Vibration over 70mph

[John Roberts]

I've noticed it a few times by now, now that I think of it, it's fine under 70, I only feel it through the seat, not through the handlebars and not through the footpegs. Probably not relevant is the fact that the rear tyre is worn down to about 2mm, tyre pressures OK, the wheel bearings were not hot, the gearbox was no hotter than usual after a 30mile run. The engine seems OK, carbs balaced last week, it pulls very well.

Hard to know where to start looking, any suggestions welcome.

 

[fayeslane]

I've noticed it a few times by now, now that I think of it, it's fine under 70, I only feel it through the seat, not through the handlebars and not through the footpegs. Probably not relevant is the fact that the rear tyre is worn down to about 2mm, tyre pressures OK, the wheel bearings were not hot, the gearbox was no hotter than usual after a 30mile run. The engine seems OK, carbs balaced last week, it pulls very well.

Hard to know where to start looking, any suggestions welcome.

Sounds like you are due for a new rear tyre pretty soon so I would replace it now and get it properly balanced to eliminate this as a source of the vibration. Any wheel weights gone missing off the rear wheel?

 

[John Roberts]

Now that I think of it the frequency is a lot higher than that produced from an out-of-balance tyre, I'm sorry to have mentioned the tyre now, it was misleading.

What sort of symptoms would a knackered drive shaft give, how could I check that?

 

[bighair]

Vibes

Hi john
Just to confirm speed related and not rpm ?
I take it you have tried it at 70 in different gears ?
Whats it like a 70 and you pull the clutch ?

 

[John Roberts]

Hi john
Just to confirm speed related and not rpm ?
I take it you have tried it at 70 in different gears ?
Whats it like a 70 and you pull the clutch ?

I'll let you know ...

Damn, the more I think about it, the more I think it's the shaft joints. How much of a job would that be, I wonder?

 

[John Roberts]

Job done, and it is a carrot. It was the drive shaft; hard to be certain of any wear in situ, there was also the normal play in the bevel drive and the gearbox to confuse things, and worryingly difficult to feel any after taking it out. Confirmed by putting the flange in a vice and clamping a self-grip on the shaft, you could feel a click when moving the grips from side to side. Actually, I got several second opinions (does that make sense?) and everyone was puzzled as to how hard it was to "tune in" to the slop.

A spirited ride just now provided the final confirmation: the vibration has gone. Feck, it does feel good.

 

[Richard A]

Thanks, John, all worn drive shaft symptom reports on these boards are useful... they certainly help me improve my confidence in being able to spot them developing.

 

[John Roberts]

Thanks, John, all worn drive shaft symptom reports on these boards are useful... they certainly help me improve my confidence in being able to spot them developing.

Here to help!

What I thought was that, since I wasn't sure of the cause of such a vibration, then the chances were that there was someone else in the same pickle, and that the diagnosis might be of use to them.

As things turned out, my "steaming in" without my usual process off humming & ha-ing and much scratching of my head paid off, the reason I took the plunge was that I simply had to get the bike ready for a biking holiday with some mates. A clear case of fool(s) rushing in ...

 

[(RIP) Bin Ridin]

Hi John, what did you do, rebuild, replace? Where did you get the bits / shaft from? Bin

 

[John Roberts]

Hi John, what did you do, rebuild, replace? Where did you get the bits / shaft from? Bin

I got a reconditioned shaft from, as ever, Motor Works. They were willing to take it back if it wasn't needed; I had explained the pressure I was under to get the vibration sorted before my trip with the lads, so I ordered one and went ahead and got the old one out ready for its arrival.

If you are interested, there's another, parallel thread at: http://www.ukgser.com/forums/showthread.php?t=311069
It's more about the possibility of changing the U/J (universal joint) itself rather than getting a new or reconditioned shaft. My replacement shaft, unlike the original, has circlips holding the joint in place; this should be DIY-repairable should that be neccessary in the future. Actually there's some excellent advice there on protection from Scottish midges too.

As to the replacement of the pesky swinging arm rubber boot, see another thread at:
http://www.ukgser.com/forums/showthread.php?t=311591
It seems that the BMW item is both easier to get on and also lasts longer: bugger.

Another thread re. torqueing things up at:
http://www.ukgser.com/forums/showthread.php?t=311556

 

[(RIP) Bin Ridin]

Thanks John, I have a vibe in my r100 which I think may be shaft-related. Bin