Speedo / Tach / Gauges: Speedometer

[mmagic]

The Champ Speedometer went into orbit and threw the needle & bearing on my first 120 mile outing in July. Speedo Trashed ! Picked up and installed a gauge set from a '59 Lark with expected calibration issues but at least I no longer have to count fence posts to estimate my speed.

I understand that Pinion gears have different teeth count to adjust for various transmissions and differential ratios. Are they interchangeable or is each teeth count matched to a corresponding teeth count internal to the transmission. In short, can I simply change the pinion gear to true up my speedometer or should I just put pieces of duck tape on the glass ??

[Bo Markham]

You need to determine what ratio your rear axle is then confer with parts book chart to tell you the correct pinion gear used with the transmission in your vehicle.

Of course, this begs the question. Was your speedo registering correctly before it went tits up, or was it off then, too? Was the transmission or rear axle replaced with womething other then what was originally installed at the factory? If this is the case and the pinion wasn't changed in the transmission at that point, then a pinion gear would correct your problem.

Unless the speedo wasn't working right before, or either component has been switched out, the replacement speedo should be registering the correct speed, unless the speedo head isn't working correctly? In this case, you would need to have your speedo serviced and calibrated.

So, there are several details to work out that will pin point the cause of the problem.

[mmagic]

Bo,
It went orbit before I had a clue whether the old one was even close. Driven gear has 15 teeth and speedo is showing about 40 when passing those electric speed signs showing 35. So an 18 tooth driven gear should be a quick fix unless the drive gear must be changed too. My question remains can I just change the pinion gear.

[StudeRich]

The Chassis Parts Catalog Speedometer Chart tells you which Drive Gear works with which Pinion Gears, normally you can go at least 2 or 3 ratios up or down before having to worry about it, but best to check the chart. As you know, Tire size is also a factor.

The other issue is after this many years as Bo said, who knows what vehicle the Trans. might be from using a different Drive gear.
The ultimate test would be; raise the rear wheels, have someone rotate the driveline in Neutral while you shine a light in the Cable hole, mark a tooth and count them, probably too much trouble and not needed, but still possible.

Your Speedometer will not be a problem, all Speedos work on the same input ratio.

[rockne10]

To answer your original question, YES! The pinions all work off the same driven gear in the trans; all you need is an appropriate speedo pinion.