I have a 86 IROC-Z with a 700R4 transmission, when I go from Park to Reverse I hear a "clunk" noise. I also get the noise when I shift from Neutral to Drive.

Could this be the Transmission Mount?

Since the transmission is working just fine with smooth shifts from 1st to 4th gears.

 

I would suspect the U-joints on the driveline first. When were the last lubed or replaced?

 

I purchased the car about 1.5 years age as a project car. I haven't touched the u-joints yet. I'll try greasing them first.

 

If the U-joints are original equipment they're not greaseable. Take a look at the yokes, if they have spring clip retainers then look and see if there's a zerk. If you don't see clips retaining the bearing cups then they're the original U joints.

While you're under there, put a floor jack under the tailshaft of the transmission and pump it up slowly while watching the transmission mount. Usually if the car doesn't already have a polyurethane mount, the rubber will be rotten, and the two halves will be ripped apart. Usually the best indicator of a broken mount is when the transmission shifts into 2nd gear at WOT the transmission slams into the side of the transmission tunnel.

 

 

It's not uncommon for the threads in the subframe to be stripped out and the bolts for the crossmember to sit loose. It's an easy check and easily fixed by tapping to an oversize

 

Guys,

Thanks for the great tips I check them out this afternoon.

 

OK i got a problem i keep breaking trans-mounts
i have the factory mount on the car to about a year ago when i put nitrous on the car that mount was just blown apart so i went to autozone and got a other rubber one for $5 and it was fine to i took the nitrous off the car now i break a mount almost every month. i checked everything even changed the motor mounts and the driveshaft and U-joints

 

It is a known problem with these cars. A damaged trans can increase this problem. Most people solve the issue with a polyurethane trans mount.

 

which is a bad idea unless you like breaking the case.

Check driveline angles, they are a common reason for mount failures

 

Running a poly mount? Never heard of anyone having problems. But that doesn't mean it doesn't happen.

 

bad driveline angle + poly mount. note, this is a next to brand new transmission