correct oil for posi 7.5 rear

[71GTKammback]

I kniw for certain that the original style 7.5 chevy rear end took auto trans fluid and not gear oil. They even had a tag on the rear end saying this. My differential is a 7.5 monza that was non posi but has been converted to posi via and Eaton unit. The oerson who did the change said they used Royal Purple in it. Should i use that or auto trans oil? Thanks guys.

[cjbiagi]

Where did you hear or see that a 7.5" rear takes automatic trans fluid??? That is totally incorrect, the spec is for gear oil is 80W90 gearoil for standard rearends. If you have a posi then you should get gear oil designed for posi rears or get the posi additive from GM. The only tag that was attached to the rearend was those with a posi indicating to use special limited slip oil.

[spencerforhire]

OP must be thinking of the T-50 5-speed; that was the first thing that I remember that took ATF instead of 80w-90 gear oil.

[71GTKammback]

Oh right, it was the 5 speed on my vega that took the tranny fluid. Thanks

[cjbiagi]

Ok, yes there were some manual transmissions that did take automatic trans fluid.....

[NVEGAR8D]

Hi,
Last year when i was in Buffalo N.Y. , I stopped into a part store and the attendant asked if i also needed some diff fluid ,so i got some for my posi monza rear end . It's Peak Performance SAE80W-90 GL5 gear oil one gal. and Sta-lube Equa-torque differential friction modifier.