Strange rear brake 'clunk' - K-Bikes.com - Excellence in Motion
 
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post #1 of 9 (permalink) Old Dec 5th, 2019, 3:57 am Thread Starter
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Strange rear brake 'clunk'

Got an '02 RS here, just done 100K kms with a strange one: a definite clunk from the rear when braking, but only at low speed? (eg walking pace coming into the home garage, just coasting in with clutch out).

I've have the swingarm out for the usual lubrication plus the weep hole mod, and all bearings (main & paralever) are smooth & 'lump free', the lower torsion arm is OK & bushes look good, all usual fittings are at OEM torques. Rear caliper is on to spec, bolts show no signs of it moving & pads are correct, not broken up, not worn, no signs of moving in the caliper... While swingarm was out I went over the rear of the frame & checked the rear crossmember too - it's OK & at spec bolt-wise.

So a bit stumped - any inmates got any ideas? Battery & iABS unit appear to be well mounted/retained so shouldn't be them moving; guess it could be something to do with the gearbox hanger but I'd guess that if its allowing movement on deceleration then surely I'd feel some sort of similar movement effect on changing gear too (eg torque load on/off/on). Rear wheel is at spec too, & thinking along same lines too even if it were that...

Cheers from the Sth Island of NZ

Max

Last edited by maxfnz; Dec 5th, 2019 at 3:58 am. Reason: i can't spell
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post #2 of 9 (permalink) Old Dec 5th, 2019, 6:04 am
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Looks like you have checked all the usual suspects. Have you checked the FD for crown wheel wear by rocking the wheel at 6 and 12 o’clock? Also, there may be wear in the pinion shaft creating excessive play with the crown although others will chime in on this. Pierre is all over these issues and will chime in for sure. Also I guess you have checked the driveshaft splines for excessive wear. Would not for a moment think that loose transmission hanger bolts would cause your problem as it’s unlikely they would come loose. Have you had the bike for long and are you aware of all the service history associated with the bike?
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post #3 of 9 (permalink) Old Dec 5th, 2019, 10:03 am
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Exhaust hanger? Missing the green Oring at the lower bolt?Cushions the clunk that one.

Lower shock bushing? That one can rust away!I have replaced one because it was rusting.

But from new they all have some slop at the splines where the driveshaft engages the final drive.A bit scary for the non initiated is to put bike in gear and work the wheel back & forth and listen to the clunk.

I was just in there yesterday....all normal!

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post #4 of 9 (permalink) Old Dec 6th, 2019, 12:55 am
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Center stand?
Take another look at the caliper. take it off, lube the slide/retainer pin with a tiny bit of neversieze , look hard at all parts to make sure everything is free.

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post #5 of 9 (permalink) Old Dec 6th, 2019, 8:16 pm
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Mr.OP?...I think I duplicated the clunk on my old bike.Old but to ,or very close to,factory specs.

Now....I won't go on and suggest the quick an easy experiment that may duplicate the clunk on the centerstand with engine off etc until I hear from you.

Benelli 50cc at 14
Yamaha RD 200 at 16
Yamaha RD 350 at 17
Honda CB 750 F at 18
Honda V45 Sabre at 24
BMW K100RS at 27
BMW R100GS at 34
BMW K1200RS at 53
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post #6 of 9 (permalink) Old Dec 11th, 2019, 5:17 am Thread Starter
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Thanks for all the ideas guys! Sorry for the delay in getting back, too mant Xmas functions ..

History - about the 4th owner from new, now just done 100000kms as I said. Prev owner seems to have had it fairly well serviced & looks reasonable from previous experience (6th BMW, 5th K). Did the usual check arounds when I bought it apart from the swingarm & the high-torque pivots, put that off until recently when I had some spare time...

FD bearing looks good, no play. Been there done all that with the R1100GS before this bike...

Spline - no visible wear when I was in there for the lube (part of the whole remove the swingarm & do the clutch weep hole, was due anyway. Sort of discounted the driveline mostly anyway as clunk occurs with clutch out too, & hopefully not too much rotational inertia at 5kms or less coasting to a stop. Could always be wrong though.

Exhaust hanger - yep, noticed that & fresh oring on recently (after removing whole shebang & new never-seeze on all the bolts...). No effect on the clunk tho.

Stand: both up and away as per ready to ride; haven't tried recreating the noise with the bike on-stand. Had sort of discounted this as there seems to be plently of clearance to moving parts and the springs seem to be doing a good job of keeping both stands in the stowed position as far as I can see? (Did check torques on the main stand carrier while I was doing the swingarm anyway - never want them to have any excuse to be loose the loads they put on the gearbox main casting!)

Swingarm: Hmmmm ... got a spare one here (after hearing the horror stories of seized pivot threads & needing sabre saws to get things out!) and lower bushing looked cylindrical & un-worn/deformed... ditto for the torque arm ones on the FD and gearbox. Only one I haven't eyeballed is the upper shock mount, tho it is to toque specs.

Caliper: Will check the pads & pins/walls for wear again; I do have the 2 types of caliper mounting bolt as well (one shouldered, one not & they are to torque although I can't 100% recollect if the leading bold is the shouldered one or not (should be from the realoem diagrams) - something to check. No visible damage to the FD mounting lugs or the caliper, threads are fine & original.

Did just think of the brake disk itself moving, but the conical screws looked in & tight when I had the FD off...
Checked rear subframe, ABS unit & battery shouldn't be able to move.

HR69996: If you can duplicate that's homework I'll take you up on! <grin> ... this has been a niggle for me for a while, a bike with a frame as substantial as the one on the K12 shouldn't go 'clunk'! (Just like the white smoke on my original K100RT...)

Again, thanks for all the help - much appreciated here.

Max
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post #7 of 9 (permalink) Old Dec 11th, 2019, 11:40 am
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First....wheel off.Move the disk back & forth quickly,a few mm is enough.Maybe with FD empty of oil.....but you should hear a faint click from the FD gears meshing.That's normal they have some lash.Lash spec is in the manuals,not easily measurable but I checked/measured mine a couple years ago and right in the middle of the spec.

Now mount the wheel.....rotate and slam the brake.Click is now a clack.Counter-rotate the wheel and slam the brake?Clack....?

If you do it twice rotating the same way you probably won't hear a clack the second time around as the gears are now meshed.Counter-rotate,gears mesh the other way and the lash click/clack can be heard.

Benelli 50cc at 14
Yamaha RD 200 at 16
Yamaha RD 350 at 17
Honda CB 750 F at 18
Honda V45 Sabre at 24
BMW K100RS at 27
BMW R100GS at 34
BMW K1200RS at 53
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post #8 of 9 (permalink) Old Dec 12th, 2019, 1:40 am
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I'll take a blind stab at this...

"I read on the 'net"... that when one suspects a problem at one end of the bike, it's usually found at the other end.

So to the OP this would suggest some attention be paid to the front of the bike... head bearings? front brake caliper? front discs?

If the bike has the Hossack front suspension, the suspects quickly multiply, prime suspect would be the ball joint or whatchamacallit.
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post #9 of 9 (permalink) Old Dec 12th, 2019, 11:02 am
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Gotta be the watchamacallit! Those things are really full of gremlins waiting to bite the unwary!

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