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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: ccarlsonnh on September 16, 2014, 10:56:00 AM

Title: K75RT weird buzz/vibe at 30mph
Post by: ccarlsonnh on September 16, 2014, 10:56:00 AM

This one has me stumped... I feel a slight but definite buzz/vibration in the handlebars right at about 30 to 33 mph indicated.  Not related to engine revs... in fact, clutch pulled in with engine at idle, it's the same.  Goes away above and below 30.  Noticeable when slowing down for a corner, etc.  Annoying and, of course, I wonder if something is going awry.  Any thoughts most welcome!

Thanks!

Title: Re: K75RT weird buzz/vibe at 30mph
Post by: pdg on September 16, 2014, 02:36:30 PM

Does it happen in every gear (that you can sensibly select)?

With the clutch pulled in, the gearbox is still being driven by the wheel, so it's possibly in there. Or -- UJ(s), wheel bearings, FD bearings - anything else that moves...

Title: Re: K75RT weird buzz/vibe at 30mph
Post by: TimTyler on September 16, 2014, 03:35:37 PM

If you can replicate the vibration on the center stand, you'll know it's not the tires, forks or steering bearings.

Title: Re: K75RT weird buzz/vibe at 30mph
Post by: ccarlsonnh on September 16, 2014, 06:16:06 PM

Thanks for the inputs!  Yes, different gears gives same vibration.  Tim, I'll try to replicate on the stand... hadn't thought of that. 

Title: Re: K75RT weird buzz/vibe at 30mph
Post by: ccarlsonnh on September 17, 2014, 10:16:19 AM

Didn't feel vibration while on center stand...

Title: Re: K75RT weird buzz/vibe at 30mph
Post by: Motorhobo on September 17, 2014, 01:22:01 PM

 I had a funny vibration once due to loose caliper mounting bolts. It's a long shot but easy to check so might as well get it out of the way.

Wheel bearings need replacing too periodically...come to think of it mine are way overdue.

Maybe also check torque on all bolts that fasten anything to the front end...maybe something's rattling in the airflow. Velocity related would appear to indicate exterior to engine/transmission, at leAst I'd try to rule exterior causes out first. Maybe there's a playing card in your spokes...

Title: Re: K75RT weird buzz/vibe at 30mph
Post by: The Mighty Gryphon on September 17, 2014, 03:05:34 PM

Specific speed unrelated to engine rpm = something is resonant in the running gear

More pronounced when decelerating = front end

My first guess is the steering damper, followed by steering head bearings, followed by the front brake rotors. 

Does it get worse when you apply the front brake at 30 mph? 

Title: Re: K75RT weird buzz/vibe at 30mph
Post by: johnny on September 17, 2014, 05:33:56 PM

tiors wheels steering bearings final drive drive shaft clutch...

j o

Title: Re: K75RT weird buzz/vibe at 30mph
Post by: ccarlsonnh on September 18, 2014, 08:59:10 AM

Thank you all... several things to have a look at!  Will start working through these over the next week or so hopefully ;-) 

Title: Re: K75RT weird buzz/vibe at 30mph
Post by: ccarlsonnh on October 03, 2014, 11:52:05 AM

Have been playing around with this with no real conclusion.  So, took it to my Beemer guru for a test drive this morning.  His take is that there is some tire vibration but not enough to be concerned about.  It really is quite subtle at this point.  If it gets worse, he'll dig into it some more.  So, for now, I just keep riding :-)