Preferred Tranny & Rear End Oil

I don't know about the tranny since mine's an auto, but I'd recommend synthetic for the rear, that is if you have all new seals. Supposed to be good for a few horses and mileage.

 

Matt

Absolutly go with the synthetic for both. Less heat, less wear. Be prepared, tho, for small leaks to appear, unless you have new seals installed. If you don't need the hassle, use a regular 80/90 wt. gear oil in both, with the posi additive in the diff., if you have a posi, which you should.

Went with Red Line gear oil for the rear...make sure it's the one with the posi fluid in it already. My M21 leaks some so I went with good 'ole Valvoline (I believe it's 85w-90). The smaller molecules of the synths flow through the cracks easier....and at $7.95 a quart. My $0.02 worth.

JR

P.S. How's that for name-dropping?

jredding38427.1674305556

Thanks for the feedback. The rear end is pretty tight - looks like it's been reworked from the way it has been sealed, but the M21 like all the other old trannies has a few leaks here and there, so I will try everyone's advice.

Nothing like a tight rear-end (sorry,couldn't resist).......My diff 's ok, too, that's why I have the synth in it. I asked the Red Line tech guys if additional limited-slip fliud was needed for proper functioning, they said a resounding NO. No chattering or clunking. Now, the oil marked NS is a different story. That has no posi fluid in it. Hope all this helps.

JR

jredding38427.3640625

I can see using dino or synth in the back of the car, but I have never oiled my rear end.  I think it would make me slid off my chair.   (sorry)

.......this might be getting out of control.

JR

jredding38427.5557060185