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Question: 1973 muncie rebuild


New member
Jan 24, 2009
St Louis, Missouri
I have a 383 with a centerforce clutch and an M21 transmission (casting 3925661, serial number P2D04B). Recently I had to remove the clutch to look for the source of a very loud noise (retainer spring clip partially broke off the back of the clutch fork). Since the tranny was down I thought it would be time for it's first rebuild. It has a few issues: I have to double clutch fourth until it warms up OR with higher rev shifts, and the tranny will pop out of gear sometimes going downhill in a low gear at low power. None of these prevent me from driving the car because I baby it mostly (did the 383 just because...).

So, I was wondering two things:
1) I'm not doing this myself, but looking at aftermarket rebuild kits I do notice some options. Like: iron mid plates, roller bearing side covers, etc. My goal is a smooth and reliable shift during normal driving throughout the RPM range. Do I need these options, or will a major rebuild kit have everything I need? Is there something else to consider?
2) I'm searching for someone near St Louis to do the rebuild. Any recommendations?



Well-known member
Sep 8, 2007
Gladstone Missouri
1969 LS-7 BB
The iron midplate is not a bad idea- if the trans has been used hard in it's life the rear bearing retainer will tend to beat the groove for the retainer in the aluminum plate. Makes it not fit like it should. Unless the side cover is worn to the point the shift fork shafts are loose, the roller bearing seems like a waste. There are several upgrades. Take a look at Autogear-- AutoGear Homepage They have quite a selection of parts- including different ratio gearsets and even gears to make your M-20 or M-21 into a full M-22. And even make 4th an overdrive gear.
I can't give you much help on someone in St. Louis- I'm in KC and went thru my trans a few months ago.


Well-known member
Sep 4, 2003
New Haven CT
The iron mid plate is a good upgrade. Some have been back ordered on/off. Another upgrade I like to use is the larger front bearing kit. I have built them with a rollerized 1st gear for road racing cars. The bearing side covers are new from Auto Gear and are a nice part but if your cover has good bores you don't really need it. Auto gear makes the new castings too and those are impressive.

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