Speedo Screwed?

[DemonDaz]

Are there any common faults on the 325 E30's that stop the speedo? This is a 1990 car with a single sensor.

I drove over a bump, and after that the speed stopped working!
I will test the resistance of the sender, but I suspect it could be cabling, not too sure where the wiring goes or where it is likely to have failed.

[Simon]

First place I would check is the sensor on the diff, as you look under the back of the car, you should just see it, make sure it's making a good contact here.

[Brianmoooore]

Wire often breaks inside the insulation just outside of the plug going into the diff. Give the wires a gentle pull.

[DemonDaz]

Thanks guys, I was going to jack it up this weekend to change the discs, looks like I better get under it and see if I can sort the speedo out.

I have found the Bentley manual nigh on useless in this instance!

[BadDave]

As well as the wires at the plug that fits the sensor,I've also found that they can braek just where the wiring comes over the rear anti roll barr
HTH

Dave

[DemonDaz]

I am now sure it is a broken wire! It is intermitant, It seemed fairly solid at the sensor, but when I drove after playing with it, the speedo works. Now it works for a while then cuts out, works again, flaps about a bit and then works some more.

So should I cut the wire and connect from the cut to the sensor, or trace it back and replace the whole lot?

[Brianmoooore]

Best is to relace the wire and plug back to inside the car, and leave a little bit longer loop to the diff than the original.

[ian332isport]

I had a similar problem where my Speedo started to get intermittent. Sometimes it would work, other times it was totally dead. I also noticed that it seemed to come back to life when I had the heater on and the car was nice and toasty inside.

I traced the signal all the way from the diff sensor to the back of the instruments, and this proved to be working fine. I pulled the instruments and stripped them down, and had a good signal path all the way to the speedo head itself.

After thoroughly checking it over, I found what appeared to be a dry solder joint on the circuit board on the speedo head. After re-soldering the joint, everything worked fine. I also checked the same joint on another speedo, and it also showed signs of a bad joint.

If you look at the circuit board on the back of the speedo (talking about VDO here, not sure if Motometer is the same), you will see several components soldered to the board. One of these is a silicon chip of some sort. This is under the big coil of wire on the side of the speedo.

In the centre of the chip, are two very wide pins. The wide pin nearest to the edge of the circuit board is quite close to another component (capacitor) that is a small rectangular shape. If you look at the solder joint for this capacitor, you will hopefully see that it looks slightly cracked around the join. You may need a magnifying glass to see it clearly. Even if you can't see a faulty joint, it is always worth heating all the joints with a bit of fresh solder as dry joints are not always visible to the eye.

Mine has been fine ever since.

Cheers,

Ian.