Reading on Novak's site i see they recomend GL-4 gear oil for the SM420. I have looked several different places and cant seem to find GL-4. I have found one brand that says "meets GL-5, GL-4, GL-3 requirements". Will that do the trick? I have also found a gear oil that penzoil makes that is specifically for GM manual transmissions, but it is over $6 a quart. Can anyone point me in the right direction?

I wouldn't use the GL-3, GL-4, Gl-5 stuff. Basically it is GL-5 so it meets the requirements for all three. However if your tranny needs GL-4, GL-5 has an additive that will cause you problems. There is some info on the Penziol site. I have found GL-4 at BI-Mart, basically and Oregon/Washington Wal-Mart type store.

Saw some of that stuff at checker auto the other day. Not sure if it was the G3, G4, or G5 combo, but I saw G-4 on it.

Dude, the 420's ancient. Made before additive laden gear oils. I've always just run 90w and never had a problem.

You could piss in one of these gearboxes and it'd still be bombproof. Use GL-5, it'll be fine.

You could piss in one of these gearboxes and it'd still be bombproof.


Untill it got below 32*.... :flipoff2:

GL4 is for gearboxes with yellow metal synchros. The GL5 eats up yellow metal and ruins the synchros in time. If your tranny has yellow metal in it you should use GL4. Pennzoil and Quaker State have GL4 and you can go to their sites and read about the yellow metal corrosion.