Here's the deal. I'm adding the limited slip additive into my 85 Z. I removed the plus in the differential case to drain a little fluid and a **** ton of fluid came out. Now I was taught to check your fluid you take the plug out abd if you can touch the fluid with your finger then your good but this one was practically full. My question is does it need to be full and if so how do I fill it past the plug?Or am right about the fluid level and it's ok to be below the plug level? Any info would be helpful. Thanks.

 

Sounds like it was over filled. You're correct. The level should be right at the bottom of the fill plug opening.

 

I have had that happen a few times. I was hoping that it would be from PO over filling. Oh no, it was because the differential was full of chunks of ring and pinion teeth. I would pull the cover and take a look.

 

I have known a few people who thought that the vent on the top of the housing was where you put oil in. Then there are the after market covers that have a fill hole that is higher than the original hole in the side of the housing. It's easy to over fill when using one of these holes. If you have an after market cover with a fill hole then you should remove the original plug and fill until oil runs out this hole.

 

I had the cover off last night checking everything out. Everything looked good. I bought this car from a body that I went to school with. It has only been a year since he got the car from his dad who bought the car new in 85. Very close to a one owner factory Z. Anyways my buddy about 6 months ago took the car to some little crap garage to have the rear end replaced...I'm thinking whoever down the work filled it up while they had it out.Seeing all that fluid come out just made me wonder. Thanks for the help guys.

 

If in doubt, Empty and Refill yourself, then you know for sure.. If it has the factory limited slip, you'll need to get the additive, Common item at the dealer.. Simple as that..