There's a M20 for sale locally Its an M20 Came out of a Corvette, but not sure if it was original to the car It had new seals front and rear, and was driving when taken out (Had I saw this a couple weeks earlier I could have test drove it) Here's what Ive got from the casting numbers Main Case Casting Number 3978764 1970 - 1974 Passenger Speedo, 32 spline Tail Housing Casting Number 3925661 1970 - 1974 Patent Number, 1" Bore Two Rings on Input Shaft - 1966 - 1974 M20 1st 2nd 3rd 4th Rev 2.52 1.88 1.46 1.00 3.11 My car has 3.42 rear end This should be a good fit. Questions I have... M20 is ok for a big block car? Speedometer cable may be on the passenger side or drivers side... I believe the TH400 is drivers side. What if the M20 is passenger side, is that a deal breaker? Considering I need to have it gone though / refreshed because I only want to install once, whats a good price? M20s seem to be cheaper than M21 or M22s And yes, Im really thinking about doing the Auto to manual swap.. its been a dream for a long time.
here's the skinny.what year is it going in?Your rear gear ratio makes a difference,it depends how you use the car.342 and M21 not a good idea on the street.M21-m22 are 220.1 and M 20 are 252.1.better for daily driving with a 3.42.I've not seen a wide ratio in a BB car. if it's a 70,it's 1" too long and your drive shaft flange is going to be incorrect.If your replacing a 71-74 your good.Shifter mounts are different and there is a definite separation of boxes.More info if you PM.Bill
The car is a 70 bu it has an updated rear end. 71+ with 3.42 Will The TH400 yoke work or do I need a TH350 yoke Since its a 71+ rear does that eliminate any drive shaft mods?
I have a M20 in my car. They will take big block power as long as it isnt whooped. You will need a th350 yoke.
Yes. Muncie m20, 21, and 22 are all the same as far where the trans bolts to the bell. As long as you have a Buick bell, any one of the three will bolt to it.
The 4 speeds have the speedo drive on the passenger side. My 70 is like that. 71 and up Muncies take a T400 yoke, earlier take a T350.
As Jason stated the 71 & newer 32 spline output Muncie uses the same yoke as a t-400. The total assembly is shorter than the t-400 so the driveshaft needs to be longer. The manual transmission driveshaft length is the same as the t-350 driveshaft length. The M-20 is the weakest of the 3 Muncies. The M-20 will live a long life behind the BBB as long as you don't power shift it at 2700-3500 rpm (max tq production). Wheel hop is another 4 speed killer. I used the M-20 for 16 years in my 455 powered 1970 GS with 13 of those years including MANY trips down the track each year at Buick race events as well as the Pure Stock races in Michigan. During this time I broke 4 M-20's with wheel hop or 3000 rpm power shifts. Speed/power shifting at 4000 rpm + is ok. Another Muncie killer is synthetic gear lube as well as GL-5 rated gear lube. The additives for brass longevity has been removed from these fluids. Fortunately Brad Penn makes a GL-4 gear lube for the older manual transmissions. The M-20 makes a great street transmission due to the low (2.52) 1st gear ratio. Makes it much easier to get the GS moving from a complete stop. For highway cruising it works real well due to the 2.52 1st gear allowing you to use less rear gear to keep rpm down while in 4th gear. Example: 2.22 1st gear x 3.42 rear gear = 7.59 effective ratio, 2.52 1st gear x 3.01 rear gear = 7.59 effective ratio.
71 and newer take the 400 yoke. Also, the 71 and newer muncies are 1 inch longer overall. I dont agree that M20's are the weakest of the bunch. The only difference between an M20 and M21 is the first gear ratio and the % drop between gears. Both still end at a 1:1 ratio in 4th. Its best to match up to your rear axle ratio and what you want he car to do. The 71 and newer muncies with the 26 input splines and 32 output splines are the best of the bunch.
Hes asking $600 I offered $500 yesterday and he said he'd think about it. He said it had fluid and seals changed in December He's changing to a 5 speed setup, he refused my offer because he needs as much money as he can for his swap Well I need to save as much money for my swap :bglasses: The date code is P2M09A - August 9th 1972 So a TH400 yoke should work. I'll just need to lengthen the drive shaft, or find a TH350 shaft. For $600 he's throwing in the corvette shifter and linkage. He has the clutch plate for an extra $50. Should I just take it for $600? A local trans performance shop quoted $300 plus parts to go though it.... I saw master rebuild kits online for $300.
I've seen Muncies go consistently for the $750 to $850 range so $600 isn't bad. If you're going through it, the thing that is usually bad is second gear. Everyone likes to bang second gear, so, take the side cover off and get a good look at the second (and third) gear syncro teeth. If the second gear syncro teeth are in good condition you know it hasn't been abused or raced. If it needs a second or third gear it isn't a big deal, they cost about $80 each.
If it was me, yes. offer him 600 and off the Vette shifter on Ebay. You'll probably get 100+ for it. Why spend $300 for someone to go through it? Just strom it in. Sounds like you shouldnt have an issue with it. For $300, I'd take the chance. its easy enough to take it out if theres a problem. But I'd take those odds any day of the week,
That looks more like a Borg Warner super T-10. Does the side cover have a bump at the center top? If not, it's a Borg Warner. The old Borg Warner's and the Saginaw's had the speedo cable on the drivers side and the Muncies had it on the passengers side.
If your decently mechanically inclined, youd be surprised how easy munchies are to rebuild. I did mine a few weeks ago, and with the aid of a how to DVD and the chassis manual it wasn't bad at all. Dare I say it was actually kinda fun...
It's a Muncie. Speedo on the passenger side. I told the guy if I can take off the side cover I'd do the $600. He agreed. Will pick it up on Tuesday.
I had assumed it would be something I might tackle vs a automatic. Automatics ate a mystery to me lol. But I do everything else myself.
