really the only way i can explain it is i hear a thud in the rear area of the car when i downshift, or engine brake unless i shift VERY gently (im easy on the clutch engage/dissengage in any case). the car also seems to jerk back and forth when this happens (not violently).the shifter doesnt bounce or anything so i wouldnt think it to be a broken trans mount. perhaps a worn out bushing in the suspension somewhere? anybody ever have this problem?


forgive my lack of description, its late and i cant sleep with this on my mind

 

Sounds like something in your rear diff. Open up the diff cover and look for metal pieces.

 

I agree. Sounds like a Posi problem.

 

Before you start ripping your differential apart, I'd check the easy stuff. Look at the trans mount, the torque arm bushing (at the trans end), loose bolts athe other end, LCA bushing, Shocks, etc. etc.

 

If it is bucking while shifting it sounds like a rear end problem. You are probobly missing a tooth or two is my guess and the bucking is when the teeth finally catch.

 

but then that would mean the bucking would be constant. this problem only occurs a couple times a week, and only on the downshift; VERY rarely does it do it when i upshift. sometimes its smooth as glass.

Ill inspect the suspension later on today, look for a worn bushing tho i wouldnt think that to be the case, i have fairly new polyurethan bushings all around.

A few people have suggested a worn U-joint

 

Poly bushings can cause binding, that's why a lot of sports racers don't use them. This could be the cause of your thump. Try lub'ing them with silicone based spray lub.

 

i had a problem when i was shifting the car into gear or costing and then mashing the gas down it my corvette and hearing a clunck and hanving a small jerk feeling and then i spit the pinnion gear threw the rear houseing coast me a lot more them it would have been just to take it to a shop and have it looked at cuase i had to replace the whole rear end

 

This is not an impossibility here, but hardly a common failure!!!!

 

i was told in a vett they acutally are common becuase most people dont rebuilt the c4 rears to the right tollerances wich just burns them right up in one way or another this was by a corvette specialty shop where i purchased the new rear . i wasnt the original owner of the car and i wasnt sure if it was ever rebuilt or not. i also had a bad pinion gear in an oldsmoble bravada wich is a 10 bolt rear but there was a grinding noise right before that one broke and it had 210,000 miles on it when it went out and again there it was a thud but also a grinding unlike the vett wich you would notice what cuased the failure was leaks in the housing and no fluid in the rear. but for him i would check universals first and mounts and work my way around looking for something else if its not then. my point in the last post was to try and figure it out and if not it might be in his beter interest to take it to a shop before he does serious damage that would cost him more not that his rear was going bad . best of luck to you

 

My '96 Z28 is doing this right now also. I just changed the diff. fluid and looked at the rear gears and they were great... no missing teeth. Next thing I am going to do is replace the u-joints on the driveshaft and if that doesn't do it, it is probably excess backlash in the gears themselves. Let me know if you find out something out!

Jeff