i want to change the diff. fluid in my 99 fullsize van and want to know about how much fluid does my diff. take. i have the 9.25 rearend with trac-lock. i know i have to buy friction modifier, and i want to put in synthetic fluid but i don't want to buy too much or not enough so i don't have to run back and forth to the store. the owners manual says to use 75-90W is that right or should i use another viscosity?

 

Buy 3 Qts + the additive
Use 75-90W
DO NOT OVER FILL!!!!
when it starts to run out of the "fill hole" take a break, let it run down to the proper level BEFORE you put the plug back in!
If it's making noise going straight down the road changing the fluid will NOT help!!!

 

well the manual says to fill it up to about 5/8" below the fill hole. i put in 1.5 quarts plus the additive and it is already to that point is there enough in there or should i put in more. i took it for a drive and let it run back down and the fluid level did not change. the diff. is not making any noise i just wanted to put in synthetic fluid.