Transmission / Overdrive: Has anyone used Marvel Mystery Oil in a Studebaker manual transmission?

[brngarage]

I have a T86 w/overdrive that sat outside for a while. I think there's some rust on the gears where I can't see it (I have the cover off), because I can't shift it. I'd like to try soaking it with Marvel Mystery Oil but I'm not sure I should use it in a transmission. Has anyone tried this?
Thanks.

[jclary]

These old transmissions are pretty darned tough and are well built. I have one that was removed from an old truck that had nearly rusted away around it in the woods for years. The truck was sitting on its chassis on the ground in such thick overgrowth that it took about an hour to hack through the brush to get to it. Mercifully, the old farmer, that gave it to me, cranked up his tractor, hooked up a log chain, and pulled the truck over on its side so that I could get to the transmission.

I took the transmission, cleaned the mud and moss off of the case, wire brushed the pilot shaft, and bolted it into my truck. With the truck up on jack stands, I poured kerosene into the transmission, placed it in gear, fired up the truck, released the clutch, and let it idle in first gear for about 15 minutes. I shut the truck off, shifted to second gear, and cranked it again, and idled the truck in second gear for 10 or 15 minutes, and did the same procedure for high gear. Then I drained the gooey smelly fluid. After that...I filled the transmission with a combination of 10 wt. oil and kerosene and ran the truck off the ground again. Only this time, I began shifting with the engine running. After assuring that I had all the gears working smoothly, I connected the overdrive solenoid and engaged the overdrive. All of this was done with the vehicle on jack stands. After about another half hour of running in this manner, I drained the transmission and refilled it with transmission oil.

That was over 30 years ago. I drove the truck to church this past Sunday...still going strong.

As strong as these transmissions are built, I'd say flush the transmission out with kero...follow up with Marvel if you'd like, and it should be O.K. If it is too stiff to shift, soaking for a few days might free it up. You need to make sure that the shifting pawls are not in conflict and attempt to rotate the shaft. You will probably need to strap the transmission down on a bench in order to get enough leverage to rotate it. Also, use a bar through the U-joint bolts at the rear of the transmission. You don't want to put a pipe wrench or anything like that on the front shaft splines that would scar or chip that shaft. I would want to have it in neutral for the first rotation, and once you get free rotation there, then take it through the gears.

Although you might think it is rust...it is just as likely to have old dried heavy gear lube and gunk impacted in moving parts that would otherwise have clearance. Soaking it might help dissolve the gunk and enable you to flush these areas. It will be stiff at first, but should free up. Good luck with it.

[nvonada]

I agree. Don't worry about it. Flush it with just about anything then fill it with GL-90 and run it. If you are extra paranoid after it has a couple hundred miles on it drain and refill again.

I realize it is not a T-86 but when I got my tractor I drained the transmission and found it contained a pint of oil and a pint of rusty water. I drained it, refilled it, and it was fine for years.

Nathan

[jackb]

just remember to finally refill with GL-1, not the other GL-2 - GL-6. You have an OD unit in there that doesn't like hypoids.....GL...I would tend to warm drain and refill w/ GL-1 after a few hundred good run miles...and let us know how it works for you

[brngarage]

Thanks to all for the advice and especially to John for the "instructions". The transmission turns freely; it just won't shift out of neutral. With the cover off, I can see the slider move just a little when I try to shift it; looks like the idea that there is "gunk" in the mechanism makes sense. I'll fill it with kerosene and let it soak for a couple of days and then try the Marvel Mystery oil.
Thanks again!

[t walgamuth]

I bought an 84 mercedes that had been flooded up high enough to get water in the intake manifold and break out a portion when it froze. We drained the diff and manual tranny, refilled and drove. No issues....although the second gear synchro got weak around 200K miles.

[StudeRich]

I agree. Don't worry about it. Flush it with just about anything then fill it with GL-90 and run it.Nathan

Please follow jackb's info, the GL is correct for gear Oil, and the 90Wt. or 85-90 is correct, but what is MORE important is that it be GL-1, no GL-4 or GL-5 with additives for Differentials.

[brngarage]

After looking at things more carefully, I believe the problem is in the "interlock" that prevents the transmission from engaging two gears at the same time. The levers are both definitely in the neutral position. I checked the parts book, and it looks like there is a small "tube" between the internal shift levers that has a spring and a couple of ball bearings that engage notches in the shift levers. I'm guessing that the ball bearings are stuck in the tube and won't release either lever to move. Does anyone know if the levers (and the "interlock") can be removed without taking the gears out?
I will be very certain to use only GL-1 when I'm ready to re-install the transmission and refill it.
Thanks again.

[brngarage]

Got the gears freed up and everything seems to work properly now. I'd like to flush the transmission before I intall it and refill with 80W90 GL-1. Is acetone a good product to use for flushing the transmission?
Thanks

[jclary]

I'd use kerosene. Let it drain very well and then fill with correct amount of transmission oil. You should be good for quite some time. I'd avoid harsh solvents.

[brngarage]

Thanks John.