1968 C-6 Speedometer gear

[ML Stephens]

I am rebuilding my 68 F250 camper Special and the Speedometer Gear is bad.
The Truck has a 390 and C-6 trans.
I have looked for a new one at LMC and Mac's but the ones they show don't look like the one I pulled out???
The one I pulled out is metal and looks kind off like the ones they sell for the 62s.
Will the plastic ones work, even if they don't look the same???
I counted the teeth and mine has 22

Any one had the same problem?


Thanks for any Help!!

Mark S

[ultraranger]

There are speedometer drive gears and there are speedometer driven gears.

The drive gear is the one located on the transmission output shaft.

The driven gear is the one located on the end of the speedometer cable.

Typical Ford drive gears come in 6, 7 & 8-tooth counts. Ford driven gears come in 16-21 tooth counts. There are 23-tooth driven gears available from the aftermarket (for low geared rear ends), but the thin plastic teeth on them generally don't last very long before they wear off. I'm unaware of a Ford 22-tooth driven gear.

There are drive/driven gears with left hand teeth and ones with right hand teeth. Left hand gears are for Ford transmissions where the speedometer cable goes into the transmission housing on the passenger side. Right hand gears go into the transmission housing on the drivers side (like a C-6).

You would have to remove the tail housing of the transmission to get an accurate count on the driven gear (the gear on the output shaft), but this is how you determine the tooth count on it; http://www.transmissioncenter.net/IMG_0816.JPG

http://www.bgsoflex.com/speedo1.html

http://www.transmissioncenter.net/speed ... Older_Ford

[ML Stephens]

Thanks, I looked at the "Driven "gear again and you are right. Its got 18 teeth.
It helps if I wear my glasses!.
I have not pulled the tail housing a part to look at the drive gear yet.
Still the ones I can find on-line don't look like the one I pulled out. Will they work?

[mmerlinn]

Still the ones I can find on-line don't look like the one I pulled out. Will they work?

Maybe. Maybe not. Depends on what the difference(s) are.

[ultraranger]

If the driven gear on the end of your truck's speedometer cable has the teeth worn off of it, there's a good possiblity that the drive gear teeth on the output shaft are worn as well.

I'm not certain how compatible a plastic driven gear would be if meshed with a metal drive gear (or vise-versa). You would probably be better off to change BOTH gears out to the newer plastic version. Both gears would be made of the same material, they would both be new, and they would wear in as a matched set.

[Art]

If the driven gear on the end of your truck's speedometer cable has the teeth worn off of it, there's a good possiblity that the drive gear teeth on the output shaft are worn as well.

I'm not certain how compatible a plastic driven gear would be if meshed with a metal drive gear (or vise-versa). You would probably be better off to change BOTH gears out to the newer plastic version. Both gears would be made of the same material, they would both be new, and they would wear in as a matched set.

Very good advice.

I know Chrysler successfully used a steel gear (machined into the output shaft) to drive the speedometer, but they also used an eccentric to set the gear mesh.

I would recommend replacing both if you are not comfortable inspecting and determining whether the drive gear is worn or not.

Be sure you get the correct helix (right hand / left hand) driven gears.

You can count the drive gear teeth by looking at how many teeth end at the flat side of the gear.

Sometimes the color of the plastic helps identify the gear tooth count.