3 Speed Tranny with 3 in a Tree (1966 Chevy C10)

[mjs94080]

What kind of gear oil do I use?

[Jurassic-1]

Usually it will take 75W - 90W gear oil.

[mjs94080]

so, its not GL-1 90 weight gear oil?

theres 75/90, 80/90, 85/90

I been reading "straight 90 weight" only.....

[66Submarine]

I have GL-1 90w in the SM420 in my truck; It's available at NAPA for $13 a gallon (IIRC).

The other stuff also works.

[mjs94080]

Killer dude! Thank u Sir!

The "other stuff", meaning, 80/90?

Originally Posted by 66Submarine

I have GL-1 90w in the SM420 in my truck; It's available at NAPA for $13 a gallon (IIRC).

The other stuff also works.

[NEWFISHER]

Yes

[rustbucket66]

Transmissions typically use 50 W and rear diffs use 80/90 W. I worked on trucks as a heavy duty mech for over 20 years and I never saw 80/90 go into a transmission.

[66Submarine]

Originally Posted by rustbucket66

Transmissions typically use 50 W and rear diffs use 80/90 W. I worked on trucks as a heavy duty mech for over 20 years and I never saw 80/90 go into a transmission.

"50W" engine/trans oil is supposedly the same viscosity as "SAE 90" gear oil; different rating method. GM themselves called for the SAE 90 (GL-1) gear oil IIRC.

80w-90 is also fine, yes. There is some debate about (at least certain) GL-5 rated oils being corrosive to yellow metal parts like synchronizer rings, so most say to use GL-4 rated oil (which is somewhat hard to find/kind of expensive IME).

I'd just swing by NAPA and pick up a jug of the SAE 90 GL-1.

[mjs94080]

Thank you guyz! You've been LOTS OF HELP! I just picked up a gallon of GL-1 sae 90.