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Author Topic: Master cylinder diaphragm  (Read 1918 times)

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OKC_Kent

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Master cylinder diaphragm
« on: September 03, 2007, 04:37:17 PM »

Mine disintegrated today when I flushed out the old fluid. I can get one here at Redline Cycle. What is the purpose of the rubber diaphragm under the cap, and can the brakes work fine without it?
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1978 KZ650 B2
Oklahoma City

spanners

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Re: Master cylinder diaphragm
« Reply #1 on: September 03, 2007, 06:46:15 PM »

Hi the rubber diaphragms dose two things i think.
 One it stops fluid leaking out and it also stops air which has water vapour in it getting in.
 the rubber is that shape because the brakes are a sealed system and when the pads wear more fluid is needed in the callipers to posh the piston out. If the top dose not let air in it will make a vacuum and stop the fluid moving making the brakes useless so the rubber is shaped to take up the space the fluid once occupied.
 Above the rubber the cap has a small breather hole to let air in and the rubber keeps the fluid separate from the air.
 Brake fluid is hygroscopic and will absorb water. If water is in brake fluid and gets hot it can boil and make bubbles and brakes will feel like they need bleeding and spongy.
   A bit long winded but I think this is right :)
  best get a new one if you can if nothing else it keeps fluid of your paint
  hope you get back on the road soon  :D
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anarki650

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Re: Master cylinder diaphragm
« Reply #2 on: September 03, 2007, 08:36:25 PM »

Thanks spanners, you made my response really easy.....Like he said!! :)
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09 Kawasaki ER6n

Omaha, NE
"Being shot out of a cannon will always be better than being squeezed out of a tube.  That is why God made fast motorcycles."  Dr. Hunter S. Thompson.

OKC_Kent

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Re: Master cylinder diaphragm
« Reply #3 on: September 03, 2007, 09:34:09 PM »

OK good enough reason to me. 

When I filled it up first I didn't notice it was torn. I installed the cap back on and went riding. I saw it was leaking out the cap so I checked it when I got home and the diaphragm was collapsed. I pulled it open and that's when it fell apart.

When I get a new one, should I fill the fluid up to the top fill line or will the new diaphragm expel  it when I put the cap back on?
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1978 KZ650 B2
Oklahoma City

BSKZ650

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Re: Master cylinder diaphragm
« Reply #4 on: September 04, 2007, 08:23:58 AM »

when I go thru the brakes I now put in dot 5 fluid, it dosent absorb water and dosent eat the paint, just make sure you clean the whole system out prior to installing the new fluid
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OKC_Kent

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Re: Master cylinder diaphragm
« Reply #5 on: September 04, 2007, 09:27:03 AM »

Yeah I think DOT 5 will be good, but I guess a total teardown and cleaning will be in order. Since my bike is a daily rider to work for me it may wait until the weekend.

I know if the rubber is torn it will leak out from under the cap. Every time I used the brake this morning I could see it seep out. I kept wiping it off with my glove, as the wind was blowing drops off and they land everywhere, maybe on my paint. This is sucking big time.
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1978 KZ650 B2
Oklahoma City

zixxerboy

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Re: Master cylinder diaphragm
« Reply #6 on: September 21, 2007, 01:28:12 PM »

BSKZ650

Can you define "clean out the old system"?

Can you flush out the old and put in new or does the entire system need to come apart and be cleaned?? If so what do use as a cleaning solvent??

I hate reg brake fliud - especially that odd feeling on the hands......
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