Speedometer broken on Rover K-Series

[wpqs]

I have a Roadsport Sv 1.6 with Rover K-series built in 2002. Unfortunately the speedo suddenly stopped working the other day. Possible causes:

1. Broken inductive sensor

2. Broken cable

3. Broken speedometer unit (display)

Can any advise the most likely cause?

Is it possible to test the speedo unit? There is a connector on the back which I presume provides DC power as well as a pulse input from the inductive sensor. I suspect sending pulses to the unit from some sort of test rig (555 timer for example) should cause the speedo needle to move. Does anyone know the specification for the pulses - 12V square pulse 50% duty cycle frequency 0-500Hz for example?

 

[Jonathan Kay]

Private Message sent.

[Wrightpayne]

There was a recent discussion on whether an alternate (non-caterham) sender was a direct replacement and IIRC the pulse rate was the same.

There are a number of different arrangements - direct cable drive (which I think we can discount), electrical sender driven by the gearbox speedo drive and a wheel sensor.

Which type do you have?

Ian

[SLR No.77]

It will be either cable drive or electronic, the older cable drive speedo has a substantial speedo cable passing through a large grommet in the bulkhead. 2002 is around the era when they were swapped to electronic, in which case there will be no speedo cable in the engine bay.

If it's electronic, you can remove the sensor from the side of the gearbox, and with the ignition on, spinning the quill between your fingers should cause movement of the speedo needle. If there's nothing it's either a broken sender or a wiring fault. The senders are expensive so check this first.

Stu.

[John Vine]

Also check the quill itself.  They've been known to break.

The pulse rate of the electronic sender is 8/rev.

JV

[wpqs]

I have electrical type as there is no mechanical drive cable entering the back of the speedometer, just an electrical connector block

[John Vine]

Re #6: 

In which case, the comments in #4 (2nd para) and #5 will apply.  It might also be down to a broken worm-gear drive in the gearbox itself, but best to check the other points first.

JV