master cylinder problem - Wrist Twisters
 
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post #1 of 8 Old 05-11-2012, 04:29 PM Thread Starter
Tirone
 
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master cylinder problem

I have an old suzuki cruiser that I'm working on. Having an issue with the front brake. The master cylinder won't release fluid into the line. I tried putting a vacuum pump on it, pulled and released the handle etc.... Nothing. I can get a new cylinder easy enough, just wondering if I'm missing something, I've never really worked on one before.

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post #2 of 8 Old 05-11-2012, 04:58 PM
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Sounds like it's due for a rebuild, or replacement.... why bother posting if you didn't bother to ask a question? I take that back. Why bother posting if you didn't bother to ask a question, or post nudies?

if you love your motorcycle, set it free.. if it comes back and hits you.. you highsided
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post #3 of 8 Old 05-11-2012, 05:33 PM Thread Starter
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Ok, instead of "just wondering if I'm missing something." I'll say "just wondering, am I missing something?". Now you have a question to answer.

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post #4 of 8 Old 05-11-2012, 07:06 PM
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First, carefully inspect the whole system for leaks, binding, cracked hoses, or anything else that indicates another problem. Pay particular attention to the condition of the fluid in the reservoir -- if it is a medium amber color all is good. If, on the other hand, it is a disgusting opaque brown color the whole system will need a thorough going through.

There are two possibilities:

-- The master cylinder primary pressure seal or the cylinder wall is damaged, allowing fluid to bypass and giving no lever. If it's just a compromised seal a rebuild will be possible, but if the cylinder is scored replace it. It's too much trouble to attempt repair without the necessary tools and knowledge.

-- The compensating port in the master cylinder is plugged, possible with a system that hasn't been serviced since it was installed at the factory, and it needs to be cleared by backflushing. The easiest way to do that is by completely retracting the piston(s) in the caliper(s) (as if I had to do that again!) -- which forces the fluid back into the master cylinder, hopefully clearing the port. If the pistons won't move the blockage will have to be manually cleared by rebuilding or replacing the master.

Rob

If it has already been done, it is safe to assume it is possible to do it.
On the other hand, if it has not been done never assume it is impossible to do it.
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post #5 of 8 Old 05-12-2012, 09:13 AM Thread Starter
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Is there any other way to try and flush that out? I just put a new line and caliper on, so there's no fluid in it. I couldn't bleed the line cause nothing was coming out. I put a vacuum pump on the caliper to try and draw the fluid down. So I ended up taking the line off the master cylinder and saw that fluid is not coming out of it. If I put my thumb over the hole and pull and release the handle there's definately some air pressure moving in and out. But nothing flows out of the resevior.

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post #6 of 8 Old 05-12-2012, 09:15 AM Thread Starter
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A cylinder of ebay is like 50 bucks, no big deal. But if its as simple as blowing some compressed air through it or something then I would just as soon save the 50.

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post #7 of 8 Old 05-12-2012, 10:30 AM
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It is possible to clear a plugged compensating port by completely emptying the reservior, covering the reservoir opening with several layers of shop towels / old t shirt / whatever else allows air to escape without bathing you and everything else in the vicinity with a fine mist of brake fluid, and blowing air into the outlet. Regulate the air pressure down to about 40 PSI at first and give it a go. If that doesn't clear it bump the pressure 10 PSI and try again. The difficulty here is the port is so small -- usually 0.5mm (0.020") that at an air pressure of 50 PSI there is only 3/4 pound of force being applied to the blockage. Usually it is enough, but if the blockage is too firm it may be necessary to physically clear it, which to do properly requires a teardown.

Hopefully the air pressure will do the trick.

Rob

If it has already been done, it is safe to assume it is possible to do it.
On the other hand, if it has not been done never assume it is impossible to do it.
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post #8 of 8 Old 05-12-2012, 07:31 PM Thread Starter
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Sounds good rob, that makes sense, ill give it a try. Thanks for the help

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