The Jumpin' Speedo

[thebttmline]

Hey,

When I am driving at low speeds - like below 25-30 - my speedo jumps back and forth between 0 and a lot (I haven't noticed if it pegs all the way over). When I get on up to 40-50, it works fine. Any idea what is causing the jumping speedo at low speeds?

Thanks,
Steve

[heep70]

Mine does the same thing. I was told the speedo cable is weak and binding up. It binds up and as it is turning at the t-case it will let loose and shot the speedo up high.

Is this in your 71 "Highboy"?

You can't get the cables any longer over the counter. Here is a place that builds them.

http://www.tacomaspeedometer.com/

[thebttmline]

Yep, it's the 71.

Any idea on a ballpark number on how much the custom cables run? Just not worrying about it is always an option...

Steve

[heep70]

Check out this post. http://fordification.com/forum/viewtopi ... ght=speedo

[thebttmline]

Thanks Greg!!

[fordman]

remove the cable from the truck. take the center rod out of the cable. blow graphite into cable housing put rod back into cable housing. spin it inside of the housing. use a drill if you like. use lots of graphite. reinstall. this doesn't always work. but may work for awhile.

[willowbilly3]

Check for any kinks or sharp bends in the cable housing too. If you have any cloicking noise from the speedo it may have a magnet clipping from lack of spacing.

[heep70]

Great research. Thanks for the input. I have wondered about that gear myself. I am going to guess that in my case if it was needed. They are probaby obsolete for my "Highboy" D24 T-Case. I guess I should follow your footsteps and research it for just in case.

[ak-1970-360]

i got a new speedo cable for my 1970 F100 4x4 right from the local ford dealership.

[F100camperspecial]

Hey, I needed a 83" speedo cable for my '72 F100 that I swapped a 205 xcase into (it had the d21 single speed xcase with 68" speedo cable). If you ask for the cable for '72 2wd F250 with a stick you get Pioneer part # CA-3010 and it fits perfect. Schuck's and Autozone have this cable, but you have to spoon feed them the part number. If you ask for a speedo cable for the 4wd all you get is 120'' chunk of speedo core.

[NM5K]

Pulling it all, I reached my finger inside the tranny port to feel if the gear was worn, and found out I could "spin" it by flicking my finger. This meant the metal spline wasn't engaging the gear any more. Since the tranny is in the shop for work, the mechanic there will see what he can do about it......................................................................................

Probably needs a new drive gear on the tranny. I think those
are also plastic like the gears that go on the ends of the cable
at the tranny end. My 68 has a pretty jumpy speedo, and it's
worse in the winter, than in the summer. I've noticed that when
it's real cold, it runs slower than when it's warm. I think the problem
is the plastic drive gear on the tranny is worn down, and the plastic
gear on the cable has trouble engaging it. In my case, it's like it's
barely touching the gear, and when colder the clearance must be
slightly greater until warmed up. I tried a new cable gear, but
didn't help. I really need a new drive gear on the tranny, but I'm
waiting until the next time I take it apart for something. As a
alternate accurate speedo, you can use a tach, and calibrate it
for mph. I did that for a good while, until someone stole the tach
I was using. I used a GPS to calibrate it.
MK

[crazy larry]

stick your finger into the hole in your tranny and feel the gear. if you feel ANY curve to it, it's worn. mine was worn less than an eighth of an inch, and it wouldn't engage. it is made of nylon so it will wear....

my ford house had the tranny gear in stock... easy fix too. four bolts to remove the tailshaft housing, if i recall, there might have been a retaining clip ring on the shaft, can't recall clearly... if it was there when i took it apart, it had a chance of going back on.....
gear slides on, new rear seal, and your in business.

i do notice a bounce, at times.....
i'm going to try the graphite trick......


stick your finger into the hole in your tranny
just wanted to say that again.....

[CJ,s 67 F100]

I just got a new one for my 67 F100 with a C6 from napa. Thay even had it on the shelf