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post #1 of 8 (permalink) Old 06-13-2007, 07:57 PM Thread Starter
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no pressure in front brakes

So I was having a problem with low pressure in my front brake. After looking over the system, I found that the seal around the master cyclinder piston were shot. just to be safe, I ordered new brake lines, water seals and master cylinder diaphram along with the piston assembly. After changing out all the parts and bleeding through the lines. it still doesn't feel like there is any pressure in the lines. if anything its worst now. this is the first time i've worked on the brake system so its probably a dumb shmuck error, but i'm not sure whats going on. any ideas?
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post #2 of 8 (permalink) Old 06-13-2007, 10:45 PM
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when you bleed the brakes, can you build up any pressure at all? How much brake fluid did you go through after your rebuild?

If you can get some pressure in the line, tie it up tight (with the pressure) and leave it set a few hours (or overnight) and bleed again. If this improves it, you may have to repeat it. Make sure you bleed the left caliper first (suppose to bleed the caliper the farthest away from the master cylinder first).

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post #3 of 8 (permalink) Old 06-13-2007, 10:57 PM Thread Starter
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it will build up a little pressure. when I open the bleed valve with and without the lever depressed there is a difference in how fast the fluid comes out. but I am still able to pull the lever all the way back to the throttle with ease. I already made sure there was no visible leaks and re-torqued all the banjo's to 18 ft-lbs. I only used about 6 ounces of fluid so far. (I am kinda worried that I haven't used enough as this is my first time ever bleeding a brake system)
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post #4 of 8 (permalink) Old 06-13-2007, 11:14 PM
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When you bleed the brakes have some one pump the and hold them, then open the bleeder while they continue to hold. After you close it they can release then repeat. make sure you don't run out of fluid in the master.

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post #5 of 8 (permalink) Old 06-14-2007, 01:44 AM Thread Starter
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I was doing by myself, but I was using twisty ties to hold the lever. I was pretty much doing it by the clymer manual, except that I didn't have any clear hose to connect to the bleed valves. I am going to run to the auto parts store in the morning and see if I can pick up something like the mityvac unit and try to bleed it again. Other than crap loads of air in the system the only thing I can think of is that the cup seals on the master cylinder piston may have turned back on themselves when I installed the new piston. how much fluid should I go through during an average bleed? I will check back tomorrow with any progress i've made
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post #6 of 8 (permalink) Old 06-14-2007, 01:00 PM
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The amount of brake fluid used depends on whether there's air in the lines or not and how much bleeding it takes to remove it. I flushed mine about a month ago and was able to do it myself using a tube attached to the zirk fitting going into a glass jar to catch the fluid and keep the tube submerged. If the bike is on the centerstand, you just straddle the front tire facing the bike and squeeze the brake lever and hold, open the bleeder valve and watch the fluid squirt out, close the valve and let up on the brake lever. Repeat it until no air is coming out of the valve. One side is shorter than the other, I think it's the left side, (facing the front of the bike, it would be your right side) which you are supposed to do first. The only gotcha is if you let the master cyl run out of fluid, which introduces more air into the lines and you're back to square one.

Of course, if you have the seals installed wrong that could be your problem. Hope this helps.

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post #7 of 8 (permalink) Old 06-14-2007, 03:11 PM Thread Starter
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I finally got the brakes back... after bleeding it alittle more and seeing tiny air bubbles come out I thought I might try to reverse bleed it. I got a old medicine syringe and attached a clear plastic tube to it. This worked wonders. I don't know where the air was hiding but the first syringe full of fluid purged an enormous amount of air from the system. a few more times on each side got my brakes back to normal.
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post #8 of 8 (permalink) Old 06-14-2007, 03:42 PM
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Glad ya got 'em working.

AKA: Tim & 'The Adventure Cycle' VROC #24567, NEVROC, SteelCity VROC

"When life throws you curves,
Aim for the apex."

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