The Stovebolt Site Forums The Shop Area Engine Shop M/20 in a 53 Truck?

Does anyone know if a muncie m/20 4 speed will bolt in to my 53 235 3 speed truck, I am looking for a easy way to get rid of the low rear end gear ratio. I did some parts research and saw the clutch spline is 1 1/8 10 spline like my muncie.I do have a 3.23 rear ready to bolt in it. Thanks Tom

I am not familiar with an m20, is it overdrive? what did it usually come in?

3.23 is not low in my book, how fast are you trying to go, 130mph?

Seriously though, this site may help with figuring gear ratios, and speed.
http://www.drivetraindirect.com/t_gear_calculator.htm

Grigg

The stock rear end is still in the truck, it has . 4.11 ratio I believe. I want to bolt in the 3.23 rear I have. I will have to go to an open drive shaft to do this [which is what I want to do]. I was asking if the m/20 would fit the bellhousing and pilot bearing and such, those trannys were used in 60s and 70s muscle cars, they have a final drive ratio of 1.1 thanks

I don't know if it will fit, but Advance Adapters should know, and have an adapter if needed.

http://www.advanceadapters.com/

If it is only a direct drive transmission then I would see no reason to use it. I imagine that it does not have the shifter coming out of the top?
The sm420 is also a direct drive, has a great low gear for the times you want to use your truck like a truck, and bolts up with absolutely no problems. And has the shifter on top, like a real transmission should.

Why do you want to use the m20?

Grigg

The M20 is the 4 speed used in early '60s GM performance cars. It's more or less a beefed up T-10. GM based it on the T-10, beefing it up for use behind the higher power engine, mainly the 421/428 Pontiacs and the 409s in the SS Impalas.
There shouldn't be any issues with putting it in, but like Grigg says, there's really no advantage to it. A T-5 would be a better choice. Better ratios and an overdrive.

Okay I'm going to fall inbetween the other two answers.

First, I have 3.08 rear gears in my 1/2-ton Suburban, and a stock SM420 (granny gear 4-speed). Its very drivable that way, reasonable top speed, pulls well in general use.

I recently took the trailer hitch off that truck because its not much good pulling a trailer (and it looked ugly).

Before OD transmissions became the popular choice they are today, swapping to a car type Saginaw 4-speed was popular. The real advantage over a granny gear 4-speed or your 3-speed is the spread between the gears.

When you shift your 3-speed you loose so many RPM that you drop below the real power band of your motor. With the car type 4-speeds your RPM drop between gears stays in the power band better.

All the documentation I've seen on this was based on a Saginaw not your Muncie. I don't recall the ratios on an M-20, but I would expect the end result to be similar.

There is more than one model of T-5 out there. It offers the advantage of overdrive, which might be nice, but they are not nearly as stout as the Muncie. Since you're running a six, unless you are going to modify it heavily that may not matter, but it would be another thing to be aware of. Especially if you are thinking someday you'll go V-8 or highly modified six.

Another thing to think about is the shifter. Any tail shaft mounted shifter is likely to poke through the floor close to or under the seat. There is a shifter available from Patrick's for the Saginaw that deals with that problem. Given the differences between the Saginaw and the Muncie I would not expect it to work on the Muncie.

I've considered the Saginaw swap and always conclude the T-5 swap makes more sense. But if I had a Saginaw or Muncie M-20/M-22 or a Super T-10 laying around most likely it would already be installed in my Suburban.

I do have a Doug Nash 4+3 which is a Super T-10 with an overdrive. It isn't a popular transmission for this kind of swap, apparently because of the computer controlled OD. That transmission may someday end up on one of my trucks, but I wouldn't suggest putting it on your list.

To answer your actual question, it will bolt right onto the bellhousing. You will have to figure out the shift linkage and get the right yoke-to-driveshaft connection, but it bolts right up. The disadvantage to a T-5 is that you have to modify the input shaft.

You might not like the 1st gear ratio of the M20, though. It may be a bit sluggish for a six depending on the gear ratio of the rearend.

With a 3.07 rearend and a 235 or 261 you want about a 2.5:1, which matches the original 2nd gear of the 4 speed with a 4.11 ratio. This puts you into 3-groove Saginaw land, but if you don't mind a bit of clutch feathering the M20 should work just fine.

The m20 is a side shifting transmission. You shouldn't have too much trouble finding a hurst type shifter to do the job. You will probably have to cut a new hole in your floor, and rebend the shifter rod to clear the seat.

The reason I wanted to use the muncie is because I have them with a 2.20 & 2.54 first gears. Kinda like use what you got. The goal is to loose the closed rear and gain a better crusing rear axle ratio. I have a fresh 383 short block in hand I might put in this winter!! Thanks for the input

As time goes by I've lost a lot of brain cells but if my memory serves me well, HURST used to make a shifter for 1955-57 Chevy cars with 4 speed trans. and bench seat. It was made to come forward to clear the seat before becoming vertical to meet your hand. The shifter would work on a T-10 or Muncie (and maybe a Saginaw) by using the correct mount and shifting rods/arms. This just might work in an AD truck. Nobody every throws away a good Hurst shifter so there has to be one out there somewhere. Hope this helps.
If I'm wrong please call my doctor so he can adjust my meds.
DAVE

Sounds like a good settup to me. Some of the older models had a smaller hole in the bell housing where the bearing retainer fits in. One model of Muncie back then was built bassicly for raceing & had poor syncros for street use. Some of the fellow Stovebolters will help out on this but that is a couple of things to watch for.