Hi All,
Trying to work out why my speedo suddenly stopped working, hoping the brains trust might be able to confirm. It's a 3 gauge cluster from a 72 leyland but it's got a 1275 out of a 1100s. Square bit in the back of the gauge makes the speedo move, so gauge is ok. The cable wouldn't turn while still connected at the gearbox, but disconnected it turns so it doesn't appear to be the cable. When it was connected and I moved the car back and forward the cable wouldn't turn. Seems like it might be a ceased/broken speedo drive? Dreading it might be an engine out job. Note car has been sitting for 20+ years and I've only just been driving it up and down the driveway recently, very close to getting it registered and don't think I'll be able to do that without a working speedo

Not really able to diagnose the problem, but most of the speedo drive parts are at the radiator end of the gearbox and should be accessible without removing the power unit.
When you moved the car 'back and forward', was it in neutral? If so, the speedo drive won't turn as it is turned by the mainshaft in the gearbox, which won't turn in neutral.
If you don't get more information before tomorrow, I can photo the bits you may need to remove to access the speedo drive parts.

I'm pretty sure the speedo drive turns relative to the road wheels regardless of what gear the car is in - including neutral.

Given whats already been tested, if you're convinced its not the cable I'd move onto trying to remove the drive gear for inspection.
It might indicate worn teeth, or the square drive peg could have rounded off.

You are right. The wheels will turn the mainshaft through the crownwheel and pinion. Apologies for misleading.

I would double check the gearbox end where the cable goes in.
Sometimes the nylon gear with the shaft fails - the square in the shaft can round.
This bit can be removed with the engine in situ. 7/16" head bolt comes out and then you can lift the alloy bit that holds the shaft in. Shaft can then come out. This but can be tight to lift out.
An akward job, especially if you have rubber cross drive shaft couplings.
But before you get into this, double check what you have done - speedo turns and cable turns freely.

There’s the bolt on the top which holds on the “speedo pinion bush assembly” - under this is the speedo pinion gear which should have a square recess. Then there’s the two bolts and the blanking plate, under this is the other speedo gear

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Ok so took the radiator out and found the problem, it appears when taking out the dash I may have pulled on the speedo cable and it's come away from the drive gear as and instead of seating centred on the inside it was skewed and on the outside doing nothing. Just fighting with the two horizontal bolts on the radiator bracket, stupidly took them out before realising what was the issue