Well I haven't had any luck. I tried resetting the brake control
module and checked all the fuses. I haven't took the gauges cover off
to look for any shorted wires yet, but that is next. I still believe
this is some kind of systematic problem and not related to any one bad
sending unit. When the problem first started the speedometer would
work fine if the "brake + anti-lock" light was NOT on. When "brake +
antilock" light was on the speedometer would start jumping around.
Like I said in my original post this all started with air in my brake
lines. I'm wondering if the brake control module might be bad and
somehow causing all these other problems. Anybody have any additional
thoughts on this weird behaviour?
> You have to go into the dianostic mode for the ABS. The light will
> brake light will flash and then you look up the problem with a repair
> manual, Speedo can be acting up from a dirty sending unit on the trans.
> or MOST LIKELY a worn or shorting wire. Like Big Al suggested reset
> the ABS computer by unplugging.
If the speedometer is jumping around as you say, the most likely cause is
the rear wheel speed sensor located on top of the rear axle. This problem
has been seen in here over and over again and replacing this sensor almost
always corrects the problem with both the speedometer and the ABS light.

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> Well I haven't had any luck. I tried resetting the brake control
> module and checked all the fuses. I haven't took the gauges cover off
[quoted text clipped - 13 lines]
> > or MOST LIKELY a worn or shorting wire. Like Big Al suggested reset
> > the ABS computer by unplugging.
Tom Lawrence - 28 Oct 2005 22:21 GMT
> If the speedometer is jumping around as you say, the most likely cause is
> the rear wheel speed sensor located on top of the rear axle.
'91 truck.... no RWSS
Tom Lawrence - 28 Oct 2005 22:25 GMT
>> If the speedometer is jumping around as you say, the most likely cause is
>> the rear wheel speed sensor located on top of the rear axle.
>
> '91 truck.... no RWSS
I hit 'send' too quick... no RWSS that has anything to do with the
speedometer. IF he has ABS, there's a rear wheel sensor - but the speedo
comes from a sending unit on the transfer case (doubt they were still using
mechanical speedometers in '91, but I'm not positive)
TBone - 28 Oct 2005 23:05 GMT
I didn't see anywhere where he gave the year but if it is a 91... I didn't
know that they were even offering anti-lock brakes in 1991.

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If at first you don't succeed, you're not cut out for skydiving
> >> If the speedometer is jumping around as you say, the most likely cause is
> >> the rear wheel speed sensor located on top of the rear axle.
[quoted text clipped - 5 lines]
> comes from a sending unit on the transfer case (doubt they were still using
> mechanical speedometers in '91, but I'm not positive)
Tom Lawrence - 29 Oct 2005 02:59 GMT
>I didn't see anywhere where he gave the year
First post of the thread.... he stated it was a '91 Dodge W250
TBone - 29 Oct 2005 06:21 GMT
I believe you, I just never saw the OP, just the one I responded to.

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If at first you don't succeed, you're not cut out for skydiving
> >I didn't see anywhere where he gave the year
>
> First post of the thread.... he stated it was a '91 Dodge W250
Big Al - 29 Oct 2005 08:27 GMT
>I didn't see anywhere where he gave the year but if it is a 91... I didn't
> know that they were even offering anti-lock brakes in 1991.
Rear wheel only, and the speedometer is electronic. Sensor is where the
speedometer cable would normally attach.
Al
Brent - 22 Nov 2005 14:52 GMT
I have tried all the things listed here and still have not solved the
problem. Things done so far:
1) changed differential speed sensor
2) checked for shorts
3) checked for error code from the ABS control module
4) changed voltage regualtor
5) bled the brakes (again)
6) replaced battery
7) checked alternator output at battery
I would like to add some new info I have noticed. The static from the
radio disappears and all the gauges read fine while vehicle is sitting
still just idling or if I'm stopped with the brake and clutch
depressed. I have noticed that the lights dim intermittently now as
well, especially if it is cold weather. I checked the alternator
output and it appears to be charging the battery however I do wonder if
perhaps the alternator is somehow causing this. There are 2 posts on
my alternator that have wires running to the voltage regulator. One of
these posts while running produces 14.8 volts, the other wildly
flucuates. Is this normal?
Thanks,
Brent McConnell