My speedometer is not working. Nylon gear looks good and gear in tranny turns. I was wondering what the shape of the nylon gear should be. By that I mean should it have some convex shape to it? The tranny gear feels concave so I assume the nylon gear should be convex in order to mesh. When I spin the nylon gear by hand it turns the speedo. When it is installed the 2 gears don't seem to be meshing. Thanks in advance for your help. Joe

 

Joe there are right hand twist & left hand twist gears. Do you have the correct one?

What tranny are you running?



John

 

Np 435 with a married dana21? single speed t-case. I pulled the speedo end and drove around. It didn't turn. It is the blue gear. If it was the wrong twist would it be mangled or not spin at all?

 

Before doing anything, remove the speedo cable from the back of the speedometer, then twist the adapter that the cable attaches to.

If the needle moves freely from 0 to 100, the problem does not lie with the speedometer.

If the teeth are stripped on the DRIVE (on the output shaft) or DRIVEN (at the end of the speedo cable) gears, the needle on the speedo won't move.

If the teeth aren't stripped, the problem lies elsewhere.

Ford has used the same nylon DRIVEN gears from 1960 thru today, so all are readily available. 16-17-18-19-20 & 21 are the various tooth counts.

Some of the DRIVE gears are available from Ford, some are not. Some are steel, some are nylon.

The DRIVE gears came with three tooth counts: 6, 7 or 8 as it depended on the rear ratio and the tire size.

Inside the speedometer cable's housing is a woven steel core. It's supposed to be lubed every so often, but most people are unaware of this.

When the lube dries out, the woven steel core binds up inside the housing and snaps.

Every autoparts store sells a woven steel core kit. You cut it to length, coat it with a fine film of white lithium grease and install it in the housing.

 

I had the exact same problem with my 70 4x4. Number dummy helped me locate a new drive gear for mine. I had to remove the transfer case and tailshaft housing to change it. the gears are not supposed to have a concave shape, my new ones were flat.