when the car is stopped with engine off too?

Paulporsche · 04:46 PM

You mean if I were to turn the engine off, coast (freewheel) and then come to a stop?

I'll have to try that.

Are you thinking motor mounts?

Paulporsche · 09-17-2008, 09:42 AM

Just to close this out. I had the front bearings repacked and tightened while I was @ my mech for a start/run problem. He also changed the front and rear pads and bled the system. The steering wheel rocking has gone away.