My speedometer on my 89 745GL 8 valve automatic is either not reading or it bounces all over the place. What could be the cause and what would be the repair
all/any help would be greatly appreciated
Thanks Rob
Problem: Wire strands in the twisted pair connecting the vehicle speed sensor to the speedometer break progrssively inside the wire insulation until the speed signal to the speedometer is intermittent or completely lost.
Primary cause: Excessive mold clamping force between the platens where the wire exits the mold, during injection molding of the waterproof silicone rubber, work hardens the copper strands making them brittle.
Secondary cause: The is no mechanical stress relief between the plug connector and the unsupported wire run to the grommet in the trunk housing. Normal but prolonged vibration/oscillation of the wire eventually fatigues the brittle section of the wire and the individual strands break one by one. Repair: Pull the connector from the vehicle speed sensor on the differential cover. Mark the plug connector with the wire colors. Dismantle the plug remove the two wires from the plug connector and pull to check the integrity of the wire strands inside the insulation. Most likely the the wire is broken or only one or two strands are still intact. Go to a Volvo dealership and buy two repair wires with waterproof connectors. They can be variously listed under old parts bulletins for the early windshield washer retrofit on a 240 or for ABS wheel sensor harness repairs for 740's. Peel/split the cover back on the harness about six inches and snip off the old wire ends. Splice in the new wires mark each end with the color of the mating wire. Restore the twisted pair configuration of the wires by twisting the new wires around one another to minimize RFI on the wire. Insert each of the marked wires into the proper receptacle of the plug. Reconnect the plug.
There is also the possibilty that the speedometer head is faulty, but the speed sensor failure is inevitable.
Bob
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