Speedo broken (4 speed box) - obvious things checked

[ashaughnessy]

My speedo isn't working. I have done the following checks:

1) Unscrewed cable from back of speedo, jacked up rear, driven the wheels on the engine, checked to see if the square inner cable was rotating - it wasn't.

2) Removed cable from gear box and gave visual inspection, looked OK. Replaced. Still didn't work (did check 1 again)

3) With cable attached to gearbox but disconnected from speedo, I couldn't turn the square inner cable by hand. With cable disconnected at both ends, I could turn the inner cable by hand (though note, in this case I was turning the inner cable at the gearbox end)

 

The gearbox is a four speed. There is no right angle drive, the cable goes straight onto the box.

 

The possible diagnoses seem to be:

1) The drive inside the gearbox is broken in some way. Is this likely and how is it fixed?

2) The cable is broken. It could possibly be snapped in the middle - the top section could be seized but the bottom section free. To check this I should disconnect it from both ends again and see if I can turn the top section. I only thought of this after I'd put it all back together again (damn!).

 

I'm hoping for diagnosis 2, which I will need to check next weekend, but just in case it isn't what about diagnosis 1 ?

 

Thanks

Anthony

 

[Allan Haighton]

For what its worth 2) is more likely. I've had 2 cables break - in each case a few inches in from the gearbox end. Seems that the bend radius as the cable exits the gearbox connection is critical.

The drive in the gearbox is a plastic pinion driven by a helical gear on the output shaft. Cant see why it should fail unless its been jammed in some way. If it is the pinion, it'll be an engine/gearbox out job.

[Chelspeed]

The worst case would be for the drive gear to have moved. It's a press fit on the gearbox output shaft and sometimes comes loose and moves along the output shaft, so it's not in the right place to drive the plastic driven gear and the speedo stops. Happened to mine at 629 miles, I know that number by heart because the speedo sat on that mileage for about 6 months before I fixed it. The only fix is gearbox out and press the gear back into the right place, mine had a dab of spot weld added to make sure it didn't move again.

 

Next best will be the plastic driven gear. This is inserted into the gearbox from under the big domed metal cap on the passenger side of the output casing opposite where the speedo cable enters the box. Never heard of this failing though. I haven't looked but would think there's enough room inside the tunnel to lever this cap out and remove the plastic driven gear for inspection.

 

Easiest will be a cable failure so lets hope it's that.

 

Personally I would take this as the perfect opportunity to change to an electronic speedo of some kind. Most can be driven off the front wheel disc bolts so you can take the speedo cable off and bin it.

[Nigel Riches]

Anthony, as previously noted the drive gear fitted to the output shaft can become misplaced, yes that happened to me also, another possibility, has the drive gear that attaches to the speedo cable seized in the housing, and chewed all the teeth off it, check it out, jack up the rear axle and have someone turn the road wheel, you should be able to see the speedo drive output gear turning.

The right angle speedo drive unit is money well spent to cure broken speedo cable problems, fitted mine back in......... the sands of time pass by... can't remember, but have had no further speedo faults, hope this has been of some assistance regards, and Happy New Year, 2hr 58m to go. Nigel.