Transmission Speedometer Gear

[Richard T.]

Can someone tell me the correct color and tooth count for the nylon transmission gear that drives the speedometer for the following rear end ratios? 3:36, 3:55, and 4:56. T-10 and Muncie Thanks

[Patrick B.]

Re: Transmission Speedometer Gear

Can someone tell me the correct color and tooth count for the nylon transmission gear that drives the speedometer for the following rear end ratios? 3:36, 3:55, and 4:56. T-10 and Muncie Thanks

Based on my recent questions about this topic, I would say that the 3.36 would use the red gear with the large 8 tooth output shaft gear;the 3.55 would use the silver gear with the large output shaft gear or the green gear with the small 8 tooth output shaft gear; the 4.56 would use the steel (not nylon) pencil gear with a rare 6 tooth output shaft gear. The 3.55 is the only rear for which pencil gears are available for either size of output shaft gears, and the same combos are used for 3.70 rears because the error is not too great. If you don't want to disassemble the transmission to change output shaft gears, there are speed changing adapters available. These combos apply to most Muncies up to about 73, with the 68 and up using plastic output shaft gears with their own color codes. These combos would represent the original equipment tires which have about 775 revolutions per mile. 775-15, F70-15 and 215/70R15 tires are all close to 775 rev/ mile.

[Terry D.]

Re: Transmission Speedometer Gear

[Patrick B.]

Re: Transmission Speedometer Gear

Terry -- That is an interesting table, Joe Lucia and other sources I found said that pencil gears with fewer than 22 teeth would not mesh correctly with the 1.76" drive gears. Have you tried any of the smaller driven gears with the 1.76 drive gear?

[Joseph L.]

Re: Transmission Speedometer Gear

Hi Richard
The topic and calculations are covered in the SoCal February 2020 newsletter.
You also need to know the tire diameter and which drive gear is installed in the transmission.
Joe

[Joe L.]

Re: Transmission Speedometer Gear

Can someone tell me the correct color and tooth count for the nylon transmission gear that drives the speedometer for the following rear end ratios? 3:36, 3:55, and 4:56. T-10 and Muncie Thanks

Richard------

It depends on year model, tire size ,and installed transmission DRIVE gear. The transmission DRIVE gear can be inferred by knowing which DRIVEN gear is now installed.

[Gerald C.]

Re: Transmission Speedometer Gear

I have 3:55 gears and the 6:70-15 Bias Ply tires on my 63 car. So.....If I interpret this chart correctly, I can use the red 21 tooth gear for either diameters of drive gears of 1.76 or 1.84 that I might have in my tranny. It looks like just different part numbers.

Thoughts??

[Joe L.]

Re: Transmission Speedometer Gear

I have 3:55 gears and the 6:70-15 Bias Ply tires on my 63 car. So.....If I interpret this chart correctly, I can use the red 21 tooth gear for either diameters of drive gears of 1.76 or 1.84 that I might have in my tranny. It looks like just different part numbers.

Thoughts??

Gerald------

The 21 tooth driven gear is only compatible and designed for use with the large (1.84") drive gear.

[Harry S.]

Re: Transmission Speedometer Gear

I know tires and other items will cause the speedometer to be off. But the day the car was produced this is what I recall.

63-67 GEAR - speedo drive in transmission, 3:08, used w/3:70 - 4:11 rear end gear ratios, (18 tooth, brown)
63-67 GEAR - speedo drive in transmission, 3:36, (20 tooth, blue)
63-67 GEAR - speedo drive in transmission, 3:55, (21 tooth, red)
63-67 GEAR - speedo drive in transmission, 3:70, (22 tooth, green)
63-67 GEAR - speedo drive in transmission, 4:11, (24 tooth, yellow)

[Gerald C.]

Re: Transmission Speedometer Gear

Joe,

Thanks for this information. Making the assumption I have the smaller 1.76" gear, what tooth count would you recommend? The speedometer is not registering at all. It does when the cable is driven by a drill, so I know it's in the tranny/plastic speedometer gear set-up.

Thanks,
Jerry

[Joe L.]

Re: Transmission Speedometer Gear

Joe,

Thanks for this information. Making the assumption I have the smaller 1.76" gear, what tooth count would you recommend? The speedometer is not registering at all. It does when the cable is driven by a drill, so I know it's in the tranny/plastic speedometer gear set-up.

Thanks,
Jerry

Jerry------

If you do have the 1.76" drive gear installed and you do have 3.55:1 rear gears, I'd say try a 22 tooth GREEN gear. That's the lowest tooth count gear that's compatible with the 1.76" drive gear. I don't think it will give an accurate speedo reading but it should drive the speedometer.

[Gerald C.]

Re: Transmission Speedometer Gear

Thanks Joe. I have a green 22 tooth and I'll try that. But having the 21 tooth red in there now will prevent the speedo from even registering??

Jerry

[Donald O.]

Re: Transmission Speedometer Gear

Joe,

Thanks for this information. Making the assumption I have the smaller 1.76" gear, what tooth count would you recommend? The speedometer is not registering at all. It does when the cable is driven by a drill, so I know it's in the tranny/plastic speedometer gear set-up.

Thanks,
Jerry

Is this a new cable, new issue ?

[Joseph L.]

Re: Transmission Speedometer Gear

Hi Jerry

As Joe Lucia said, IF you have a 1.76" dia. drive gear installed, a 22 tooth green 0.870" dia. driven gear will get your speedo registering, or you have other problems. A 22 tooth green is what usually come with a 3.70 and 1.76" drive gear.

A 21 tooth red 0.810" dia. driven gear may not mesh with a 1.76" dia. drive gear. There may be no reading. A 22 tooth green 0.870" dia. driven gear, may be one tooth greater than that red gear, but is not in the same gear family. They do not work.

Think of it this way: Replace an M21 first gear into an M20 gearbox. Change nothing else.

Joe

[Joe L.]

Re: Transmission Speedometer Gear

Thanks Joe. I have a green 22 tooth and I'll try that. But having the 21 tooth red in there now will prevent the speedo from even registering??

Jerry

Jerry------


Well, if you have the 1.76" DRIVE gear installed, the red 21 tooth DRIVEN gear MIGHT not mesh with it. However, I would think there would be enough "interaction" that you would get some kind of speedometer needle movement.