m20 repair - Chevelle Tech
Transmission & Driveline Transmissions and Differentials

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post #1 of 13 (permalink) Old May 23rd, 20, 2:19 PM Thread Starter
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Andy
 
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Location: wichita, ks
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m20 repair

My muncie m20 tarted popping out of 2nd and than it would just grind going into 2nd. I noticed that there was quite a gap between 1st gear and its synchro before I tore it down. When disassembling, I found the snap ring on the rear bearing of the mainshaft had broken in half and fallen off, and the mainshaft moved forward. I am wondering if any of you have seen anything like this before, what the cause may be and how to prevent this from recurring after repairs are made. The car is a 70 Chevelle with original 396 and is an original 4 speed car, although this isnt the original transmission. I have the factory trans but it has a fragged 1st gear and its an m21 which I never really liked.
thanks in advance

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post #2 of 13 (permalink) Old May 23rd, 20, 10:56 PM
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Re: m20 repair

Andy, look up DZAUTO, aka Tom Parsons, he is a Muncie expert and is in Mustang, Okla, good luck with your trans!!
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post #3 of 13 (permalink) Old May 23rd, 20, 11:05 PM
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Re: m20 repair

Paul Cangliosi at 5speeds.com is also an excellent resource.
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post #4 of 13 (permalink) Old May 24th, 20, 3:04 AM
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Re: m20 repair

What did your synchros, hubs & sliders look like when you tore it apart? Was there any damage to the mainshaft?

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post #5 of 13 (permalink) Old May 24th, 20, 8:24 AM Thread Starter
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Andy
 
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Re: m20 repair

The syncros and sliders really look pretty good. No damage other than the snap ring that I have seen.

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post #6 of 13 (permalink) Old May 24th, 20, 10:25 AM
 
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Re: m20 repair

Tom did mine a year or so ago. I drove up from Dallas to deliver it to him. He did a great job.
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post #7 of 13 (permalink) Old May 24th, 20, 12:24 PM Thread Starter
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Andy
 
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Re: m20 repair

The more I think about it and look at it, I think the snap ring was probably defective or re-used. I cant see how enough force could be pushing fwd on the main shaft to break the snap ring without causing major damage to the shaft or case. I have Paul's book and I plan to rebuild it myself. I'll probably take the gear set from the m20 and put them in the m21 case.

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post #8 of 13 (permalink) Old May 24th, 20, 10:26 PM Thread Starter
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Andy
 
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Re: m20 repair

Okay, so it looks like I need an input gear and a rebuild kit to get this back together. I see d&l transmission gets recommendations so I may buy from them. Rock Auto has parts for a whole lot cheaper from USA Standard Gear, is that stuff garbage, or ok to use?

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post #9 of 13 (permalink) Old May 24th, 20, 11:05 PM
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Re: m20 repair

For the BEST results, go with d&l or the above vendor 5speeds.com. Don't go cheap on your transmission parts and good luck with your car!!
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post #10 of 13 (permalink) Old May 25th, 20, 3:03 AM
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Re: m20 repair

I've rebuilt two M20s in the past year with parts from Paul at 5speeds.com. Paul doesn't use a generic parts kits, he assembles the best small parts like heavy duty dimpled bronze thrust washers & higher quality syncro rings, etc. And he has his own custom designed replacement parts such as print o seal gaskets & an extended fit countershaft which is helpful for preventing oil leaks.

Plus he is the guy who literally wrote the book on rebuilding these transmissions & is active here on the forums lending his expertise. Why not buy from the source?
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post #11 of 13 (permalink) Old May 25th, 20, 8:58 AM
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Re: m20 repair

Ditto on 5speeds,rebuilt several muncies with Pauls stuff.It's quality and if you have any questions he'll be glad to answer them for ya if ya call him.
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post #12 of 13 (permalink) Old May 25th, 20, 11:01 AM Thread Starter
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Andy
 
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Re: m20 repair

Okay, thats what I thought. What does everyone think of torque lock sliders? Paul Cangliosi doesn't seem to like them.

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post #13 of 13 (permalink) Old May 25th, 20, 2:15 PM
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Re: m20 repair

Quote:
Originally Posted by wolf396 View Post
Okay, thats what I thought. What does everyone think of torque lock sliders? Paul Cangliosi doesn't seem to like them.

No need for them unless you have worn gear engagement teeth, IMO. If your original hubs & sliders are in good shape, you can reuse them. If not, I would look at Pauls matching zero rok assemblies. He selects matched pairs with very tight tolerances which make for smoother shifts.

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