I called the owner of the local small NAPA store who I know personally. He walks around to the floor while I am still on the phone and tells me that he has two one-gallon jugs of GL 4 in stock. This seems to be consistent with the information Jason posted. Amazon also has some GL 4. The reason for the GL4 is that there is something in GL5 that attacks the internals of manual transmissions.
I have a gallon of it on the shelf for my car. The GL5 is too slick for the brass snychros. It must be GL4 only. Most heavy weights are sold as both GL5 and GL4 compliant which is were the trouble comes from.
I recently rebuilt the old Saginaw 3 speed from my 72 Skylark. Surprisingly, the old synchros and bearings looked remarkably good. Does anyone know what the original gear oil specification was in the early Seventies? I'm struggling to find gear oil locally (in pourable quart bottles) that is not a combined GL-4/GL-5 grade. The only GL-4 grade is Sta-Lube 85W-90 at $40 per gallon or O-Reilly's house brand MasterPro SAE 140 for about half the price. Since these are only in gallon jugs, pouring it into the transmission might be a pain in the neck. I did find some Pennzoil Synchromesh that is rated GL-3. Would this be a good lube for a rebuilt Saginaw? The research I've been able to accomplish so far seems to indicate that a GL-3 gear oil has none of the sulfur compounds that GL-5 has (and GL-4 is supposed to have, but at half the level). Instead it sounds like the additive is mostly ZDDP as a wear preventative. I'm unsure if this is the best gear oil or not. If anyone has any insight, I sure would appreciate it!
Without the slipyoke, wouldn’t it all just leak back out the tailhousing? The slipyoke is pressed on to the driveshaft via the front u-joint, so I can’t just stick it in there.
