Speedometer gear question

[KerryG]

I've got a '65 with 4-speed manual transmission. The cars speedometer has always indicated about 25% slower than actual speed (which really bugs me!). The car originally had an automatic transmission, so I'm reasonably sure that's were the problem originated.

Now, I don't have a clue as how to figure what the proper speedomter gear should be, but I reasoned that with a 2.80 rearend (lowest ratio available), that the gear with the least teeth would be about right. So I ordered a 16 tooth gear for a 4-speed manual. I took it to a shop and the mechanic that tried to install it said it was too short, and it wouldn't work. He believed the gear was simply labeled/packaged incorrectly and it wasn't the correct gear for a 4-speed manual transmission. I double checked the color label, and it certainly appears correct to me.

The mechanic said the gear I gave him was about 1/2" shorter than the gear currently in the car. So now I'm completely lost because I don't have any idea why the gears length should be different, or were to get the proper length gear. Can anybody help?

Thanks,
Kerry

 

[D.Hearne]

Mustangs Unlimited.com has the correct gears. The gears for automatics don't work on std transmissions. You might also need to replace the drive gear on the tailshaft. Why did you need to bring it to a mechanic in the first place? The driven gear is very simple to change, all you need is to jack the car up, remove the retainer bolt from the clip holding the cable in place, pull the cable, slide the retainer clip from the gear, slide the gear off the cable end, and reverse the process to re-install. Takes about 10-15 minutes tops to do this. Replacing the driven gear is a little more complicated, you have to remove the tailshaft housing to do it, but takes simple hand tools to do the whole job in less than an hour.

 

[D.Hearne]

Mustangs Unlimited also has a formula listed in their catalog to figure which gear(s) you need.

 

[65racecoupe]

Also, your local Ford parts department at the Ford Dealership should help you. I got mine there for about 7 bucks. Just tell them what tranny, gears, etc you have.