Tacho Cable replacement

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Mar 7, 2005
I have replaced my tacho cable in an effort to get a sticking tacho to work. When removing the cable from the tacho drive the o-ring seal fell out - all twisted a streched. Yes I did have an oil leak from the bottom of the cable.

I have a replacement o-ring but I'm not sure if it goes above or below the circlip. My parts manual does not have that level of detail.

Any suggestions?
I am not sure what circlip your are refering to... there is a groove in the drive gear - and the o-ring fits into that groove (#3 in pic).
Tacho Cable replacement


I hope that helps.


Thanks for the photos... I haven't removes the tacho drive from the bike - only the cable.

I have just set up a 'photo-site' so I can ad photos of the parts in question.

I will try and use words and pictures to explain my problem tomorrow.


The O-ring doesn't go inside the cable, rather on the tach drive shaft inside the drive housing. The circlip is on the intermediate piece inside the lower end of the tach cable. The intermidiate adapts the square drive end of the cable to the slotted end of the tach drive shaft.
I took thet the tacho drive apart today but didn''t find what I thought I would find.

I have attached a picture of the parts.

Tacho Cable replacement

I hope this works...

The tacho drive shaft had 3 o-rings at the bottom of the shaft. There is no grove in the shaft (point 3) for an o-ring.

Any thoughts?
Tach drive


You may have the tach drive type that already has an oil seal. That would account for no o-ring groove. Do you see an seal at the top of the outer housing? If so, you don't need any o-rings.
The older style gear did not have the groove and o-ring at point 3. It just used a single o-ring at the base. (I have the older style). I've heard of people using three o-rings there instead of doing the oil seal mod.

The housing does not have a seal that I can see.

When I unscrewed the cable an o-ring seal did fall out. It was no longer an o-shape.

It may have had 4 o-rings at the bottom of the shaft to make it a tight fit.

What are my options? Get a more recent shaft with the o-ring in position 3 or get a seal on the housing?

1. Try to find the correct sized Norton O ring. (Guaranteed to leak again)
2. Replace shaft with later model that has O ring groove. (Most likely will leak again)
3. Have housing modified for seal. (Best solution)
4. Go to Industrial supply that has large selection of O rings and build pyramid of O rings in taper of housing. I heard of people getting three, I was only able to get two. So far so good, however it doesn't really count because it is a backup for the grooved O ring and I have less than 500 mi. since completed.
Tach Drive


Thinking about it, I believe the oil seal is at the bottom of the housing. I know the one drawback is that the shaft doesn't get oil after the seal conversion. Check again and if there is no seal I would go that way. The o-ring will eventually fail and leak. Having all those o-rings on your drive doesn't sound right. Without a grove cut in the shaft there's no room for then unless someone has machined out the inner part of the housing. In any case there should not be an o-ring in the cable end.
Thanks Guys & Debby,

I will purchase a new tacho gear drive with provision for the o-ring. It should work for the short-term.

I do like the idea of getting the housing modified so that I can fit a proper oil seal. I will try and find a local place that does the mod.

tach drive

As illf8ed mentioned, after the oil seal conversion is done, no engine oil is able to lube the tach drive shaft. The o-ring at the top of the shaft also restricts tach cable lubricant from this area.

I had the tach drive fix done on my Mk III about fifteen years ago. It never leaked afterwards. I don't lube the tach cable very often, perhaps annually at best. Therefore, the drive housing itself becomes another maintenance spot. This should be taken apart, cleaned and lubed at least once a year. Don't ask how I found out.
I fixed the tacho leak by installing the correct part and oil seal. Lets see how long it lasts. If it leaks again I will get the housing machined and the lip-seal installed.

I also got my tacho serviced - it was sticking. As soon as I disassembled the basic parts I could see it was a job for experts.

Everthing seemed to be working well ... until the ride on the weekend. The occassional miss developed into a permanent miss. Looks like I blew a headgasket. Well that explains one of the oil leaks.


Waiting for parts to arrive.

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