Master Cylinder Ripped Diaphragm

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28 Jul 2015 16:33 #683182 by razmo99
Master Cylinder Ripped Diaphragm was created by razmo99
Hello,
I recently did a brake job on my z500.
the diaphragm for the master cylinder is ripped.
Currently no brake fluid is making it to the brakes or even out of the Master Cylinder into the Brake lines.

My question is can a ripped diaphragm cause this or is it something else?

- Z500 B4
-GPZ900R A9-10 ish

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03 Aug 2015 15:53 - 03 Aug 2015 16:00 #684116 by weales
Replied by weales on topic Master Cylinder Ripped Diaphragm
When you say you "Did a brake job" what did you actually do? (I assume that you changed the pads ...?)
A ripped diaphragm shouldn't cause this problem as long as there's enough fluid in the reservoir to supply the system.
Sounds like something is blocking the Master cylinder supply line - maybe a piece of the diaphragm?
Also there may be some air which has been allowed into the system during the "brake job" - which needs to to be bled out. Are you getting good pressure at the brake lever ? If not, or there's a spongy feel, then there's air in the system.

Current Project
1968 Norton P11A Desert Sled
Other bike (and daily ride)
2004 Yamaha FZR 600
Previous Bikes
78 Z1-R (resto)
91 Zephyr 750
73 Mach IV (Resto)
78 Z1-R
78 Z1-R (stolen)
76 Z900
76 Z650
73 Mach IV
72 Mach III
Last edit: 03 Aug 2015 16:00 by weales. Reason: add text

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03 Aug 2015 16:32 - 03 Aug 2015 16:35 #684125 by Tyrell Corp
Replied by Tyrell Corp on topic Master Cylinder Ripped Diaphragm
No, the diaphragm is just to seal the air away from the fluid, but allowing some level fall as the pads wear. The early z500 front MC it is the same part as the z900 z1000 etc.

After you top up and bleed, I like to reverse bleed, let the bubbles float up to the top as you slowly pump the brake lever. Put some protection on your tank and clocks as brake fluid is nasty stuff -also squeezing the lever can make it squirt out of the top of open master cylinder. You can even vacuum bleed if you have the right tool.

35 years later it is likely your mc piston and/or bore needs attention. You can use any master cylinder you like if you aren't too fussy about originiality, just make sure the bore size is the same.

1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces
Last edit: 03 Aug 2015 16:35 by Tyrell Corp.

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03 Aug 2015 18:08 #684139 by razmo99
Replied by razmo99 on topic Master Cylinder Ripped Diaphragm
Thank you for your replies.
By brake job I meant replacing the seals on the callipers. I also painted them.
I ended up pulling apart the front and rear MC the rear was leaking the front was not.

The front MC had heaps of crap in it but it wasn't leaking. Even after cleaning it out. No fluid was making it out of the MC.
I am not sure exactly but I think the diaphragm maintains air pressure in the MC and allows fluid to be sucked down into the piston to be pushed out into the lines. I have ordered another diaphragm and am hoping that will resolve the problem.

- Z500 B4
-GPZ900R A9-10 ish

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03 Aug 2015 20:39 #684162 by weales
Replied by weales on topic Master Cylinder Ripped Diaphragm
If there was a lot of crap in the MC you'll need to flush it all out really well. You may find that the relief port in the MC is blocked. This port can be as small as .009" and a tiny bit of crap can easily block it. I had this trouble on my Z1-R and it wan't until I cleared this with a correctly sized drill that I could pump fluid through the system and bleed the air out.

Current Project
1968 Norton P11A Desert Sled
Other bike (and daily ride)
2004 Yamaha FZR 600
Previous Bikes
78 Z1-R (resto)
91 Zephyr 750
73 Mach IV (Resto)
78 Z1-R
78 Z1-R (stolen)
76 Z900
76 Z650
73 Mach IV
72 Mach III

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03 Aug 2015 21:05 #684168 by Tyrell Corp
Replied by Tyrell Corp on topic Master Cylinder Ripped Diaphragm
You can remove the master cylinder piston and check the bore for scoring etc.

1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces

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04 Aug 2015 17:31 #684333 by razmo99
Replied by razmo99 on topic Master Cylinder Ripped Diaphragm
I have already removed the bore and cleaned it all out. It was cover with this rust looking sludge.
reassembled it and it doesn't seem to leak.

I have checked the ports for blockages and they seem to be clear. I have confirmed that a small amount of brake fluid is making it down the line after a couple of days the MC was empty.

- Z500 B4
-GPZ900R A9-10 ish

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