1969 Muncie M21

[wisemanz28]

What fluid would you guys recommend to use in my Muncie M21 Transmission ? I've had the trans rebuilt (twice) and after both rebuilds I am having the same shifting issues ( upshifting from 2nd to 3rd ). I'm thinking I might have the wrong fluid in it which is casing the hard shifting problems.

[L78racer]

use GL-4 type gear lube.

[bcmiller]

Sta Lube gear oil - 85w-90. NOT synthetic.

[Z10Mike]

Agreed - Do NOT use synthetic.  I made that mistake before I consulted this forum and my shift quality was horrible in a freshly rebuilt M20.  Box had about 150 miles on it when I drained and replaced with the mineral based GL-4(?) spec and it is like a different gear box.  Much better shift quality.

[BillOhio]

I got sta lube at napa

[Kelley W King]

Since 2nd to 3rd uses both syncros, on rebuild were both replaced? If not was one and not the other? My guy if one is fine he always replaces the slider in the good one so both are new. If not the 1 to2 shift will feel different from the 3 to 4. You could be leaving 2nd with a used slider and entering 3rd on a new one which takes more effort.

[L78racer]

brad penn

[Stingr69]

I would be looking hard at your shifter assembly.  Specifically the adjustment method used, and checking for the proper parts for the assembly.

How did you adjust it?

[HawkX66]

What fluid would you guys recommend to use in my Muncie M21 Transmission ? I've had the trans rebuilt (twice) and after both rebuilds I am having the same shifting issues ( upshifting from 2nd to 3rd ). I'm thinking I might have the wrong fluid in it which is casing the hard shifting problems.

Have you gotten stuck in 2nd and not been able to get it out? It happened to me last night on a "clean out the carbon" shift through the gears. I had to pull over and slide the shift lever on the trans back. It shifted fine after that, but I haven't shifted it as hard since then. Ours sounds like a similar issue possibly, but I don't believe mine is due to fluid issues. Maybe shift forks? I just went through my trans in June and everything looked fine, but I'm not exactly a trans expert.

I would be looking hard at your shifter assembly.  Specifically the adjustment method used, and checking for the proper parts for the assembly.

How did you adjust it?

I adjusted mine according to the Hurst recommendations. I used their little plastic alignment tool.

[wisemanz28]

I also thought it was a shifter issue or even a clutch issue, so I swapped my rebuilt trans out for another Muncie that I knew had no problems with it at all. The car shifted smoothly (upshifts and downshifts)

[69Z28]

Agree with the NO synthetic. Made the mistake putting it in the 4 speed trans of my 81 HD Lowrider. One thing I found that was needing to replace though when I put it in was the clutch main shaft seal...If you have a leak, it will show up. Not designed for these older machines. Sta lube Gear Oil 85x-90.

[Kelley W King]

I agree with stingr69. If not your syncros, maybe be the shifter. Easyer to adjust than pulling the trans. Even not driving your shifter should come out of 2nd and just click into neutral. My trans guy does the adjustment on the bench as part of his rebuild.
I doubt the lube is your problem.

[Stingr69]

If the adjustment is good, the parts are suspect. 

Mix and match with other years will cause this. Wrong levers will bolt up, but not be tight enough fit causing the problem.  Throw will be off too.  1 gear still partially engaged while you are trying to get to the next one will block you.

[wisemanz28]

Thanks for all the advise. I did change the fluid with Sta Lube and while I was under there I noticed my 1st/2nd gear shifting rod backing nuts were very loose, which was causing the 2nd gear to hang up. Readjusted and tightened everything and now it shifts like a dream.