What oil to use for transmission, and diff? Diff is a limited slip, and has manual trans. What Weight? Best brand?

 

Given your username, are you asking for an 85 GSL? There is a lot of debate on this as people prefer different brands and will deviate from the factory specified weight. I have used Redline MT90 in my manual transmission on my FB's for years and have had great luck! I have been running Motul in my Porsche 944 and the stuff is also amazing.

For the rear differential, if you have a limited slip differential, you will need a friction modifier or buy a gear oil with a modifier already added in to the gear oil. Amsoil 80W90 has treated me well over the years. I have also used Royal Purple 80W90 in the rear diff on my 85GS and its been fine and has given me 0 issues! If I need to add a friction modifier, I use BG LSII.

 

Im asking for a gs on what oil to use

 

The answer can be found here for diff: http://www.foxed.ca/rx7manual/manual...rear_axles.pdf

12A - Standard rearend (non-LSD) 1.3 quarts
12A - LSD rearend 1.6 quarts
SAE80W for 0 degrees or lower
SAE90W for 0 degrees or higher

Brand is up to preference

For LSD ensure to include LSD additive. Ford make a good one.

Manual trans uses same oil. About 1.5 Quarts from the top of my head. Ensure to remove filler bolt first before removing drain plug on trans.

 

any 80/90 weight gear oil will suffice. with the drum brake rear u won't need the additive necessary if it were an lsd.

 

Amsoil here. i've always heard good things about Redline transmission lubricants - since the 90s, and would like to try it someday, but so far i have only used their motor oils.

80W90 is good and as Mazdaverx713b said, you will need an additive for the LSD.

 

Amsoil 80/90

 

Redline MT90 in the manual trans, Redline 75W90ns (NS has no lube additive) then I add 1-2oz of additive in the rear. I find the one with the additive in it have too much, and can make the rear slip. None at all will lead to binding in the rear (you'll hear it). You want enough to stop the binding but not make your rear end crazy loose. I race my 85 GSL, so maybe for regular driving the slippy rear won't be as noticeable. Dunno. I do know I change trans and rear fluids annually, and the rear smells horrible when I do... I don't know why it stinks so bad.

 

cosign on this. minus the royal purple. had a bad experience with that brand a while back and never used them since (im old)