Speedometer Cable Frustration

[70_F100]

You have no hope of finding the right gear(s) without knowing the tire size, gear ratio and tranny type.

[JMcTurnan]

I know all but the gear ratio
c-4 tranny, 15"x10" rims, I believe it has a 9" rear end

[70_F100]

Rim size doesn't matter. Tire size does. Whether you have a 9" rear versus a Dana 44 or Dana 60 doesn't matter.

Gear ratio is VERY important.

The speedometer is calibrated to the number of revolutions the driveshaft makes as opposed to the distance travelled by the tires.

Both the gear ratio and tire size have an effect on this. Neither the rear end size/model or rim size affect this calculation.

[JMcTurnan]

Ok, ill see if I can get tire size, and look at the rear end inspection plate and see if I can get some numbers, hopefully its on there.

[loglat]

Alright, I'm out of ideas. I've replaced the cable and the gear. Turning the cable from the transmission end makes the needle move, but when i plug it all in, I get nothing. I even removed the instument panel and watched to see if the cable moved at all... even with me wiggling it, pushing it in and out... I got nothing. There's no reason why this thing shouldnt be working. Anyone?

[70_F100]

Is it an automatic or manual tranny, 2WD or 4WD?

[fordman]

on an automatic C6 2wd trans the drive gear on the end of the transmission shaft drives the plastic gear on the speedo cable or cable houisng. depending on which trans tail shaft you have. early or late. if the cable is good and it will spin the cluster from the gear upward. then it must be something inside the transmission. the only thing inside the transmission is the drive gear on the tail shaft. can you look inside and see the drive gear?

[loglat]

I've got the manual 4 speed NP435, 2wd. For whatever reason, something just isnt engaging right. I havent looked inside, but I felt the drive gear and it seemed like it would be ok. Sometimes when I was driving, a turn to the left or right would make it bump for half a second and quit. I can't imagine the problem being with the transmission. Maybe somehow I've managed to mess up getting the square peg into the square hole correctly. I'll fart around with it some more tomorrow.

[fordman]

mayeb just the cable end is loose ont he transmission housing it screws onto. it could be a stripped square end too i guess.

[70_F100]

If the speedometer works when you turn the cable at the transmission end, your problem is, most likely, on that end. Something is preventing the driven gear from turning.

The drive gear on the output shaft of the transmission is held tight by compression from the output yoke.

There's a very good chance that a little wear has taken place in the rear of the transmission, causing the drive gear to spin on the shaft.

To eliminate that possibility, take the u-joint down, and tighten the output yoke retaining nut with an impact wrench. You won't overtighten it, and it may just take 1/4 turn or less of the nut to provide enough compression to cure your problem.

[loglat]

Thanks 70. I'll give it a shot. The little bit of wiggle i could get without taking down the u-joint seemed appropriate on the inside of the tranny. We'll see what happens. Im out of ideas.

[loglat]

I haven't gotten to tightening up that retaining nut yet, but I felt of the drive gear again today and it feels like it's too far forward. What's up with that? Is it just my imagination? It's not loose... I can't move it with my finger. This weekend I should get around to taking that U-joint down.

[bjde0b]

I read a post a while back that made a lot of sense. Drive down the road with your GPS (or your friends if you don't have one) and record your speedometer speed and the GPS speed. Count the teeth on the speedo gear and multiply it by the ratio of the speeds to determine the correct gear teeth.

[Supermike]

I read a post a while back that made a lot of sense. Drive down the road with your GPS (or your friends if you don't have one) and record your speedometer speed and the GPS speed. Count the teeth on the speedo gear and multiply it by the ratio of the speeds to determine the correct gear teeth.

That's how I figured out how far "off" my speedo was... but I'm not messing with it right now. I just add 4-5mph to however fast I'm going.

But this totally explains why some old dudes always drive their trucks so slow. They THINK they're going 60, when in reality they're going like 50-55.

[zakt]

I hate the mechanical speedos... therefore Im putting that sterling 10.25 in the rear with the VSS sensor (toner ring) and putting a electric speedo in