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MG Midget and Sprite Technical - Speedo not working

My speedo has stopped working. It worked for about 25 miles after the car passed its first MOT for years. I suspected a broken cable so I disconnected it at the gearbox gave the inner a good pull and nothing moved, when spinning the inner around with my fingers the speedo would flick up with a reading, reconnected the cable and it worked for about 400 yards. I have checked the connection to the speedo and this seems to be ok,disconnected at the gearbox again and the same thing spin the inner the speedo reads reconnect and no speedo. Could there be a problem with the gearbox? It does jump out of reverse..

Thanks Ian
I Pickering

The speedo cable is driven by a pinion on the output shaft on the gearbox. This can come adrift as the method of locking it to the shaft relies on the tightness of a nut rather than a keyway. There is no solution to this other than removing the gearbox inorder to strip it down to tighten it all up. On my car it does a mixture of driving and slipping, tending to slip on overrun to the extent that the speedo drops to "0". At steady speed the speedo is steady, so I wonder (based on experience of one!) whether if this is the cause as it seems to have lost all drive.

Tightening up the knurled ring on both ends of the speedo cable is a bit hit and miss. Could it be that it is feeling "tight" before it is fully home? Could this let the square drive end of the inner come out of the female part of the pair?

It is also worth looking at the gear which engages with the pinion on the gearbox (look in Moss catalogue to see what you are dealing with). You can unscrew the housing (plastic)from the gearbox and the driven gear and shaft come with it. I believe you need to drain a bit of oil out first as it is below the "full" level. I know that on the bench it is possible to use a finger in the recess to feel the pinion on gearbox shaft and check if it is really loose. Whether this can be done in situ I don't know and if it can I wonder whether you can get your finger out again!

Removing engine, gearbox and mechanic as one might be a challenge!
G Williams (Graeme)

Ian,
The cable should be free to move when pulled from one end.
To check its not broken, I would disconnect it from both ends - it should pull out - if it will not move out its likely to be broken.

Its possible the broken ends are meshing enough to give a reading when moved slowly.

I would try that first to elimate the cable.

R.
richard boobier

Ian,
the other alternative is that it could be the speedo that's be faulty (usually cable but I've had both go)

if you disconnect the cable at the speedo end and secure it where you or a passenger can see if it turns regularly as you drive the car, if necessary you could put a (very?) slight resistance to it to check the cable is fully connected
Nigel Atkins

I had speedo and cable gone when I took on my car. Most frustrating to work out what's happening. Took Nigels advice after I had replaced cable and no effect. (my original cable was snapped off at the speedo end but never having seen one I had no idea how it connected). Then put drill on speedo cable gearbox end (be careful not to damage it or the speedo by going too rough at it) and found speedo duff as well.
Dave Squire (1500)

Thanks for all the advice I have got a new cable to fit. Thought I would try this first as its still the original cable. Will try to do this over the weekend in between refurbishing a shed and going to the Coventry festival of transport at Stoneleigh.
Thanks Ian
I Pickering

I had a speedo cable on which the inner would work its way down inside the outer cable until it came out of "mesh" with the drive connection at the speedometer. After a couple of times pulling it back up so that it would reconnect, I realised that there was a disc just down inside the end of the outer cable.

The disc, plastic I think, was a push fit onto the inner cable and was intended to stop the inner from creeping down. But the disc itself had move up the cable, so wasn't doing its job any more. Pulling the inner up with pliers whilst forcing the disk down again solved the problem.

I don't know if they are all like that, or even if it was some little fix from a PO.
Guy W

Ian,
if you're at Coventry Festival of Motoring, Stoneleigh (a strange event half the time the participants aren't at the show) on Sunday pop over to the Sporting Bears Dream Rides area and say 'hello' (it'll probably be tucked away somewhere) and then you can confirm what a show stopping car I have - and what good looks, athleticism and charm I have
Nigel Atkins

Ian: You can recognise Nigel, he's the one with a handbook in his lapel.
Graeme Williams

Changed the cable today, the old one is not broken and seems to be ok. Speedo works ok tried the car on the axle stands and it reads. But the thread is not good on the nylon part it connects to on the gearbox. Does anybody have this part? as it seems no longer stocked by the normal suppliers.
Thanks Ian
I Pickering

Try ebay, or Richard Wooley will probably have one. I think my replacement came from Andy Jennings.
Graeme Williams

By the way, inside the unit there is a tiny o ring which is probably worth replacing at the same time.
Graeme Williams

Done about 50 miles today speedo worked with the new cable. I don't understand this the old cable looked fine and was not broken but hey its working now.
I Pickering

Ian,
As I mentioned earlier, the inner cables have a habit of working their way down and eventually disengage with the drive at the speedo head, even though the outer is still properly screwed on. Maybe that is all that had happened to the old one? Fitting a new cable has solved it, and may well be a good fix for some years to come.
Guy W

This thread was discussed between 18/08/2013 and 01/09/2013

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