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Old 03-12-2012, 08:02 PM
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Questions on M21 with broken gears

Hey guys I have two questions here I just picked up an M21 Muncie 4 speed it has a couple of broken teeth on what I believe to be 1st and 3rd would it be better to replace all 4 gears or just the two that have missing teeth? Also when I was checking out gears I found a rollerized 1st gear what is the point of this is it worth going with or should I just stick with the original style. Its going behind a 350ci right now and eventually a big block.

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Old 03-12-2012, 10:05 PM
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muncie m21

if none of the other gears are worn then leave them but be sure to check them good and no sense upgrading the 1st gear cause that tranny will handle a big block all day long hope this helps
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Old 03-13-2012, 06:59 AM
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Be sure that the cluster gear is undamaged. Check the other gears for wear pattern. Being old skool, I see no advantage to a roller 1st gear. Most of the damage to gears inflicted is from torque/impact and sticky tires. The aluminum case flexes under extreme conditions.

I drag raced a 4-speed big block car back in the day. When using Muncie, I had to have several backup trans ready. Changed to B/Warner based units and problems solved..
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Old 03-13-2012, 07:34 AM
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[QUOTE=BOBCRMAN@aol. When using Muncie, I had to have several backup trans ready. QUOTE]


I have checked all the teeth there is minimal wear but for the most part everything looked good except for those few teeth. What was the main problem you had with the muncie is there anything I can do to re enforce its weak spots?

Jon
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Old 03-13-2012, 08:18 AM
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Rollerized 1st gear is used to reduce the friction/heat generated when the trans isnt in 1st gear. It allows the trans to run cooler, and probably frees up a small amount of power. Great for street cars, road course cars etc. Not good for dragracing; in theory, the hard launching of the car can flatten the needle rollers over time.
Is it an Auto Gear roller 1st?

We designed our version of the rollerized 1st to use a NEW 1st gear, specifically with the needle bearing; older versions (even available from GM I believe at one time) just punched a larger hole in a stock gear to accommodate the roller bearing, this screwed with the heat treatment of the gear and most didn't last long.

Make sure if you're buying an Auto Gear roller kit it comes with 4 parts: the correct gear for the rollerized 1st, the needle bearing, the spacer and the sleeve

Since you're in there, Id replace the whole gearset, gears tend to wear into each other and this can lead to noise and vibration. Also think about an iron midplate to add some strength to the factory case; if not a Supercase

Bobs right...check the cluster for nicks/wear and also verify that the gears arent worn unevenly
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Old 03-13-2012, 08:21 AM
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Heres a modified PDF that explains how they work.
Attached Files
File Type: pdf Scan001.pdf (1.14 MB, 62 views)
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Old 03-14-2012, 07:39 PM
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Thanks guys you have been a great help I think im going to go ahead and replace all the gears and go with the roller 1st gear.
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