Broken diff?
 

Just need to verify something......

Car in the air, out of gear, spin one of the rear wheels and the other does not move. Something tells me this isn't right. Car in the air, in gear, both wheels spin.

if you look really close you can see the opposite side axle make what looks like an attempt to move. That's in the air, out of gear. It's as if, it clears the backlash and then doesn't go anywhere. It's acting like an open diff. I just need some confirmation or a correction please....

Does it make any noises when driving?

Dale

It's not running right now.... it will be soon

My March 1992 FD R1 with a 3.909 diff:

Tires in air, trans in neutral: rotate one wheel and the other will barely move then stop moving, does it from both sides and either CC or CW rotation.
Tires in air, trans in 4th: rotate one wheel and other rotates in the opposite direction, does it from both sides and either CC or CW rotation.

Wow....

I guess what it comes down to is I dont understand the relationship between the the gear the trans is in and how the diff decides to spin 1 or both wheels because of it. Just thinking about it, I dont think it should influence it at all. The car will be running again by the weekend, I will report back.....

There is enough brake drag to prevent the opposite wheel from rotating, since the trans is out of gear. In that case the prop shaft is easier to spin than the opposite wheel, so the prop shaft spins. That is totally normal. In gear is the only true test for the diff. I suspect there is nothing wrong.

The fd has a torsen type diff which acts like an open when there is no resistance at all, the mid air test doesnt do much good with it.

Correct - there has to be some torque (furnished by the prop shaft) on both wheels to make a Torsen engage.

I guess I'm just crazy. Of the fds I've worked on. I just never not seen both wheels spin. I messed with it again today and it was the same results as I described earlier. This time though, driveshaft removed I spun the diff at the flange and both wheels spun. So sitting there, spin it from the wheels and only 1 spins but spin it at the flange and they both spin. Drive shaft and trans installed, same result.

the clutch is being replaced which is why the car is the way it is....... for context

but thanks everyone, I've just never seen it act this way before on any fd I've ever messed with. Both wheels have ALWAYS spun. So I just needed clarification as to whether or not this scenario was an indication of a problem.

The car is running again and theres definitely something weird happening. Going from gear to gear in a normal manner the car gets squirrely. It's as if power is only being sent to the rear left wheel the way it kicks sideways. Also, when rolling backwards with the car not running, you can hear a creaking/light grinding sound coming from the rear.

Have you guys experienced anything with the stock diff that would indicate some sort of failure or malfunction?

Change the diff fluid and look for a lot of shavings on the drain plug. Also if you have low pressure in one or both of the rear tires the rear end will do REALLY weird stuff.

Dale

Or if you have different types/sizes of tires L v R.

Could easily be pads, bent dust shield or wheel bearings in the likely descending order for a grind, usually a clunk involved, if teeth break.

The definitive way though to find out if there's something amiss with the diff, is to pull the cover, rather than internet sleuthing. On the hoist, can change a complete diff in a bit more than an hour even with diff pump plumbing. Probably takes longer to pull and reseal the cover, remembering last time I did it, but if you undo the 2 diff mount bolts, the axles make a good support for the diff on the subframe while you do your dirty deed.