HOW DO I IDENTIFY REPLACEMENT TYPE OF SPEED SENSOR - 4.3

[Griff43V8]

Suspect gearbox speed sensor needs replacement

92 J reg 4.3, black rimmed instruments

what reading should a functioning sensor have?

If defective, how do I identify replacement type?

Not been under for long time, is it just a sump plug type hall sensor fitting? - Dont want to disturb any drive shaft or anything - will oil come out at that height?

thanks

[phillpot]

The early cars had the speedo sensor in the gearbox, same as the V8s, I don't know when they changed to the sensor thingy fitted to the diff?

If it is like this one you then have a choice of 4 or 8 pulse item. Get it wrong and you speedo will read half or double speed!

This is a 4 pulse, left over from my Griffith ownership days and speedo "issues". There does not appear to be any visual identification other than looking into a tiny hole and counting the segments go past per full turn of the cog?

[Griff43V8]

OOOH, didnt want to disturb any gear / have oil leak

would ideally like to check elec resistance if value is known first

Yes, it is definitely in the gearbox

Dont suppose u know any TVR enthusiast spare time mechanics who would do some basic mechanical recommissioning in Kettering Northants?

Arthritic pensioner!

Need fuel pipes, clutch cylinders replacing to drive to local MOT

rust free 23k mls 4.3 in dry garage

cheers

[phillpot]

No oil comes out when you change it, but it is a fiddle to get at.

Electronics aren't my strong point but I don't think there is a resistance to check???


sorry but can't help with a mechanic.

[Griff43V8]

ok, thks

[Loubaruch]

If the later speed sensor that sits above the propshaft on my 1996 Griffith is a similar electronic device to your gearbox sensor then this may be useful.

Resistance = 35 Ohms

With the multimeter on its lowest volts range (1 volt on mine) By passing a powerful magnet across the face of the sensor the voltmeter gives a small kick.

My sensor is otherwise working fine, and has been removed during a body lift to sort the outriggers.

[blitzracing]

I think the speed sensor shown in the photos previously is for the LT77 gear box from the SD1 used in early Griffs. This is a really odd sort of inductive trigger unit that uses power from the speedo to make it work, so its not passive and cant be simply resistance tested and unfortunately only swapping it out is the best way of testing. I suspect they changed to the toothed wheel on the diff when changing to the Ford gearbox. The latter type of sensor is nothing more than a coil wrapped around a magnet that produces a tiny pulse as the metal teeth go past the magnetic end. As already stated this can be simply resistance checked once unplugged. There is not much to go wrong, but water can get into it via the wires and corrode in the internal solder joints so it goes open circuit.

[Griff43V8]

blitzracing said:

I think the speed sensor shown in the photos previously is for the LT77 gear box from the SD1 used in early Griffs. This is a really odd sort of inductive trigger unit that uses power from the speedo to make it work, so its not passive and cant be simply resistance tested and unfortunately only swapping it out is the best way of testing. I suspect they changed to the toothed wheel on the diff when changing to the Ford gearbox. The latter type of sensor is nothing more than a coil wrapped around a magnet that produces a tiny pulse as the metal teeth go past the magnetic end. As already stated this can be simply resistance checked once unplugged. There is not much to go wrong, but water can get into it via the wires and corrode in the internal solder joints so it goes open circuit.

Many thanks for clearing that up, now wondering how i can check out other speedo bits before buying a £150 sensor!

Was working fine, then next time i drove it, it wasnt! Cant rule out mice I guess - didnt want to take dash out again.. - cant even remember how to do it (just wood fascia)