how strong is the muncie 21 close ratio 4 speed???

thinking of adding a gear vendor unit, but if this is a weak transmission, maybe i would be better off with a tremec unit.

any thoughts??

 

B/W Super T-10 is as strong as a M-22 and is found 1977 to 1979 close ratio 4sp vettes

 

I have been running a M21 behind a 509CI/550HP big block for 2 summers now with no problem. I don't beat the crap out of it nor do I run street drag radials or big tires in the back that will hook it up real hard. I really think what would kill it or the rear end components is how hard and how often you beat on it and how hard you hook it up.

 

I believe the M-22 is the close ratio..... or am I wrong?

 

The M-22 was the extreme heavy duty transmission.

I believe the M-21 was available in both standard and close ratio applications.

Strength wise, it can take ALMOST anything you can throw at it. I'd say go try to blow it up before spending the coin on a new one. Depending on your application, it may be fine.

 

You are talking pure FANTASY! here. GM version of BW Super T-10 is not so "super" gears are standard alloy vs high nickle alloy for aftermaket Super T-10 and M22 four speeds. The aftermarket Super T-10 had high nickle gears, toque lock synchro sliders and a nodular iron main case. GM later T-10 units have aluminum (weak) main cases (funny thing to note, while 74 Vettes had T-10, SD455 Trans Am used Muncie gearbox and also the 454 Chevy cars maybe GM was a little worried about the T-10.) Getting back to the subject the M-21 was used behind 425HP 427 and 435HP 427 Vettes but, I wouldn't run one hard behind a 400+HP motor.

 

What would your reservations be? If GM put them behind 400+ hp big blocks (keep in mind several of these motors were severly low-balled hp wise), it would seem they should be good (and I'm theorizing here) to 600 hp or so.

 

The M 20 was a standard duty wide ratio
M 21 was a standard duty close ratio
M 22 was the heavy duty close ratio

 

thanks for the clarification

 

The big thing that will kill the Muncie is today's tires. Anything wider or stickier than a stock tire is asking for trouble...(ask me how I know that)

 

worn out thrust washers on the cluster gear will
cause all sorts of problems in the 4 speeds
if the trans has alot of miles, its a good idea to have
it freshened up with new bearings and synchros
some extra strength can be found by replacing the stock
aluminum midplate with an iron unit


clicky