im swapping a damaged rear axle out of my 91 rs with a new set off ebay. im wondering what type of replacement differental fluid i should use and how much? thanks

 

One of the beter synthetics, such as Mobil1, Amsoil. Red Line, etc. 75W-90 or some such. The exact numbers aren't real critical. NOT the super thick stuff like 85W-140.

 

i use M1 and amsoil 85w-90 with no problems. if you have a clutch type posi use the gm posi additive.

 

85W140 is just VERY slightly (only ONE step!!) thicker than 75W90, and is a very good choice for our axle's!!
85W140 synthetic has almost the same weight as 75W90 dino!!(but is superior in every way!)
Synthetic oils are due to the way they are made always slightly thinner when compared to a not synthetic oil of the same specifications.
You just can't compare weight specs. of engine oil with gear oil!
F.i. XW90 gear oil compares to Xw40 engine oil and XW140 compares to XW50 engine oil (you see, only ONE step.....)
Know what you're talking about before giving any advise!!!!

 

I have a question related to this, I have read somewhere that with the top of the line synthetic rear end lubes, ie. Royal Purple, Red Line, etc., the posi additive is not required. Is this a true statement or is it bogus. Thanks in advance.

 

that's what they say but for 6 dollars a bottle i'll use the gm posi additive reguardless of what the oil makers say

 

when i put in my slp zexel torsen, do i need to use the posi additive, cause it doesnt use clutches does it?

 

don't need the posi additive if you don't have clutches.

 

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