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I took my transmission apart to fix a few issues, one of them being the speedometer gear. I had a 7 tooth and needed an 8 tooth. I noticed after putting it back together, when I put the transmission in reverse and rotate the input shaft, the speedometer driven gear rotates maybe 1/4 turn (if that) and then stops rotating. It seems to work fine in the forward gears. Is this behavior normal?
I did notice with the old gears, after backing up at a higher than usual speed, the speedometer no longer worked. When I took the driven gear out, some of the teeth had been ground off and the rest of the teeth were in pretty poor shape. I’m wondering if the position of the drive gear has anything to do with this. It wasn’t centered on the hole for the driven gear before, it was slightly towards the rear of the transmission, and I put the new one in roughly the same spot.
What was the status of that metal clip that secures it on shaft? Also, how freely did the speedometer cable spin? Did you check that and maybe oil it and use a battery powered drill to turn it? I know disconnecting from back of speedometer housing is a bit of a pain.
What was the status of that metal clip that secures it on shaft? Also, how freely did the speedometer cable spin? Did you check that and maybe oil it and use a battery powered drill to turn it? I know disconnecting from back of speedometer housing is a bit of a pain.
Mine has the steel drive gear that’s pressed on, so no metal clip. I’ve tested the speedometer with the drill and greased the cable and it works fine.
Here is what the driven gear looked like when I pulled it out:
I played with the transmission a little more and found that it does the same thing while spinning in the forward gears, but it takes longer to stop spinning. So I’m thinking it is because of the position of the drive gear. Here’s a photo of the current position of the gear:
Muncie 4-speeds originally had three different diameter speedometer drive gears. The six-tooth gear (no longer available) had no driven-gear options except for one steel 20T pencil gear. The parts resource guide lists two major diameter drive gears: 1.76 and 1.84 inches.
Driven pencil gears come in tooth count ranges that coincide with the size of the drive gear.General Motors discontinued the 1.76-inch drive gears and the corresponding driven gears. Because the 1.84-inch diameter was used in automatics, the cable-threaded fittings and driven pencil gears have been reproduced. AGE makes additional 7- and 9-tooth gears to work with these standardized pencil gears. It is now possible to calibrate your speedometer for a wider combination of rear axle and tire sizes.
also excerpted: Notice that the diameter of the blue gear is smaller than that of the yellow gear. Small-diameter pencils work with 1.84-inch drive gears; the range is 17 to 22 teeth. Large-diameter pencils work with 1.76-inch drive gears; the range is 22 to 25 teeth.
Last edited by keithl1967; Jan 22, 2019 at 08:39 PM.
I’ve got the 1.84” 8 tooth drive gear with an 18 tooth driven gear, which sounds like a compatible combo. Previously I had a 1.84” 7 tooth drive gear with an 18 tooth driven gear, and that worked (but read slow) until the driven gear got destroyed as shown in the first photo.
The problem seems to be solved. I took it apart and moved the drive gear towards the mid plate so it would be centered in the hole. The drive gear now rotates without stopping in either direction.
Muncie speedometer driven gear
