[Glenn and Laureen]

Looking for advice on how to get the speedometer and odometer functional again on my 1984 Classic. It has a DD6v92 engine with an Allison MT654 transmission. The speedometer and odometer both quit working about a year ago when our voltage regulator and alternator burned out while we were on the road from Austin to Tom's place in Arizona. When that happened everything electrical in the coach got a big surge or series of surges and lots of components were ruined, from marker lights to the circuit board in our refrigerator. I am more concerned about getting the odometer working because I want it to reflect actual mileage on the coach as closely as possible. I can and do monitor the speed with my GPS.

Observations: The speedometer needle on the Stewart-Warner speedometer/odometer in the dash swings back and forth without ever settling down to a constant mark. It will swing from 0-80 when starting off and then vary back and forth by about 30 mph while driving at a constant speed. The center of the swing back and forth is approximately the correct speed, based on a comparison to the GPS. The odometer will sometimes tick over 1 or 2 miles during a 20 mile drive but does not move at a constant rate and does not move at all most of the time.

I took the sender unit and associated items off at the transmission housing and inspected. Did not see any broken tangs and items looked well lubricated. Took the sending unit off the stalk and used an electric drill to spin the sender. Laureen said the speedometer responded but did not stay at a uniform speed even when the drill speed seemed to be constant. We also previously confirmed continuity between the sending unit and the speedometer. With the entire stalk assembly out, I hand turned the tang that fits into the transmission housing and observed that the tang going into the signal generator on the other end turned as well. Tried to make sure the tangs fit into the grooves when reassembling. 

I have replaced the original sending unit with an old "new" one off the shelf with the same results. Replaced the connectors on the wires from the sending unit to the speedometer.

Don't know what to do next. Is there something to inspect or replace on the speedometer head unit itself? Should I replace the speedometer/odometer unit in the dash? Should I take the stalk of items off the transmission again and clean, re-lube and reassemble? Is it possible there is some electrical issue interfering with the signals going from the sending unit to speedometer in the dash that would cause erratic behavior? 

Would like to get this resolved in the next couple of weeks before heading up to Spearfish. Thanks for any suggestions.

[MrE]

I would check your grounds, seems to be a common issue.

[HoosierDaddy]

I thought the speedometer in my ‘78 was broke. I ordered a new one. Once I removed the old one I found a broken light bulb inside the speedo. I have a new electronic one in box. If u are interested PM me.

[Mageeacres]

I have the same issue with the swinging needle back and forth although my odometer does work ok. I was thinking the grounds need to be checked as Jon suggested. That’s where I would begin.

[Richard]

So...........this is my .02.

Buy electronic speedo and tach. Install the speedo sensor/sender on the driveshaft. Install the tach sender/sensor circuit on the alternator.

You guys are dealing with mechanical units. The unit is going to behave wonky if the spinning cable has any stutter to it. The chances of a corroded cable or housing in a coach of that age is high.

If you do pull the cable and get it all cleaned and greased, you still may have problems with the gears in the readout units. You will faint when you see what it costs to repair the old mechanical units. More than a new electronic unit.

And on the 6V92, the tach cable is driven by a gear unit that fits on the top of the engine much like a distributor. Ask @chockwald if he ever found a replacement.