noise determination help?

[mlm0]

On my 1989 vette with auto transmission, when I let up on the gas and then apply gas, I get a clunking noise that sounds like it is coming from rear of car. Happens almost every time, but does not happen under normal up shifting. Is there a way to determine if its a drive shaft u joint, half shaft u joint or problem with slop in rear gears, before I just start throwing money at the problem? I replaced the rear upper and lower control rods on both sides with new bushings. Car has 46000 miles.

 

[hcbph]

Noise

My money's on the half-shaft u-joints. Jack it up, grab the half-shaft and hold it tight and try to move the tire forward and rearward and see if there's motion. Could be either side and either end, but I'm guessing it would be on the outside u-joint. If they're bad, I suspect you'll feel something, I did on mine.

 

[mlm0]

thanks, I'll give that a try. If that's it, have any idea of how much it cost to have one replaced.

 

[hcbph]

Cost

My mechanic quoted me $600 to do all 4, u-joints cost a little over $100 for 4 at Rockauto. If you want to see what's involved, check the first part of this thread: C4 - Rear Hub Replacement - Corvette Forum : DigitalCorvettes.com Corvette Forums
I did mine the other month, I had to get a few extra things, mine still came in under $200. It's really not that hard to do if you're mechanically inclined and have some basic tools plus a few that are a little more specialized. Biggest problem I ran into was dropping some bolts during reassembly, not easy to find them once dropped.

If apart, do both on a side.

 

[WhalePirot]

Recommend the Spicer, non-zerk fitting ones; stronger.

 

[Hib Halverson]

Inspect the powertrain mounts in the rear. Repair/replace as necessary.

Also, inspect the bolts and nuts holding the C-beam to both the rear axle housing and the transmission tail housing.

 

[hcbph]

U-Joints

Recommend the Spicer, non-zerk fitting ones; stronger.

I used the Moog zerkless ones. My convertible had the Spicer ones in it, they had gone to heck in a handbasket. Bunch of rust along with a number of the needle bearings being virtually gone from the rust and apparent lack of lube. Unless someone does a lot of drag racing, I suspect either brand will work and if installed correctly should go a while. I don't know if my old ones were done correctly or not as they were going bad when I bought the car. I know the new ones were done right though so that's what's important.