pulsing front brake

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bvdl
On the Road
Posts: 14
Joined: Sun Sep 10, 2017 7:08 pm

pulsing front brake

Post by bvdl » Thu Oct 12, 2017 3:43 pm

When front braking, the braking force is intermittent, not smooth in behaviour.
I saw stuff on youtube about bobbins inside the rotors can get clogged with brakedust and other debris, not allowing the floating part of the disk to move over the bobbins anymore.
There are some cool workaround tips on youtube, allowing you to use a bolt and nut on tension through the bobbin you want to clean by rotating it and use a tiny drop of WD40. The dirt should get removed that way, and afterwards zou can clean the bobbins and the whole disk with lots of brakecleaner.
The only problem being: there are no holes in the bobbins, leaving this option unusable for me...
What do you suggest? The rotors are far from worn out so replacing isn't the most economic solution it seems to me...

Thank you for any help.

andybaggies
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Joined: Mon Feb 16, 2015 4:31 pm
Location: Wiltshire

Re: pulsing front brake

Post by andybaggies » Fri Oct 13, 2017 11:11 am

I've had similar issues, most apparent when gentle braking, and discovered the following:

The master cylinder piston can get sticky in it's action. On mine you could hear a gentle 'eeek' when applying the brake at standstill in the garage. A quick grease of it's rubber boot inside & out using brake safe red rubber grease smoothed things out.

I've previously cleaned the disks by first dry brushing with large, small & tooth brushes & then using a disk brake cleaner spray. For a thorough job remove the calipers and do the pads & crevices especially around the pistons.

The brake pistons & seals may need a full refurb which isn't the nicest job in the world see viewtopic.php?f=13&t=4850&p=37147#p37147 It is also possible to pump the pistons part way out to clean & grease 'em. With brake safe red rubber grease of course.

bvdl
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Posts: 14
Joined: Sun Sep 10, 2017 7:08 pm

Re: pulsing front brake

Post by bvdl » Fri Oct 13, 2017 1:17 pm

Hi, thank you for the advice!
I would have never thought a gripping piston could cause the braking to pulsate. It's exactly as you describe, while gently braking. I'll look into the pistons when I get to the coming forkoil job.

andybaggies
On the Road
Posts: 234
Joined: Mon Feb 16, 2015 4:31 pm
Location: Wiltshire

Re: pulsing front brake

Post by andybaggies » Fri Oct 13, 2017 6:18 pm

when I get to the coming forkoil job
Changing the fokr oil may well also help.

I used to noticed some stutter marks on one of the fork legs and thought I could be suffering from a little chatter/stiction which may have being giving the impression of pulsing. Both these symptoms disappeared when I recently replaced the fork cartridges for Matris items.

So perhaps when you do the job try to thoroughly clean both the cartridges & the fork internals. I used white spirit but I'm not entirely sure how appropriate it will be for any rubber items that may be in the cartridges.

Andy B

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