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I am trying to get my speedo adjusted to read properly. I have changed from a 19 to a 20 tooth gear and it helped, but still 8+/- off. I have a 21 ordered, but I don't if it will make up the difference. I found a company that will custom make one for me, but I need to supply the axle ratio, transmission type, engine type, and tire size to order it. I have no idea what the transmission came out of, but it is a C6. I am assuming the rearend is original, but I am unsure of the ratio.
The transmission's tag reads:
PGD BC16 G22
E1TP FB 02845
The rearend's tag reads:
WBG-F2
3.89 4EC 301
Door ID reads (if needed):
F10JK543B14
114 B F100 381 D 12
5000 114 3600 53
Thanks for your help,
Mike
P.S. Major milestone for the '64 today - It was the first day in 6 plus years the truck was able to be driven for the continuous daily errands. Receive two compliments on it already. Thanks for helping me get it to that point.
You effect your calibration by changing tire diameter. I had a 20mph discrepancy after putting C6 in place of 3sp. Going from 29" tires to 31" halfed the discrepancy (truck was going slower than speedo indicated) Fortunately a 22tooth gear (max availible) bought it to correct. I needed tires anyway, If your tires are good, then the cost of a conversion gearbox (for speedo cable drive) is probably cheaper than new wheels and tires.
When I run my winter tires which are 235 75 r15's I have to use a 16 tooth gear, With my 33 12.5 15's I run a 21. My Ford man here says it is normally 4 to 5 miles difference for each tooth .If your speed ometer is reading low you need to go up in tooth count and vice versa. Hope this helps.Also it is easy to tell the difference in the speedo's the 16 is white, the 21 is green and they have a bunch of different ones here in stock for my truck.
the gear ratio on the rearend is the first three numbers on the second line of the tag which in your case are 3.89. It's an open differential. If it had limited slip it would read 3L89.
Where did you find someone to custom make your speedo gear for you? Mine is off big time. When the speedometer reads 70 you are goung between mile markers in 40 seconds which calculates out to 90MPH!!!!! If you could provide the address for the company I would greatly appreciate it. Thanks
Well I had it backwards on the speedo gears. I just changed to my summer tires today. When i pulled out the speedo gear for the P237 75r15's it was the 20 tooth gear. I put my other one on and it is the 16 tooth gear for the running of the 33x12.5x15's. And it is approx 4 to 5 miles an hour per tooth off. If your speedometer is showing a higher speed than you are running. reduce the number of teeth on the speedo gear 1 tooth for ever 4 to 5 miles an hour that it is reading fast.
Sorry for give you the wrong info the first. Glad I changed those tires today.
Thanks for your help. I was given the number to Obsolete Ford Parts, from the local Ford shop. He had one made up for his truck. Their number is (405) 631-3933. I am going to order mine today now that wnelson was able to figure out my rearend ratio. THANKS! I was told you will need to know engine size, type of tranmission, tire size, and rear axle ratio. I'll let you know if anything is different once I order mine today. Thanks again for your help.
Could you get me the part number for the 22 tooth gear, please. I put the 21 in today and it actually brought it down more than I thought. My Ford shop said the highest gear available for the C6 is 21, but if I could get the part number they would order it. I tried to call the Ford Obsolete for the custom speedo order, but the line was busy both times I called. I wanted to see what the difference would be from the 21 to 22. Thanks,
Just found out they close at 6 pm Central Time. I will call tomorrow and get the address for you.
wnelson,
Thanks for identifying the gear ratio. I didn't realize it was that low. I was going to guess from the info the salvage yard gave me, who said it was probably a 2.80:1 for that year.
Most speedometer shops have what I call ratio boxes. They fit inline with the speedometer cable and have changable gearing inside them. You may see them on larger 2ton and so on trucks. I used to work on school buses and we had a Stewart-Warner kit that had cable adapters, boxes, and various gears with a chart to select the internal gearing. A really neat item in all.