halfmoontrail

This should be an easy one for a gearbox guru -- I have a '70 W30 4-speed car (now has TH400). Over the years I picked up a completely rebuilt Muncie 4-speed, decodes as a '71 M20 from a Nova.

Any issues with using it behind a 455? I have bellhousing/flywheel and all the 4-speed parts. What about cross-member and driveshaft (including yokes)?

Thanks, Steve

PS: Is this trans likely to offer more value to a Nova fan, and I could find another for my 442?

joe_padavano

The wide ratio M20 will bolt right in. Just get a clutch disk to match the splines (I don't remember when GM made the switch from 10 splines to 26 on the input shaft). Tailhousing and output shaft are the same as an Olds trans. Of course, you'll need the correct driveshaft and yoke for a four speed. The M22 uses the larger TH400 yoke, but the M20 and M21 use the same yoke as a TH350.

halfmoontrail

Thanks, Joe - I appreciate it.
Steve

allyolds68

What rear end gear ratio are you running? You shouldn't run much lower (numerically higher) than 3.55's with an M20. I'm pretty sure W30's ran an M21 or M22 as the standard tranny.

jensenracing77

you will need a longer driveshaft but the yoke is the same as the 400. All 71 and newer muncies went to the bigger 400 style output shaft.

anthonyP

If looking for originality, the M-20 (wide ratio) was not available in the '70 442 or W-30, only the M-21 (close ratio) & standard HD 3-speed manual.

An exception - the factory did install the M-20 in 442's with A/C, even though according to the factory brochure A/C was not available in a manual trans 442 - due to the M-21 trans not being available with a ratio lower (numerically) than 3.42 & A/C cars available with no higher (numerically) than a 3.23 ratio rear axle.

oldsmobiledave

In 1972 the W-30 came with 3.42 gears standard while 3.73s were optional with either the T400 or the M-20. My 4 speed 1972 W-30 is so equipped.

lemoldsnut

I had a 69 Cutlass once with a 350 M20 and 3:08 gears. Was very long legged