Transmission VS Gear oil

[tucsonlx]

What is the difference between manual transmission oil and regular gear oil for a differential? The reason that I ask is that I have 10 quarts of Redline MT-90 that I used to put in the transmission of my old truck. I was going to swap the diff fluid in my LX to some synthetics and I was wondering if I could save $50 and use this or if I am better off just spending some extra and buying some Mobil 1 or Redline oil specifically for the differentials? I would assume that the transmission oil just has more additives in it for smoother shifting, would this hurt the seals or anything in the differential? Thanks for the help.
Aaron

 

[Doc]

I don't konw the specifics, but I know gear oil smells a whole lot worse than tranny fluid.

No, you can't use tranny fluid in your diff's, I hear it causes BIG problems.

 

[RavenTai]

[quote author=Doc link=board=2;threadid=17199;start=msg166855#msg166855 date=1086016409]No, you can't use tranny fluid in your diff's, I hear it causes BIG problems.
[/quote]

He wants to use a manual transmission fluid not an Automatic Transmission Fluid,

Used to be 90wt was 90wt and could be used in either diffs or transmissions, but we are starting to see a separation and specialization between the two with GL-4 for transmissions and Gl-5 for diffs with many applications calling for the use of either,

MT90 is about the right viscosity and it should have no more effect on seals than any other true synthetic gear oil but it is specialized for transmissions it has a lot of friction modifiers and additives for synchro's not found in most gear oils, I do not know what effect his would have in a simple diff, it would probably play hell on one with a clutch type locker or posi but would have no effect on the 80's locker, also MT-90 is a GL-4 diffs usually call for GL-5 but IIRC the 80 specs either EDIT ***see below

This would be a excellent question for the gear oil section over at BITOG, they could give you a better answer

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=forum;f=16:DaysPrune=1000

 

[RavenTai]

just checked the owners manual, the Transfer can take GL-4 or GL-5 the diffs take only GL-5

so MT-90 is not suitable for the diffs, possibly use it in the transfer case?

 

[Jonathan_Ferguson]

so MT-90 is not suitable for the diffs, possibly use it in the transfer case?

Synthetic SAE 90 GL-4 should be fine in the Transfercase, As the Manual says SAE 75W/90 GL-4 or GL-5.

 

[cary]

GL-5 for the diffs has different additives to prevent it from being sheared apart. It used to be those same additives would eat the brass syncros in a GL-4 speced gear box so fluid was one spec or the other. Bottom line is do not use a GL-4 oil in the diffs as it will not provide adaquate protection. Go buy some Redline 75w-90 gear oil for the diffs.

Cary