Speedo Transducer V8
Discussion
Currently a V8S owner, previously a Wedge owner/contributor I wondered if anyone would have any experience concerning speedo transducers?
I've just completed a body-off chassis chassis repair. While we were lifting off the body the one wire we failed to disconnect, until too late, was the speedo. The connector pulled apart, ripping out the wiring. This has been repaired, but having put all back together now the speedo no longer works. All wiring feeds to speedo work but we are unable to get any sort of signal from the transducer. We have removed it and tried spinning it with a drill but there is absolutely nothing coming from it. I'm not the wiring expert on this, my buddy mechanic is, so may not be able to answer any queries on tracing the fault. We are at a bit of a loss as to why the transducer fails to provide any response to meter or LED - any thoughts anyone....please?
Many thanks Steve
I've just completed a body-off chassis chassis repair. While we were lifting off the body the one wire we failed to disconnect, until too late, was the speedo. The connector pulled apart, ripping out the wiring. This has been repaired, but having put all back together now the speedo no longer works. All wiring feeds to speedo work but we are unable to get any sort of signal from the transducer. We have removed it and tried spinning it with a drill but there is absolutely nothing coming from it. I'm not the wiring expert on this, my buddy mechanic is, so may not be able to answer any queries on tracing the fault. We are at a bit of a loss as to why the transducer fails to provide any response to meter or LED - any thoughts anyone....please?
Many thanks Steve
Oo oo, I know, me me me! 
At least, I do if it's the same design as the SD1 item...
The transducer doesn't actually generate any output as such (that you can measure by a multimeter, anyway). There's a 12v feed in one side and the other side goes to the speedo. Spinning the transducer rotates an 8-legged metal rotor, the legs trigger a magnetic pickup and the output is a series of pulses superimposed on the 12v rail out to the speedo.
The transducer is potted in epoxy so if you broke one of the wires, it's history, unless you can dig the potting out and repair it (I've done it for my car, the cruise control uses the same pickup).
ETA: did you get the wires wrong way round when reconnecting? It won't work backwards...
At least, I do if it's the same design as the SD1 item...
The transducer doesn't actually generate any output as such (that you can measure by a multimeter, anyway). There's a 12v feed in one side and the other side goes to the speedo. Spinning the transducer rotates an 8-legged metal rotor, the legs trigger a magnetic pickup and the output is a series of pulses superimposed on the 12v rail out to the speedo.
The transducer is potted in epoxy so if you broke one of the wires, it's history, unless you can dig the potting out and repair it (I've done it for my car, the cruise control uses the same pickup).
ETA: did you get the wires wrong way round when reconnecting? It won't work backwards...
Edited by Wedg1e on Wednesday 10th October 20:33
Hi Wedg1e
It sounds like the same part. We managed to dremmel out the epoxy down to the contacts (one of the wires was broken, but we think it should still have worked as it was). Re-soldered the offending wire, and hot glued to provide support, but of course don't know if it works as we could get no feedback from testing. We tried the new connectors both ways round as a starting point. We've run out of ideas as what to test next - and i guess the 'dismantled' transducer has got to be top of the list now!
Steve
It sounds like the same part. We managed to dremmel out the epoxy down to the contacts (one of the wires was broken, but we think it should still have worked as it was). Re-soldered the offending wire, and hot glued to provide support, but of course don't know if it works as we could get no feedback from testing. We tried the new connectors both ways round as a starting point. We've run out of ideas as what to test next - and i guess the 'dismantled' transducer has got to be top of the list now!
Steve
Is this the gearbox-mounted pickup or the cable-driven one as used on the Rangey?
What I found when testing my cruise control was that the cruise ECU didn't get any meaningful pulses from the pickup so I assumed the pickup was dead. A spare one showed the same, which is why I pulled one apart!
Then the penny dropped that it would normally be used with the SD1's electronic speedo, and I surmised that the speedo must provide some sort of load to the pickup. I duly soldered a resistor from the output of the pickup to earth and hey presto, a pulse train appeared - you need an oscilloscope to see the pulses, of course.
What I found when testing my cruise control was that the cruise ECU didn't get any meaningful pulses from the pickup so I assumed the pickup was dead. A spare one showed the same, which is why I pulled one apart!
Then the penny dropped that it would normally be used with the SD1's electronic speedo, and I surmised that the speedo must provide some sort of load to the pickup. I duly soldered a resistor from the output of the pickup to earth and hey presto, a pulse train appeared - you need an oscilloscope to see the pulses, of course.
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