Found that with just the key (engine off) on the speedometer jumps around, it even jumps around when I disconnect the signal line to it, appears as thou the speedometer is defective internally. will post more when I know.

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Ed
94 30' Breakaway side entry
230 Cummins, Alison 6 speed
Sparton chassis

I had a similar issue - the gauges seem to read a bit low, and the speedometer sometimes twitches when the turn signal is on. I excercised the instrument panel connector and the fuse - I haven't had it flashed up to see if that cured the problem, nor have I cleaned the connection from the main bus to the fuse box.

I talked to Palo Alto Speedometer about this problem and they say that the speedometer is defective. They could take it apart but they doubt that the internal components that need to be changed would not be available any longer from VDO. The new speedometers have a LCD odometer and a red pointer, doesn't match my gauge set.

When I finish all the lther stuff I am doing, I will pull the speedometer apart and do some trouble shooting, I have a vast stock pile of electronic parts (was a EE in another life) so I think I could get it repaired, I may have the shop take it apart because they know how to get the bezel off without damage.

Will post when I have more info.

Ed,

I suspect that assessment by the shop is what we in Florida refer to as a cross between a large sausage and an alligator - a "Croc of Baloney". My symptoms are somewhat similar (but use the GM gauge set), and I'm convinced it's a power-supply problem. As you know, these electronic marvels generally either work or don't work, and if there's erratic behavior, it's usually in the signal and/or reference voltage supplies.

I think you're on the right track.

quote:

Originally posted by MWrench:
Found that with just the key (engine off) on the speedometer jumps around, it even jumps around when I disconnect the signal line to it,

Are you looking for something like these?



http://www.custominstrumentpanels.com/newpage2.htm

quote:

Originally posted by Rusty:
I had a similar issue - the gauges seem to read a bit low, and the speedometer sometimes twitches when the turn signal is on.

It's might be a bad ground Rusty!

The problem with grounding bus bars is that not all grounds are equal. They use a screw thru each wire and sometimes one or two come loose. This could be the problem.

In my Barth the gauges were reading low. It was traced back to the entire sub panel frame that the dash was mounted to. I had to add an additional ground wire from the frame of the dashboard to the frame of the coach. I also wound up cleaning a bus bar mount in the dash area. The bus bar connected every ground wire to that dash panel thru the mounting screws.

I clipped my test light and volt meters to the dash panel and had the hardest time tracing it out cause I was looking for a problem and was grounded to the problem.

The proper way to do this is with a volt meter. Hook the ground of the volt meter to the ground of the (very good ground) engine. Start touching everything with the red test probe to everything you think is a ground. Like the case of the radio, the ground for the cigarette lighter, the steering column, the dash light ground etc.

Chances are you will get a low to middle voltage reading. You should get nothing at all. Turn on the signal lights while doing it and see if the volt meter fluctuates. Now try adding a temp ground wire from the engine to the dash in the "same areas". If you have a bad ground it will now work better.

I have a mechanical speedo so the only thing I had a problem with was low voltage and dim lights caused by a bad ground.

quote:

Originally posted by Bill N.Y.:

quote:

Originally posted by MWrench:
Found that with just the key (engine off) on the speedometer jumps around, it even jumps around when I disconnect the signal line to it,

quote:

Originally posted by Rusty:
I had a similar issue - the gauges seem to read a bit low, and the speedometer sometimes twitches when the turn signal is on.

It's might be a bad ground Rusty!

I agree - I should have mentioned that I include ground in all cases where a circuit is suspect, expecially with these symptoms. Since ground for the temp and oil pressure are at the senders, I started with the hot side...but since the ground busses make connection through a couple of screws, they're next on my project list.

I can deffinitely say mine isn't grounds, I can power up the speedometer with a separate voltage source and with nothing running, the inputs can be shorted together (not the power lead) and it still jumps around. I have scoped the internal voltage regulator and it is VERY noisey, I think one of the electrolytic caps on the internal supply has failed, just have to get to it! Will post after I check it.

quote:

Originally posted by MWrench:
I can deffinitely say mine isn't grounds, I can power up the speedometer with a separate voltage source and with nothing running, the inputs can be shorted together (not the power lead) and it still jumps around. I have scoped the internal voltage regulator and it is VERY noisey, I think one of the electrolytic caps on the internal supply has failed, just have to get to it! Will post after I check it.

That could be the source of my issues - if it's an electrolytic with a short - or if there's a problem with the bleeder resistor...it is an erratic error I'm dealing with.

If it's the regulator, there ought to be one ad Radio Shack that would work.

An oddity on my '87 Ford van is that the instruments (VM, Fuel, and temp) all run on 6 V reduced from 12 V by a mechanical regulator, which is also erratic. I have parts from RS to make a solid-state regulator. For the moment, until the regulator in there quits, I have the voltage clamped with a little circuit.

quote:

Originally posted by Rusty:
[QUOTE]Originally posted by MWrench:
all run on 6 V reduced from 12 V by a mechanical regulator, which is also erratic.

FYI: In a pinch I've used a dash dimmer switch to test out lower voltage circuit patterns. It works well and it's already in the vehicle.

MINE JUMPS AROUND AND DOES NOT GO OVER 30MPH NORTH TRAIL SAID SENDING UNIT THEY SAID THEY WOULD FIX
LENNY

northtrail has a sending unit off the trans waiting for me when i can drive again in a few weeks.
lenny

This is the one problem I have had that fixed itself. When I picked the unit up from Florida last spring, it would rest at zero and jump up to somewhere close to the speed you were traveling and then back down again. For some reason, after a couple thousand miles, the speedometer got more and more accurate. I would have forgotten about the problem entirely if I was'nt reminded.