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Offline Goldfinger

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knowcking sound rear braking
« on: August 12, 2019, 08:41:57 AM »
Hi I am new to the forum, but could do with a bit of advice. I recently changed the tyre on my rear wheel. Looked at the you tube videos borrowed a paddock stand got the bike in the air. Removed the rear wheel and slide the brake off the slide replaced tyre and replaced wheel and new tyre. The rear brake felt really odd at first at low speed needed a real hard press to get any  braking. Then my friend told me that under hard braking there was a real hard metallic knocking noise. I could not hear it but I could feel it. I have taken the wheel on and off 4 times now and before torqueing the nut pressed the brake to reseat it properly still no low speed braking and definitely a massive knock under more extreme brake force. I have checked the caliper no movement in that and it is on the slide correctly. There is only one way it can go on and nothing loose anywhere. Anyone had similar and suspects that they know the answer it is driving me mad. Bike is a s1000r 2018 sport thanks
« Last Edit: August 12, 2019, 09:06:56 AM by Goldfinger »

Offline rogracer

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Re: knowcking sound rear braking
« Reply #1 on: August 13, 2019, 01:36:54 PM »
Same in all gears?  How about with the clutch pulled in?

Offline Goldfinger

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Re: knowcking sound rear braking
« Reply #2 on: August 13, 2019, 02:04:32 PM »
I decided to take it into the dealer as they had only recently serviced the bike and to their credit they agreed to have a look at it. They took it out for a road test and also popped it on the rolling road to check the brakes. They also took off the ABS to check that the brake could lock up the rear wheel. They also checked all of the safety points on the bike and also had the front end raised to check the head bearing. They have attributed the noise to the ABS, kicking in, I thought it was way to clunky, but perhaps this is because I have been used to another bike. !!! Anyway big thanks to Cotswolds BMW who took the time out to look over the bike and give me some piece of mind. Thanks for your response

Offline rogracer

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Re: knowcking sound rear braking
« Reply #3 on: August 13, 2019, 03:50:29 PM »
 Hard time believing it is the ABS. My original question remains.

Offline Enzio

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Re: knowcking sound rear braking
« Reply #4 on: August 14, 2019, 06:34:08 AM »
ABS does not cause a knocking noise - not in my case anyway.

I would think you need to look at what could cause a metallic noise:
- Axle - perhaps it is loose/not torqued correctly?
- Wheel bearing - are all the spacers where they should be? does the wheel spin freely without any drag?
- Caliper bracket - there is a small tolerance between the bracket and swing arm locating groove, a loose axle may cause it to rotate.
- Caliper sliding pins - worn or loose pins may cause the caliper to move with the disc while engaged.
- Brake pads - if they are stuck or not moving seated properly in the caliper it may cause the pad to erratically.
- Brake disc - has it or the ABS ring been loosened for any reason?
- Cush drive - although known to be a bit weak on these bikes, I would expect it to make a noise under acceleration rather than braking.

Basically - go through the whole rear assembly carefully. You might be glad you did.
I have had the good fortune of a shop losing my spacer between my sprocket carrier and wheel on a previous bike....no need to tell you it is a bit alarming when the bearing fails and your sprocket nuts hit the swingarm....

I got nothing.....

Offline Goldfinger

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Re: knowcking sound rear braking
« Reply #5 on: August 14, 2019, 10:17:57 AM »
Hi thanks for the response.
I will check the axle nut for tightness and torque again, but if it was not tight there would surely be some movement on acceleration and braking?
The spacers have all been assembled correctly none missing the bike has only done 4400 miles so I am not expecting to have any wear in the bearings
The pads are a curious one, when I removed the brake caliper the pads dropped out of the caliper but were secured by the pin, before I re-inserted the disc I clicked them back into place and they accepted the disc correctly. I don't think I did anything wrong there but this could be a starting point.

In regard to the caliper and the slide, I was concerned about this as the slide and the caliper have a lot more tolerance than I thought that they would, the caliper slides easily on to the mount and when the axle is not located there is a bit of play in the slide and the caliper. Once the axle is located and the nut tightened there is zero play in the caliper arm and the slide. But I double checked this there is only one way that the caliper and the slide can be mated together, there is no room for it to be assembled incorrectly ??
The ABS ring has not been removed.

Thank you

Offline rogracer

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Re: knowcking sound rear braking
« Reply #6 on: August 14, 2019, 02:29:40 PM »
So the reason I asked about the gear and clutch pull is because applying the rear brake causes reverse torque in the drivetrain. If the slipper clutch is malfunctioning I think it could cause such a noise when applying the rear brake. If it the behavior changes with gear or with the clutch pulled in....it may indicate a problem with the  clutch.

Offline Goldfinger

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Re: knowcking sound rear braking
« Reply #7 on: August 14, 2019, 03:27:33 PM »
Ah I understand and thanks for the clarification. I don't know is the answer I only tried it with the bike in gear at a relatively low speed coming off the throttle and applying the brake hard in essence emergency stop without the front brake. Will do some more testing and let you know

Online SimonUK

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Re: knowcking sound rear braking
« Reply #8 on: August 14, 2019, 08:55:18 PM »
*Originally Posted by Goldfinger [+]
Ah I understand and thanks for the clarification. I don't know is the answer I only tried it with the bike in gear at a relatively low speed coming off the throttle and applying the brake hard in essence emergency stop without the front brake. Will do some more testing and let you know

I still think this maybe the ABS kicking in, it is pretty crude on the rear brake. you could turn off the ABS and see if you still get the knocking when using the rear brake. but BE CAREFUL.

 


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