Help with Muncie speedo gears
 

As many may know, our 69 Chevelle when found was missing the M21 so I took one off the shelf that I had (originally came out of a Pontiac) and rebuilt it using the correct Chevelle tailhousing. What I am not sure about is what speedometer drive and driven gear I need for the 4.10 with F70x15 tires. From talking with Eric at Crash Enterprises we came up with a small 8 tooth metal drive gear and a large yellow 24 tooth driven gear when used in conjunction with the .7333 speedo reducer. Can anyone else concur with this information before I put it all back together or offer other insight? I also could use part numbers if you have them.

Another question, does the 69 4.10 car use the offset BW rectangular adapter or the round 90* adapter? Thanks in advance for your help.
Rick

Gear clculations
 

Rick,
will any of this help?
https://www.cartechbooks.com/techtip...e-speedometer/

Paul

I did the math and with an 8 tooth drive gear, and a 27 inch tall tire (746.96 revolutions per mile) it is in fact a 24.47 driven gear that you need.

24 will work fine.

Yes and no. I had been there already and it helped but not completely. The real stickler that I am dealing with is that the car came with F70x15 NOT F70x14 which is a different diameter and it throws a slight wrench into things. Same for the speedo reducer.

my 69 4:10 Chevelle uses the straight adapter.

Interesting John. M22 or M21? Do you have a photo of the adapter by chance so that I can see what the straight one looks like? Thanks

m22 trans. As far as I know the reducer was original but who knows I bought the car in 1991 any thing could have happened before that.

Ok, good. That is the same SW piece that I have though I have not confirmed which ratio I need yet with the F70x15. Thanks for posting that John.

Would it be the same ratio as a Yenko Camaro. Doesnt Chad have any pictures of his adapter from the blue Yenko Chevelle

I haven't had a chance to call and ask him yet. I have several but of course, the one area of the transmission I did not take a photo of was the adapter. Go figure. I got a great shot of the XF trans stamp on the top but no adapter.

As far as being the same as the Camaro I do not know why it would not be. M21, 4.10, F70x15, all things being equal. The gears I posted at the beginning were the Camaro ones but just trying to confirm.

SW date code chart in case anyone is interested.

Rick, I sent you an email that might help you with the reducer.

The only thing I will add is to rebuild it before install. Mine had very dry grease inside that was pretty much solid.
From the various photos I have seen, it seems like they went from Phillips head screws to hex around 1975 or so.

FWIW, the '70 Yenko Nova's used the round units with a .8333 ratio.

Based on all the information I have had sent to me, called to me, etc (and thanks to all who did that) I have come up with 6261794 or 3708144 (depending on plastic vs metal gear) drive gear which natural in finish and 8 tooth, 3987919 driven gear opaque and 19 tooth and 3932220 .7333 adapter. The kicker is that is what is shown for the F70x14 tire. I can find NO information on what may have come with the F70x15 tire combo.

Photo is from the Ed Cunneen Copo Connection Source Book

Thanks John but those gear part numbers are for a Turbo 400 not an M21 unfortunately.