Speedo going abit mad intermittently

[les5709]

Hi All,

Having an intermittent issue with the speedo. Seems to just have a mind of its own at times and flicks up to all sorts of speeds. It can also just dies and sit at zero.

Anyone have any suggestions that I can look at?

If i hook it up to the computer with the Noble software is it likely to tell me if the sensor was faulty?

Thanks again
Steve

[Lucozade]

My 3R has the sensor in the drivers side front wheel rear hub. My speedo goes crazy after heavy rain or if I've washed it.

You could try sanding off excess rust from the hub nut.

A good test is to put the ignition on and have a look to see if the light at the sensor illuminates. If it doesn't try repositioning it by loosening the nut.

Eventually you will have to change the sensor.

[daddysumo]

Lucozade said:

My 3R has the sensor in the drivers side front wheel rear hub. My speedo goes crazy after heavy rain or if I've washed it.

You could try sanding off excess rust from the hub nut.

A good test is to put the ignition on and have a look to see if the light at the sensor illuminates. If it doesn't try repositioning it by loosening the nut.

Eventually you will have to change the sensor.

Steves is a 2.5 so will be gearbox driven if it still has the 5 speed...

[sjc]

That was the first sign of my alternator packing up.

[les5709]

sjc said:

That was the first sign of my alternator packing up.

I hope not, I only had it replaced and all the wiring done around it last year. Surely they cant be that hard on alternators

[les5709]

daddysumo said:

Lucozade said:

My 3R has the sensor in the drivers side front wheel rear hub. My speedo goes crazy after heavy rain or if I've washed it.

You could try sanding off excess rust from the hub nut.

A good test is to put the ignition on and have a look to see if the light at the sensor illuminates. If it doesn't try repositioning it by loosening the nut.

Eventually you will have to change the sensor.

Steves is a 2.5 so will be gearbox driven if it still has the 5 speed...

Could the same be applied to excess rust etc around the sensor at the gearbox?

[sjc]

les5709 said:

sjc said:

That was the first sign of my alternator packing up.

I hope not, I only had it replaced and all the wiring done around it last year. Surely they cant be that hard on alternators

My original lasted 7 years so hopefully not!

[Gadgeroonie]

Lucozade said:

My 3R has the sensor in the drivers side front wheel rear hub. My speedo goes crazy after heavy rain or if I've washed it.

You could try sanding off excess rust from the hub nut.

A good test is to put the ignition on and have a look to see if the light at the sensor illuminates. If it doesn't try repositioning it by loosening the nut.

Eventually you will have to change the sensor.

i think it is a magnetic sensor not an optical one

is it possible to reduce the air gap between the hub and the sensor ?

[D_G]

You can try giving the gearbox connector a clean, it's the three pin one poking out the top of the gearbox. For testing it has a 12v ignition, earth and DC output for the speedo.

[AMG Merc]

D_G said:

You can try giving the gearbox connector a clean, it's the three pin one poking out the top of the gearbox. For testing it has a 12v ignition, earth and DC output for the speedo.

DG, AFAIK earlier 5-speeders took an electric feed directly from the gearbox via the loom. OP must have a 6-speed box - they take the pickup from the hub sensor - pain in the butt that the setup is.

[AMG Merc]

Steve, firstly TADS (eventually)!.

Inspect the sensor, is it pointing squarly at a tooth? Try drying the sensor off with a hairdryer (this cured mine for a couple of years) - and before any of you smart feers comments why I've got a hairdryer in the house - STOP NOW

I wouldn't bother moving the sensor closer to/from the toothed spigot wheel as its rarely the problem. Basically the sensor has a shelf life as it lives and works in a nasty place Unfortunatley with this setup, the factory (and TVR used to do this too) drilles a hole in the hub carrier and then permamently glues the sensor in. Process is hub hang off (or right off), drill old sensor out, fit new one, run new cable back to dash. They cost around £80 plus up to 3 hours labour depending on how difficult it is to remove the old one.

[alex s]

Its a 5 speed. Will be the sensor/wiring on the gearbox. As bondy said, no hub sensor on the 5 speed. When I had a 5 speed box it did this. was a short on the wiring at the gearbox sensor.

[brappage]

Mine is not as intermittent as the Op's but the revs and speedo do seem to "jump" in small incriments as opposed to a clean smooth sweep, not sure if this is a common thing or could be related to something similar.

[Hollowpockets]

My speedo is also jumping all over the place, sometimes stays on 0, sometimes bounces to 190 but never reads right. Got a new sensor, how easy are they to change? G

[daddysumo]

Hollowpockets said:

My speedo is also jumping all over the place, sometimes stays on 0, sometimes bounces to 190 but never reads right. Got a new sensor, how easy are they to change? G

Hardest part is knocking the old sensor out.. especially if done on the car with the trigger wheel still in place. After that just bond/mastic the new one in with 0.5 mm ish gap to the trigger wheels highest point using so called adjusting nut..

[Hollowpockets]

Cheers Steve,

[Rob_W]

See if you have a really small spanner or buy a really cheap one and grind off as much as you can to get it inside the upright to loosen off/tighten up. The sensor does need to be close.

[Gadgeroonie]

les5709 said:

I hope not, I only had it replaced and all the wiring done around it last year. Surely they cant be that hard on alternators

i heard if you rev a 2.5 hard it can overcharge and will eventually fry the alternator

[les5709]

Hi all,

I been away from the net a few days so thanks for all your tips and suggestions.

Steve