Calling all speedometer (experts)

[Keith G.]

I need to speedup my speedometer by 15 miles an hour. I took out a 22 tooth gear and need to put in a 19 tooth gear, I think. The 19 tooth is to small in diameter, what color or tooth count do I need is the tail houseing to make the 19 tooth work. 1967 4 speed.

[Edward J.]

Re: Calling all speedometer (experts)

Keith, you may want to post some info. like tire size, rear axle gear ratio, transmisson type, there maybe a few different drive gears and many driven gears. this should help you get it right.

Of coarse if you have a calabration problem with the speedo is self, it may not help.

[Wayne M.]

Re: Calling all speedometer (experts)

I need to speedup my speedometer by 15 miles an hour. I took out a 22 tooth gear and need to put in a 19 tooth gear, I think. The 19 tooth is to small in diameter, what color or tooth count do I need is the tail houseing to make the 19 tooth work. 1967 4 speed.

If you took out a green 22 tooth driven gear (which would have been a factory choice), then you're out of luck finding a lower-tooth gear that will mesh with your 8-tooth steel drive gear (on the trans output shaft). All plastic gears below the 22-tooth count are of the small-diameter family.

[Duke W.]

Re: Calling all speedometer (experts)

I need to speedup my speedometer by 15 miles an hour. I took out a 22 tooth gear and need to put in a 19 tooth gear, I think. The 19 tooth is to small in diameter, what color or tooth count do I need is the tail houseing to make the 19 tooth work. 1967 4 speed.

At what speed? Speedometer error is usually "gain error" where the error is a certain percent at all speeds. So if it's off X MPH at 60, it will be off X/2 at 30 and 2x at 120. A constant speedo error is called "offset error", and it's possible to have a combination of both.

As stated you need to state the axle ratio and tire size and post your test data. Then we can tell you the proper color/tooth count driven gear.

If that doesn't get it within reasonable calibration, then there could be a problem in the speedometer head.

Duke

[Keith G.]

Re: Calling all speedometer (experts)

336 gears, 205x15 tires, at 60 the speedometer reads 45, took a green 22 tooth out, 21 and down won't work with the output shaft gear, can I special order a 19 tooth in the bigger diameter. I see CC has a 22 tooth silver for sale, I thought all 22s were green??????

[Edward J.]

Re: Calling all speedometer (experts)

Keith, there are two possiablitys for the output shaft drive gear, I am going through this now with a 64 4 spd. trans. for a frenids corvette, 3.08-3.55 is one gear and the other gear is for 3.70-4.11,your transmisson drive gear maybe of the wrong gear, I think the driven gear for 3.36 is blue 19 teeth, drive gear 8 teeth -metal.

Keep in mind that if this problem is as of recent, then you may a speedo calibration problem.

[Wayne M.]

Re: Calling all speedometer (experts)

..... I see CC has a 22 tooth silver for sale, I thought all 22s were green??????

Used to be the case, back in the '60s. But sometime later (Joe L. could probably tell us when) they introduced a 22-tooth silver (gray ?) small diameter family gear (#3987922) to permit speedo adjustment without changing the larger 8-tooth steel gear designed for the 21-tooth and lower family of plastic gears

Pic is of both color 22-tooth gears.

[Dick W.]

Re: Calling all speedometer (experts)

First question, has it always been this far off, or has it changed over time?

[Keith G.]

Re: Calling all speedometer (experts)

Just got the car, looked like a heck of a lot of work just to get tail shaft off, it's a driver, think I'll leave well enough alone. I did try two 19 tooth gears, a 20 and a 21, with no difference, so quite sure I need a gear of bigger diameter. The 22 is about 1/8 taller then the others. Thanks to all.

[Dick W.]

Re: Calling all speedometer (experts)

Keith, figure out how slow it is at 60 mph. Then convert it to a percentage. Go to a HD truck parts dealer and obtain a S S White speedometer adapter with the percentage correction you need. You will need to know the size of the speedo cable end for them to install the proper ends. At one time they were available from Generous Motors, but long discontinued.