I have a non-turbo '82 280ZX with (I believe) the R180 diff. Whenever I shift (or otherwise abruptly apply power to the rear end) I hear and feel a loud "THUNK".

From what I can tell after jacking the back end up, one of the half-shafts seems loose. With the car in gear, if I try turning it, it moves a few degrees in either direction. If I do the same thing with the other one, it does not move at all.

Does anyone know what would cause this and, more importantly, what I can do to fix it. I have already drained and replaced the gear lube in the diff.

 

Alot of the time that thunk can come from the solid diff mount wearing out or your U joints starting to go. Give those a good inspection. From what it kinda sounds like one of your u joints in your half shaft are starting to go. You could pull the boot on it to inspect but make sure you get a replacement boot from your local parts store first or zcarsource.com or thezstore.com.

 

it's the diff mount I'm sure, mine's ****ed up too. it's not a solid mount, it's some rubber piece of crap lol

 

Yeah, my guess is the rear diff mount. Part#55476-p6560
I just picked up a new one a couple days ago. That mount is two part with rubber inbetween just like a motor mount. Its very common for them to be completely seperated and it's not easy to find a good one at the junkyard.

Jack the rear of the car up and support it with jack stands at the rear
jack points with the wheels off the ground. Have a friend you trust start it up, put it in gear and let the clutch out to make it clunk while you watch. If the mount is bad the
the diff will jump around. If it passes this test then your problem is a u-joint or cv joint.

 

more likely you got a R200 in an 82. the R180 looking at it from the rear is more of a rectangle about 6+ inches horizontal. the R 200 is more square about 8+ inches horizontal. with out a ruler they look a lot alike. but the above is still valid.

 

its prolly both actually, but id do that u-joint first. i had one actually crack and come apart, not fun. altho mine was caused by power and abuse check to make sure your ebrake isnt sticking either or even the caliper, that helps wear parts out faster.

 

I agree with Shady it probably is both; cause and effect.

A worn diff mount puts alot of stress on a halfshaft u-joint from the angle change under a heavy load. Like high rpm clutch drops with sticky tires.

I broke an outer u-joint just like that once while passing a car on the highway at about 70mph. It was pretty dramatic because the lose axle flopped around alot and wiped out the brake line and also put a good dent right next to the fuel pump... Luckily it was right before an exit and I was able to coast to a stop (with no brakes) up the exit ramp.

Something to note also is that if you jack the rearend up by the bottom of the differential it compresses the mount with the wieght of the car making it easy to miss the fact it's worn out.
Mark.