Speedo not working - please help
Discussion
So I've had Trevor for 10 years, a 1999 4L Chimaera. The speedo was always a little difficult with the standard jump to 10 mph after moving for a while. The rev counter then started to become more problematic and started dancing whilst driving up and down. I tried to get someone to fix them but no one could take it on. I eventually ended up buying two new ones both from Caerbont.
I left them into my mechanic a year and a half ago to get them fitted. I'll not go into the story but boiled down the TVR is back with me and the speedo still doesn't work. He fitted both dials but couldn't get the speedo to work. Initially he said it was because of the Transducer so I ordered and got a Speedo Transducer - M0631 from TVRSSW and he fitted it. It still does not work, £1,000 later. TBH I feel a little like committing hari-kari in the garage but my wife wouldn't be impressed instead she wants me to get the car fixed so it can be sold. I can get the car MOT'd until the speedo is fixed.
So going up the road the speedo when the entire turns on goes from 0-180 and drops back to 0 (this would appear normal) when driving it says at 0 whilst building up speed and then jumps to 30. When driving at a constant 30 is jumps and drops between 30 and 20, occasionally dropping back to 0. This is more or less constant.
Is there anyone who has experience of this and can suggest a fix for this. I really am at my wits end and it would have been cheaper to drive the car to the mainland and get someone there to do it (we live in Northern Ireland) and the one guy who fixed TVRs here has retired, he was brilliant. If someone can come up with a solution I will try to fix a mechanic here who could implement it.
Really desperate, everything else with the car is 100% but this essentially prevents me driving Trevor and selling him.
All suggestions received.
Peter
I left them into my mechanic a year and a half ago to get them fitted. I'll not go into the story but boiled down the TVR is back with me and the speedo still doesn't work. He fitted both dials but couldn't get the speedo to work. Initially he said it was because of the Transducer so I ordered and got a Speedo Transducer - M0631 from TVRSSW and he fitted it. It still does not work, £1,000 later. TBH I feel a little like committing hari-kari in the garage but my wife wouldn't be impressed instead she wants me to get the car fixed so it can be sold. I can get the car MOT'd until the speedo is fixed.
So going up the road the speedo when the entire turns on goes from 0-180 and drops back to 0 (this would appear normal) when driving it says at 0 whilst building up speed and then jumps to 30. When driving at a constant 30 is jumps and drops between 30 and 20, occasionally dropping back to 0. This is more or less constant.
Is there anyone who has experience of this and can suggest a fix for this. I really am at my wits end and it would have been cheaper to drive the car to the mainland and get someone there to do it (we live in Northern Ireland) and the one guy who fixed TVRs here has retired, he was brilliant. If someone can come up with a solution I will try to fix a mechanic here who could implement it.
Really desperate, everything else with the car is 100% but this essentially prevents me driving Trevor and selling him.
All suggestions received.
Peter
Belle427 said:
I would first start by checking the air gap at the sensor, it has been known for some sensors to be set a lot closer than others to give a stable signal.
Only other thing i can suggest is checking the compatibility of your new gauges with regards to calibration etc.
^ This.Only other thing i can suggest is checking the compatibility of your new gauges with regards to calibration etc.
My speedo stopped working recently. I bought a new sensor & it only worked sporadically after fitting.
I then found out from helpful people on this forum that the correct sensor gap is different for black bezel gauges & silver ones.
My gauges are silver bezel & once the sensor gap was reduced to 0.3 mm it worked fine.
Not sure this is helpful but heres how I fixed mine when mileage got stuck at 199,999 and yes I thought it was far fetched but it worked.
Remove dash top
Loosen speedo bracket and swivel speedo 280 degrees so it's upside down.
Jack rear wheels off the ground
Start the engine
Put it in 2nd gear and let rear wheels rotate so speed is about 20mph at idle
Tap the speedo gently with a heavy rubber handled screw driver until it starts working properly again
I ASSURE YOU IT WORKED ON MINE !!
Remove dash top
Loosen speedo bracket and swivel speedo 280 degrees so it's upside down.
Jack rear wheels off the ground
Start the engine
Put it in 2nd gear and let rear wheels rotate so speed is about 20mph at idle
Tap the speedo gently with a heavy rubber handled screw driver until it starts working properly again
I ASSURE YOU IT WORKED ON MINE !!
Edited by blaze_away on Tuesday 30th April 15:54
A little science behind it all. The diff sensor is just a coil of wire around a magnet. As the toothed wheel goes past it , it alters the magnet field enough to produce a tiny voltage. This voltage goes up a bit as the seed increases which is why Speedos suddenly burst into life.The Speedo has to be sensitive enough to trigger on this small voltage but it has a long cable run from the back plus the car is glass fibre. This means earth's are super critical or electrical noise gets on the signal and it won't trigger the Speedo as it should. There is also a piggy back box that sits in parallel to the Speedo input and grabs the signal to feed into the ECU. This produces a fake speed signal of between 30 and 50 mph to allow the idle control to work correctly so if you have RoverGauge you can see if the ECU is getting the speed signal as it should. In terms of trouble shooting, get the sensor and close to the toothed wheel as practical and make sure the connection at the back are clean and corrosion free to maximise the voltage.
blitzracing said:
A little science behind it all. The diff sensor is just a coil of wire around a magnet. As the toothed wheel goes past it , it alters the magnet field enough to produce a tiny voltage. This voltage goes up a bit as the seed increases which is why Speedos suddenly burst into life.The Speedo has to be sensitive enough to trigger on this small voltage but it has a long cable run from the back plus the car is glass fibre. This means earth's are super critical or electrical noise gets on the signal and it won't trigger the Speedo as it should. There is also a piggy back box that sits in parallel to the Speedo input and grabs the signal to feed into the ECU. This produces a fake speed signal of between 30 and 50 mph to allow the idle control to work correctly so if you have RoverGauge you can see if the ECU is getting the speed signal as it should. In terms of trouble shooting, get the sensor and close to the toothed wheel as practical and make sure the connection at the back are clean and corrosion free to maximise the voltage.
Thank you - this sort of expert advice is invaluable.8Speed said:
Belle427 said:
I would first start by checking the air gap at the sensor, it has been known for some sensors to be set a lot closer than others to give a stable signal.
Only other thing i can suggest is checking the compatibility of your new gauges with regards to calibration etc.
^ This.Only other thing i can suggest is checking the compatibility of your new gauges with regards to calibration etc.
My speedo stopped working recently. I bought a new sensor & it only worked sporadically after fitting.
I then found out from helpful people on this forum that the correct sensor gap is different for black bezel gauges & silver ones.
My gauges are silver bezel & once the sensor gap was reduced to 0.3 mm it worked fine.
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