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My speedometer went out suddenly the other day. The needle shakily climbs to about 20 mph then drops down to zero. Odometer is not running either but tach and other dash components are fine.
Speedo cable. May just need lube, may need complete replacement. Depends. It's not easy to lubricate, but there are kits available just for that porpoise.
Check both ends. Make sure they're not damaged/rounded off. Make sure they twist together, ie the cable isn't broken in the middle.
the speedo cable hooks up at the transfer case. I have heard of that that threaded collar backing off when it connects to the T/C. It is also possible the speedo drive gear at the T/C has become stripped.
could be this stuff or what Pat (2toyguy) mentioned above
Did some more troubleshooting. Both cable ends look fine. I pulled the plastic speedo drive gear and it looks ok to me. I disconnected both ends of the cable and when I hand turn one end the other end matches rotation.
What's odd is when I leave the trans side connected but disconnect the speedo side, driving with the gauge cluster out and watching the end of the cable.
It spins with the transmission in 1st and 2nd gear, strong enough that I cannot stop the cable with my hand.
In 3rd it continues spinning in low RPM but at high RPM it stops rotating altogether. Then as they drop below around 2k it begins spinning again.
In 4th it spins in low and stops in mid and high RPM, and in 5th it does not spin at all.
I feel I may be seeing two things here.
One is that the speedo drive at the transmission seems to stop giving input to the cable in higher gears, especially at high RPM.
The other is that the speedometer is not picking up the input from the cable when it does spin in low gears. I shined a light in the back of the speedo and the connecting hole appears to be square. So there seems to be a problem in that little mechanism as well.
Any thoughts/advice from here? Really appreciate the help so far.
It's a cheap thing to replace. The speedo cable. I would still replace it. Maybe the worm gear it attaches to, as well. I can see some damage to the plastic gear in the pictures above. Because it's plastic, not only does it take very little damage to keep it from functioning correctly, it takes very little wear and tear to perform that damage.
The metal gear IN the transfer case looks to be in good shape to me, for what that's worth.
The mechanism in the speedo should be square, to match the end of the cable. It's square, or at least it should be, anywho. In your pictures, it looks to be in pretty good shape. Sometimes, the cable will "stick" when rotating, due to a need for lube inside the casing. You can see it slow, or stop when moving, and the release suddenly, spinning faster to take the tension off.
If it were me, to see how things are moving, jack the rear axle up, and put it on jackstands, with the front tires well chocked. Then you can sit there, and run the truck as "fast" as you like, with the gauge set out, and the cable ends visible, and watch the cable end in relative safety. When you're actually moving around, you may miss something the cable is doing once in a while, since you really are, hopefully, watching the road and other people, more than the cable.
Again, IF it were me, which it's not, I'd replace the cable, AND the plastic gear that drives it. It's not expensive, and it's easy to do. Hardest part is pushing the cable up, around, through, over, and under, to get it where it's supposed to go
12-03-2021 | 07:22 AM
