I have a 1992 and it seems when you are driving at a regular speed and you take your foot off the gas pedal you can feel a slight movement in the rear end as well as if you then put your foot on the gas and begin to to accelerate you can feel the same slip or movement at the very second you touch the gas pedal.

What should I look for and how can I terst to see what is causing this!
Other than that the acceration and everything is great with the car, no hesitation only the slight slip feeling at the split second you take your foot off the gas pedal or when you put you your foot on the gas pedal to begin to re-accelerate.
No slip or movement when starting off from a dead stop!

Thanks for any advice..

 

Start with the batwing bolts and the C-beam bolts. Make sure the batwing bolts are tight but on the C-beam check to make sure the holes aren't now ovals instead of round.

The rubber bushings for the rear (trailing links etc) should be checked too.

BTW when was your last four wheel alignment?

 

OP: My money is on the C-beam joint(s) slipping, especially if you notice the holes in the aluminum are oval instead of round. This is usually accompanied with a ridge of aluminum on the C-beam around the edges of the steel washers - a dead giveaway the joint is not secure.

Bill Boudreau has some pretty nifty C-beam plates that address the squirming at the joints - the differential joint, especially - not to mention making dis-assembly/reassembly so much easier they are worth the cost if they did nothing else, IMO

 

ckeck your u-joints, may be coming apart

 

Thanks I will check all the C-beam and U-joints.
I know I have a little sqeek from time to time on the rear passangers side and I did spray W-D 40 on the U-joints and it seemed to help with the sqeek but does come back once in awhile, how will I tell if the U-joints are bad?

Thanks so far!

 

U-joints have nothing to do with the C-beam anchor points and their propensity to wiggle loose...assuming you're commenting on my post??

 

You can pretty much isolate issues with the C-beam by re-torquing the 4 bolts to spec and go for a test ride and see if that helped. If it did, then perhaps removing and cleaning the contact surfaces and (I've used) Locktite applied between the C-beam and the differential in conjunction with the Beam Plates (mentioned). I've dropped the hammer many times on a 500+ hp LT5 and the rear end no longer kicks or squirms in any way...Just sayin.

As mentioned, there are other bushings; e.g., the bat wings and control arms, dog-bones, etc. at play as well.

Well, I've never heard of WD-40 being used to detect a u-joint issue. Due to the cup seal, I question if it would be possible to get much WD enough to make a difference in there. But, for the sake of argument, if WD does quiet a u-joint, I'd take it as a sign to replace the joint(s) immediately.

Far as testing u-joints, if there is any rotational or lateral "slop" in a universal joint, it is a dead giveaway that it needs to be replaced. You might have to pry on the joint to see if there is any lateral play, and twist the shaft back and forth to attempt to discover any play.

And, usually there is a poping or ticking noise at low rpm too. By the time you start feeling vibration that increases with drive train speed, it is a pretty good chance at least one of the u-joints in the drive shaft is bad.

Another source of a popping or ticking noise, especially when shifting from a forward to reverse or visa versa is the bearings in the wheel hub.

There are a total of 6 u-joints in the C4 IRS. Spicer is the manufacture recommended for the ZR-1 as well as the Vipers, far as u-joints go. You want the ones that do not have a grease fitting, as that fitting tends to weaken the joint.

I'd try checking and re-torquing the bolts on the C-beam first, and then move on from there in a methodical approach.

 

While it might be C-beam looseness, bushings, U-joint wear, etc. I'd bet on the thrust angle just being off. A 4-wheel alignment with a careful rear toe-rod adjustment should correct this. Loose rod ends on the rear toe rods or mis-matched LH/RH tires could also be the culprit, but I'll still put my money on the toe-rods.

 

Good information, I'll keep looking until I find something that isn't right!

Thanks again everyone!!

 

I've been chasing this problem for years. Rebuilt and replaced every last item in the rear suspension possible.
Called Killebrew. Measured and videoed every last link and bushing.

What was the changer? Rear toe setting. With as close to zero thrust angle as possible.
Make sure the dog bone bushings are solid. The toe rod ends are tight.
Have the alignment guy not compensate for the road crown.
Add just a bit of toe in to keep the rear end tracking straight. 0.10 degree is good.

This is not a common problem yet those that have experienced it have yet to discover it's resolution.
PM me if you'd like I can go into greater detail.

 

Check your toe-rod ends.

 

I had the same issue. It got progressivly worse until I started hearing a thunk. I replaced all half shaft ujoints today, problem solved. It could be multiple items.

 

Alot of things to check and eliminate!!!

You guys have been very helpful so far!

Thanks to everyone...

Chris

 

You dont specify whether you were seeking a solution with the WD-40 or if you were simply testing the joint. WD-40 is a very short term water displacement that also happens to have a short term "oiling" effect.

I highly recommend you choose wisely the locations where you spray wd-40. Most of the time it just attracts dirt and LEADS to a failure.

 

There will be sign of rust coming from under the bearing seals.

 

rear alignment, happened to me !