Speedometer problem
 

I have a '93 XJS and the speedometer will work up to about 50mph in the morning when I first start driving it and then will drop to zero. After it warms up, it will sometimes go to 30 and will always go back to zero if I hit the brakes or cut on the lights. I have tried grounding the instrument panel ground better, nothing. I moved the shim gaskets on the rear axle sensor closer and further away, nothing. Don't know what else to check. Has anyone else seen this or have a fix??? Thanks, Chris

As far as telling you what to test, I'm no good. The most common problem we've seen is the sending unit on the diff. Problem is, they are on back order new and I've sold all my used units. I've sold a few (very few) speedo gauges, but they are few and far between.

Hmm, I seem to have the same problem with my '90 XJS sometimes.

I wondering if anyone had found a fix. My XJS is a little earlier, 1983, but a similar problem - the speedo works sometimes, then stops working, then starts again (sometimes). It is probably not working about 70% of the time, while isn't bad for mileage (keeps the car newer) may not be so good as far as speeding fines.

I bought a radar detector that has a built in GPS and it has a digital read out of my speed. So I guess the answer is...no. I got a new set of gears and will be pulling the rear end out when my bearing kit shows up. Would be nice to know a way to test the sending unit while I have it apart.

Yes a GPS would be an easy solution and useful too.
I've been doing extra research on the matter and it sounds like the speedo transducer is the most likely culprit (located at the rear of the transmission) so I will try replacing that in the near future.

if and when i get my XJS working, ill be redoing the entire gauge panle in brushed aluminum and autometer.

On your car the speedo is driven off the gearbox by a little generator in the LHS towards the rear. IT has a two wire cable coming out of it about 6 inches long with a two pin plug on the end, which plugs into a loom wire beside the gearbox that comes down through a grommet from the LHS of the tunnel.

If you work though the system you will find the trouble. Could be the generator packing up/slipping on its drive cog, could be a dirty plug connection. Could be a poor earth or poor signal connection into the instrument cluster. Could be all of the above!

Hope this helps

Greg

......and, by the way, the wires run very close to the LH exhaust pipe, sometimes flopping against it


Cheers
DD

Hello,

It could also be your speedometer interface module, which recieves its information from the sensor on the differential that Ken mentioned earlier.. On the 95/96's failure of the interface module, the sensor at the differential, or the wiring in between, will cause speedometer problems, high idle, and what sounds like alternator noise thru the radio speakers.

The speed modulator is available from www.jaguarclassicparts.com for about 30 dollars, the wire can be fixed cheaply, but the sensor is the very hard to find part.

Good luck

Thanks Greg in France and Doug for adding useful info - they are all possibilities and will be looked at when I get the car back again (it's at the panel beaters at the moment getting the floor of the boot (trunk) replaced).

I have a problem that my speedo works when it feels like it (95 4.0l xjs) when it's not working I still have the odometer working it's just the speedometer that packs in. Can anyone tell me if the transducer is on the gearbox or the diff on my model. Also exactly where is the modulator located.ANY advice will be welcomed. Thanks guys.
ERIC