69 AIM Transmission Numbers

[John A.]

Tranny question - The 69 AIM lists two different part numbers for the M21 transmission – one for the 350/350 and one for the 427/390 and no other M21 options… ??? Can anybody explain the difference between the two different transmissions – are they interchangeable? (Sorry I don’t have the part numbers handy for the post!) Thanks

[Joe L.]

Re: 69 AIM Transmission Numbers

John------

The transmission are completely interchangeable. The only difference between them is the installed speedometer gear set. The "L-36 M-21 transmission" contained a GM #3924098 speedo DRIVE gear and a GM #3860343 DRIVEN gear. The "L-46 M-21 transmission" contained a GM #3924097 speedo DRIVE gear and a GM #3860346 DRIVEN gear.

The transmission part numbers shown were actually used for more applications than just those specified in the AIM.

[John A.]

Re: 69 AIM Transmission Numbers

Joe,

Would the L36 speedo gear part numbers you mentioned also apply to the L68?

Thanks again!

[Joe L.]

Re: 69 AIM Transmission Numbers

John-----

Yes, they would apply to any 1969 L-36, L-68 or any other engine with M-21, M-20, or M-22 and 3.36:1 rear axle ratio.

[Joe L.]

Addendum

By the way, the part numbers that I provided are ORIGINAL part numbers; neither are currently available under those numbers:

GM #3924098= GM #6261794 (MUST be used with clip GM #1373122 and is applicable ONLY to ORIGINAL 68-70 Muncie mainshafts)

GM #3860343= GM #3987920

[John A.]

Re: Addendum

Joe,

What would be the part number combination for a 3.08 rear… Are these gears color coded?

[Joe L.]

Re: Addendum

John-----

3.08:1 speedo gears

DRIVE= GM #6261794------8 teeth------light green

DRIVEN= GM #3987919------ 19 teeth-----natural color (very light tan)