Differential Problem
 

I have been noticing a slight clunk/noise from the rear when first starting off or when shifting to second recently. I was thinking it might be the U-joints in the driveshaft, but after getting under there today and looking I think it has something to do with the differential.
I felt the driveshaft and it felt solid, but when I turned it I could feel slop/play in the area of where it connects to the diff. It would rotate about 1/2 inch either way before spinning the wheels. It just felt like something is worn out. The drivetrain has ~150+K miles on it with a few drag seasons. I searched quite a bit and couldn't find exactly what this means. Is something broken or just wearing out? What is involved with repairing it? Thanks.

how did your front diff mount look?

How's your front diff mount? Can you move it up and down at all? A clunk when starting off or with harsh throttle engagement can be a broken front mount. https://www.rx7club.com/2nd-generation-specific-1986-1992-17/pinion-snubber-diff-mount-replacement-convertible-876959/

I know about the diff mount, thanks guys. It's not the diff mount. I have a pinion snubber, so the diff can't really move at all. As I said there is slop/play in the section after the driveline inside the diff casing. I was reading it could be a worn out LSD or some problem with setting backlash. I just don't know squat about the diff area yet. I imagine I will just have a local driveline shop take a look.

all diffs have play in them.
if it's one clunk when you shift, it's your diff mount. mine looked fine until i put it in a vice an pushed on it opening up a large crack.
if it's a series of light clunks that change with RPM, it's probably your inboard CV joint.

Well I guess it could be. I didn't thoroughly inspect it. It's not really a clunk just hard to put into words what it sounds and feels like.

this is what im getting and its brutal!!!! happens when im in boost.....

and there not light clunks there hard savage clunks that i can feel hitting the underside....

if i remember correctly. the CV joins should have zero rotational play in them. if there is then head to the part store buy a new one and swap it out. it's really not that difficult.

what? zero play? it is easy to swap out i just replaced them with some i bought off a forum member...unless its those new ones that have gone bad

i'd look into it more then just relying on me. i haven't looked into the exact criteria on CV shaft replacement requirements. I know mine is clicking so i'll ask a mechanic about them next time i see him.

i see because i swapped out the axles and i got clicking while turning on the other axles so i know what to hear for. but the clunking i get is similar to a broken front diff mount where the front of the differential hits the car...exept its like a series of hard blows that u can actually feel!i will drop the subframe soon and replace everything including the cv shafts but i kinda want to know what the issue acutally is...im thinking its the lsd, could is be the lsd?

check your drive shaft for play

u have the yolks looked fine, ill have to check for play

/Thread Jack... LOL hope we both get it fixed.

Well after changing out my 3rd rear diff this week i have come to find that what you're describing(in my experiance) was a broken spider gear

i was kinda wondering if it would be that i was hoping it wasnt but i would figure the car would not move at all if it were to be broken no?

you will move just fine, but you will hear a clunk in any turn, and occasionally in a straight line. it will usually originate from one side, unless both sides are broken. the swap isnt horrible, just a pain if you follow the haynes manual (and dont drop the sub frame). I have an extra one available (with a catch) if that turns out to be the cause. hope it works out for you

Pm me with further info. thanks.

the issue was that the rear swaybar was hitting up top because the car is lowered and the minor wheel hop was contributing to the harsh clunking....raised the car up 2 inches and installed a preloaded pinion snubber....good bye clunking

I'm haveing the same problem as the OP. Even while babying the car the clunks are brutal. My front diff mount has been welded up nice and solid so its not that. Not my uv joints either, already changed them. Happens at any takeoff or any shift, doesn't matter how soft and gentle u try to be. It feels like the diff smacking the car but that isn't possible. How would I check the half shafts coming out of the diff? Btw, my clunks ALWAYS happen, not just turning or any other special condition. Any help would b appreciated.

post a video, put the car on a lift and take a closer look, is your car lowered?

Factory ride height in the back. What's the correct way to check the half shaft axles coming out of the diff? I have spares if they're bad

Not the half shaft axles or cv axles period. I popped them out and checked. Still no idea what's causing this