TR2/3/3A TR3 Tach cable keeps braking

[Coastalman]

Hello to the Triumph area of the BCF. I usually hang out in the Austin Healey area, but today I am asking for help for an older friend of mine who has a TR3. His car tach was doing fine last year and toward the end of the summer the tach cable broke right at the connection to the distributor. He ordered a new cable, installed it and it worked for about 15 minutes and then broke at the same location. If those of you who have fixed a problem like this would guide me, I'll help my friend fix the problem. He has ordered another cable, but is hesitant to install it until he can figure out what caused the other cables to break. Thanks for any help!
Charlie

 

[TR3driver]

My guess, the bushing inside the tach head is dry. When it's cool, it still turns with only light drag, but the drag is enough to cause it to get hot and bind after running for awhile. Had the same problem with one of my Stags' speedo (except it was the angle drive that kept breaking).

Very careful lubrication might fix it (just one or two drops of 3-in-1 or similar, to the edge of the bushing inside where the cable attaches), but it's probably better to have the head serviced (or replaced, which is what I did).

 

[CJD]

It sounds like the end fitting for the cable sheath may be bent...or just not seating completely straight into the drive. That puts the cable into the drive at an angle. When it spins, it then acts like a little fatigue machine.

John