Jumpy Speedo Needle

[davidgsmith]

Whatever steady speed I may be going, the speedo needle seems to jump erratically higher to about an extra 5mph. Has anyone else had this symptom and possibly a remedy?

Thanks in advance.

David

[Rhodri]

Possibly the speedo cable on its way out, make sure that there are no tight curves in it.

[davidgsmith]

not sure whether it will be the cable or the gauge?? or both!!

[gwr]

David,

 

An erratic speedo (or tacho) is often caused by a fault in the drive to the instrument. Easiest to rectify is the drive not being seated properly in the back of the gauge. Unscrew the drive cable and make sure that the corners of the inner drive cable that goes into the back of the speedo aren't rounded. Make sure that when you refit it the cable it sits squarely on the back of the speedo and that the knurled knob is fully tightened (hand-tight). If that doesn't cure it, make sure that there are no sharp bends in the length of the cable. Make sure that the inner cable isn't broken (it's possible for the inner cable to be broken and still turn the speedo).

 

At worst one of the drive cogs in the speedo itself is broken, worn, missing teeth, or the wrong size (hence the incorrect reading). In which case a refurb/reaclibration might be needed. Costs about £50. Speedy Cables are good.

 

Let us know how you get on.

[vivdownunder]

Hi David,

 

This is a fairly common TR phenomena.

 

You can disconnect the speedo cable at the speedo, and and run a bit of light sewing machine oil down to lube it, and often this helps. But when the cable dries out or has too tight a radius, it tends to let out intermittent weird squealing sounds like some animal trapped under the dash.

 

Sometimes the inner cable frays and catches on the cable housing, and thus needs replacing.

 

When you reconnect the speedo cable, try leaving the knurled nut not done up fully tight. A bit of slack here sometimes helps.

 

Often it's down to the speedo itself needing to be cleaned of accumulated dust, and lubricated. They dry out at the input spindle where the cable slots in.

 

On rare occasions it's the input drive down at the gearbox end starting to go on the blink, but try the above first.

 

One of those should nail it.

 

Regards,

 

Viv.

[TR 2100]

This is a fairly common TR phenomena.

 

Something of an understatement! ALL the 3s and 4s I've owned 'jumped' and

they all had their own characteristics. Wavering a bit then a flick upwards was

the most common. Can't remember if this was the same for the two 6s I've

owned. I came to accept this as part of TR motoring, due to a combination of

the less-than-desirable routing with perhaps general wear and tear thrown in.

 

To expect a steady needle is a bit optimistic in my view. It may be achievable

but I don't think I would feel I was driving a TR if the needle didn't waver and

jump a bit.

 

AlanR

[Don Elliott]

I fully agree with Alan, but finally I have mine finally managed to set mine up without a quiver, never mind a flicker. I changed the speedo cable (sheath and inner cable) in my TR3A with overdrive about 6 or 7 years ago. The reason for changing at that time was that I had starter troubles and when I re-installed the starter, I didn't notice that I had squeezed the speedo cable between the starter against the engine block (and pan flange) so the sheath got pinched and ruined the cable. The one I put in 6 years ago seemed to be OK but after a while, it started swinging like crazy. I couldn't get rid of it. What I found was the outer sheath for the speedo cable had torn (shredded) where it feeds straight out from the overdrive on the TR3A (no 90 degree drive) against the hole in the floor pan and this caused friction so the inner cable was not turning as it should have been. Now I have a piece of hose about 12 to 15" long that I fitted over the small (top) end all the way along to the big end before installing the sheath and cable. This will protect the sheath from future damage by the sharp edge of the hole in my floor pan.

 

So this spring, I bought a new speedo cable and sheath and installed it. I knew it was turning because the trip- and regular-miles counters were advancing. But the needle for the MPH was not moving. On another forum, I read where the collar at the top end where it is attached to the rear of the speedometer was too long. So I checked mine and sure enough, it was 3/16" too long. In this condition, this collar which keeps the inner cable central in the sheath was adding axial pressure onto the innards of the speedo and preventing the needle from moving. Out with the cable. My neighbour has a lathe and in minutes we had this collar shorter by 3/16". But it still wouldn't work. So out came the cable for the third time. I measured the dimensions of the square end where it is inserted into the overdrive output point. The square end wouldn't go in far enough because the square end was a few thou oversize. I ground the square a bit and not it's resolved and not a quiver. I look at it at 70 MPH and I can believe that it's really working. It is rock solid.

Edited May 31, 2008 by Don Elliott