Bouncing Betty Speedometer Needle

[Got_All_4]

TR250's speedo needle was bouncing all over the place and speed was unreadable. I replaced the cable hoping that would work (it did on the TR3) but it only improved it. Still slightly bounces up to 45 mph straightens up nicely at 50mph. Just a slight bounce till 70mph then smooths out. What else can be going on here. Drive gear? Speedo it's self?

 

[Tinster]

It could be the inner cable is not inserted far enough
into the speedo or tranny to fully engage.

That can result in bouncing needle.

d

 

[70herald]

Or it could be the speedo itself. I had a similar problem with my speedo until it broke the cable. Last week, I took it apart and found that the mechanism barely would turn. less than two hours work and it now works properly. To bad the engine is all partly disassembled or I could test the speedo.
Here are instructions:
https://home.comcast.net/~rhodes/speedo.pdf

 

[sail]

Look for this thread originally posted 1/28/08 by davidk "speedometer needle jumping"

https://www.britishcarforum.com/bcforum/ubbthreads.php/topics/459827/1

I just received my speedo back from Nisonger. This must be very common as it was on a preprinted card.

Important Notice: Examination of this instrument has revealed the presence of an excessive amount of oil which had entered via the flexible drive.
Before replacing it in the vehicle from which it was taken, please ensure that the inner and outer flexible drive is free from excessive lubricant and that whatever oil seal is fitted to the engine/gearbox end is in good condition and properly installed.
Lubrication of the inner core should consist of the application of a good quality low temperature grease; all excess should be wiped off with a rag before assembly of the flexible drive.

 

[angelfj1]

Also, make sure that the cable has no kinks anywhere. This is critical and be sure the cable is lubricated. Lithium grease is good for this. Is this a standard or OD transmission? If OD, check the right-angle drive to be sure it is operating smoothly.

 

[Got_All_4]

This is a standard non OD trany. I did lube the cable with a thin oil. For sure no kinks. The cable comes straight out of the trany with a long bend that is attached to the brake lines with a cable tie. Then it make the journey up through the grommets and another long bend into the fire wall and to the back of the instrument.

 

[angelfj1]

Remove the speedo from the dash but leave the end of the cable protruding so you can watch the inner cable move. Either with someone else driving or with the rear wheels off the ground, watch the cable turn as you change speed. Is the motion smooth or jerky? If it's jerky, your cable is either bad or needs better lube. Go to a motorbike shop and ask for speedo lube. Comes in a small tube like toothpaste. BUT don't over do it. Some mechanics only lube the bottom 2/3 of the cable. The lubricant can/will move up the cable and can enter the back of the speedo and really gum up the works. If the cable is fine, AND the speedo is still jerky, you need to send it for R&R

 

[TRDejaVu]

If the cable is fine, AND the speedo is still jerky, you need to send it for R&R

I followed Tony Rhodes instruction document and took mine apart over the winter. I cleaned it (quite a bit of oil sludge from the cable had got onto the drag cup), found no obvious wear items and put it back together. It worked nicely for a few miles then started sticking. Took it apart again and gave the "too clean" drag cup a little 3-in-1 oil. Has worked very nicely for about 500 miles with only the slightest occasional flicker.