Since my ownership 4.5 years ago I always noticed more bump steer than any other 928 I have owned.
I have Replaced:
1. Inner & outer tie rods.
2. Lower control Arms torqued to 82 ft lbs
3. Upper control Arms torqued to 120 Ft. lbs
4. Rack bushing (Delrin)
5. Alignment after 1-4.
The only thing I suspect is the steering rack which is original.
What do I look at next?

 

Are the control arm bushings solid?

 

Bump steer is usually caused by too-low ride height. Is your front height within spec?

How about shocks, how old?

Beyond that, is car is still on original a-arms (and thus original bushings)? I frankly don’t know if that alone would cause bump steer. But I do know that refreshing those (from Mark Anderson) along with new shocks and hey, while you’re there, wheel bearings too, will make the car ride like new again. And you’ve already done the tie rods and Delrin rack mounts.

PS make sure car is settled before fully tightening the upper and lower A-arm bolts. Car must also obviously be fully settled before any alignment (the aligners didn’t lift up the front prior to alignment, I hope).

 

Perhaps you can describe what you have felt that caused you to perceive bump steer was occurring?

The other point I note is that you state the lower control arms were torqued to 82 ft lbs. That is the torque setting for the rear most bolts but not the front ones that are rated st about 50 ft lbs. If indeed you did set the front bolts at 82 ft lbs I would be concerned as to whether the poor things have damaged/stripped their threads causing the arm to bounce about some- hopefully not the case but..?

 

The shocks were replaced with upper "A" Arms from Mark. Same with the lower "A" arms. Ride Height is adjusted at 170mm. No bolts were stripped. As I stated the problem existed before replacement of said parts

 

Did you drop the car to the ground before you torqued the A-arms? GB had a specific procedure for their replacement.

 

I had a set of Uniroyal tires on my S8 and the feeling was like driving on pudding. After 1000 miles I throw the set in the trash and the Michelins after that drove fantastic .

 

Yes, after the new control arms didn’t settle. The new bushings left the ride height too high. I loosen the lower control arms drove a couple of blocks and retorqued and it settled. I’m talking about steering wheel moving wildly over uneven pavement. I have video but it’s to large to post.

 

has the rack been replaced?

 

Just throwing out ideas and I’m not very familiar with later 928s but what about the “donut” on the steering shaft that connects to the rack?

 

Wheel details? Offsets, tire and wheel sizes?

 

Changing the wheel set is an easy task but the donut is also an good idea!

 

Stan,

The rack has not been replaced. That’s the only thing in the front end that is not new. This is my suspicion. Didn’t want to throw parts at it without checking with the knowledge base here. I didn’t mention that upper & lower ball joints HAVE been replaced.

 

Wheels are 17” cup 1’s. Continental Extreme Sport DW. (GTS sizes)

 

Donut?