Rear brake problem, puzzled?

[CoronaBoner]

Hi

This time its my Mille, it just doesn't work at all now.

I can push the pedal all the way down (which seems to far as your foot has to be at a funny angle.) and I get zero bite on the brake.

I checked the pads and they look almost new. So I whipped them out and sure enough the pistons were stuck. Bit of gods piss and a quick bleed and the pistons are working fine.

Put it all back together again, go down the road and it still don't work.
Can someone explain how the rear master cylinder works or what could go wrong with it? as I'm 100% sure the caliper/pads and brake fluid are fine.
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2004 RSV Factory

Cluck cluck chicken

[Kickstart]

Hi

Basically the master cylinder is just a tube with a piston, one big hole at the end leading to the caliper, one small hole half way down the side leading the the reservior. Spring in there to push the piston back. As you press the pedal the piston move, covering the small hole and then pushing fluid out of the large hole. Release the lever and the small hole is uncovered again allowing fluid in.

To be honest if it is anything like the RS125 then the banjo bolt on top of the master cylinder is the highest point of the system (and on some bikes the bleed nipple in on the bottom of the caliper, a pretty useless position). Wrap a rag around the banjo, press the lever and keep it pressed while you crack off the banjo and do it up again.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[CoronaBoner]

Ah I see now.

Yes you are right, the nipple is right at the bottom of the caliper with the banjo at the top. Can I ask how that is a silly position, is it to do with the way the fluid is pushed around the caliper?

Anyway I'll give it a crack tomorrow and report back.

cheers.
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2004 RSV Factory

Cluck cluck chicken

[Kickstart]

Hi

Its a silly idea as you want to get rid of the air in the system, and the air tends to stay in the high points of the system. So with the bleed nipple at the bottom you tend to just pump fluid through without getting rid of the air.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[CoronaBoner]

Yep it worked! kickstart is spot on.

Is really improtant how you angle it when bleeding. I found an awesome write up on the subject on Aprilia forum, shows you different ways of bleeding, even a reverse way by injecting through the bleed nipple. Has pics and everything. https://www.apriliaforum.com/forums/showthread.php?t=15500
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2004 RSV Factory

Cluck cluck chicken

[shammon]

Yip all good stuff on that link. i have to say injecting via the caliper sorted out my probs, much better than the normal way.
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