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.

[morgant]

Right behind the e-brake on the left side.

Yup, it was there waiting to stare me right in the face.

I traced it from the transmission to the speedometer and looks pretty easy to replace. Unfortunately, I probably will need to replace as I discovered the problem while tracing it. It was run alongside the exhaust downpipe and the casing has melted in one spot where it must've vibrated against the exhaust.

I did a quick browse of our host's SIII section and didn't see the replacement cable there. Anyone know where it is on the RN site or who else has this part?

I'll run it differently when I reinstall so I don't run into this problem again, naturally.

[weatherm]

How do you lubricate the cable? Mine wiggle some also... I have heard a lot of people saying to lube it but how do you actually do it?

Thanks!

[DADAMS]

Lubing Speedo Cable

If you don't have it fully out and on a bench, the steps would be to remove the dash panel to gain access to the back of the gauge. Unscrew the knurled retainer from the back of the speedo and free up the cable assembly from the back of the gauge. The cable in the center can then be withdrawn from the casing for cleaning.

I used Kerosene to clean the cable and housing, but I did my on the bench so I was able to flush Kerosene through the housing to wash out the 45 year old ick that had built up within. Obviously, don't flush the casing unless it is disconnected from the tranny...

After the cable is cleaned off it can be lubed (with ???, above threads say either light grease or 90wt, I don't know which is correct, but either should do) and threaded back into the casing.

It will likely be fussy getting the square section to feed back into the drive gear at the transmission end. It will take a bit of twist-and-push to get it to seat and may take a several tries to get it. Feeding from the dash-down is way easier than frogging around with the retainer screws at the tranny end, so don't take that end apart unless you need to. You could spend an afternoon trying to put those three little screws back in place...

[weatherm]

Roger so if my trans ever goes then I'll worry about it b/c I would rather do it right ( the whole thing) than to just clean the tip.

Thanks for the info!

[morgant]

Only just getting around to actually installing the PRC2065 (SPEEDOMETER CABLE RHD SERIES III) that I ordered from our hosts a few months ago and discovered that it doesn't have the square extension on the end of the cable that actually inserts into the transfer box. I'd assume that I either need the additional part (not sure what it'd be called) or need to remove the one from my old cable and attach it to the new cable. It doesn't seem worn so I'm not worried about reusing it if I can, but how would I do so?

Also, how would the cable have been run originally? The cable I'm replacing was zip-tied to the frame in one spot and then run up under the bonnet next to the exhaust down pipe (where it had been tapping the exhaust and melted the casing, hence the need for replacement as it's binding).