# Muncie Transmission Question about an M20



## Josh.AZ.GTO (Jul 11, 2009)

I have been currently cruising through ebay sales and craigslist adds looking for a good rebuilt or rebuildable Muncie 4spd transmission for my 70. It currently has a 70' (I believe) 350 motor mated with a TH400 transmission. My car was originally a manual trans car and I would like to convert back to this setup. 

Now that being said.... I know little about transmissions, or should I say little about what I am looking for or should be taking note of, while looking.

For instance, I found this one on craigslist locally.

MUNCIE FOUR - SPEED NICE !

After decoding it, it is from a 1970 GM vehicle but for Chevelles only... something to do with tailhousing. I'm assuming tailhousing can be changed???? 

My 70 is a 455 car that came with a 12 bolt rear (not sure of the ratio) but I think I will fall somewhere between 3.55 to 3.73 gear set when time comes to rebuild the rear end or modify. I have heard with higher rear end ratios a M20 would be a good candidate (I'd prefer an M22, but requires a lot more $$$$). 

So all this being said.... going from an automatic transmission to a manual transmission .... what should I be looking for as far as input/output shafts and splines? Do the engines mate up nicely to both automatic and manual transmissions? What extra pieces would I need to complete the swap back to manual?

Finally,
What is a good price to pay for a M20 completely rebuilt?


----------



## pontiac (Mar 6, 2011)

front trans splines mate to the clutch disc and rear trans splines match to the driveshaft yoke. For GM, you can get what you need to mate up, so whatever the trans has, you can get a match. No need to switch tail housing unless trans is too long, then it could be that the driveshaft can not be shortened properly and the shifter could be an issue. Would never buy a rebuilt trans without a warranty unless my mechanic has opened it up and looked inside when the seller is present. Prices are crazy. you will need everything for the swap, pedal, bell housing, pressure plate, shifter, etc.


----------



## geeteeohguy (Feb 2, 2008)

Agreed. The big difference with the tailhouseing is that the Chevy has the speedo cable outlet on the pass. side. Needs to be on the driver's side. The standard 4 speed for the '70 455 was an M22 muncie, which has stronger gears than the M20 or 21. The rear end ratio for the 12 bolt 455 cars was about a 3.31. With a 455 (or even a 400) you really don't want the limitations of a 3.55-3.73 gear. My choice would be a 3.31 max, and preferably a 3.08. You can bet a brand new M22 trans from tbtrans on line for about $1750. I've gotten parts from them, and they have excellent service. As stated above, any used trans buy is suspect and would need to be checked out by a good technician prior to installation.


----------



## Josh.AZ.GTO (Jul 11, 2009)

Just checked my PHS. Says car came with 3.31 rear gear.


----------



## 66tempestGT (Nov 28, 2009)

you can put in a chevelle speedo cable for about 12 dollars from oriellys.


----------



## peahrens (Jun 7, 2010)

For what it's worth...my experience with my '66 GTO. It came with a M21 that was in such bad shape the local 4-speed guru said to give up on it...bought a sorta rebuilt one he had done for another guy for $425 (in 1992) cobbled together with spare parts the guys had, probably new soft parts, etc. 

In 2008 I had some drivetrain work done and my mechanic said the front case was so bad it couldn't be bolted up securely...and could not be repaired (or it would cost too much). So my choices became (1) find a better front case, (2) get another rebuilt unit with presumeably better used/new parts or (3) go for a new one. I took my mechanic's advice and went new, a T&B Transmission & Gear M21, which was $1575 plus $85 shipping in 2008. I became sold that they were a quality supplier, including using quality components. They pointed out it had very minor differences from the original...I think some external stiffening ribs that improve the case but look slightly different...I didn't care about that. They were helpful on the phone. I've only got a few hundred miles on it by now, and it's still pretty "stiff". I'm really glad I went the new route...little to worry about.


----------



## ALKYGTO (Mar 29, 2010)

Consider the 5 speed too if your going to spend that much.


----------



## geeteeohguy (Feb 2, 2008)

The cases on the original Muncies wear where the countershaft rides, and leak oil there. They can be re-bushed, and repaired, but almost nobody does it. A new unit would eliminate this issue altogether. As I said earlier, I got great customer service and parts dealing with TB trans.


----------



## ALKYGTO (Mar 29, 2010)

Find yourself one of the "Dearborn" 3 speeds your car was born with. You can probably get one for free if you look hard enough. They have a cast iron case and are pretty durable. Set everything up with that tranny and when you have enough coin saved up get that 4 or 5 speed and the most you'll have to change would be the clutch disc if there is a different spline count. Just another option. :cheers


----------

