J reg 940s estate - speedo and trip meter work intermittently and there is no pattern to when either stops / starts to work again. On occasion both stop working. Sometimes they both work perfectly for a couple of hundred miles! Sometimes the trip will work, stop for a while, then start again but not on any particular digit.
The temporary failure of the speedo usually occurs after engine ignition - although car is stationary, the speedo needle will immediately read perhaps 30mph and then drops to zero from then on. It usually won't recommence working correctly till after the journeys end and the car has been parked for a while.
Can anyone point an accusing finger cos it baffles me!!!

(Apologies in advance if I am slow to respond - AOL makes using this site virtually impossible!!)

 

Speedos have two major parts: the pick up at the differential which is a wire that can chafe or break, and the speedo itself with associated electricals in the instrument pod. By your symptoms I'd think that it's the speedo itself. I have a similar situation with my '92 940GL: I was getting constantly good odometer, but very spotty speedometer reading. I just changed the speedo unit with a junkyard speedo and this one is totally dead-shows nothing at all times, so I am back to the junkyard to get yet a another unit.

 

Many thanks for your response.
I am wondering if it may be the diferential end though as the speedo and mileometer and trip all work perfectly ok, but sporadically, and don't "stick" on particular digits etc.
For some time there has been a hidden "rattle" at the back of the car (underneath) which didn't show itself when jacked up and new exhaust fitted so I am wondering whether the prob could be where the cable is attached - maybe it is coming adrift?
When I get the means to I will take a closer look at how it all works under there and see if there are any clues.
As you can tell, I'm no mechanic!!