Wonky Speedometer

[morgant]

My new truck is finally home! Now I can start the rest of the repairs to get it really drivable...

One thing I noticed when I test drove and initially attempted to drive it home was that the speedometer needle jumps around wildly while driving. The rear shocks are shot and I was driving it down a patched mountain road, so I didn't care too much about it at the time.

On Sunday evening when I drove it home I noticed that it tends to jump up to the proper speed, fall back down, then jump back up again constantly, but when it 4th gear it only jumps up to about 1/2-2/3 of the actual speed. Any tips as to troubleshooting? Is this likely loose wiring, a ground issue, or a faulty speedometer?

[4flattires]

Lubricate the cable.

Jeff

[mechman]

Lubricate the cable.

Jeff

Seconded. A little light grease will fix that right up. Get on it soon, before it hangs up and breaks.

Mech

[BackInA88]

I had the same problem and did all the usual checks, cable etc.
Mine ended up being the speedo.

Steve

[Sputnicker]

I'd try the cable first, but if the problem is with the speedometer and you are up for it, here is a good tutorial on how to address it:

http://pcbunn.cithep.caltech.edu/jjb/TR6/speedo.pdf

[DADAMS]

Its more of a project, but it may be the drive gear that is mounted to the output shaft on the rear of the transfer case is loose.

When I was changing the seal on the output shaft of mine, I found that the nut was not torqued properly and allowed the drive gear to spin freely (and randomly).

I'm not back on the road yet to find out if it was a fix, but I think its pretty likely that was part of the problem. Of course I cleaned and lubed the cable, so there will be no way of knowing for sure what the actual fix was... (assuming it is fixed)

[DADAMS]

By the way, what is the proper lube for the cable? Mechman states grease above... I used Marvel to clean and free up the cable, Is that enough or should I actually give it a smear of grease?

[morgant]

Seconded. A little light grease will fix that right up. Get on it soon, before it hangs up and breaks.

Excellent.

I flipped through my Haynes "Blue Book" last night and didn't see anything about the speedometer or cable, but I haven't read it front-to-back yet. Probably missed it. Crawled under for a peek this morning, but didn't have time to really trace anything out. Specifically where does it attach to the transmission?

@Sputnicker, thanks for that speedo tech doc, that'll definitely help get me through whatever the problem turns out to be.

[BackInA88]

Right behind the e-brake on the left side.


Steve

[ScottT]

Speedo cable is the issue. They are right to say lub it before it breaks. Mine broke during a trip. It left a shard in the T-case that way a pain to get out to the handbrake back plate.