VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 Speedometer Gears

I have a 3:55 ring gear and pinion coming for the 52 Deluxe, replacing the 4:11. Obviously the speedometer will not read properly unless I change the gears in transmission output shaft. Questions: 1. Where can I find the gears? FS only offers 55 and up? 2. Will I only need to change the driven gear, I.E. the gear at the end of the cable or will I have to change the worm drive gear on the output shaft as well? Thanks for input and ideas. Ron

Ron Check with some of the speedometer repair place’s you should be able get a ratio adapter that will go on the trans and the cable hook to it.
When I put the 3.55 gears in the pickup I had one that I think was a 1.1 and that got it real close

Been there, done that! The ratio adapter is the easiest way to go. I did it the hard way and got a set of Powerglide 3.55 rear end speedometer gears. The driven gear that screws into the transmission case is easy to replace, just unscrew the old assembly and screw in the new. The hard part is the driving gear because it is pressed onto the front of the u-joint spider, where as on the three speed it is mounted on the transmission tail shaft. You have to cut the gear off the u-joint and machine the inside diameter to fit the 3 speed tail shaft.

Denny, is THIS what you're talking about?

The blue plastic gear pictured is for 1955 and up models.
In 1952 the (metal) gear came with the fitting that threads into the case and was not removable.
An adapter is an external unit that inserts between the original fitting and gear and the cable than attaches to it.
Chevrolet even used adaptors for various large truck applications where gear combinations were not available due to many ratios and tire sizes.

This is what the mechanical ratio adapter looks like. You provide the company some details on your ratio change and speedometer error and they match with a stocked unit or build a custom geared device in a box that mounts inline with your speedo cable.

OK, thanks gents.

Thanks a lot for the information and input. Located a local speedometer repair guy who has kits to make up what I need. He recommends putting everything together and use GPS to drive EXACTLY 10 miles then compare to the odemeter distance and adjust accordingly. Will go with his recommendation. Thanks again

Ron, is that Cushman Speedometer Repair?

I know Chris Cushman, but this is actually Phil Knighton, who specializes in older speedometers while Cushman does mostly 29 and newer.

Thanks Ron.

Interesting discussion. One problem you will always have with speedometers and correction is whether you want the new ratio to give accurate speed or distance on the odometer. My experience is that they are typically about 3 or 4% different with the speedometer reading high. Sometimes that can be corrected within the speedometer head itself.

Always make the gearing match the odometer, as that is how the speedometer is designed to work. If the speed is too far off once the gearing is correct, get the speedometer re-calibrated.