i have a bone stock (suspension wise) 91 z28, except KYB GR-2 in the front and gas-a-just in the rear.

have noted that at high speeds (such as 70+ on the highway), while in a corner (typical highway gentle corner), and when encountering rough roads, sometimes the rear end of the car "skips" a bit and seems to move the entire rear of the car an inch or two sideways.

the sensation only lasts an instant, and no steering correction is needed (i coudln't correct fast enough for it if i wanted to anyways).

I assume this is one of my rear tires losing contact with the ground.

I did not notice much of a difference when I went from the stock shocks to the kyb's. nor did i notice much of a difference from going to good tires (goodyear f1 gsd3) vs. junk tires.

do i need more shock to control the rear springs? or perhaps a softer rear spring? I have given the car a serious side to side shake while sitting still, and I can't find any suspension peices that are worn or lose.

i also don't know if this is just normal for a 3rdgen fbody. I spend most of my time in a car with independent rear suspension, so maybe this is just characteristic of a solid rear axle of the 3rdgen design? I don't remember my 71 (rear leafs) ever doing this.

also, if this is in any way attributable to chassis stiffness, i already have a set of spohn subframe connectors waiting to be installed.

 

Its a combination of low dampen force shocks and worn rubber bushings. The bump "impact" is dribbling the reearend laterally like a basketball. KYB gas-a-just are not much better than stock shocks. Great tires though!

 

aftermarket panhard (track) bar would probably help keep rear planted better, or you can box the factory piece for less flex.

 

well, i figured out the problem the other day.

I had the rear tires off to do the rear brakes...have had the rear tires off dozens of times. I don't know how i missed it (I really don't!) but the passenger side swaybar end link was TOAST. two of the four rubber bushings were completely gone and the other two were splitting and crappy.

I didn't have new endlinks handy, so I threw in two old rubber bushings from a spare endlink.. WOW. that made about an 80% difference, the car was so much more stable feeling. by stable...I mean that it would drive straight through rough road without feeling like the seat was moving left to right an inch or two...

So, then I ordered four brand new 1LE endlinks from GM and swapped them out...

problem 100% solved. the left/right sensation is completely gone, and the cornering stability/confidence of the car is very noticably improved. it's like a whole different car now. I never realized swaybars made that big of a difference...even for straight line driving!

Now I need to hurry up and replace all the rest of the rubber with new.

 

my car does the same thing from hitting bumps. any significant bump in the road taken at a slight corner will throw the rear of the car to a random side a little bit. i have heard that this is just because ofthe nature of the torque arm suspensions our cars have.

 

that's what i thought, ... until i fixed the problem.

the car now tracks as straight as my 88 fiero through bumps and rough roads.

if you don't know - fiero is four wheel independent suspension, and the 88 has upgraded suspension that is actually quite good...

suggest you look at the suspension and start replacing the worn out stuff.