Another Transmission Speedo Gear Question

[Bob Malone #35242]

My '60 has what I'm told is a Muncie (sp?) 4 speed tranny. My recently restored speedo indicates 10 mph faster than actual speed at 60 mph. I remember from my youth that there is a fairly simple speedo cable gear change at the tranny end to correct this problem. What do I need to know in order to get a correct gear? I assume rear end ratio is one item. I don't know what my rear end is except it is really looowwwww.
Someone point me in the right direction please.

[Wayne K.]

Re: Another Transmission Speedo Gear Question

Bob,

Before going gear crazy confirm the following:

1) rear end ratio. Raise rear wheels so they both turn freely. Mark driveshaft and count the number of times it turns per 1 complete turn of a wheel. This will get you close. Example; 3 1/2 turns is probably a 3:55 to 1.

2) Next make sure your tire circumference/size is correct for your model as delivered.

3) Also confirm that your odometer is off. If the odometer measures correctly
then the problem isn't the gear provided your running the correct tire size. If they are both off the same % then your GM supplier should be able to provide you with the correct gear. If just the speedo is off then you probably have a calibration issue.

Hope this gets you started.

Wayne

[Roy B.]

Re: Another Transmission Speedo Gear Question

There are shops that carry different driven gears and can check your actual speed. Or driven gears come in different colors which in turn have more or less teeth.
To increase the reading of the speedometer decrease the driven gear teeth . To decrease, increase the teeth.By adding or reducing TWO teeth will add or reduce 5MPH to your reading.
Gear color # of teeth
Brown 18
Natural 19
Blue 20
Red 21
Green 22
Black 23
Yellow 24
Clear 25
If any one needs a long gear but can only find the short gear ,speed shop have an adapter you can get to make a short one long.
I hope this can help .

[Bob Malone #35242]

Re: Another Transmission Speedo Gear Question

Great info. Thanks Wayne and Roy. I appreciate it.

[Doug Flaten]

Re: Pull the Speedo Gear

Expanding on the info Roy posted. You could pull the speedo gear and count the teeth. In order to slow down your indicated speed, you will need one that has more teeth and thus will take longer to make one revolution. I am not clear if if you are saying your indicated speed is 70 and real speed is 60, or your indicated speed is 60 and the real speed is 50. Depending which it is, you have an error of 14.2% to 16.6% respectively. You will likely need a gear with 3 more teeth than what your are currently running. Take the number of teeth you want to add, and divide that by your current tooth count. That will give you the Percent correction you are making. Each tooth is going to change the indicated speed by roughly 5%. You can calculate the correct tooth count or buy a couple of different sizes.

[Bob Malone #35242]

Re: Pull the Speedo Gear

My indicated speed is 70, actual speed is 60.