tr7triumph.com

I am hoping someone will have the answer to this annoying trait my car has !!
The speedometer jumps around randomly and by 10-15 mph at most speeds. I have tested the speedo head itself using an electric drill to drive it and it is as steady as a rock, so eliminating the speedo itself. Have fitted two new replacement cables, which seem ok for a few hundred miles but the shakes and jumping comes back .....grrrrrrr. The second cable I fitted was the shorter version as compared to the longer 'spitfire' one so it is the correct length. The routing is from the side of the gearbox drive and over the bell housing through the grommet and straight into the speedo head, so assume this to be correct.

Divine guidance and words of wisdom please before I resort to a box of matches as the cure !!

thanks

John

It either has a strange twist in the sheath, the fitting at the trans is loose and moves around or the cable is under stress where it attaches to the speedo/transmission.

You mentioned shorter/longer cables. Do you have a counter (some have one for Ox sensor or EGR. The gears can apparently dry out. I cleaned and greased mine but didn't change anything. I had a smooth speedo, then for some reason it started to go jerky (after disconnecting it to take out instrument pod). I got three cables of three slightly different lengths. I used the shortest one ultimately although I had to change the angle of the counter to connect it. I lubed it with special cable lube, you don't want it too close to speedo end as it works it's way up and into speedo (not good). It still wavered a little so I left it. I haven't noticed it the last year or so, so I guess it settled down. Now that you mentioned it I'll have to pay special attention to it to see if there still is some there. Thanks a lot. Lol.

If its a UK car I don't think it will have a counter, that was generally US cars (FI?). My speedo wavers a lot to 30mph then settles down OK. I tried a new speedo cable but it made no difference. There are no sharp kinks or anything. I suppose it could possibly be wear/backlash in the speedo drive gear. I just accepted it as part of an old car and live with it.

You are correct mine is a UK spec car and there is no gear mech as the US versions have.......perhaps the cable lube idea may help and will also have a look at any potential 'play' at the gear drive end and see if anything can be felt there....good ideas and appreciated

To close this one, I have fitted a new cable and as if by magic now have a smooth and jump free reading needle so I can only guess the other cable even though only done a few thousand miles has waved the white flag !
Hey Ho !! Much happiness again !
John