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post #1 of 3 (permalink) Old 08-08-2013, 06:08 PM Thread Starter
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Brake Problem

Hello, all:

I recently rebuilt the front calipers on a sport bike. 1996 ZX9R. Bike is in new condition. I have rebuilt many brake calipers over the years, master cylinders too, so I am very familiar with hydraulics. But this time I have run into a real stumper.

Replaced front master cylinder with a Nissin Daytona 19 mm radial master cylinder. Replaced hoses with new Galfer lines. Bled system of all air, but was unable to get pressure at the lever.

After bleeding both using the master cylinder and with a Mity Vac, and having the same results over and over, I bled the system using my car bleeder, a KD pressure bleeder. Well, this produced a firm lever, until I removed the system from the top of the reservoir. Again, the lever went all the way to the bar.

I found no leaks. Used 3M Leak Detection Powder to check, had some very slight seepage at a couple of banjo bolts, but those were fixed prior to the last bleed, and I should have had pressure even with that seepage. Seems strange that the lever was firm with the bleeder but without it, it was not.

Any ideas? Thanks in advance for any suggestions.

Fuster

"...If you can meet with triumph and disaster, and treat those two imposters the same....you'll be a Man, my Son!"

- Rudyard Kipling
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post #2 of 3 (permalink) Old 08-09-2013, 04:52 PM
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This reminds me of the very same issue Vash was seeing when he did a brake caliper rebuild. He ended up just replacing them. I know, not helpful

A missing o-ring would probably leak, so that's not likely. The new rubber gaskets are unlikely issues, assuming you changed them. You cleaned out the races for the rubber parts, right?

I'd be thinking master cylinder, really. The reason is that anything lower would leak, but up by the resevoir you could pull in air with no apparent leak, necessarily.

You did the air evacuation in the order spec'd by the service manual, right?

I just rebuilt my calipers and it took a LONG time to get to firmness, but that was because the pistons were fully disengaged. Now its good.

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post #3 of 3 (permalink) Old 08-09-2013, 05:29 PM Thread Starter
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Brake Tech, who sold me the master cylinder, contacted the U.S. distributor for Nissin and got a procedure for me to test the master cylinder. I will report my findings in a few days, I plan to test it tomorrow.

If it cannot develop pressure isolated from the rest of the system, they will replace the master cylinder.

Fuster

"...If you can meet with triumph and disaster, and treat those two imposters the same....you'll be a Man, my Son!"

- Rudyard Kipling
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