Differential Gear Oil?

The '73 TSM calls for MiL-L-2105B for the Dana 30 and Dana 44, is GL4 an acceptable replacement?

 

Yes. Yup You can use GL-5 in the differentials no problem. If you have a clutch type limited slip like a factory Trac-loc you will need to add friction modifier.
You want to use GL-4 in the transmission.

 

Can gl4 also be used in the diffs, or just the tranny?

 

You can use GL4 in the differential, but most people don't because GL5 works just as well and is generally cheaper.

 

GL-4 is fine anywhere. It is GL-5 that needs to not be used where there are brass or bronze parts

 

See my reply right after your initial question.

 

I use 90wt GL-1 in my transmissions and differentials, with the additive for limited slip differentials in my CJ5 which has the Powr-Loc.

 

Cool, thanks!

 

Will his work in my 68 front diff?

Slim pickings here in the flaps.

 

My apologies to everyone. I thought I had posted GL-4 is ok in the differential but GL-5 is ok and less expensive. I blame my lysdexia and head traumas.

 

That will work in the differentials but expensive. Regular dino (mineral based) oil is fine.
If you have new gears and need to break them in do not run it. Run mineral based until broken in.

 

Sorry I didn't say, but I have a locker in my front axle, that's why I'm not sure what to use for diff fluid.

 

It depends on whether you have a locker or a limited slip. Limited slips like the friction modifiers.
-Donny

 

I have a limited slip.
So, gl5, with a little bottle of friction modifier will go in my diff?

 

Is it a clutch type or gear type limited slip? A torsen gear type wont need the friction modifier.

 

Clutch type:

 

That’s a gear type locker not a limited slip. Lock-Rite, Aussie locker, etc. No additive needed.
Pretty much only clutch type limited slips need friction modifier additive. Units like Powerlock, Trac-Loc, GM G-80, etc. etc.

 

I use straight GL-5 Mobil One in all my PowrLoks with zero problems and get normal wear which is very many thousands of miles on a standard clutch pack.

 

Thank you for the clarification. Normal 80/90 then, I'll be fine?