Speedo Problem

[HeyAndy]

Speedo has packed up although the mileometer still works. Any ideas? Not sure where to look or start.

Your thoughts and ideas are welcome. MOT due next week. Gulp!!

[blaineuk]

should still pass the MOT as long as you don't say anything

[york33]

Well yes, either hope he doesn't notice it

or

Send it off for repair quickly, mine behaved like that when I got her. Sent it off, back two days later fully functional.

cheers
Dave

[wedg1e]

If the milo is still running, the cable must be intact. Usual speedo design: the cable engages with a drive shaft inside the speedo instrument, which is generally sealed to stop tampering (usually the bezel that holds the glass in, is crimped around a flange on the front of the instrument housing. Almost impossible to remove without leaving major evidence!).
The drive shaft has a 'worm drive' on it, which meshes with the mileometer mechanism. Hence the 'clocking' trick of using a Black and Decker on the cable to wind off a few miles; since the milo is permanently driven it works both ways...
The end of the drive shaft has a circular magnet on it: this fits inside (but doesn't touch) a steel cup. The cup is attached to the rear of the speedo needle, and there's a return spring to swing the needle down to zero.
So... as the cable spins the drive shaft, the magnet induces a magnetic field in the steel cup, which lifts the speedo needle. The tension of the return spring and the magnetic field strength effectively determine the response of the instrument.
If the cable snaps, the mileometer doesn't get driven. In your case it is, so either the needle is stuck, the magnet has fallen off or evil forces are at work on the gubbins (technical term ).


Of course the above is complete bollocks with a electronic speedo... but you wouldn't normally find one of those on a Wedge...


Ian

[bluewedge350]

The speedo isn't required for an MOT, you simply need a method for determining the speed of the car, and the rev counter is deemed to be ok for that... as long as you can memorise the mph/1000rpm in each gear

John

[HeyAndy]

Thanx so far! I'm gonna give speedy cables a ring to see if they will recon the speedo. Not a serious problem I know but annoying just the same. I'll let you know how I get on.

[york33]

www.jdo1.com is where mine went. Think he's a one man band but job done well

[grady]

Or use/mount a hand-held GPS. Grady