'78 150 4x4 400 w/C6

My speedometer/odometer does not work. The cables don't appear noticeably broken/damaged. I looked at where the cable goes into the back of the tranny on the passenger side and something looks broken or deteriorated. I can see part way into the plastic gear and the seal is sort of hanging out...doesn't look right.

Can I just unbolt the clip/housing and remove the speedo gear or will tranny fluid come out? I'm not sure if it is a dry area of the housing or not.

Thanks!

 

You can just take out the gear.

 

Thanks Recoil. Now to identify it....

 

There are TWO different speedometer gears in the transmission.

The plastic DRIVEN gear is on the end of the cable. The same ones have been used from 1960 thru today...and so...are available from Ford.

16-17-18-19-20 & 21 tooth gears are offered. The prices range from $2.00 to $3.76 each.

Some 4 speed trucks have a fiber or iron DRIVEN gear. These are obsolete, but usually can be found.
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The speedometer's DRIVE gear is on the output shaft of the transmission.

There are several different types, some are steel, some are plastic. Tooth counts are 6-7-8.

However, the DRIVE gear used with the C6 transmission is made as part of the output shaft, cannot be bought by itself.

 

the only seal that i have seen on the end of the speedo cable is a rubber O-ring and if you can see that then your speedo gear isnt against the drive gear in the tranny hence no speedo, all you should have to do is seat this flush in the hole and secure it with the keeper and speedo cable bolt and it should work just fine if the teeth arent gone from the small gear on the end of the cable....if they are then you will need to replace it...and as numberdummy said they have different numbers of teeth and usualy diferent colors to indicate this at a glance, (i know these lil tid bit of infermation from first hand knowledge..lol..)..as long as there the same color then just count the teeth and if its the same just remove the c-clip that holds it on the end of the cable and slide the replacment gear on and re-enstal the c-clip and your good to go....

 

Well, I got it out today and it turns out the gear in the tranny was ok and the o-ring was intact. Sombody had smeared a gob of sealant around it and that was what was hanging out.

I pulled the instrument panel and discovered the outer cable sleeve had come away from the round 'plug' that connects to the rear of the inst. panel.

So, I put that all back together and the speedometer/odom works BUT it jiggles up and down rapidly below 40 mph, then evens out to a very fine jiggle.

What would cause that? Is the cable binding in the sleeve?

 

now the woble issue i know nothing about..lol...i have that problem my self....lol
mine will work fine most of the time and then go completely hay wire others...lol....and every thing seems to be were it should be as far as being in the proper placment...

 

Wondering if you know how many teeth are on the plastic gear for a 78 F150 4x4 automatic. I got mine out, and the teeth are all worn... So I can't tell.

Dumb question - will fixing this also fix the not-spinning odometer?