The Stovebolt Site Forums The Shop Area Driveline Gear oil for transmission

I currently have a synthetic gear oil in the transmission of my '56 half ton and notice the gears grinding once it gets hot and I try to shift into 1st. I've read here that the synthetics can cause the synchros in older transmissions to have difficulty and I'm wondering if that's what's going on. The transmission is a Saginaw 3-speed manufactured in 1967.

get some 85-140 non synthetic. it is not a slippery as the synthetic and will actually slow things down and make shifting gears smoother.

The Saginaw has a fully-synchronized 1st. gear, so if it's grinding you've either got a bad blocker ring in the synchro, or the lube is too slippery. Try draining the transmission, run a solvent like mineral spirits or Diesel fuel for a few minutes, and refill with straight 90 weight or 85W-140. I had a similar problem with a Kawasaki motorcycle after adding some Kroil to the engine oil to free up the rings after years in storage- - - -the clutch started slipping! There was a common crankcase between the engine and the transmission, and the Kroil was causing the wet clutch to slip. A flush and refill solved the problem.
Jerry

Go To NAPA and get some GL4 gear oil

Jerry, when I put the solvent or whatever in the transmission, do I drive it around like that for a short time and then drain or just fill it, let it sit, and then draiin it?

Don't drive- - - -the solvent destroys the lubrication qualities. Just jack up a rear wheel and run it in gear for a few minutes. Non-loaded running doesn't hurt anything, but you don't want to put any stress on the gears and bearings.
Jerry

So I just checked out some Valvoline 85-140 at my FLAPS. It says it is rated for GL4 and GL5 applications but does not say whether it is synthetic or non-synthetic. Do synthetic gear oils always say "synthetic" on the container? There is also a Lucas gear oil that says it is "conventional oil" and GL4. Will either of these be OK?

Joe

Get the Valvoline. If it were synthetic it would say on the bottle.

OK, thanks a lot.

Well I just did this--drained the gear oil out, ran mineral spirits in the trans for a bit, drained that, and then filled it with 85-140 non synthetic. The transmission still grinds when shifting into first. The only difference is it now grinds when shifting into reverse as well. It usually doesn't do it until I've been driving for a while. Sometimes it won't do it at all. At this point, I guess I'm looking at a blocker ring or an adjustment. Does that make sense?

I'd adjust the clutch and lower the idle down some and see what happens. If it still grinds going into first and reverse its surgery time.

I'll check my idle speed and the pedal freeplay. It's been a while since I've looked at the shift/clutch linkages, so I'll get under there and see if there's anything obviously wrong.

I think this problem might be linkage-related because when I use a little extra force pulling the shift in toward me on 1st and reverse, it doesn't grind.