Not having much luck finding an M20 with fine spline (26) input and 32 spline output. The M20 gear set is $500 on ebay (just a first blush) and was wondering how hard it is to swap them out?
Greg, I would pay and have someone install them for you. Can you install the synchros and bearings yourself ? (tools and skills) http://www.5speeds.com/cart/index.php?route=product/product&path=33&product_id=51 If it is your numbers matching trans have it upgraded. If not, sell it (m21) and buy a quality rebuilt (m20). I have very little knowledge, your post was unanswered for too long so ttt for you.
Greg, Its really not bad as long as you have the tools and a good guide. I purchased a highly recommended Muncie rebuilding DVD and played it on my laptop as I went step by step and rebuilt my m20. I was actually surprised how well it went. A few things that are a necessity to do it easily are GOOD snap ring pliers, some sort of shop press (I used a 20ton hydraulic and it worked out perfectly), and a spare set of hands. I had never been inside a Muncie and was pleasantly surprised how it was not all that difficult to do.
I will keep that in mind. Oddly enough, the more I'm driving it, the better I'm getting at taking off without killing it and/or rev too high. I actually took off on a hill without rolling back or killing it yesterday. I think I'll see what happens when I put some 275-60/15 tires on the back.
Even though the M-20 has a lower 1st. gear starting ratio, the bad part is the wide separation between 3rd. & 4th.
You must have a 2.73 rear. If you have anything below a 3.23 rear you probably want an M20. My 70 Vette has a 3.70 rear, big tires and an M21 and it doesn't have enough first gear. I hate the M21, there's almost no difference between 2nd and 3rd gear. I have been considering changing to a 3.08 rear and an M20. First gear would be even worse but I wouldn't be revving 3,500 at 70 MPH. These transmissions are easy to rebuild, I was rebuilding them for a Chevy dealer when I was 16. I did my first Saginaw 3 speed when I was 12. Of course, now I'm 61 and nothing is easy anymore. I wish I had that youthful energy and brain again. From the research I've done, you only need to change two gears, the input and cluster. While you're at it you may as well replace the bearings, syncro rings, detent keys and springs. You can get a good quality rebuild kit for $170 from Ed Harnett and a cheap kit from EvilBay for $100. The input gear with 26 spline is $120 new and $50 used and cluster gears are about the same price so you're at $420 for new good stuff or $200 for used cheap stuff. Pay attention to the cluster gear pin size. The early ones were 7/8 and later were 1", you need to know that when you order the cluster. Also look at your second gear syncro teeth, second gear usually take a a beating. If they are chipped you'll need to replace second for another $65.
Mine is a stock 71 GS 350 with 3.08 rear gears, M21 4 speed and it is a dog off the line. I easily shift 1st to 3rd with no issues and often only downshift to 2nd when not coming to a full stop then shifting straight to 4th so the width between the gears isn't the issue for me. I've only ever had a Mopar 4 speed apart prior to this. It had a cracked 2nd synchro (broken by my overzealous, younger brother home on leave from the Navy) that I replaced. I don't remember it being too difficult but I have certainly grown lazy in my old age. I'm going to scout out the local transmission shops to see if any of them are willing to take on the job and have any clue what I'm talking about.
