I just got a 9 bolt from the junkyard today, and I would like to put some new fluid in it.

Is it 75w90, 80w90, 75w140, 80w140?

GL4 or GL5?

What posi/limited slip additives do you recommend?

Thanks

 

75W90 Mobil 1, GM 1052358 additive.

 

well, the posi additive for ( 9 bolt rears) is up in the air since gm no longer has that specific part number but, some are using the one listed above my self included- until I see why not to

 

CRC offers a product that meets the GM specification. Their's is called "Equa-Torque" and is P/N SL2411. I know that without the additive, my Borg axle chatters more than some of my former girlfriends.

 

If I use synthetic my posi does not hold, If I use regular gear oil and the additive my posi does not hold. I have to run regular Gear Lube with no attitive for it to catch. 20,000 and no additive my my rear works perfectly and I dont hear a thing. Yea I know the posi is somehwat shot but I havent had to put any money into it yet.