VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 1929 passenger. Details of the driven speedo gearbox gear and shaft.

Hello to all.
Very grateful for some help with the speedo transmission gear. 1929 AC passenger car, right hand drive car with speedometer cable attaching to the left hand side of the transmission (perhaps all do this).

The gear on my driven shaft is loose from the shaft and needs to be mounted on. There is a place around the middle of the shaft where the gear clearly needs to be located (it sticks here), and here there are a couple of flats (see pic below).

Questions:
1. The teeth of the gear are bevelled on one end. Does the bevelled end point towards the cable side, or is it the opposite?
2. What is the distance from the end of the gear to the end of the shaft?
3. What is the length of the spacer part nr. 354756 that slides on the shaft between the gear and the cable end?
Thanks very much for any help.
Dave.

Hello Anagriff,
Don't know much about the details of your speedometer gear drive assembly, but I would guess that the beveled edge of the gear would face into the transmission as in your top picture. It may help in getting the gears to mesh during assembly. Just guessing. Others should know about the assembly. Good Luck. Harry

Am I seeing uneven wear at what you describe as the beveled edge? If I remember correctly the gear in mine had no bevel.

I agree! The gear in my car didn't have a bevel either. From looking at the photo, the gear shown is definitely worn.

thanks for the comments. I'll assume that the gear is meant to be centred around the flats in the shaft, and press the gear onto the shaft and see how it goes.

I saw a photograph of a 1929 Chevrolet driven speedo gear the other day, from an Australian car, and got a shock. The teeth are inclined in the opposite direction to what mine are (mine is the one in the pic above). The owner was sure his was correct, and further said that 1928 and earlier sloped in the opposite direction. I would be very grateful if someone who knows could tell me if the gear in the pic above is correct for 1929, or not.

Thanks,
Dave

I don't know the answer to that question, but I can tell you they wont directly interchange.

If you change the direction the driven gear teeth lean, you must also change the direction driving gear teeth lean. Otherwise, the gears wont mesh. (I believe Chevrolet sold them only as sets.)

Unless the position of the driven gear (above vs below) the driveshaft has also changed, a gear with teeth leaning the opposite way will turn the opposite way.

Speedometers work on some sort of magnetic pull or friction. On the sort of speedometer that we see on most cars, with a needle, and a dial, and zero to the left, you have to drive it anticlockwise, as seen looking into it's fitting from the rear. This is so that the needle will go clockwise as viewed from the drivers seat. There really isn't any way around this.

To get this anticlockwise rotation at the back of the speedometer, the gear would have to turn clockwise, as viewed from the outside looking in to the fitting on the transmission where the cable attaches.

A drum type speedometer could be designed to rotate either way. You would just have to look at it closely and see which way the drum would have to move to get from 0 to 10.

An example: When Chevrolet went from mechanical brakes to hydraulic (I think it was 1936), the speedometer cable had to move, probably to clear the master cylinder. I think they moved it from the bottom to the top. Both versions exited on the left side of the transmission. This change would have caused the speedometer cable to rotate backwards, so they changed the lean of the gear teeth on both the drive gear and the driven gear to get the rotation correct.

A cable exit on the right side of the transmission would require opposite leaning of the gear teeth, all else being equal.

For clockwise rotation as viewed from the outside of the transmission:

Left side exit, below the driveshaft center: Teeth on driven gear lean left
Left side exit, above the driveshaft center: Teeth on driven gear lean right
Right side exit, below the driveshaft center: Teeth on driven gear lean right
Right side exit, above the driveshaft center: Teeth on driven gear lean left

Drive gear teeth always lean opposite of driven gear teeth.

Corrections welcome.......

Thanks bloo for this. In sorting this out I have seen 1929 cars with the cable exiting both on the left side and the right side, and these are both Australian cars, which surprised me. But I think with all this info I'll be able to sort it out now.