I recently changed the differential fluid in my 89 GTU's with Valvoline synthetic gear oil (75w90? ). Now after doing so I was looking at the owner's manual and noticed that it states to only use SAE 90 in a LSD. What gives?? Should I be looking to change that oil again or am I safe? Any comments?

 

yea most ne 90 weight 75+ long as its gear lube

 

That's the same stuff in my Rex's Diff.

 

U'll be fine w/ that. I use that too.

 

I don't think synthetic gear oil was used very much in 1989. Your fine.

 

Just don't drive it hard when cold or first starting out and the 75W90 should be fine. The 75W is a little thin when cold.