Ok, so I am at my wits end here trying to fix this problem. Everything in the suspension front and rear is new and that includes coil springs. The steering gear box was rebuilt by Redhead Steering Gears and I have aligned the idler arm with the steering arm. I have replaced the rag joint with the Astro Van mod to a universal joint. The power steering pump is a reman. Strut towers were replaced but not GM originals. The frame has a wonder bar and the gear box is tight to the frame rail. I have had it aligned first at factory specs and then just recently at the street settings listed in other threads here which put the struts at or near the limits of the strut tower adjustments. Still I have darting with a little movement in the steering wheel and particularly when hitting ruts. I have tried two different sets of all 4 tires and wheels. Blizzak snow tires are on it now with a set of older factory wheels but it does this with my new BF Goodrich raised white letter tires on restored original factory wheels. The original wheels were checked for straight with no problems there. I have focused on the front end but wondering if the back end could be the problem.

Anybody got any ideas. Bad power steering pump? Something with the LCA's in the rear (poly urethane bushings there and in the sway bar? Misaligned rear axle (anyway to check that)? Something with my posi-traction rear end?

Thanks for any ideas....

 

It's called Bump Steer my friend.
if you car is lowered, it worsens the issue.
i have the same Z Redhead box as well, it's nice ain't it!

Google "Bump steer testing" and find out how bad your Toe out is on suspension compression and Decompression.
i haven't fixed my cars Bump steer yet, but it's over 1/8in toe out on 3in of a-arm compression.
that's bad for daily driving and kills proformance at the Autocross.
​​​​​​​That Toe out causes your car to wonder
There are many bump steer correction kits available $150 range

 

Hi, thanks. The car is factory stock, I have owned it since it was new. It does act like bump steer however I had previously read all the info I could find on bump steer and adjusted the idler arm per the factory adjustment versus the steering arm. I then had it aligned to the following after reading the posts here about best alignment. I don't remember which setting but the guy said he couldn't quite get one of the settings to where I asked..

Caster Left 4, Right 4.5
Camber Left -0.5, Right -0.5
Toe In at 3/32

The guy said he had it set at 3/32 toe out. Since he misunderstood he went back into the shop and said he reset it to 3/32 toe in. Don't know for sure if he did...

Just checked ride height at the top of the fender (I know there are a lot of factors on this but) and have 27 3/4" at both fronts with 28 1/2" on left rear and 28" on right rear. Right now I have Blizzak 215/70R15 tires all around which are 0.9 inches taller than my stock 215/65R15 tires. So, with stock tires the ride height would be 27 1/4" both fronts with 28 left rear and 27 1/2 right rear. At about 40,000 miles ago I replace coils springs all the way around, new bushing, new ball joints, new steering linkage. Guessing the new coils at that time lifted the ride height..

I don't know what the toe is on compression. Any easy way to check that? If it is out with compression, what would that indicate is bad?

 

I would bet money that you still have toe out. You can check it quick and easy at home with someone to help you. Get 2 yardsticks or something along those lines. One person holds theirs against the tire so it's just above the bottom of the rim ( gets past the tire bulge). Then with a tape measure measure the distance in front and in back of the tire. The front should be closer together than the back. Bump steer while is a possibility it's unlikely to be the cause from your discription