Mon, 15 Sep 1997
Hello!
I have no tips, story or even photo, at least not yet, as I bought my car, chassis 7372, an early S, this past week. However, I've had some time to find a few points of trouble. One that annoys me greatly is the tachometer, which has a very peculiar way of counting. According to the tacho, the car idles at about 3500 rpm. It works alright from there and up, and if I put it in gear and hit the brakes, the tacho will go down below 2000, so it's not physically stuck. Any ideas?
Regards
Magnus Geijer
mj30715@janus.swipnet.se
Magnus -
Fourteen or so years ago when I bought my '63 P1800, chassis number 6647, I had the same sort of problem. There is a box called a "sender," about the size of a cigarette pack, fastened to the air intake behind the grille, that controls the travel of the tachometer needle. Using a hand-held tachometer, I compared readings with the tach in the car and found that the car's tach was reading about double the correct RPMs.
Deducing the sender to be kaput, I bought a potientiometer (variable resistor or "pot") at a local Radio Shack store and soldered it between the positive lead to the tach and the tachometer positive terminal. Revved the engine to 3,000 RPMs (an average setting), stuck a block under the throttle linkage to hold it there, and adjusted the potentiometer until the the car's tach said 3,000. Put a drop of glue on the pot stem, and I had a working tachometer.
I still wondered what the sender was for. At the time, Volvo was trying to sell them for $300 (a great deal more than a simple resistor). After observing a twenty-percent variation in the tachometer readings from summer to winter using the speedometer for reference, I became convinced that the sender would be named more appropriately a temperature attenuator. I even mentioned this to another P1800 enthusiast once, but he replied that it was a sender.
-Glenn.