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I have a M-20 Muncie Transmission that won't stay in 3rd. gear when you take your foot off of the gas. Everything else is OK.
I rebuilt the tranny last year, with a rebuild kit, and also replaced 2nd. & 3rd. gear, along with both Clutch sliders. I also replaced both shift forks. I did nit have this problem prior to rebuilding it.

Does anyone have any ideas what might be wrong?

Thanks
 

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Third gear is bad or the slider for the 3-4 shift. Probably both.
Too many missed gears going for third.
Bob
 

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muncie

Your stops need set on the shifter...

Since you replaced the sliders,sincros,and 3 gear.. There really isn't many other options...

Is it a compitition style shifter??? Or a factory shifter???


Keith
 

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Whatever you do, don't try to hold it in 3rd (or any other gear) by forcing the shifter. That will surely screw it up even worse.

Look on the front and rear of the shifter body. On each end, there should be a bolt that looks like it's not holding anything, and a jam nut holding that bolt tight. That's the shifter stop adjuster bolt. It keeps you from putting too much pressure on the fork/slider junction when shifting hard. If it's adjusted too tight, it won't let let the slider move all the way into engagement, and that will cause it to slip out of gear.



The front one has a loose jam nut, and the back one has no jam nut. Asking for trouble, for sure.
 

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shifter

Jim, Thats a perfect picture.....


tlauerjr, Looking at the above picture... You will need to back off both the stop bolts. First remove the shifter boot, console, etc..Anything that needs to go to gain access to the bolts.

Then loosen the jam nuts and back the bolts off...

Put the shifter in 1st gear, turn the bolt until it contacts the shifter arm and snug the jam nut..This is the stop for 1st and 3rd.

Then repete for 2nd gear... This is the stop for 2nd and 4th.

Take the car for a ride and see how it shifts... You may neeed to fine tune ( more stop or less stop) in 1 turn increments to really dial it in...

Keith
 

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If my memory serves me correctly, the front stop bolt is for 2nd & 4th gears, and the rear is for 1st & 3rd. But I have not messed with one since ~1972, so somebody correct me if I'm wrong.
 

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Discussion Starter #9
Thanks for everbodies suggestions. I am going to put a new slider in and adjust the stops. It will be awhile before I put it back in, as I have some more things I need to get done to the car first.
 

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I've got the same problem. New gear/slider/fork. When shifting, it sometimes has that...click- click where the synchros are lining up and it drops in. Other times, it does the click....and does not seem to fully engage, and then hops out on decel. If the stops were set wrong, it wouldn't be intermittent. Have been told it was a sloppy midplate, allowing the whole cluster to shift back and forth. Just an idea.
 

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Trany coming out of gear

I had a similar problem on a '56 Chevy step-side pickup that had a 409 with the truck 4 speed. Bought it off a used car lot for only $260 about 30 years ago. It needed a lot of TLC. Jumping out of gear was one of the problems. I took the top off the trany for inspection. Gears and synchros appeared new. I then took the trany out and to the machine shop I was using at the time and asked them to just do an inspection, no work, and give be a bid. When I came back the machinist said the gears and synchros were new but all the bearings were worn out and he had replaced them. I was not happy with him for replacing the bearings without permission. I begrudgily paid the bill of $50 for parts and repair. I reinstalled the trany and it worked perfect. The bearings were so worn it allowed internal vibration which led it to popping out of gear.

Let us know what you find.
 

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BT74 said:
I've got the same problem. New gear/slider/fork. When shifting, it sometimes has that...click- click where the synchros are lining up and it drops in. Other times, it does the click....and does not seem to fully engage, and then hops out on decel. If the stops were set wrong, it wouldn't be intermittent. Have been told it was a sloppy midplate, allowing the whole cluster to shift back and forth. Just an idea.
The only way this can happen is if there is a missing snap ring... There is no such thing as a sloppy mid plate allowing the main shaft to move...It's stabilized between the main case and the tail housing with 6 bolts.

I have seen dozens of muncies with miss-adjusted stops that work fine on one gear change and jump out or grind on the next...

I am not sure i understand why everyone wants to start throwning parts at a transmission that may only need a simple shifter adjustmnet??????

Keith
 
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