Jump to content

Discovery 300tdi speedometer


Donald Sherburn
 Share

Recommended Posts

Sons speedometer dial "jumping" all over the place when travelling normally, 30mph reversing out of drive!!!etc etc. Have cleaned up speed sensor electrical connector, no improvement, taken apart & cleaned speed sensor, no improvement, replaced sensor with new part, still no joy. Speedometer instrument removed, needle moving freely with no stickyness at all. Looked at all related items on forum, only thing I found was when renewing sensor no sealing washer supplied so not fitted & "inner" drive to sensor not removed or cleaned as unsure whether it can be removed easily. Can the sensor be checked with multimeter or even hooking sensor up to an electric drill and spinning it??

Looking for answers from you knowledgeable people as I am not willing to "permanently" lend son my hand held GPS!! (He has requested it as an easy fix), thanks in anticipation.

Link to comment
Share on other sites

Sons speedometer dial "jumping" all over the place when travelling normally, 30mph reversing out of drive!!!etc etc. Have cleaned up speed sensor electrical connector, no improvement, taken apart & cleaned speed sensor, no improvement, replaced sensor with new part, still no joy. Speedometer instrument removed, needle moving freely with no stickyness at all. Looked at all related items on forum, only thing I found was when renewing sensor no sealing washer supplied so not fitted & "inner" drive to sensor not removed or cleaned as unsure whether it can be removed easily. Can the sensor be checked with multimeter or even hooking sensor up to an electric drill and spinning it??

Looking for answers from you knowledgeable people as I am not willing to "permanently" lend son my hand held GPS!! (He has requested it as an easy fix), thanks in anticipation.

I would suggest jacking a rear wheel up, then with the sensor removed get someone to spin the wheel (transfer box in neutral to reduce drag) then see if the square drive on the rear output housing rotates freely and smoothly. If it does I would then look at the voltage regulator as I have heard this can cause similar symptoms.

Link to comment
Share on other sites

Have rebuilt 3 transfer boxes in the last couple of months so its quite fresh in my mind. As BogMonster says the collar that holds the sqaure drive/plastic gear will come out once the transducer is removed by putting a screwdriver under the outer lip and levering it out, the only resistance should be the O-ring but if its been in there a while without being disturbed in may be a bit stiffer with crud build up. It may be possible that if the original transducer had seized in some way it may have restricted the drive member and stripped the plastic teeth (just a hunch). If you want to check the worm drive collar inside the housing, that just unbolts off the back of the transfer box once the prop and handbrake is disconnected.

Link to comment
Share on other sites

The sensor is a magnetic reed switch with a spinning magnet so it closes twice for every revolution. The sensor is driven by a short speedo cable and this could have failed.

the sensor is double ended, the big hexagonal nut comes off and you can see the end of the rotor. On a small number of cars there was a mechanical speedo and an electronic speed transducer, typically these were early 14CUx EFi V8 RRC, the 14CUx needs a road speed signal (also handy on police cars with 2 speedos)

You can unscrew the existing speedo cable and try spinning the sensor with a hand drill or long narrow screwdriver.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy