What do y'all think? Speed sensor or speedo?

[Fackler Rebel]

Been riding my scooter to work this week, my 78 Chevy is in the shop. Noticed yesterday afternoon that the speedo wasn't reading right, way slow for my speed. Turned it off at a red light and did the calibration thing again like I've done for the last 6 years. That seemed to correct the slow speed reading but now it appears to register the correct speed, just a little slow going back to 0 mph as I slow down. Sensor or speedo?

Reb

[BWP 5p]

If your sensor is like mine.........it's pretty easy to pull out and clean off. I'd sure start there, up to even replacing it before I considered replacing the $peedo!

[steelworker]

Originally Posted by Fackler Rebel

Turned it off at a red light and did the calibration thing again like I've done for the last 6 years.

Recalibrate? Is that an aftermarket speedo you're talking about, because the stock speedo cannot be recalibrated, to my knowledge.

[Fackler Rebel]

My operator manual says, ignition to on, wait until the speedo dips to zero and rebounds and then take the run/stop switch to on, then hit the start button. Been doing that for the last six years and no it is a stock HD speedometer.

Reb

[steelworker]

If that's the case with my speedo, then I just learned something. A bit late, though, as I replaced it with a mini digital speedo over the winter.

[BWP 5p]

Originally Posted by steelworker

If that's the case with my speedo, then I just learned something. A bit late, though, as I replaced it with a mini digital speedo over the winter.

Now you have something to post in the "It's Friday, what have you learned thread"

I learned that a Coleman 2 gal water jug will come off at speeds up to 115mph! Who knew?

I did go back out and found it along the road today............shows a few battle scars, but otherwise

[steelworker]

Originally Posted by Fackler Rebel

My operator manual says, ignition to on, wait until the speedo dips to zero and rebounds and then take the run/stop switch to on, then hit the start button. Been doing that for the last six years and no it is a stock HD speedometer.
Reb

Originally Posted by steelworker

If that's the case with my speedo, then I just learned something. A bit late, though, as I replaced it with a mini digital speedo over the winter.

You piqued my curiosity, so I just checked my owner's manual, and there's nothing about waiting for the speedo needle to bounce, so I guess they must have changed something between '98 and '00.

Originally Posted by BWP 5p

Now you have something to post in the "It's Friday, what have you learned thread"

Yeah, I have learned something!

Reb, d'ya wanna buy a secondhand speedo? One careful owner since new, never been over 70mph?

Seriously, though, I'm looking at my factory manual, and if you have a multimeter the following test is worth trying...

At the block connector (under the seat on my bike) for the three wires from the sensor, with the ignition switched on and the connector connected (prise out the rubber bung from one end of the connector to get the meter probes in) check:

1. Is there 6-12VDC on the RED wire in the connector?

If NO, check for broken circuit between the connector and the speedo, and in the feed wire (ORANGE/WHITE) to the speedo. If in good condition, then replace the speedo.
If YES...

2. Check for continuity to ground in the BLACK wire in the connector.

If NO continuity to ground, check for bad connections. If all are ok, replace speedo.
If there IS continuity to ground...

3. Check for voltage on the WHITE wire in the connector. Jack the rear wheel off the ground and turn it. The voltage from the sensor should read 6-12VDC when a gear tooth is ABSENT under it, and 0-1VDC when no gear tooth is PRESENT under it.

If 6-12VDC is not present, replace speedo.
If 6-12VDC is present, but there is no fluctuation to 0-1VDC, remove the speed sensor and check for accumulation of debris on the end. If debris is not present, replace the speed sensor. If debris is present, clean and replace sensor and repeat test #3. If there is still no fluctuation, replace sensor.


After this, if the ORANGE/WHITE feed wire to the speedo is showing 12VDC and the black earth wire from the speedo is continuous to earth, then it looks like your speedo has gone south.