Vibration around 80 mph-

[Roger Chatterton]

I have noticed that when bike gets to around 75 - 80 mph ( 5K rpm), there is a kind of rumbling/vibration that seems to come from the rear of the bike. Push past 80, or drop below 75, the rumbling goes away.
Bike is 100 GS PD, Tourance tyres ( new-ish), gearbox has been reconditioned about 15K miles ago, and drive shaft seemed good.
The bike has, as far as I know , done around 50K miles. There is no noticeable notch when spinning the rear wheel and no wobble to rear wheel when riding, and bike is rock steady up to 90+ mph.

So, any ideas ? I am concerned that it might be the final drive bearing, or drive shaft ....

 

[(RIP) pastyman]

Wheel balance??

 

[Roger Chatterton]

Pastyman - thanks, not impossible, but not really that kind of vibration- more a rumbling, but I will put that "on the list" ! But easy solution if that's what it is .

 

[Mike the Bike]

It sounds like something is simply resonating at that speed - a bit like a bridge goes crazy in a certain wind speed. It can't be much else if it comes and goes either side of that speed band.

So difficult to easily fix - maybe a slight tweak to carburation ?

 

[Beemerboff]

Peel back the rubber boots and check both front and rear UJs - even the slightest bit play and they should be replaced - they can let go and it mkes a heck of a mess when that happens.

 

[Voyager]

Check the rubber mounting bobbin on the rear of the silencer.

I had one come apart (its not obvious at rest) and was convinced it was the driveshaft.

Easy fix

Bob.

 

[Mick13]

Could be rear wheel balancing

 

[Roger Chatterton]

Thanks for the suggestions -checked the silencer mounting rubber bobbin, and that looks fine, and silencer very firmly mounted.
Could be wheel balancing - MOT time soon, so might get wheel checked then.
Sympathetic resonances - could be, but not that kind of vibration somehow.

So, had another thought - could the "slime" in the tyres cause anything like this ? I think the slime is called "PunctuSeal" or something similar - had it in the tyres for the last few summer tours, and have always had this "drumming" sound from the bike -

 

[fayeslane]

So, had another thought - could the "slime" in the tyres cause anything like this ? I think the slime is called "PunctuSeal" or something similar - had it in the tyres for the last few summer tours, and have always had this "drumming" sound from the bike -

Most of these products that I have seen are only recommended for speeds under 80kmh so I have never used them. You might be onto something here but to find out you would need to remove the tyre and the goo and try it. Any chance of swapping the wheel with an inmate for a non slime one for a easier test?

 

[Roger Chatterton]

Hi Fayeslane,
had a look on the box of the Puncture Seal, and read through the instructions etc., and absolutely no mention of recommended speed limitation. Doubt anyone would use a product that limited them to 50 mph all the time - I certainly wouldn't.
Maybe you're thinking of the foam stuff you add after a puncture ? I'm referring to the slime that lives permanently in the tyre, and seals any leak as it happens.
I have this in both tyres. ( Tourances - old style).

As you say would be interesting to compare with tyres without slime - anyone ?

 

[Toad]

I suspect the problem may be associated with doing 80 on an airhead.

 

[Roger Chatterton]

I suspect the problem may be associated with doing 80 on an airhead.

Yes probably - it goes away at 90-95 mph !

 

[(RIP) pastyman]

I have used Ultraseal on Bertha with Tourances with no ill effects at any speed. in fact their blurb states that the sealant helps to balance the wheel by naturally dispersing the fluid within the tyre. You dont say whether it is ultraseal that you are using. Does sound like an imbalance in one of your wheels though.

 

[(RIP) Arkwright]

Puncture Safe/Ultraseal

There are no speed restrictions with Puncture Safe (as it is now known), when you take a tyre off with it in you will find a thin coating on the inside of the tyre, look at the amount you put in, it can't do anything else! I use it in everything, it got me back from France one night without even knowing I had a puncture! Funny old things GSPD's, all sorts of funny noises, vibrations and habits (unlike mono's) but have a charm all of their own!

 

[Roger Chatterton]

I have used Ultraseal on Bertha with Tourances with no ill effects at any speed. in fact their blurb states that the sealant helps to balance the wheel by naturally dispersing the fluid within the tyre. You dont say whether it is ultraseal that you are using. Does sound like an imbalance in one of your wheels though.

The slime I'm using is called Puncture Seal, and is what Ultra Seal is now marketed as, I think I'm right in saying.
I agree with possibility of a wheel imbalance, and assume it is the rear wheel where the problem might lie. If it was the front wheel, then I guess I'd get wheel wobble/steering anomalies, which I don't !