5 speed gearbox - speedo drive gear - what holds the worm on the output shaft?

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Richard Price
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5 speed gearbox - speedo drive gear - what holds the worm on the output shaft?

I've been looking at a car today where the speedo has stopped working.

Having proved the wiring and the sender, I found that the speedo drive gear was not turning. I've removed the cap and the speedo drive gear, but it seems that the worm on the gearbox output shaft is not in the correct position.

What holds the worm gear on the output shaft? Is it simply pressed into position, and retained by friction?

SM25T
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Yes ... I think it is crimped in place.
Richard Price
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So, If I make a hole in the tunnel, I should be able to lever it back into position.....

SM25T
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Have you prised the blanking cap off on the nearside ? You can then just push gear out of that hole then. New cap can be pressed into place with a bit of silicone around the edge ... using a big pair of sliding jaw pipe fitting pliers ... all in situ.
Richard Price
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Yes, the cap is off, and the driven gear is out. when the driven gear is in place, its not engaging with the worm...

I can just about feel the worm, and tell that its not aligned with the driven gear :-(

SM25T
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Ahhh .... I was thinking of gear on speedo drive shaft ..... can't help ref the worm .... Phone call to Road & Race ?
BlackSeven
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Assuming this is a type 9 the worm gear is a friction fit onto the main shaft. The worm gear has an internal star shape and the main shaft is plain. I have pressed a number of these on and off type 9 main shafts shafts and they have always been secure - requiring a hydraulic press. If yours has somehow come adrift, in order to investigate and repair I imagine you'll be looking at a replacement worm gear which will require removal of the box, and then the tail housing (this will require you to mark and remove the 5th gear locking plate first). Even if you could somehow lever the worm gear back into place with the box and tail housing in-situ I can't see how you would avoid the worm gear moving along the shaft again?

Rob

Keith_T
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Think I had something similar.   Millwood told me a fix would involve removing and dismantling gearbox.

Ended up fitting a Racetech electronic speedo which seemed easier and much cheaper option (once I'd bought the sensor bracket from Caterham).

Best of luck!

BlackSeven
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An electronic speedo and stand alone sensor sounds like the best option to me although if you are handy with the spanners you can have the engine and box out of a seven in a couple of hours and assuming you have access to a press, replacement of the worm gear is very straightforward.

Rob

Paul Deslandes
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Richard

If you find that you need to dismantle the box to realign the speedo drive gear, I would recommend that you get hold of a copy of the Haynes Gearbox Overhaul Manual which has details of how to take Ford B & N gearboxes apart and reassemble, including the position of the drive gear on the output shaft.  This is specified as 123 - 124mm between the back of the drive gear and the next item towards the gears which is a retaining circlip. 

Depending on which way it's moved, you may need either a puller if the gap is too small, or a means to press it further onto the shaft if it's too great.  You might be able to move it either way using a big spanner over the shaft to protect the gear and an even bigger hammer to tap it along.  Alternatively you can improvise a press as the end of the shaft has a Whitworth thread into which you can screw suitable studding.  Using a nut and large washer on the studding and a piece of tubing etc you can press the gear along the shaft.

Seems odd that it should have moved though and I wonder whether it was repositioned incorrectly during an earlier rebuild and they couldn't be bothered to take it all apart again to put it right.

Paul

BlackSeven
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I'd urge caution in any effort to reposition the existing worm gear on the shaft; very likely to be a waste of time I'm afraid. The two components need to be an interference fit. If a steel worm gear interference fitted onto a steel shaft has "walked" along the shaft through nothing more than its interaction with a nylon speedo cable drive gear then something isn't right with the relative sizing of the gear and shaft and the same will almost certainly happen again. I'd either do the job properly and fit a new worm gear (they are widely available and not expensive) or go with an electronically driven speedo. 

Rob