rearend "clunking"

[crause]

Quick question, when I first got my Vette the rearend would clunk and jump when turning. Usually after an extended period of forward driving time. I was told to change the rearend fluid and put in GM additive to stop this. I did this and put in one bottle of this additive. The clunking did get much better but never stopped. I think it is getting worse the more I drive it. Should I put in another bottle of additive or could my problems be something else.

Thanks,

Andy

 

[cntrhub]

Could be those clutch packs in the diff. might be wearing out? You did right by adding the special clutch pack additive. I doubt adding more (higher ratio) will help. You might want to dump the diff. case oil more often. Sometimes fresh gear oil/w additive helps for a little while.
Did you add a bottle and not change the diff. case oil? This could be your problem also. Dump the case oil and add new with both oils.

 

[crause]

I used a vacuum pump to suck out as much of the old fluid as I could and think I got most of it. I then put in fresh rearend fluid. One of the bottles was Slick 50 gear oil. I then put in the additive.

Thanks Sherry, I am going to jack her up this weekend and try to get to all those ujoints and grease them up.

The car only has 40k original miles so I hope the clutch plates are not worn out.

Andy

 

[68Roadster]

That mysterious noise....

Andy,
This question has been posed many times on this forum and you wouldn't believe the number of possibilities mentioned. My car does this too and another Vette I had suffered also. You might also checke the following:

1. If you have a bad u-joint, it tends to knock/clunk when put under a load. My 81 used to do it when I got on the gas, usually going around a corner. Popping the half shafts out and looking at the joints confirmed my suspicion.

2. My 68 does it after loading up the car (straightaway high speed, fast cornering), coming to a stop and then proceeding on. It makes a noticeable couple of clunks that you can feel in your butt. When in for an alignment, Stingray6974 verified that the side yokes in the differential were worn and needed to be replaced.

3. Wheel bearings, worn spindle.......not fun to diagnose, even worse to pay for......

Good luck tracking it down. You might try a search on the subject and see what I have forgotten......

 

[69MyWay]

your posi clutch unit has failed.

i had the same problem with killer.

i had the rear rebuilt when i did the frame off, but only had done bearings and seals.

just yanked it during the 6 speed conversion, and had new clutch assembly installed.....now she is smooth as silk, and the posi locks up perfect with just enough slip so as to not clutter, shutter, and clunk when making turns and just starting off.

 

[crause]

Sounds like a major job. Can you pull the chunk without dropping the whole rearend? I only have 40k on the car, should it have gone out this "soon"?

Andy

 

[69MyWay]

Sounds like a major job. Can you pull the chunk without dropping the whole rearend? I only have 40k on the car, should it have gone out this "soon"?

Andy

you have to drop the whole thing.

often sitting makes the posi clutch go bad.

 

[Roy]

Rear End "Clunk" while Turning

The main suspect would be the spindle shafts that connect to the yoke are worn. To check this, grab the wheel/tire at top and bottom and rock back and forth. You will probably hear and feel the worn ends of the spindle shafts slapping.

Most Corvettes with over 80,000 miles suffer from this problem and it is expensive and a PITA to repair. Handling suffers but most owners live with it, most of whom don't even know they have the problem. The best way to prevent this wear is to change rear end fluid every 10,000 miles.

Do not put that garbage Slick 50 in anything, especially your posi-traction rear end that depends on a balance of lubrication and friction for the plates to work properly.

 

[crause]

Roy,

I thought about the Slick 50 issue after I put it in. I don't know what I was thinking when I put it in. I am going to suck it all out and start all over with the GM additive and GM gear oil. If this doesn't fix the problem I will start trouble shooting the rearend.

Thanks for all the advice.

Andy

 

[JBWeaver]

Ckeck the rear end mount. If its lose or worn it will cause a clunk. Easy and cheap to replace. It's a good place to start.