most people putting MTL in their transmission? why is that? i would think MT90 would be better? also i filled the trans about 2.5 and the rear diff 1.5 quarts. that sound right? that was listed in the manual. i had the car up on jack stands so i couldnt tell if it was full and i didnt want to add more incase it overfilled.

 

agree mtl 70W80 is too thin for hard driven/mod'd FD.

But MT90, blended for good shifting, might not be best choise for LSD rear. redline suggests 75W90 gear oil, and I use an extra shot of friction modifier.

 

MT oils are not for the diff. You don't need friction modifier, either -- the Torsen doesn't need it.

-Max

 

Agreed, I used MT90 in my tranny and Redline 75W90 gear oil in my diff and had nothing but the best results.

 

It doesn't 'need' it, but amount of torsen lock can be tweaked based on fluid friction. torsens are all about friction. My preference for my mixed use is less lock, achieved with the extra shot of modifier (slick stuff).

 

WRONG
The friction modifier is for clutch plates, of which the torsen has none. Syn gear oil is as slick as you can get unless you go to teflon or something. Regardless, the torsen is designed to work with the exact coefficient of friction of gear oil. Anything else can just hurt.

 

tmiked and maxcooper are correct.

The Redline that I have used on a 230k miles FD with original diff and tranny is the MT90 in the tranny and 75/90NS in the diff.

Right now I have the Shockproof Redline diff fluid, but I will be going back to the 75/90NS to go back to the original HP and MPG when I was running it.

THe Shockproof is so thick. I think it's in the mid100~ weight. It's idle for people that race, and beat their diffs alot.

 

Hogwash. If it is designed for and exact friction factor only, then they would specify the exact lube, and you could not run both dino 85W90 and alternatively "as slick as you can get" syn gear oil. "Gear oil" does not have an exact friction coefficient.

No clutch plates, but lots of critical friction surfaces of similar function, that are not the gear meshes. Enough friction to turn the redline gear oil black after 4-6 track events at a road course.

If you want a lot of lock, run redline NS gear oil, MT90, or dino gear oil. For less lock, shockproof or synth with xtra modifier. Mazda specs both GL4 and GL5 for the diff.

 

so the problem im going to have with the mt90 in the rear diff is going to be too much wheel spin?

 

I thought it was too much wheel hop?

 

I noticed virtually no difference between the diff fluids that I used on the torsen's performance.........

 

try it. mazda says a GL4 is ok, but redline obviously does not recommend it for diff's. main issue could be too much locking/grab, and spinning both wheels in wet conditions/corners.

http://www.redlineoil.com/redlineoil/gearolti.htm#75W90

redline would recommend their 75W90 gear oil. call them.