Board logo

Speedo "jumps"
scoobyis2cool - 27/9/04 at 01:20 PM

I had my SVA this morning and there was a problem with the speedo - although it seemed accurate most of the time, every now and then the needle would jump by about 10mph and then drop back down again. This was as the inspector was accelerating gradually.

Can anyone think why this would be happening? My best guess is that the sensor is giving some kind of a fluctuating signal, would this happen if the sensor was positioned too close to the magnets or maybe if its mounting bracket was vibrating, altering the clearance between the sensor and the magnets?

Cheers

Pete

locoboy - 27/9/04 at 01:38 PM

sounds like the first port of call to me - good luck with the re-test.

ady8077 - 27/9/04 at 07:50 PM

Hi Pete

Is it a greenguage speedo with the reed switch?

If so i had a simular prob and had to move the sensor closer to the magnets, it still flicks slightly but only past 90

Adrian

scoobyis2cool - 27/9/04 at 08:04 PM

Hi Adrian,

No it's a Smiths Instruments gauge from their Telemetrix range, but it sounds like it could well be the same problem.

Did you find that it would suddenly flick up by about 10mph and then drop back to the correct value?

I'll get it up on axle stands and open up the prop tunnel tomorrow and see if I can sort it out

Cheers

Pete

GasGasGas - 27/9/04 at 08:16 PM

Could be a voltage spike, is there a voltage regulator on it or the instrument loom ?

scoobyis2cool - 27/9/04 at 08:17 PM

quote:
Originally posted by GasGasGas
Could be a voltage spike, is there a voltage regulator on it or the instrument loom ?


I don't really know what one looks like but I'm pretty sure there isn't one in my loom!

Pete

David Jenkins - 27/9/04 at 08:51 PM

quote:
Originally posted by scoobyis2cool
No it's a Smiths Instruments gauge from their Telemetrix range...


Smiths, CA and Greengauges are all the same company, working from the same address in Caerbont, S. Wales. Always useful to know, when you've got a problem.

I go for moving the sensor closer to the magnets.

Happy problem solving!

David

ady8077 - 27/9/04 at 09:04 PM

Hi Pete

Mine went about 10 mph above and below, got worst at 60 mph, my gaps about 1mm now and is steady till past 80

Adrian

Hellfire - 28/9/04 at 08:07 AM

As stated course of action... good luck with the retest!

scoobyis2cool - 28/9/04 at 09:35 AM

Well looks like the replies are pretty unanimous. I was a bit worried when I fitted the sensor, the bracket was only fairly flimsy ally and I was worried about it vibrating, if only I'd replaced it at the time!

Oh well, I'd better get out to the garage and start ripping my car apart again...

Cheers

Pete

Hellfire - 29/9/04 at 08:27 AM

Scoob - isn't that pretty much par for the course?

scoobyis2cool - 29/9/04 at 08:38 AM

quote:
Originally posted by Hellfire
Scoob - isn't that pretty much par for the course?


You're not wrong there! It seems that every week my car goes from the finished vehicle to a pile of bits and back again at least 5 times!

Pete

SteveO - 29/9/04 at 06:07 PM

I had the same problem and failed my SVA.
Its caused by too many magnets on the prop and the sensor not picking up the gaps at high speed or in my case above 50mph. i phoned CA and they told me to reduce and use 1 or 2 magnets only- used 2 which was enough to pass SVA but its not accurate; even with the gap very close. I might reduce to 1 magnet and see if it better. The bike speedo is good as a second backup.

Steve