Rear Diff Oil

[TooMuchMuscle]

I cant find my factory diesel booklet and am waiting for my Helms catalog but need to know what oil to run in my rear diff. Will 90W Gear Oil work? Thanks

[thechevyhdman]

NO NO NO....The rear end must use a 75w 90 or a 75 w 140 rated synthetic oil. The oil must be a GL-5 rated synthetic lube. I personally used Valvoline SynPower 75w90 oil for use in Hypoid gears. It was pricey like most syn. oils $7 or 8 bucks a quart. get 5 quarts of it as I thought it would take 4 only but mine took almost another 1/4 to 1/2 bottle more. Theres been alot of threads on this topic... Get it done ASAP.