Speedo jumping about

[kojak]

Cant use search as it aint working.

My speedo needle is jumping about but the mileometer is ok. Any ideas?

[Tanguero]

Crud in the speedo sensor gap or it needs adjusting. Its on the drivers side of the diff. A single thickness of paper is about the right gap.

[PuffsBack]

Speedo sensor, thats what mine did before giving up the ghost. Changed mine successfully a few weeks back

http://www.pistonheads.com/gassing/topic.asp?h=0&a... Sensor Part Number&mid=49498

[kojak]

Cheers. Will have a look

[optimax sniffer]

Check the speedo transducer gap as suggested, but it could also time for a big fuse change.

When my speedo started acting up it was down to the alternator breaking down and supplying wildly differing outputs, any where from +14v to negative numbers!

[kojak]

Never thought of the big fuse. Had probs with rev counter few years ago which turned out to be big fuse. Didnt realise it could affect the speedo.

Cheers

[Gazzab]

Have you forgotten to secure your specs properly?

[kevin63]

I'm on my third speedo sensor now, I may just have bad luck but it does generally seem a common problem on TVRs.

[cerbera8]

Sometimes speedo sensors fix themselves. My speedo stopped working and started working again after a few days. That was a couple of months ago now. Been fine since

[kojak]

Its stopped working now. Even the mileometer has stopped. I'll leave it a while and see if it corrects itself. As if....lol.

[kevin63]

kojak said:

Its stopped working now. Even the mileometer has stopped. I'll leave it a while and see if it corrects itself. As if....lol.

You never know as I've had a speedo bulb go that seems to have repaired it's self, after all, TVRs are special cars with special powers

[vroom]

Speedo sensors rarely fail- unless the clearance is set too small such that they 'interfere' on a hot day due to expansion resulting in internal damage!

What does fail is the poor wiring back to the dash etc...

I've had 2 TVRs with previous history of replacement sensors which only temporarily cure the prob.

First check the gap between toothed wheel and the sensor head and the wiring before changing...

Also on one Chim, I had a dry joint in the dash between the speedo head and the pulse converter. It was a nightmare to find.

All imho of course.

[Rufus Roughcut]

vroom said:

........... poor wiring back to the dash etc...

^^ as Nick said.

When my speedo went intermittent, i.e. anything below 40, I traced it back to the connector plug near the diff.
On inspection there were no obvious signs of anything wrong, a squirt of contact cleaner and all's well.
Is it possible the signal is so small that any 'resistance' in the wiring could cause problems?