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Speedometer and odometer stopped working

james944

james944

New member
Hi. I have a 1984 944 lux. A few months ago my speedometer and odometer stopped working both at the same time. Could anyone give me some advice as to what may be the cause of the problem. I've checked the cable to n/s front spindle and its still in tact. Managed to remove the sensor closest to the engine of the two but the other is trickier as the hot water flow switch gets in the way.

Any help would get appreciated. Thanks.
 
James, if you have an '84 model the speedo is cable driven according to PET, and if you have lost speed and odo then the likelyhood is that the cable has broken. Having said that the drive comes from a square hole in the N/S grease cap, secured with a circlip. The circlip can come off and over time the cable works itself out of the drive hole so you might be lucky and just have to relocate it back in the hole and replace the circlip.

Part number for the cable is 211 957 801 E I believe
 
Hey. Thanks for the reply.

I've checked the dust cap and the circlip was still in place securing the cable. Do you believe I should go ahead with replacing the cable? There isn't anything else I could check first? I'm ready to replace both front wheel bearing also so this seems a suitable time to do both.

Cheers.
 
Have you removed the speedo head, raised the NSF wheel and turned it to check that the cable end turns?
 
That is a possibility I will now check for as I will have to detach the cluster. I will check for blown bulbs also. Is there anything else I could look for while doing this procedure?

Thanks, James.
 
Its not that much of a pain to take the cluster out, but if you have hands like an octopus with an eye on the end of each tentacle you might be able to reach up behind the instrument and unscrew the connector and check to see if the end of the cable turns easily. If it does then it's broken because you would be trying to turn the wheel with the cable if there was no break in it. Cables do go but then again the speedo heads also pack up. It might be that one of the plastic gears inside the gauge has cracked. The pinion in the worm/pinion drive to the odo is notorious for cracking but there are other gears which could go the same way. To investigate inside the head it will be necessary to peel back the rolled edge of the bezel to remove it and take a look inside. The speedo just pushes out towards the rear of the car and is held by a ribbed rubber ring.
 
As above basically, but the cable drives the magnet which moves the speedo needle directly, ie no gears to break,so I would go with cable broken or circlip off.

It is possible the screwed ends of the cable have come loose, either end, I didn't tighten the speedo end once and it worked ok but rattled!
 
Hate to be a pedant but the cable entry on the speedo head is oblique to the rotational axis of the magnet so there is a skew gear of some kind to transfer the drive to the magnet, but as it is about 8 years since I repaired my odometer I cant remeber the configuration exactly.
 
IF I remember (big if!) the magnetic section of the rotor just passes close to the one attached to the needle, the angle between them is (almost) immaterial, thats why you get a pulsing effect at very low speed.

I have had several different car speedos apart and cant remember which one is which, so not 100% on that.
 
You are almost quite right, the magnet poles passing the aluminium cup that is behind the dial face induce an eddy current in the non-ferrous aluminium which makes the cup behave like an elctromagnet which is then attratcted to the poles of the magnet, FSD is resisted by a hair spring and the faster the rotation the more eddy current and more torque to turn the cup. All that is basic physiscs and some interesting lectures about this very thing were the subject of some Royal Institution Christmas Lectures many years ago, probably one of Professor Sir Eric Laithwaite's, and as I say your basic theory is unflawed, but the cable screws to the connection which is at about 30 degrees to the vertical face of the back of the speedo so there must be a pair of gears to take drive to the magnet. As the thrust face of the magnet spindle wears the clearance increases and this changing clearance is the reason for a wavering needle. There is another factor to the wavering; a poorly routed cable will cause a binding point and the cable will wind up fractionally then unwind as the cable overcomes the resistance giving inconsistant speed to the magnet. usually a slow waver is the magnet and a fast more like flickering is usually the cable, which may simply need lubricating
 
speedo image from PET

F1EA81ED73994CB5B01F534242E5E3EA.jpg
 
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