Speedo, just when I thought I'd fixed it

[Garry7]

Finally got around to sorting this today. First had to redo the mod that CC had done, they had wedged the twisted cable ends into the connector pin and stuck with sealant, proper job? All came out when we had to disconnect it when car stopped on the Italian tour due to failed rear wheel sensor.

Soldered the cable in then refitted connector and adjusted sender to same gap as the previous one.

Test drive gives a flickering needle up to 55-60 then settles to rock steady as speed increases. Mileage recording is way out too, recorded about 12 miles on approx 25 mile drive.

So, have I messed the earthing up or is the adjustment still not right?

All ideas gratefully received, this is driving me nuts, 5th sender in 4 years!

Thanks, Garry

[Jonathan Kay]

That's a very big number of replacements: did it ever work perfectly?

Is it the sort for which there's a factory advisory note on earthing differently?

Any relation to engine temperature: there was a fascinating report of something like that...

I'd go for the gap and try adjusting it regardless of what it was before. Is yours the sort where the sensor unit flickers when it's working?

Jonathan

[Garry7]

Hi Jonathan, it has worked properly between failures, yes. When they fail the instrument fuse blows and the car stops dead. Roadside cure is to disconnect the sensor, replace the fuse and carry on!

Not temperature related at all. Will make some adjustments next time it's dry.

Sensor should flicker but I've no idea how you are supposed to see it.

[John Vine]

Sounds like either (1) the sensor air-gap is wrong (could be too small or too big), or (2) the loom earth wire between sensor and speedo is picking up stray interference. 

Re 1:

Set the air-gap at 1.0mm. Switch on ignition and turn the hub slowly.  The little LED at the tip of the sensor (where the wire enters) should light up as each tooth on the reluctor ring passes by.  Check this for a full revolution of the hub.  If the LED fails to light at a particular tooth, reduce the sensor gap until it does light up.  Then run the test again until the LED lights up for every tooth.

Re 2:

CC's Workshop Notice WN572 describes an earth mod to reduce/eliminate this interference.  It involves creating a new chassis earthing point much closer to the sensor.  If you need a copy of WN572, blatmail me your email address.

JV

[Jonathan Kay]

I think he's done 2 from a previous thread...

I can't explain the blowing fuses from an intermittent opening of an earth. But did you ever try replacing the fuse without touching the sensor?

Doesn't sound like that heat-related wiring saga (can anyone find it?) but how about intermittent moisture causing a feed to short?

Jonathan

[John Vine]

I think he's done 2 from a previous thread...

Ah, I didn't know that.  I think the fuse-blowing could be caused by chafing of the sensor lead leading to a short.

JV

[Jonathan Kay]

The start of the saga, including someone offering helpful advice on setting the sensor... 

;-)

Jonathan

[John Vine]

Ho ho!  I'd forgotten that thread.  Oh well....as someone once said:  "I don't recall ever suffering from memory problems".

JV

[Garry7]

Hi JV,

Tried swapping the fuse first when it failed on the tour.

CC did the mod, bodged it as described above, love the professionals.

Thanks for describing the light trick, will do that next, always wondered what flashed where :-).

Wiil adjust as you suggest, thanks.

[Ian B]

Not really a fix, but maybe a possible alternative if all else fails?: 

http://www.carbuildersolutions.com/uk/gps-speedo-signal-converter

[Garry7]

Finally had some time to get back to this today.

Thanks to JV I finally figured out the light trick, two attempts at adjustment and it seems to be working correctly for both speed and mileage, fingers crossed it lasts a while.

[Jonathan Kay]

Well done.

Jonathan

[Garry7]

Cheers, it was really beginning to get me annoyed  

looking forward to getting out now.

[John Vine]

Well done, Garry.  Pleased I could help.

JV

[nigelpugh]

Hi Guys,

just another word of thanks for this information, it helped me sort out the intermittent speedo on my new Superlight Twenty.

i did check the gap in the sensor when I built the car, but for some reason the speedo just stopped working at about 70mph.

Checked it again yesterday, and made sure the gap was as close to 1mm as I could get, and also made sure we had trigger on the led on the sensor for a full rotation of the drive shaft.

quick test drive and I am pleased to report that it works fine at all speeds now.

thanks again for the information.

oh and such a nice sunny evening as we had last night,,we even went out for a spin to our local classic car meet,where as you can see my little Superlight had some Interetsing company!

 

 

[Martin J]

Just to add for those with this type of speed senor......

Mine failed & when I investigated the fine wire just fell out of the sensor. A new one was sourced from CC, not cheap at £65 & that lasted a few days before blowing the ignition fuse & leaving me stranded.  Once recovered home (I wasn't far away but had no tools or spare fuses with me) I unplugged the sensor, replaced the fuse & the engine ran perfectly. 

I ran it for a while like that (satnav for speed) before CC swapped it out. 

So, if you get stuck the car runs perfectly without the sensor.