67 4-speed wr?

[Justin N.]

Dear Members,
I have a question about my close or wide ratio Muncie and a # on the case. My tranny tag was still attached and it reads 3870354. CC's catalog says it's a (wide ratio) M20 for a 66-67. It has the blue speedo gear and I've counted the revolutions of the carrier yoke to confirm the 3:36 posi ratio. The input shaft has one(1)ridge at the base which I was told is an M21 close ratio. Two(2) ridges is the wide ratio M20, and no ridges is an M22 rock crusher. Also, there are the markings P7T12, on the opposite side from the plate. Are these the build date #'s? The vin ends 7s106252 which is supposed to built around Dec. 19th. Thank you much.

Justin

[Mark #28455]

Re: 67 4-speed wr?

It wasn't until October of 1968 that the factory stamped the trans case with an A B or C to designate the internal gear ratios (M20, 21, or 22) so many owners have substituted internal gears (m20 for M21 etc.) as long as the entire set of gears is swapped it will work fine. Usually cars with the M21 or M22 had a 3.73 or better rear but this isn't written in stone. What engine did your car originally have? Did it have AC (those cars are all usually M20 equipped).

The P7T12 is the date code for December 12 of the 1967 model year (actually Dec 1966). As long as your car's VIN is 106252 consider yourself very lucky that you likely have the original trans case for your car.

[Duke W.]

Re: 67 4-speed wr?

In case you have a Heinz 57 gearbox, you can easily determine if it is WR of CR by computing the rev drop ratio between third and fourth gear. A wide ratio is 1.46-1.51, depending on the year, a CR is 1.28 or 1.31 for early T-10s.

A convenient way to measure is to bring the revs up to 3000 third and note the EXACT speedo reading. Then achieve this speed in fourth and note revs. If revs are about 2000-2100 its a WR; if 2300-2400 its a CR.

Duke

[Jimmy B.]

Re: 67 4-speed wr?

Justin:

My M20 has the following: 1) tank sticker: 02M20AA 2) protecto plate: P7C08 3) trans main case: 3885010 4) stamp: P7C08 5) stamp: 7S114122
6) tail housing 3857584 7) metal tag 3870354 side cover 3884685
9) blue speedometer gear

my rear end from the protecto plate: AM0307W
stamp: AM 3 7 67

Hope this helps.

Jimmy Blakely

[John H.]

Re: 67 4-speed wr?

Since you have it out of the car, just put it in first gear and see how many revolutions of the input shaft it takes to produce one full revolution of the output shaft; 2-1/2 turns is an M20, 2-1/4 turns is an M21.

[Justin N.]

Re: 67 4-speed wr?

Thank you all for your help and support. John I got 2 1/2 turns for the full revolution of the outshaft, M20 wide ratio it is!

Justin

[John H.]

Re: 67 4-speed wr?

Justin -

My known-original '67 M20 has the same steel Muncie part number tag as yours does.