Redline MT-90 ok for rear diff?

I need to do a fluid swap on my rear end and have a bunch of new MT-90 left over from tranny fluid swap. Wondering if it is ok to use MT-90 in the 8.25 since it's 75W-90 which is what I think the diffs call for? Thanks!

NO! MT-90 is GL-4 & for transmissions. You need GL-5. Something like this:

https://www.summitracing.com/parts/...ynthetic-oil&gclid=CKSvspuP39QCFQItaQodkPMNJg

Been running 50/50 40w and Lucas in both axles for about 40K miles.

30W in the trans.

eightsevenzero said:

I need to do a fluid swap on my rear end and have a bunch of new MT-90 left over from tranny fluid swap. Wondering if it is ok to use MT-90 in the 8.25 since it's 75W-90 which is what I think the diffs call for? Thanks!

Click to expand...

Not a good idea at all, you need high sulfur in the rear end diffy fluid, and some limited slip additive. MT-90 has neither.

md21722 said:

NO! MT-90 is GL-4 & for transmissions. You need GL-5. Something like this:

https://www.summitracing.com/parts/...ynthetic-oil&gclid=CKSvspuP39QCFQItaQodkPMNJg

Click to expand...

Just clarify for future readers it is not for use in Automatic transmissions. Yes MT-90 Is great for manual transmissions with brass synchros. I thought MT-90 was sulfur free GL-3 ? GL-4 has too much sulfur IIRC.

Jeep Driver said:

Been running 50/50 40w and Lucas in both axles for about 40K miles.

30W in the trans.

Click to expand...

Not a good idea for either, especially the rear ends. They need high sulfur and a limited slip additive. MT-90 is far better for a manual transmissions, its synthetic. Never to be used in automatics, just to be clear..

Hey Ecomike,

You are correct, never for automatics. I didn't think it needed clarification since OP was referencing his manual tranny in the first post, but may help someone. In manual transmissions I've only seen references to GL-4 or motor oil. I have never really seen a use for GL-3 and forgot it existed (if it still does).

Cheer!

GL-4 can have tons of sulfur that can eat brass synchros fast. Ask me how I know, LOL

md21722 said:

Hey Ecomike,

You are correct, never for automatics. I didn't think it needed clarification since OP was referencing his manual tranny in the first post, but may help someone. In manual transmissions I've only seen references to GL-4 or motor oil. I have never really seen a use for GL-3 and forgot it existed (if it still does).

Cheer!

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MT-90 has zero sulfur!!! Other GL-4's may 1/2 as much sulfur as GL-5

http://machinerylubrication.com/Read/30366/gear-oil-applications

"While a manual transmission does in fact have gears, it may also contain other components such as synchronizers. The gears and synchronizers have seemingly conflicting requirements. In general, the higher the GL rating, the higher the extreme pressure (EP) protection provided. This is great for reliability and wear reduction in hardened gear sets, but it can spell disaster for synchronizers. EP additives are often made of a sulfur/phosphorus compound that will adhere to metal surfaces through polar attraction. Once they have coated a metal surface, these additives need only to be introduced to heat and/or pressure (from a collapsing lubricant film) to spring into action and start doing their job. In a hardened gear set, this adds a great deal of wear protection as well as life and reliability to the component.
However, because of the mechanism in which these EP additives work, when they are introduced to softer yellow metals, the results can be disastrous. They attach in the same manner (metal-wetting polar attraction), and when heat and/or pressure is introduced, the additives will chemically attack the softer yellow metals. This aggressive attack can prematurely wear out synchronizers.
GL-4 products typically use about half the sulfur/phosphorus additives of their GL-5 counterparts. "

md21722 said:

Hey Ecomike,

You are correct, never for automatics. I didn't think it needed clarification since OP was referencing his manual tranny in the first post, but may help someone. In manual transmissions I've only seen references to GL-4 or motor oil. I have never really seen a use for GL-3 and forgot it existed (if it still does).

Cheer!

Click to expand...

GL-4 (or was it 3?) nearly ate my Brass synchros in 2-3 days, about 100-200 miles on a new parts Man-Tranny. It would no longer shift.

Switching to Redline solved the problem