Annoying vibe at 70mph

[jjdugen]

Bit long....sorry!
CBR 900 RR 1997.
I've been fighting this one for months. Rides fine until I hit approx 70 per. Then an odd vibe starts up, felt mostly in the L/H footrest, at first.
It is most noticeable on a steady state throttle, bimbling along in motorway traffic. The odd thing is that it changes with suspension flex, a sort of yawing vibe in tune with the slight suspension movement.
I have.....
Changed all back wheel bearings, non showing any wear. Changed chain and sprockets, DID and Talon, adjusted the chain through tight to slack, checked all engine mount bolts, all tight.
I did suspect that the chain might be rattling on the swing arm rubber, but that is smooth and shows no wear point. There is nothing in the front sprocket cover causing interference, I took that off to eliminate.
My thoughts are turning to the output shaft bearing, but would have thought this would grumble at all speeds. (It has no play that I can feel).
Anyone have a gearbox output bearing fail and what were the symptoms?
Cheers
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The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
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[groovylee]

have you checked the wheel balance?
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Past - 1988 honda revere 600, 1996 kawasaki gpz500s, 1999 Yamaha R6

Current - 2002 Aprilia RSV1000R & 1999 Kawasaki ZX6R

[jjdugen]

Forgot about fitting the new tyre, balanced and then re-checked.
This is not tyre balance, I know that well enough. This is a tingly, grating, annoying vibe. BTW.... Its only at this speed and under these conditions, its fine at... higher speeds, (on a private road, of course), right through to 130 plus.
The output bearing is a complete engine strip so I need to know before diving in, especially as the motor runs perfectly in all other respects.
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi?

[chris-red]

does it feel different depending on what gear you are in?
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[Polarbear]

Vibration is such a difficult thing to pin point.

If it does happen at 70 only, yes, it could be the output shaft bearing. How about the front wheel bearings first, a much easier and cheap fix and if it doesn't cure it you haven't lost too much.

Can you remove the chain and front sprocket and see if there is any roughness/movement in the output shaft bearing?
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Triumph Trophy Launch Edition

[Vincent]

Must be transmission or engine related if you're feeling it through the peg and yes.........worn bearing noise can resonate at specific RPM. Have you unintentionally over-tightend the chain or had a tight-spot recently? Both could damage the output shaft bearing.
If you're feeling adventurous, and /or brave, how about getting the back wheel off the ground, running the motor in gear, remove the sprocket cover and listen to the shaft with some sort of stethoscope?
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Space Is Deep

[jjdugen]

I'll answer your points in order.
Any gear, 4th 5th 6th as long as its a steady state throttle at 70mph.
Front wheel bearings checked, smooth as silk.
I have hoisted its back end up and run it, problem is, there is no load to replicate the conditions and the chain thrash makes hearing anything untoward impossible.

I've looked carefully at all metalwork in any proximity for bright spots that might be interference, but all seems well.
Thankfully its nearing winter as it looks like an engine strip. Can't say I'm looking forward to it, might be the parting of the ways for my old girl and me!
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi?