Hi! I change tranny in my ford f100 56 to a c6 and the speedometer gauge went crazy any tip? Thanks Simson.

 

What did you have in it before the C6...a C4? The speedometer should be the same with either transmission. What do you mean by crazy? What exactly is it doing? My guess is that the speedometer gear in the C6 does not have the same number of teeth as the one in your previous transmission. They may be interchangable if you had a C4 but I'm not sure. If they are interchangeable are then all you have to do is put your gear from the C4 in the C6...

 

If both DRIVEN gears are plastic, the same ones have been used since 1960 and thru today.

16-17-18-19-20 & 21 tooth gears are available.

Driven Speedo gear: On the end of the speedo cable.

If the driven gear is stripped, and this is somewhat common, the speedo needle can go ballistic.

Some C6's have plastic driven gears, some are fiber, some are cast iron, it all depends on the year/application the C6 is from.
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The Speedo DRIVE gear is on the output shaft, but...

On C6's, there is no replaceable drive gear, as it's made as part of the output shaft itself.

 

Well i drive the car today and there coming a loud noice from the speedogauge and i have a brand new speedo cable. Then i buy the car there was no cable.

 

Bye the way the earlier owner change stock engine and trans to a 351w and c6 trans but he never install a speedocable.

 

So if I am understanding your situation correctly, this is the first time you have had the speedometer hooked up, is that correct?

As was mentioned before, the drive gear in the transmission may be stripped or have a broken tooth, your new cable shouldn't be a problem; but the speedometer itself may need cleaning or lubrication - it may be binding in one place causing the needle to jump up and down. The sound you hear will sound a little like a buzz saw or a zipper being zipped very quickly.

 

Driven gear on the end of cable. Drive gear on the output shaft.

The drive gear is not replaceable on a C6...as it's made as part of the output shaft.

My guess is, the driven gear is stripped.

 

If the noise is coming from the speedometer then the speedometer head may starting to seize up. That's probably why it wasn't hooked up when you got it. Try spinning the speedometer by hand without the cable attached and see if it turns easily or makes a noise. If it make a noise when you spin it or if it does not spin easily, it may be time for a speedometer head repair or replace.

 

Yes the needle jump up and down and have a buzz sound i mount it off and look if there are some problem .thanks for your help.

 

One way to tell is to disconnect the cable at the transmission, remove the driven gear and turn the cable with a hand drill. It should turn freely. If it does not or you feel a "sticky spot," or if it makes the noise, it is the speedometer, if it doean't, it is the driven gear.