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I have been concerned about the sponginess of my front brakes and could not bleed them adequately. So, I decided to remove the master cylinder and have a look to check for dirt and contimination. After I got in there I found that the cylinder and the 2 holes were full of gunk as were the piston, cups, and inside of the bore. It was terrible and took me a few hours to clean it all out.

After cleaning, I reassembled it, hooked everything back up, put some new fluid in, cracked the bleeder valve on the right tire, and began pumping the brake handle. I was expecting to feel some pressure and see fluid squirting out of the bleeder valve after pumping a few times.

What I experieced was quite different. I pumped the handle like crazy and nothing happened. There was very little resistance on the brake handle. Then I closed the bleeder valve and began pumping again. Nothing. No pressure ever built up.

The question I have is do I need to purchase a rebuild kit for the master cylinder- everything seemed OK after I cleaned it? Or am I missing something in my methodology that is not allowing the master cylider to be primed and hence work correctly?

Thanks in advance - hopefully someone can help me out as I need to get this back together by this weekend if at all possible.

JM Wolfe
 

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Hello JM. The brakes and clutch on theWings can be a pain to bleed. I took the advice of someone here and I loosened the hose union at the master cylinder end, then got a large syringe and injected brake fluid through the nipple. I had a friend at the MC end and when the fluid started to run clear out of the union he nipped the bolt up. Instantly hard lever!
If you do this make sure plenty of plastic bags are covering the paintwork.
 

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wolfej1 wrote:
What I experieced was quite different. I pumped the handle like crazy and nothing happened. There was very little resistance on the brake handle. Then I closed the bleeder valve and began pumping again. Nothing. No pressure ever built up.
JM, one way to get a system primed is to open one of the bleeder screws and apply a little vacuum on the bleeder. You can do this with a hand vacuum pump or by applying suction by mouth to a tube pushed on the bleeder. If you use the mouth method, use a long, clear tube so you can see the fluid coming, an 8' piece of vinyl tube that press fits onto the bleeder will work okay. Keep the reservoir on the master full, don't want to suck in more air. Once you have some solid fluid coming out of the bleeder, do the same job on the other caliper. This should remove enough air to get the bleeding working. Make sure you don't let up on the pedal while the bleeder screw is open or you will defeat your own efforts. It's very difficult to do this job single handed, you need some one to pump and hold the brake pedal while you work on the calipers.
 

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Thanks all

What are the symptoms of a Master Cylinder that needs to be rebuilt?
 

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Main symptom is that the pedal won't hold, just keeps going down with steady pressure. Or the pedal goes the the bottom no matter how much you bleed it.
 

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The guys are on the button wolfej1..

Think of the master cylinder as a pump. It must be primed before it will work. Fluid needs to be drawn down into the cylinder bore so the piston can push it out. I use a hand pump which is inserted into the bleeder screw hole and actually sucks the brake fluid out thru the caliper from the resevoir. That primes the cylinder and bleeding is normal. However, if the piston & seals are worn out, no amount of priming or pumping will give you a solid feel..

When you assembled the master cylinder, did you lubricate all the parts heavily with dot 4 brake fluid?
 

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Assuming your talking about the 81, 1100 it may be a good idea to rebuild the master cylinders, front and back,based on age alone. And consider replacing the brake lines as well, if they are original they will most likely be soft. Good Luck
 
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