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So yesterday two events happened; first thing was it felt as if a hidden giant hand was holding me back as I needed more and more throttle to keep frwd momentum. This lasted for only 5 seconds.
Then five or ten minutes later I was coming up on a fast downhill right hand bend and when I squeezed the front brake lever....nothing. No pressure. So after shitting my pants used the back brake and leaned more.
I took it easy to the petrol station 10 minutes away and by the time I arrived brake lever pressure was good again (even my heart rate had settled LOL).

Rode 90 minutes home and brakes were trouble free, although I took it easy and didn't test them to the limit.

I believe both incidents are related and the problem is within the calipers. The first symptom mentioned sounds like a stuck piston, but the loss of pressure?
Does everyone agree? And what should I look for?

Cheers.
 

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Stuck brake piston. Boiled the fluid so you had no brakes. Fluid cooled down and your brake returned. Pull the pads out, check them (replace as necessary) and clean the pistons and then blead the brakes and you should be fine.
 

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Check pad thickness and wear pattern. If they are worn uneven it can cause them to stick or jam and not return properly. If the pads are too worn the pistons have to come out to far and can stick. Check rotor thickness too, same reason. Definitely replace the fluid after you overheated it . This will give you a chance to see if everything works and returns as it should.
 

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Discussion Starter #4
Tnx fellas. The pads are new (1000 - 1,500 klm).
Will check pistons and flush with new brake fluid. Rotor thickness is a tad under 4.9mm.
 

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this happened to me once on my 1098. it ended up being a master cylinder slowly dying. The Seal would sometimes let all the fluid passed instead of building the pressure up to compress the brakes. Every few squeezes itd go all the way to the grip with zero resistance. Hope this helps!
 

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In addition check the little vent notch in the M/C cap and the rubber bellows under it. If the vent is blocked, pressure builds up in the reservoir when the brake fluid gets hot and expands applying the brakes. This condition intensifies when the fluid is old and has absorbed moisture so change the fluid too.
 

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Sorry, there's no way that enough pressure can build up in the reservoir to apply the brakes.

When partially plugged with debris, the master cylinder vent port will result in brake application until enough fluid is released back into the reservoir. Further, a partially plugged replenishing port will slow refilling the master cylinder and account for a momentary loss of system pressure. Cleaning out the debris from both ports will solve the problems.
Master Cylinder.png
 
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