Skruball73

What is going on when I shift? I have a 350 with a 3.55 rear end, I don't know what size manual tranny I have, so when I shift, I hear and feel a clunk or thud from behind me....if I am very careful in my shifting, I don't feel it at all or as much. :confused:

Marks69BB

Could be your halfshaft and/or driveshaft ujoints are loose or starting to go. Also, could be that your diff oil needs to be changed out with new oil and posi additive from your local GM dealer.

TQ67

Sounds to me like it could be a bad U-joint in the drive shaft, or one of the half-shafts. It is at least worth investigating.

Larry B.

Sounds like bad u-joint(s). There are six total and they will make clunking noises if even one is bad. :smash:

Skruball73

That's what I was thinking but was not sure...next question is, what could possible damage be to a vette if one of the u joints failed or dropped?

NorthVette

Does it thud at you when you back up as well? When mine "thudded" at me when the TH350 would shift, and constantly thud at me in reverse, I finally figured out that it was the cushion at the front of the diff. I wouldn't recomend driving it until you troubleshoot and fix it.

fwayne

I broke a half-shaft u-joint during a "launch" once. The spinning half-shaft bent my shock and took a chunk out of my fiberglass monospring. Not a pleasant sound, either.

Mr.Gearhead

I think you may want to check out the shock mount. Mine was shaped like a D from years of abuse. It happens, the mount and bushing get worn. I checked everything but this and still had the clunk when I started out or when I mashed the throttle quickly then let off. The mount should be round where the rear shock bolts. Good luck... :D

Skruball73

I don't recall if it thuds in reverse or not...I don't think so, but I will have to check that in a little bit.

Skruball73

you know, I have noticed that it happens not only when I am shifting but also if I am already in gear, like in 3rd and maybe 2nd and not really going fast, or not in a situation where I can finish the progression and I let off the gas but still in gear...when I hit the gas again, it will bump or thud a little bit. Does this sound like it would be the u-joints or this shock mount you are talking about?

TQ67

I would also check the engine and transmission mounts while you're hunting. I had wierd symptoms when one, or both of those went.

faster69

check the cushion on the diff. mine did the same thing. Rick :yesnod:

Chris Fowler

Cusion on the diff was missing on mine when I got it. I'd get a thud or thunk when I shifted too. But I also got it if I just let off the gas and then hit the gas again, without shifting.