Speedo Earth Modification

[Jonathan Kay]

Having done this a few times now I can get going again in about 15 mins

That's a wheel sensor rather than gearbox? Are you sure it's the sensor that fails first rather than an intermittent wiring problem? Which sensors are you using?

Jonathan

PS:  A resettable circuit breaker might take a few minutes off that... :-)

[tomwood]

Good news! Mine is now fixed.

special thanks to JV for the hints/tips/WN etc

In my case, the sensor was simply too close to the reluctor ring. A simple readjustment and it was all sorted. when I tested it originally the light on the end was permanently on regardless of wheel rotation, moved the sensor a bit further away and all is well.

Tom

[John Vine]

Good news, Tom.  Glad it's working OK.  For info, did you happen to measure the final gap?  They seem to work best at about 1mm.

And just to clarify for the benefit of others who may be having the same problem....yes, the sensor LED should come on as each tooth on the reluctor ring passes by, but should go off again in between.

JV

[tomwood]

Hi John,

i didn't measure it afterwards actually but I did before I adjusted anything. The gap was initially well under 1mm, probably about .75mm

I widened it a lot and then progressively moved it closer until it was lighting correctly. I would guess that the gap now is about 1mm as you suggest.

for others completing this task, to be clear the sensor lights up at the end where the cable enters it and not on the very tip that hovers over the reluctor ring.

Tom

[Garry7]

Hi Jonathan,

Confirmed the sensors each time - using the CC supplied gold plated ones!

Like the resettable circuit breaker idea though

[Jonathan Kay]

Thanks.

Is there a tried or recommended alternative sensor?

Jonathan

[Jonathan Kay]

Like the resettable circuit breaker idea though

You can get both resettable circuit breakers and replacement fuses that illuminate on blowing that physically fit sockets for blade fuses and come in appropriate ratings.

Everyone seems happy with those regardless of source.

But I don't think I've yet seen a resettable circuit breaker that illuminates on blowing... the closest would be the ones where the reset button pops out or similar.

Jonathan

[Rogercsr7]

Still in the south of France (not expecting any sympathy) with a knackered speedo. Lots of help from you good people out there and I'm poised to replace sensor and sort earth on my return to Blighty. Today I've been entertaining the locals with my head buried in the rear wheel arch confirming that the sensor does operate as it should ie the led switches on/off as the wheel rotates. As Neilcsr described, the sensor isn't lined up with the wheel very well, but it seems to work. Anyone else out there that has a slow reading speedo ( read 30, doing 80, no sticking needle) with a sensor that appears to be reading ok? Views on what else may be broken are very welcome.

Thanks, Roger

[John Vine]

When you say "switches on/off as the wheel rotates", does it light up for every tooth on the reluctor ring (44 teeth IIRC)?

And another thought...

Does the speedo register speeds below 30 correctly, or does it read low at all speeds?

If the latter, it would be worth checking that the pulse code is correct.   This is the six-digit code set via the odometer display that tells the speedo how many pulses (that is, LED on/off) per mile the sensor is sending to the speedo.  Normally, once set, the code doesn't alter, but inadvertent poking about with the trip reset rubber button can alter it by accident.

Assuming your rear tyres are 245/40 R15 CR500s, the code should be 038544 or close.

To check, turn on the ignition and press the trip reset button for 3 seconds. (Do this straightaway, before the mileage reading appears.)  The six-digit code is displayed.  If it's nowhere near 038544, I'll post up details of how to set it.

ETA: Does your odometer/trip also under-read, or does it increment in a plausible way?

JV

 

[Rogercsr7]

Thanks John, that's really interesting. Filled with fuel just before getting on the ferry and reset the trip. I wonder? Joining the Portofino bash tomorrow, but will check code as soon I get an opportunity. As far as I could tell ( car on jack, no axle stand, bright sunshine and turning hub best I could) the LED was illuminating consistently as the castellated wheel revolved. The speedo is slow across the speed range, nothing much registering below 20, then slowly dragging itself round to 30 on the dial as speed increases through 30 - 80. Defiantly a case of "go slow" not "go then stop"

thanks, Roger

[Rogercsr7]

Good morning,

Just checked the speedo code as JV advised, reading 108564 - a long way out. So a reset desirable if you could post how to do it.

Thanks, Roger

[Jonathan Kay]

Instructions for Caerbont instruments.

Jonathan

[John Vine]

Hi Roger,

Looks like that's the problem.  With your value of 108564, a displayed speed of 30 equates to around 85 true.

JK's link takes you to the correct Caerbont page.  You need the "Electronic (2004 to date)" link, which downloads a PDF. 

"Press the reset button for 2-3 seconds, the LCD will show the calibration number currently set. Each digit within the calibration number will flash in turn for approximately 2 seconds. When a digit is flashing, each depression of the reset button will increment the digit by one. Once the last (right-most) digit has been set/reset, the whole number will flash."

Then switch off the ignition to save the new value.

As I surmised above, the value for your tyres is probably 038544.  In case you have different tyres, there's a table here for a range of tyre sizes.  If the new code value is still significantly out, you can fine-tune it with a bit of simple ratio maths!

JV

[Rogercsr7]

Public thank you to JV, speedo back in operation thanks to excellent instructions. Will follow up other aspects of speedo calibration etc on my return. 

Worth mentioning that I had a backup plan. Damian of Chapman cars kindly offered to set up the speedo for me if my attempt failed. Just had to catch him at the right time as he got back to the hotel after the all night disco! Seriously though, thanks for the offer of help.

Roger

[John Vine]

Thank you for your kind words, Roger.  Glad it's all working OK.

JV