I fitted a new speedo cable last week and have had problems with the speedo suddenly stop working after a km or two..

Today I pulled the cable out from the dash and put a small spring from a biro pen over the end of the cable behind the speedo to see if that would help keep some tension on it but still no good..

Can anyone tell me what could be the problem why it just stops working???

Mine used to occasionally do this but it was a smiths mini K center console type speedo. What used to happen was that the needle used to get stuck because the screws holding the speedo onto the tripple guage center binnacle were on too tight hence pushing the chrome suround and glass and subsequently the face of the speedo into the speedo housing. This was enough to make the weak speedo needle stick.

Another thing, the speedo is driven by a tiny square cable inside of the speedo cable. Are you sure that the replacement speedo cable is
1) screwed or clipped on tight so that the drive is not spinning inside the speedo or engine end?
2) did the new cable have sufficient amount of that center cable sticking out? I suspect that some of the after market cables are not exactly to spec...

One other thing to look at is that your new cable is not too short or too long. Short can lead to the above. Long means it maybe too cinked and hence bounces around or worste, snap.

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Lillee - 1969 Morris Mini K

1) screwed or clipped on tight so that the drive is not spinning inside the speedo or engine end?
As far as I can tell it all seems good.

2) did the new cable have sufficient amount of that center cable sticking out? I suspect that some of the after market cables are not exactly to spec...

The new cable is 45mm longer than the original.. Trouble was that the old one had the same problem near the end of its life..

Check to see if the inner drive is turning when the wheels turn....you can do this by hand with it safely up on stands and in gear or you can remove the speedo and take it for a drive around the block.

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"Show me the Mini!"

Just pulled it all apart again and put the old cable back in to try it. I can see the inner cable turning when the wheels are turned but when I put the connection on to the back of the speedo it just won't go, well it will go for about 10 secs then the needle stops working..

Got me beat at the moment but I will keep trying tomorrow..

Grab hold of the top of cable, see if you can turn it by hand. I've seen the square drive bit at bottom wear nearly round, then they gouge a groove in the cable and it stops being driven.....

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

The inner cable turns ok by hand Doc. I have just got in from the shed after having another go at it, couldn't wait until tomorrow and it seems to be working ok now.

I ended up using the old cable and it seems the trick is to have the cable as straight as possible. A drive tomorrow will tell me if it remains fixed..

45cm too long sounds far too long. You will have problems with kinking and all sort of issues. If the old one works then just lube that up and continue using it. It should work until the inside cable eventually snaps.

If you suspect it to be the speedo the easiest thing to do is connected to the engine side of the cable to a power drill using a suitable socket, or carefully tightenning it onto the chuck of the drill and spin it. If the speedo spins as normal then it's not the drive side of the speedo.

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Lillee - 1969 Morris Mini K

45mm to long..

I have tried it with a drill and the speedo itself works ok..