66 M21 mucie drive gear?

[Brian K.]

In 1966 did GM use the 1.74 or the 1.85 drive gear in the M21 tranny? Thanks sincerely Brian K.

[Joe L.]

Re: 66 M21 mucie drive gear?

In 1966 did GM use the 1.74 or the 1.85 drive gear in the M21 tranny? Thanks sincerely Brian K.

Brian------

Assuming that you're talking about SPEEDOMETER drive gear, it depends upon what the installed rear gear ratio was in the car that the transmission was originally installed in. In general, rear gear ratios of 3.08:1 to 3.55:1 used the larger drive gear. Rear gear ratios of 3.70:1 to 4.11:1 used the smaller drive gear.

[Brian K.]

Re: 66 M21 mucie drive gear?

Thanks Joe, yes I was talking about the speedometer drive gear. I'll take a caliper to it. Sincerely Brian

[Wayne M.]

Re: 66 M21 mucie drive gear?

Thanks Joe, yes I was talking about the speedometer drive gear. I'll take a caliper to it. Sincerely Brian

I assume the gear is on the bench. Take another caliper measure, this time on the width (tends to be more accurate than measuring diameter) The 1.85" OD should be 0.61" thick, and the 1.75" OD should be 0.531" thick.

Of course, there's always a 6-tooth, third drive gear, for 4.56 axle ratios: 1.922" OD and 0.453" thick.

[Brian K.]

Re: 66 M21 mucie drive gear?

Thanks Wayne, I'll do those measurements also. Sincerely Brian

[Brian K.]

Re: 66 M21 mucie drive gear?

Hey Joe the numbers man!! I got the 1.75 drive gear in my M21. Do you happen to have the GM part # for the speedo gear for a 3.70's rear end, I believe it's green 22 tooth? Thanks for all the help guys sincerely Brian

[Joe L.]

Re: 66 M21 mucie drive gear?

Hey Joe the numbers man!! I got the 1.75 drive gear in my M21. Do you happen to have the GM part # for the speedo gear for a 3.70's rear end, I believe it's green 22 tooth? Thanks for all the help guys sincerely Brian

Brian-----


The green 22 tooth gear is GM #3860345.

[Brian K.]

Re: 66 M21 mucie drive gear?

Thanks Joe!