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'Notchy' front brake - '17 Evo


bikerpet
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I haven't looked at this issue yet, it just surfaced today so it could be an obvious fix.

When I squeeze the front brake I find I squeeze a little and nothing really happens, then suddenly it goes "click" (no idea if it's audible, just what it feels like) and the brake comes on. From there on it's quite normal and works fine. Release the brake, squeeze again and same thing.

Maybe sticky caliper pistons? Or master cylinder piston? Or in the pushrod or lever pivot maybe? Perhaps even the disk not floating properly?

Anyone else experienced this and have any solutions before I start pulling things apart.

On another note the back brake heated up on a long descent the other day and the fluid must have expanded and wasn't getting back past the M/C so the brake started to bind. Odd because it's never done so before and I've not changed anything. I loosened off the pedal stop, but it was barely hitting the stop so I'm not convinced that's the issue. The pedal return spring doesn't pull the pedal up any further now anyway, although the pedal is certainly free to move - spring is fully collapsed. Maybe tweaking the piston rod?

Cheers.

EDIT: I took a look this morning and decided the front pads were a bit thin so replaced them and that seems to have fixed it. The old ones weren't as thin as I used to let the pads on my GasGas get, but perhaps the Grimeca are more sensitive - or perhaps it's a built in indicator?

Edited by bikerpet
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Hi, I had a similar problem with my 18 Evo 200 and ended up fitting a master cylinder repair kit which fixed the issue. 

I think the little rubber o rings swell up inside the cylinder and stick rather than move freely. From memory a kit was around £20 from my local Beta dealer. 

Hope you get it sorted... 

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8 hours ago, RichC said:

Hi, I had a similar problem with my 18 Evo 200 and ended up fitting a master cylinder repair kit which fixed the issue. 

I think the little rubber o rings swell up inside the cylinder and stick rather than move freely. From memory a kit was around £20 from my local Beta dealer. 

Hope you get it sorted... 

Thanks.

Hopefully it's as simple as the new pads I've fitted - haven't ridden it yet, but in the shed they definitely feel better. If not I'll look at the master cylinder kit.

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Might be that with thin pads the pistons were out far enough to tip a little to one side and jam slightly, with the rear brake you must make sure that with the pedal relaxed there is no pressure at all on the mcyl push rod, you need to be able to "rattle" the lever up and down a bit without it moving the pushrod, any pressure on it blocks the fluid return to the reservoir and binds the brake.

 

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Sounds like I might need to do some mods to the rear brake setup. I've backed the pedal stop bolt right in, so there's plenty of free play at the pedal, but the return spring doesn't lift the pedal off the push rod/piston despite being fully collapsed and apparently undamaged. I'll try adjusting the push rod until I get some free play, but I feel like I'm going to end up with the pedal well below where I want it at rest and at bite. Seems like the solution might be a slightly shorter spring. It just seems weird that it's been perfect since new in Sept. last year and now the adjustments are all out of whack. I checked the pads, there's plenty of life left in them (Obviously don't use them enough ;)). Not a big deal really, just something to work through.

Front pads - just measured them. Bang on 2.0 mm at their thinnest point! Who'd of thought to take notice of an owners manual! :rolleyes:

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3 hours ago, dan williams said:

It is possible to damage the return spring in master cylinders. If that happens the master cylinder piston may not return properly. One of those weird little things that can be a real pain to diagnose. 

That's a good thought - I haven't looked inside the Beta MC before. EDIT: Just looked at the Beta MC exploded view and it appears there's no internal return spring. 

I did shorten the pedal return spring a little today to give the pedal/rod some free play, so I'll see if that makes any difference. If not I'll dig into the cylinder.

Edited by bikerpet
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The external return spring does not need to pull the rod clear of the piston inside the master cylinder. They never do they are too long, and seem a bit pointless.

You need to ensure that the rod is not constantly pushing on the piston and preventing it from having full travel.

The rear can bind if the pads are low or from dirt build up on the caliper seals as well as from issues at the master cylinder end.

Edited by totty79
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  • 1 month later...

Not sure exactly what fixed this, but it is.

I shortened the pedal spring a little which took any pressure off the master cylinder piston. I also cleaned and cycled the caliper pistons (in-situ) and swapped the pads side for side as they had worn unevenly. Getting a bit thin, but still well above minimum at any place.

Problem gone. 

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