So in reading about rear diff gear oils and the 8.8, I have read quite a few different things.

Don't wanna F up my diff if possible. Yall are both using non-synthetic 75w140 or 85w correct? Seems most folks on the mustang forums are going with 75w90 for their 8.8s with friction modifier. About how much are you putting in there and do you use a friction modifier?

I ordered the pump but will just head to autozone tomorrow to get the oil and modifier (if needed). Thanks again for yalls help with a rear diff noob.

 

I use Amsoil Severe Gear (75w150 synthentic). Not positive, but I believe friction modifier is only needed if you use non-synthetic (conventional) gear oil.

 

What type of LSD is in the rear end, clutch or helical? Clutch type requires friction modifier, helical doesn't. I've heard you don't need friction modifier if you use synthetic in a clutch type lsd which I found out is BS first hand. Your clunking while turning indicates to me that you have a clutch type lsd which may just require a little more friction modifier put in, the clunk noise is the lsd clutches grabbing while 1 wheel wants to turn faster then the other during a turn. 75w140 will do and friction modifier if you have a clutch LSD.

 

I have no idea on the LSD in there. I have owned the car a week now and am still a rookie in regards to rear differential. So you are saying to use synthetic 75w140 AND friction modifier? I can afford to take it to someone, but I prefer to learn on my own... I have avoiding learning about rear diffs long enough.

Maybe I have some youtube videos to watch today... plan on changing the rear diff oil tomorrow.