Brake problem - Page 3 - MVAgusta.net
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post #21 of 27 (permalink) Old 03-13-2012, 02:08 AM
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Well you know how theory sometimes get shafted by bad practice. I have seen the young blokes come over the hill at Barbs with their front wheels locking up in the air, as the wheel hits the gorund there is an almighty lot of ooh's and aah's before the bike spares roll down the hill. They overfill the reservoirs, as the fluid expands with nowhere to go - I would have thought the pressure would built up enough to cause this. I do speak under correction though.

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post #22 of 27 (permalink) Old 03-13-2012, 06:53 AM
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That is so worth bearing in mind tho Donsy ..You paint the picture very vividly...

A combination of factors maybe ..Over filled reservoir with moisture in the system.?

They must put a maximum fill level on the master cylinder reservoir for some reason ..


joe

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post #23 of 27 (permalink) Old 03-13-2012, 09:08 AM Thread Starter
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I've just checked the fluid level. It is a couple of mm below MAX level.

Tomorrow I'll take my bike to my master mechanic. Hope I'll find out the reason for my problem

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post #24 of 27 (permalink) Old 03-13-2012, 01:11 PM
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Quote:
Originally Posted by gotojoe View Post

They must put a maximum fill level on the master cylinder reservoir for some reason ..


joe
only since they had plastic reservoirs (some BMWs with sight glasses excepted)

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post #25 of 27 (permalink) Old 09-16-2019, 07:19 PM
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So I thought I'd revive this discussion as my F4 is experiencing locked front brakes after a few stops too. I've removed the calipers and cleaned the pistons and the brake fluid has been changed in the last week. The symptoms are that brakes work fine when cold and the lever travel is normal. However after a few stops and when the rotors get hot, the brakes lock up and the brake lever feels like you are braking hard as soon as you try to pull the lever.

As expected when inspecting the calipers, when I tried to push the pistons back in the calipers they move the other 2 pistons outward. However, when I constrained the movement of the other pair of pistons and tried to open up the remaining pair, I was unable to do it because so.

My interpretation is that something is not allowing the brake fluid to evacuate the caliper. Am I correct in thinking that my master cylinder is the only explanation for not letting brake fluid evacuate the calipers when the brakes are not applied?
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post #26 of 27 (permalink) Old 09-16-2019, 08:51 PM
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Your master cylinder piston is not being allowed to retract all the way. Take the lever off and I will bet the brakes "un-lock".

Did you replace the lever recently???
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post #27 of 27 (permalink) Old 09-17-2019, 04:14 PM
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This is a very good thread!!! Most everyone's advise is good and reasonable. Over the years I've seen all of these symptoms and problems! Clean, fresh and correctly serviced usually cures brake woes.

I think Ed and Knurl are probably right the master is jammed/dirt fouled or the MC piston is too far out and it won't compress now. With Brembo MCs I've seen this problem happen from having the front brake lever pulled outward by accident or when changing a lever out and allowing the MC piston to get pulled out past the check valve.

My first thought is the master cylinder is the problem

Of course check fluid levels and caliper piston travel & retract & cleanliness, over filling can be a bad thing...

Water/Condensation causes this symptom but has to get pretty hot first

No one really needs DOT 5.0/5.1 fluids anymore. There are extremely good DOT 4 fluids available that will not let you down even racing/track riding.

At the track I always have a spare Brembo MC just in case of a MC problem. Spare levers too. I've used Ate Super Blue fluid for years without any issues or concerns. There are many others of this quality out there. Motul RBF 600 comes to mind.

Keep in mind that even if the brake pads are still okay, thicker pads help to shield the calipers (& fluid) from heat and help keep braking optimum. at @ 50% wear I change them out. When you change pads it is a great time deburr the rotor holes & slots and to get some rubber gloves, new scotch pads & acetone and clean the brake surfaces. Amazing how much better braking feels with really clean rotors.

Skonda hope you get it resolved soon, best of luck!

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