On a typical drive around town, the speedometer will not be functioning. Then it will work for awhile -sometime only seconds, sometimes for the duration of the trip. As time passes, the percentage that it fails to work increases.
Is there some "owner servicable part"? It's the family driver, so I hate for the wife or kids to try to guage their speed according to the tachometer. Thanks for any help.
Jim
I have the same problem, when it does not work I just bang the dash and it works again.
You have a problem with an electrical connection between the rear axle (differential) and the speedo head or the grounding (earthing) of the instrument panel.
Cheers, Peter.
Mine did the same thing -- the shop I was taking it to (before I gave up with them and found a dealership willing to work on high-mileage Volvo's in Mt. Kisco, NY) said it was probably electrical but it would take a bit of work to track it down since there was no obvious wiring fault. Rather than spend a lot to fix this (I can use the tach to pretty much tell how fast I am going), I put it off and figured I try to fix it myself when I had some time and the problem got really annoying.
When the meter went dead and worked less than 10% of the time, I decided to fix it, and first traced as much of thw wiring as I could. Seeing no obvious fault and continuity was fine in the segments which I tested, I got an entire instrument panel from a wrecked 740 and just changed out the whole thing, and the speedometer (as well as other instruments) works great now. The panel was about $175 from a wrecked car lot in Suffolk County, NY (basically a lot near Patchouge (sp?) LI where you can just go to the wrecked car, tell them the part you want, and if it is still in the car they take it out for you).
It was a pain to open up the front panel on my 740, but it also afforded me an opportunity to fix a few bulbs and clean out some dust which had accumulated on the display.
I was initially told it was an electrical wiring/grounding problem, so I wasn't sure a new panel would make a difference, but right after I put it in the needle never varied and still shows the correct speed (no jumping around or staying at ~10mph when the tach says 2.8 and you know you are doing 75 or so....)
So if you have checked all the wiring and the grounding, and it seems fine, it *may* be that the "circuit board" (for lack of a better term) or the speedometer itself is a bit flaky, and if you want to spend $200 or so, you may want to try replacing it to see if the problem lies there.
Good luck!
-Doug snipped-for-privacy@interpage.net
tachometer.
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