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So, I previously had a problem with the rear brake locking up but that was due to the adjustment of the brake lever, so the brake was constantly riding until the fluid boiled and locked up the brake. I adjusted it and there is now about 2 - 3mm of play before the rear brake engages.

Today I experienced another problem. After a long hard ride (about 166km, 103 miles) with lots of twisties, I noticed after returning home that my brake fluid has dropped to the minimum line and it appears that my fluid boiled over because the entire swing arm assembly is full of brake fluid. This doesnt seem normal at all. Yeah I was using the rear brake a lot more than usual due to the twisties but would it be enough to cause the fluid to boil over?

Perhaps my brake fluid cap isnt sealing correctly? When I got the bike there was some black rubber thing in the reservoir that I had never seen in any bike before, so I took it out. It wasnt an O-Ring, it was a v-shaped hollow rubber cylinder that seemed to take up quite a lot of space.

Any advice would be appreciated.

Thanks
 

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Is it possible you are resting your foot on the brake?

Some masters have a float to reduce air exposure. Air exposure leads to water absorption which boils at a lower temperature.
 

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Discussion Starter #3
Is it possible you are resting your foot on the brake?

Some masters have a float to reduce air exposure. Air exposure leads to water absorption which boils at a lower temperature.
I ride with my foot off to the side, sometimes even under the brake. Perhaps I should put that rubber back in and see what happens, maybe it works and solves the problem.

I've noticed though that there is absolutely no seal on the cap though. Is that normal?
 

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Perhaps my brake fluid cap isnt sealing correctly?
Nope,the cap on your rear brake fluid reservoir is not sealing correctly Daniel.


When I got the bike there was some black rubber thing in the reservoir that I had never seen in any bike before, so I took it out.
And this is why the cap on your rear brake fluid reservoir is not sealing correctly Daniel,you've removed the seal.


It wasnt an O-Ring, it was a v-shaped hollow rubber cylinder that seemed to take up quite a lot of space.
That rubber part is called a diaphragm. It's purpose is to seal out ingress dirt and moisture to keep it from contaminating your brake fluid. Brake fluid is hygroscopic,which means it absorbs moisture and it does so at a pretty fast rate. You don't want moisture in your brake fluid because it lowers the fluid's boiling point which leads to spongy brake feel or worst case scenario total brake failure.

Master cylinder reservoir diaphragms come in many different shapes,see the pics below. The reason the diaphragm is V-shaped and hollow is that as your brake pads wear down the pistons have to extend farther out in the brake caliper which causes the fluid level in the reservoir to drop,the diaphragm has to somehow move along with that lowering fluid level.

The diaphragm provides an airtight/watertight seal around the reservoir cup and if it was just a solid piece of rubber it wouldn't be able to move downward with the brake fluid level as the brake pads wore down. That's why the diaphragm is built like a bellows so that it can expand and extend downward with the lowering brake fluid level.


I noticed after returning home that my brake fluid has dropped to the minimum line and it appears that my fluid boiled over because the entire swing arm assembly is full of brake fluid.
Your swing arm was coated with brake fluid because you removed the diaphragm. Without the diaphragm installed the brake fluid in your rear reservoir was sloshing around and with nothing to prevent it from escaping it just slowly covered your swing arm in brake fluid.

Bleed out your rear brake fluid Daniel as it's now contaminated with ingress dirt and moisture,install the diaphragm,and put in some fresh brake fluid then go ride the snot outta that Monster.
 

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It seems like your first move should be to re bleed the rear brake with new fluid, preferably with some high quality Dot 4 or Dot 5.1 brake fluid to be sure you have fresh fluid with the highest possible boiling point available.

Maybe you could take off the rear brake caliper to inspect that the pistons move freely, clean and grease to be sure all is operating OK.
 

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Discussion Starter #6
stoshmonster, buddy, you just saved my bacon as well as teaching me something new. I can not thank you enough, I will pass this information onto my other bike buddies.

Thank you
 

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I'm no expert at riding twisty roads, but I doubt I use my rear brake much when riding them. That's why Mr. Brembo supplied me with those two big ones in the front, isn't it ? I thought the idea was to transfer weight forward to cause the bike to be easier to turn in and not wash out.
 

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Discussion Starter #8
If you apply front brake too hard in a turn, it will lock the steering to the side you are turning and throw you off the bike. You also have a bit more leaning control while using the rear brake.
 

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I had the rear brake of my 916 lockup due to being adjusted (by the dealer at a service) with too little play.

On the ride home from the service the bike felt slow and then eventually came to a stop with the rear pads on fire.

I called the dealer they collected the bike reset the play and fitted new pads and it seemed OK again however a year or so later it needed a new rear caliper as the seals were leaking, I assume the caliper cooking had damaged the seals?
 

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If you apply front brake too hard in a turn, it will lock the steering to the side you are turning and throw you off the bike. You also have a bit more leaning control while using the rear brake.
Well, of course it will. The key is not applying it too hard, isn't it ?:wink2:
 
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