1963 Speedo Gear Drive

[Jerry Coia]

I need an answer on the speedo drive gear for my 1963 Powerglide car. It has a 3.08:1 rear end and it registers 40 MPH while a test car registers 50 mph. I'm trying to figure out what # of teeth I need in the car.

Thanks,

Jerry # 11656

[Joe L.]

Re: 1963 Speedo Gear Drive

Jerry-----

Assuming that you have the correct DRIVE gear installed in the transmission AND that your tires are close to the stock 6.70-15 OD, then you require a blue, 20 tooth DRIVEN gear of GM #3987920. This gear is still available from GM and most Chevrolet dealers should stock it.

[Duke W.]

Re: 1963 Speedo Gear Drive

Drive gear - 3708144, 8T

Driven gear w/3.08 - 3987918, 18T
.................w/3.36 - 3987920, 20T

Poweglide uses the same drive and driven gears as manual transmissions with the same axle ratio.

Duke

[Mike McKown]

Re: 1963 Speedo Gear Drive

Jerry:

On some cars, one tooth on the plastic driven gear is worth about 5 mph. If this be the case with your car, you need to subtract two teeth off what you now have on the driven gear. Only use this method if you do not want to go to the trouble and expense of determining what drive gear you actually have in your transmission. There may be another way but the only way I know is to pull the tailhousing off the transmission and measure the drive gear diameter against a known correct one. There may even be a part number stamped on the drive gear. I don't remember. They used several different drive gears and they are compatible with only certain driven gears. If you get an incompatible combination, you will chew up the plastic driven gear.

Mike