I've swapped an M20 into my '71 350 car that originally had an M21 and still has 3.08 rear gears. It was a big improvement. However, like Tim Allen's character on Tool Time, I want more! I'm presented with a pair of options that work out to be monetarily pretty equal and looking for thoughts of others. I don't have to go with those thoughts but I want some pros and cons if anyone has any that might sway my mood. First option - I have access to an old but brand new Doug Nash 4+1 with a 3.28:1 first gear and 1:1 fifth gear. My car is already setup for the Muncie with a 26-spline input and 32-spline output. My question is if the Hurst shifter will come up through the existing hole in the floor AND is the cross member/mount going to work? Second option - Have my spare Muncie M21 (original to the car) rebuilt as an M23Z (2.98:1 first, 1:1 fourth) transmission, which I know will bolt in and the shifter will work without question. Either one is going to run me about $2,000, give or take the cost of oil or welding a few bits.
I have the 4+1 in two of my 66's. I modded the shifter mounting plates to move the shifters forward. They're close to stock location. The trans crossmember needed to be moved back, it's longer than the stock 4 speed. I don't think it's longer than a st400. I'll guess it'll fit in your 71 without issue. I love the close ratio 4+1 behind the 300, but gears are too close for the 401. I'm running 2.79 and 2.93 rears
My suggestion? Buy a copy of Paul Cangialosi's Muncie 4 speed book and how to video, order the parts from him and have at it. Rebuild it yourself! I havent done one yet, but quite honestly, it really doesn't look that difficult to rebuild yourself. In the video, he's got the whole thing torn down in 20 minutes if that. We've both tackled much more complicated jobs than rebuilding a 4 speed. Plus I think it would make a great thread on here
I really like the idea of the 5 speed making it launch like 4.56:1 and cruising with 3.08:1 gears. I'd hate to screw up a set of gears that cost me $900. There's a guy I grew up with that could rebuild it. I figure I need a full rebuild kit with bearings and all for $300 and I'd throw him a couple of hundred for the favor. With the 2.98:1 first gear of the M23Z it would only launch like 4.10:1 rear gears. If I tackle it myself and don't get it right, I can always be used as a cautionary tale of woe.
Either option sound really good to me. I’m not going to advise on things I don’t know about, but I’m definitely following this thread!
I rebuilt my M20 using Paul Cangliosi's book and videos. He has his own YouTube channel. He is personally very helpful as well. I am happy to share my learning with you. Do it! It's not that hard.
Yeah. You need a press to remove the speedometer gear. You could just take it to a shop and have them press it off for you. Check Paul C's videos and see how he does it. He shows how to use the press to remove all the gears off in one shot.
I too rebuilt one using Paul's video. Turned out great, that trans worked like new. I eventually replaced it with an auto gear m23 with the steep first gear you mentioned just for strength and some extra launch on the strip, but functionally my m20 was great after the rebuild.
