[cdoggy81]

Talking to guy in the neighborhood one day when I told him I was looking for a 4 spd tranny for the 70 Firebird 350 that currently has a 3spd in it. He said he has this Muncie 4 spd for many many years but has no idea what it is.
Can you all help me identify it & if it could work in my Pontiac?
Thanks!

Looks like 3885010 on the one side.

3884685 on the other side.

[steve25]

A Muncie will have a 7 bolt side cover, and a Aluminum case.
The input gear in the case will have , none, one or two grooves.

No grooves is the M22 / rock crusher/ 2.20 first gear.

One groove is M21 standard duty/ 2.20 first.

Two grooves is the M20 standard duty, 2.52 first / wide ratio.

All 64 to 70 Muncies are interchangeable .and the 71 to 74 models are interchangeable.

The difference’s are the early have 10 spline input and TB350 size output shaft.

Late models have 26 input and TB400 size output shaft.
A BW trans has a 9 bolt side cover.

That trans in your picture is a two groove version and would hold up fine behind a 350 cid engine for everyday street .

[Held for Ransom]

Wide ratio Muncie that came from a 1966 Chevrolet.

[gtorich]

Originally Posted by steve25

A Muncie will have a 7 bolt side cover, and a Aluminum case.
The input gear in the case will have , none, one or two grooves.

No grooves is the M22 / rock crusher/ 2.20 first gear.

One groove is M21 standard duty/ 2.20 first.

Two grooves is the M20 standard duty, 2.52 first / wide ratio.

All 64 to 70 Muncies are interchangeable .and the 71 to 74 models are interchangeable.

The difference’s are the early have 10 spline input and TB350 size output shaft.

Late models have 26 input and TB400 size output shaft.
A BW trans has a 9 bolt side cover.

That trans in your picture is a two groove version and would hold up fine behind a 350 cid engine for everyday street .

Steve, not for sure but i think the 63-65 M-20 did not have any grooves............without them being the rockcrusher............i may be wrong on that.

[gtorich]

Muncie 4-speeds were produced in two different ratios wide-ratio (M-20) and close-ratio (M-21). An extra heavy duty close-ratio version (M-22) was also offered on many of the big-block high-performance models.The choice of transmission was dictated by the engine size and rear-axle ratio. Axle ratios of 3.73 and lower (numerically higher) came with close-ratio transmissions, while axle ratios of 3.55 and higher (numerically lower) used wide-ratio transmissions.

Ratios
Year Type Rings 1st 2nd 3rd 4th Rev
1963 - 1965 M20 None 2.56 1.91 1.48 1.00 3.16
1966 - 1974 M20 Two 2.52 1.88 1.46 1.00 3.11
1963 - 1974 M21 One 2.20 1.64 1.28 1.00 2.27
1967 - 1974 M22 None 2.20 1.64 1.28 1.00 2.27
Input Shaft Tooth Count and Splines
Input Shaft Output Shaft
Year Type Rings Splines Tooth Count Splines
1963 - 1965 M20 None 10 24 27
1966 - 1970 M20 Two 10 21 27
1970 - 1974 M20 Two 26 21 32
1963 - 1970 M21 One 10 26 27
1970 - 1974 M21 One 26 26 32
1967 - 1970 M22 None 10 26 27
1969 - 1974 M22 None 26 26 32
A M22 gearbox has a 20 degree h

Just a little more info............i know my 65 M-20 has no rings on it, 10 spline........dont have the orginial case numbers anymore, have a super case on it now with a iron mid plate............

[geeteeohguy]

Originally Posted by Held for Ransom

Wide ratio Muncie that came from a 1966 Chevrolet.

Correct. And a perfect trans for your Firebird.

[400 Lemans]

Pontiac muncies usually have the speedo gear on the driver side. You may have to get a new cable to reach the pass side or change tailshaft housing.

[Lemans64]

I'll give you 100 bucks for it, LOL. Nobody beat me to the punch line so figured I was ok. LOL.
https://www.5speeds.com/muncie2.htm
Looks to be m20 65-67 for the case number anyway.

[george kujanski]

And Chevy, with a passenger side speedo.

I happen to be looking for a rebuilt m20 with driver side speedo. Also the earlier Muncies had. 7/8” countershaft pin. The later ones were 1” and better.

George

[sdbob]

As was said 66. It should have the 1 " counter shaft. Serial number example P0101. Muncie "P"lant,January 1. Serial number stamped by hand at factory Would identify further. Same case number in late 1966-1967 would have 'ears' that are thicker and rear of main case would be thicker. I got this info from Paul Cangialosi 's book for rebuilding Muncie transmisions

[cdoggy81]

Good info & thanks guys!
Now the hard questions…. :-)

If I have the m13 3spd in it now what all would I need for the swap?

What is it worth? $300-$400-$500?

Are the current m13 ratios 2.54-1.88-1.00 ?
If so going to the m20 ratios of 2.52-1.88-1.46-1.00 should make a nice street cruiser behind the Pontiac 350 (2800 cam) & a 3.08 posi I would assume.

[steve25]

All the info you need for the swap is already in this string, please read it through again.

[Held for Ransom]

Final drive for both transmissions is 1:1.
You have to purchase the 4 speed shifter assy for the Firebird. My opinion, not worth the money or time to swap out.

[steve25]

If the 3 speed he has now has a iron case, then to me it’s worth the time to make the swap. ( less weight/ added gear step) , so then it’s just the purchase cost factor.

[KEN CROCIE]

My original wide ratio from my 64 gto has a ten spline input, no rings and 7/8" countershaft.

[steve25]

Somewhere along the time line for these the grooves in the input shaft started to show up, so anyone know the details on this?

[turbo69bird]

One thing I didn’t see mentioned is an easy way to identify a M22. They will always have 2 drain plugs while a 20-21 will have one drain plug.
At least in there original configuration

[Held for Ransom]

Originally Posted by turbo69bird

One thing I didn’t see mentioned is an easy way to identify a M22. They will always have 2 drain plugs while a 20-21 will have one drain plug.
At least in there original configuration

In their original configuration, I believe all 3925661 (late '70 to '74) cases came with both holes tapped.

[Held for Ransom]

Originally Posted by steve25

If the 3 speed he has now has a iron case, then to me it’s worth the time to make the swap. ( less weight/ added gear step) , so then it’s just the purchase cost factor.

He wants it for cruising. A difference of say 20 lbs. in the center of a car is not going to make that much of a change. And shifting that extra time over and over gets to be a nuisance in stop light traffic.

[steve25]

I agree that it can get laborious in traffic, but there always been that mystique of having a console boot with a chrome shaft sticking out that has a ball on it with a H pattern just for the 4 forward gears.