speedometer failure

[billmaine]

My '92 5spd manual's speedometer quit. First off, I'm no mechanic but am lucky enough to have a son who is (aircraft; not diesels but he's clever!). My manual indicates this type speedometer is not cable driven but is electronic. My son's question before he tackles the repair for me is should he be approaching the fix from the transmission end of things or pull the dash and look there for the problem? I just didn't want to pull the whole dash if it's more likely the other end. Either way, apparently there's a new sensor or electronic connection in my future. Apologies up front for not being more articulate mechanically speaking.

 

[AlK]

This is a fairly common problem on the first gen trucks. On 4x4 trucks the sensor is located on the transfer case and on 2 w drives it is located on the transmission. Start under the truck. Disconnect the electrical connection and remove the unit from the transfer case/or the transmission. Clean the electrical connections and take the unit apart and clean everything and inspect for any damage. If no damage parts reassemble and see if that helps. I did that on mine about 3 years ago and no problems.

I would also suggest that you do a search in the first gen forum.

---

Al

 

[BushWakr - RIP]

I think the first place to look is on the transmission or the transfer case. On 2WD trucks the speed sensor and gear assembly is mounted on the transmission; on the 4WD it is mounted on the T-Case.

There is an electrical connection which can get fouled.

The gear drive assembly would be the next item to look at. It can be removed and checked to confirm it's function. I'm not certain as to the particular year, but at one point (earlier 1st Gens) the electronic speed sensor has indexing numbers on it, newer one's don't. Just make note of all relavant positions and you'll be fine.

The gear assembly has a square drive internal 'socket' and on the transmission side provides the square 'shaft' to drive it.

Confirm the gear assembly internals are turning freely, and that the 'socket' is not rounded out.



Some have mentioned that a loose tailshaft yoke can also cause this. Once the yoke retaining nut is tightened to spec the problem has gone away. Since I have an auto, I can't say for sure, but I have heard this many times in the past.



Bob.

 

[jakestrailer]

At about 100k miles my speedo quit, I found that the square shaft was spinning inside the square drive on the gear on the transfer case. I'm not cheap but when they priced me a new gear I about fell over. I just ended up putting a small piece of heavy paper over they end of the shaft and reinstalled it. It makes a shim and tightened up the square drive. 20k miles later, still working fine

 

[Bob Beauchaine]

I had a similar problem with my '93. It turned out to be the output nut that holds the rear u joint shaft on at the back of the transmission. Drop the driveline at the transmission at remove the nut holding it in place, locktite the nut then re-torque it. I forget the torque value but can find it if you need it. The speedo drive gear is held in place by the pressure this nut puts on it and will not turn or turn sporadically - that was my problem.

Good luck

Bob