M20 trans
Thread Starter
Instructor
Joined: Jan 2012
Posts: 242
Likes: 7
From: Fair Oaks, CA
M20 trans
Has anybody heard of a design flaw in the late model M20 trans in 1967 regarding what’s called an anti backlash ring or star of death? Rivets come loose and tear up your casing.
Racer
Joined: Oct 2011
Posts: 453
Likes: 81
From: Honaker Kentucky
I don't remember the exact year the star was first used but I thought it was 1968. I have rebuilt several muncie m20s with the anti backlash star. 2 that I remember had the star previously removed. I have talked to others who said they were a problem and they removed them during a rebuild. . I left them on and never had a problem. Roy
Le Mans Master
Joined: Nov 2015
Posts: 7,472
Likes: 2,647
From: Really Central IL Illinois
R66 had the anti-clunk device (ring) on the front of the counter shaft, if that is what you are referring to as the anti-backlash ring. It was suppose to absorb the counter shaft movement and stop the "clunk" when shifting into reverse. When I disassembled the transmission, I found pieces in the bottom of the case and the ring on the counter shaft but no damage. I believe it was one year only "66" and the service overhaul manual states to remove it, but I can't remember the details as it has been about 8 years ago.
Race Director
Joined: Mar 2001
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From: Mustang OK
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I've been rebuilding 4spds (mostly Muncies) for over 50yrs,
About 67-68, the anti-backlash gear was added to the front (ONLY) of M20 cluster gears. Also, about 68, the anti-rattle springs were added to the main shaft for reverse gear. WITHOUT EXCEPTION, I have removed both the anti-lash gear on the M20 cluster gears and the anti-rattle springs from the main shaft.
To remove the anti-lash gear on M20 clusters, I first grind off the rivet heads and remove the gear and spring. Then I use a flat nose punch and drive out the rivets from the gear.
About 67-68, the anti-backlash gear was added to the front (ONLY) of M20 cluster gears. Also, about 68, the anti-rattle springs were added to the main shaft for reverse gear. WITHOUT EXCEPTION, I have removed both the anti-lash gear on the M20 cluster gears and the anti-rattle springs from the main shaft.
To remove the anti-lash gear on M20 clusters, I first grind off the rivet heads and remove the gear and spring. Then I use a flat nose punch and drive out the rivets from the gear.
Race Director
Joined: Jan 2003
Posts: 17,693
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From: Central Arkansas
it probably varies considerably by region. I would say here in AR around $350 to $450 for a transmission- differential shop if no major components require replacement. That was my experience for removing the transmission myself and carrying it in. If gears, or slider/ hubs, or forks need replacing, or they remove/install the transmission, etc that would be extra. I finally decided to start rebuilding my own which with a modest expenditure on tools, is a lot less.
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Le Mans Master
Joined: Sep 2008
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From: Lake Minnetonka, Mn
2018 C1 of Year Finalist
Once you have it out, don't skimp on replacing parts. To me, the biggest chore is pulling and installing. Tearing them down and rebuilding is a piece of cake. Generally, 2/3 gear needs to be looked at, as well as the slider components and brass synchro rings. There are components like your input and main shaft bearing that may be OK, but like I said, once you have it down, you are spending nickels and dimes to replace a lot of the parts. You can do this yourself. No major tools are required
