Muncie M20 Transmission

Ever since I had my Muncie M20 rebuild I have had issue with 1 and 2 gear popping out of gear as I coasted down a hill. Supposedly everything that was worn was replaced.  Needless to say after asking the builder about it, his comments were…”I’ve never heard anything like that”? Really, you build Muncie’s and never heard of one popping out of gear?

While I have it out to replace the clutch I thought I would look into the issue and some other items about it. First, the builder used lock washers on the bearing retainer. This interfered with getting the transmission into the bell housing. So I decided to replace the lock washers with correct French locks. As I went to torque the bolts down, two bolt threads were stripped and I need to heli coil them.

After heli coils were put in, I flushed the transmission to get any aluminum shavings and the heli coil tang out.

Then I decided to take the transmission to a shop so we could remove the side cover and inspect any issues.

Just as I suspected the 1-2 slider was worn and it was the original slider used on gears that required a torque lock slider. The slider appears to be pretty worn.

I called AutoGear on replacement slider hub assembles and any other parts they recommended for me to replace. Their torque lock sliders are not as aggressive as the other venders and they use hardened hubs. I also got 4 new synchro rings, new detent levers, hd spring to improve the positive shift feeling. They also make a hd shift fork that are steel that they suggested I go to.

So now the transmission is in the shop getting the parts replaced. Hopefully we will have a little better shifting Muncie when I get it back.



One thought on “Muncie M20 Transmission

  1. My 68 Camaro’s M21 had the same problem. With my M21, I actually got it into both 1st and 2nd gears simultaneously which locked up the back wheels. Turned out the main case had stretched due to hard shifting. I opened it up and found the the front bearing was not tight in it’s hole. I took the bearing out and put a straight edge on the front surface of the main case and I could see that it was pushed out. The center where the bearing goes was high. I had to replace the main case. Maybe that is your issue.

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