90 740GL wagon w/erratic speedometer

[redknitter]

Works sometimes, but mostly not. We've replaced the speed sensor and the speedometer head (both were, I think, used parts; know speedometer head was). Each time, think it's OK, then it starts acting up again. We've been told that those are the only two parts involved . . . failure (when it does work) seems to be related to a) my foot on the accelator (as in, it works as long as I keep some pressure on pedal, but first time I have to come completely off, needle drops and usually stays down); and b) hitting bumps on the road (as in, it can be working well; I hit a bump and needle dips and returns, or drops like a rock and stays down). If it's not working when I start the car, it won't work that whole trip. Sometimes it tries to work when I start the car, and then I lose it in one of the previously detailed circumstances. This is a nerve-wracking way to travel! When speedometer isn't working, odometer and tripometer are dead, too. Thanks for any help.

[billofdurham]

Welcome to Matthew's Volvo Site.

We've been told that those are the only two parts involved .

They are, apart from the cable that connects the two. Have you checked the connections, especially at the sensor? They tend to have a hard time, stuck under the car, having all sorts of rubbish thrown over them day in, day out.

Seriously, check the connections and clean them thoroughly.

On my 740 I had a different speedo problem which was resolved by replacing the cable. When I got the cable off it was in a very sorry state.

Bill.