Need help on speedometer trouble shooting test

[jwakil]

I posted this problem before about my speedometer reading too low. It's basically reads 30 mph when I'm going 60+, doesn't go above ~40mph, and not even registering until after I get past 20mph. It's not even a linear response of needle to actual speed. Anyway, I have check all the wires to the speedo and they all seem fine. I also was told of an issue where the magnets from a circular disk in the differential are prone to fall off and to do the following test:

1. Raise one of the rear wheel
2. Pull the wires from the sensor that plugs on the side of the tranny, put an ohm meter across the sensor pins.
3. Rotate the wheel slowly and count the number of blips that the ohm meter registers (should be 8).

I have done the above test multiple times with no success. The ohm meter is always reading open circuit, no closures. I have tried both wheels off the ground together, each wheel of the ground one at a time. What could I be doing wrong and what else can I check?

[universeman]

Have you tested continuity on the wires?

Take the road wheels off with the car on jackstands and start it up, put it in gear, and see if anything changes with your reading. Careful with that setup though....

[rick-l]

If you checked your ohm meter and trust it it might be time to buy a new sensor.

[jwakil]

Originally Posted by universeman

Have you tested continuity on the wires?

Take the road wheels off with the car on jackstands and start it up, put it in gear, and see if anything changes with your reading. Careful with that setup though....

That would be tough as I have to actually hold the ohm meter pins in the receptacle for the sensor. I would have to rig up some pins that can go in the holes and stay there without me holding them, or do the reading at the speedo end of the wires. (That's probably much easier).