smyth1

is there a way to test the sensor on the diff?i have no speedo or odo.thanks

Lizard928

unplug the cruise control brain, and there is two pins to measure with a volt meter, as you spin the rear diff it will go from continuity to no continuity.

jpitman2

You could also do it at the plug in the spare wheel well, as thats the nearest connector. I doubt the sensor has failed - its just a reed relay triggered by 8(9?) magnets in an alloy ring bolted to ring gear. Most of these issues are wiring related - start by checking the spare wheel well connector is clean and bright. Then check for make/break at the central board. After that , wiring to the pod - the connectors that carry leads into the instruments may need cleaning, and bending to improve contact - mine did!
jp 83 Euro S T 54k

Hilton

Have you checked the sensor is still attached to the back of the diff housing?

My 87 was missing it.. just two bare wires by the rear of the diff housing, and no sign of the sensor, M6 bolt or wire hold-down

Dave928S

You did an LSD install some time back and siliconed the cover on ... are the ring and sensor actually there?

Glenn Evans

Alloy (ie aluminium alloy) ring? The (eight) magnets are embedded in the ring gear itself.

smiffypr

No Glenn, the magnets are in an aluminium disc bolted onto the side of the diff, (opposite side to the ring gear), see picture page 39-8 of WM. And John, you shouldn't say alloy to indicate ally.
Smiffy

smyth1

i did check the connector in the tire well and it looked ok if it's the right one.it had the shieilded wire along with two browns if i recall correctly.3 pin connecter.yes i did rebuild the diff and cleaned the magnetic pickup.and reinstalled the sensor to the back cover.it did not work before that either.any other suggestions to try and trouble shoot speedo and odo?thanks

Lizard928

Looking to see it is there is one thing.
Did you test the sensor as suggested?

Though I would put money on the problem being a bad solder joint on the speedo.

depami

Are all years two wire or are some three wire?

My 82 has a brown and green wire. Connect an ohm meter between them and turn the wheels. It should make and bread continuity.

SeanR

This is pertinent information.

Has the speedo worked since this was performed?

Bill Ball

In the 1990 PSD, the magnet disc can come loose - I've seen it happen. The sensor itself and the rest of the circuit tested good by taping some magnets on a sanding disc and using that with my electric drill to simulate the magnet disc. The faster the drill rotated the magnets by the sensor, the higher the speed readout on the instrument panel. But the rotating diff itself would not send a signal. When we opened the diff, we found the magnet disc was completely loose. In 1991, the speed sensor was moved to one of the front wheels.

In the earlier diff like you should have, the magnet disc is "pinned" on the right side of the LSD. I don't know if the disc can come loose like the 1990 PSD can. If you get no response from Colin's original test suggestion, you might figure some way to simlate the disc operation like I did.

Lizard928

Bill and Sean, this is why I suggested what I did. It will remove this from the equation.

smyth1

speedo or odo has not worked since i have had the car.i did rebuild the diff and cleaned every thing and reintstalled magnetic disc as well as sensor.

Dave928S

Time to test the output as Colin has suggested. Check at the closest point to the sensor output (at the connector in the wheel well) and go from there back up the line.

Establishing output has to be your first test.