Just recently picked up a 61 F100's stepside and am getting into some the "easier" fixes. One of the first things is my speedometer. It is off exactly 20 mph off (fast, showing 70 while going 50)...or so I thought. I have been checking my speed with GPS. I noticed today that at lower speeds it's only 10mph off. Before I go ordering a new speedo gear, is there something else off here?

Thanks,
Adam

 

Hey Adam, welcome to FTE!

Part of it has to do with tire size as you might imagine. I expect if you get the correct driven gear it will be very close, at most speeds.

 

I knew that played a factor as well, but never thought it would be that drastic. I had a jeep I went from stock to 33's on a few years ago and it only affected it 2-3 mph. I'll do the tooth calculation and order a gear. 20mph should be pretty easy to figure out. We'll see how that works out.

 

Welcome to FTE

There are THREE different types of speedometer DRIVEN gears (at the end of the cable where it fits into the trans). One type is steel, the other two are nylon, but their shape is different.

See car parts catalog pic below. There's no pic like this for 1957/63 trucks, 1964/72 truck pic doesn't show type 2.

TYPE 4: If steel, they're obsolete, not reproduced, some are available NOS

TYPE 3/3A/3C nylon gear is available from Ford and auto parts stores, 16 thru 21 teeth are available.

TYPE 2 nylon gear is reproduced by Dennis Carpenter.

But, if your truck has P-Metric radials, the speedo will never read 100% correct as P metrics are a different shape than the original bias ply tires these trucks were only available with.

 

No, I'm saying tire size plays a role, not that they are solely responsible for the error seen.

 

If you've got the steel type, you may be out of luck. I've tried multiple places and found none, let alone a gear with the right number of teeth.

~Steve

 

Look on the gear for the actual Ford part number, may be similar to this: 01T-17271-A