Gizmo52

So when I got my tuck the odometer didn't work. I did my research to find out that the gears breaking is a common issue. So I proceded to take the cluster apart and replaced the gears. The odometer still wasn't working. Then one night I lightly backed into a pole and it started working. It worked for about 40000 miles then quit again. I took the cluster apart again and the gears are OK. My speedo works perfect and I checked all the circuits and commections in for the cluster and everything for the cluster its self has a good connection.

My speed sensor is a two wire type. The truck is a 1990 d250 with the getrag 5speed.

I haven't replaced the speed sensor because the speedo works fine so that shouldn't be the issue. I lubed up the gears in the odometer and it didn't help. All my wire connections are fine from the 2 plugs at the back of the cluster to the three pin connector to the speedo/odometer. The wires from those pins to the circuit board have good connection. And the two small wires from the circuit board to the speedo portion have a good connection.

As far as the circuit board for the odometer I don't know if all of the components are working correctly. I also haven't tracked the wires from the cluster to the connector by the turbo. But from the connector by the turbo to the connector for the speed sensor all wires look OK.

I'm out of possoble ideas... Any help is greatly appteciated!

Thanks in advance everyone.
​

thrashingcows

Most likely it IS the speed sensor. When you hit the pole the jarring probably knocked something internally and the VSS started working. They do fail....

edwinsmith

Aside from the common problem of connectors corroding and becoming intermittent, there are other problems with printed circuit boards that are ubiquitous now. Solder joints will eventually fail under vibration and become intermittent. Another little known problem is tin-whiskers. The tin in solder will sprout tiny whiskers of crystalline tin metal which can grow long enough to short out adjacent circuits on PCB's.

You description of 'it didn't work, bump, it started working, then it stopped working', is a classic intermittent circuit problem. Unfortunately sometimes all you can do it throw parts at it until it stays fixed.

The belief that 'I checked that part THEN therefore it's still good NOW' has led many people astray.

Edwin

Gizmo52

i thought that if the speedo works then the vss is good though?

Gizmo52

I replaced the gears over two years ago and hit the pole about a month after that. Just recently (3 months ago) its stopped working randomly. I checked all things I listed yesterday. As far as the tin whiskers goes I don't see any signs of it.

edwinsmith

Sorry, I misread your post. Assuming the speedometer and the odometer run off the same sensor in the trans then I would suspect a problem in the speedometer itself. My speedometer is all mechanical being an 89 so I'll have to defer to others on this list with more experience with your system.

My comment about the tin-whiskers is general in nature for electronics. The actual whiskers are microscopic.

Edwin

Gizmo52

No worries! I appreciate the input and information.

thrashingcows

I had one that would work for a few weeks, then stop for a few days, then start and work fine for a month or two, then stop for just a few hours. Replaced the VSS and has been working steady ever since.

Gizmo52

So youre saying your odometer would work randomly and your speed would work all the time and you replaced your VSS and now everything works all the time?

Gizmo52

Anyone have any ideas?

N. Besonderes

I hate these electronic gauges and all of the electronic Barbra Streisand sensors and connections and completely unnecessary PCM's that are required to make them work!

I had one in a 91.5 1/2ton gasser that turned the odometer but not the speedo.
The gauge in my current rig started giving me trouble a little over a year ago. It started bouncing the needle, then quit working pretty much altogether for a couple of weeks. Then I loosened and re-tightened the VSS and it has been working flawlessly for at least a good year.
I have a couple of spare, old-school, cable-driven, speedometers and gauge housings from the junk yard, and a speedo cable on hand for when my original, electronic one finally gives up the ghost.
Only problem with that is, they only record 5 digits on the odometer. I guess I could make some tally marks with white paint on the black face of the gauge for every hundred thousand miles though.

-Niemand

Gizmo52

Just an update. I checked all the components on the circuit board and everything seems to be in working order. I reflowed all of the solder joints but that didn't make a difference.

So that leaves 3 things. Either the motor for the odometer went bad (possible but no replacement), there's a fault with the speed sensor (not likely but only 20 bucks), or the intigrated circuit on the board failed international (possible and only 5 bucks.)

The intigrated circuit is an ITT UAF 2115 circuit which runs the trip and odometer. So I ordered that and a new VSS. Once I et them in I'll post an update if either fixed my issue. If they done fix it then I guess I'm SOL because I can't find a new motor.
​​​​​

edwinsmith

I downloaded the data sheet on that chip. From the block diagram it consists of a frequency to current converter to drive the speed meter and a stepper motor driver to drive the odometer. So if one is working and not the other I would suspect the circuitry in the head unit. If the odometer isn't working then the stepper motor circuit is faulty.

Edwin

Gizmo52

my only issue is the odometer not working. My speedo works fine. but I figured about 20 bucks worth of parts couldnt hurt to try. I can't find a replacement motor anywhere.

edwinsmith

Steppers are fairly simple motors. It's 2 windings and they are energized one in one direction then the other then the first in the opposite direction then the other and so on. Check out the windings with an ohmmeter for continuity. This assumes the armature isn't stuck or the geartrain is working freely.

The speedo end at the trans is a simple pulse generator and the circuit generates the proper switchings for the stepper to run. The other part converts the pulses into current i.e. more pulses to more current.

Edwin