[6d7gto]

What is the best oil to put in a newly rebuilt Muncie 4 speed?

[455Grandville]

Gear oil. 80w-90.

[Murf]

Sta-Lube SL24229 API/GL-4 Multi-Purpose Gear Oil, 32 Fl Oz https://smile.amazon.com/dp/B000KKHO...4EJSQBRA1X0YWJ

This is what I’ve always used. Can be found at most NAPA stores. It is GL4 rated. Suppose to be better for transmission’s with brass syncos although a lot of guys swear by GL5 lube.


Murf

[geeteeohguy]

Originally Posted by Murf

Sta-Lube SL24229 API/GL-4 Multi-Purpose Gear Oil, 32 Fl Oz https://smile.amazon.com/dp/B000KKHO...4EJSQBRA1X0YWJ

This is what I’ve always used. Can be found at most NAPA stores. It is GL4 rated. Suppose to be better for transmission’s with brass syncos although a lot of guys swear by GL5 lube.


Murf

This^^^^^. GL4 is better for the synchros in terms of friction co-efficient. The brass getting eaten is a lie perpetuated by the internet. There are no instances of it actually happening anywhere or any place that I have been able to find in the past 40 years.

[6d7gto]

Originally Posted by Murf

Sta-Lube SL24229 API/GL-4 Multi-Purpose Gear Oil, 32 Fl Oz https://smile.amazon.com/dp/B000KKHO...4EJSQBRA1X0YWJ

This is what I’ve always used. Can be found at most NAPA stores. It is GL4 rated. Suppose to be better for transmission’s with brass syncos although a lot of guys swear by GL5 lube.


Murf

Ordered a quart through your link. Thank you and all who responded.

[Sirrotica]

FWIW, decades ago I believe it was Hot Rod magazine that suggested adding 10% STP on a 4 speed rebuild. I tried the suggestion after rebuilding a T-10 and a few Muncie's, all the transmissions shifted like a knife through soft butter with the STP added. I would do it again today if I was wanting a smooth shifting manual transmission.

[chrisp]

Sta-Lube SL24229 API/GL-4