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Old 05-02-2004, 01:56 PM
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Master Cylinder losing fluid

I have a 69 pontiac Lemans, drums all around, and I replaced the last master cylinder because it would intermittently lose fluid out the rear end, which was presumably sucked into the turbobooster and injected into the engine. Good news is, the brake fluid injection cured a main seal leak I had that was costing me a quart of oil every 50 miles. Bad news is, the new (rebuilt-Kragen), is apparently doing the same thing, with the 2 separate resevoirs alternately losing fluid, and signs of leakage showing where it bolts onto the turbobooster. Also, very hard pedal w/new MC, pedal was ok w/the old one. My question is, could there be something amiss with the car that's causing the MC to go bad in this way ? Seems kind of odd to me that I'm having the exact same problem twice. Haven't adjusted anything on the brake system itself, except for replacing the linings at about the same time I replaced the MC. Any and all input appreciated..

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Old 05-03-2004, 12:58 PM
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Doesn't anybody know if there are factors in the brake system, (brake pedal rod length, etc.), that could be causing MC's to leak in this way ? I'm perfectly willing to swap out another MC, but don't want to do it before solving any causative problem that might exist. Everybody I've talked to can't come up with any reason they think this is happening, but just thought I'd check here in case any brake savvy person has had this experience..
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Old 05-03-2004, 02:35 PM
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go here and look to the left of your screen, and check out the tech section. it's been a big help to me, but i can't say i've truely licked my stopping problem yet...... so i'll say no more.

have you checked the wheel cylinders for leaks?
i've never heard of brake fluid being sucked into the manifold by vacuum.

call me crazy?..........
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Old 05-04-2004, 02:10 PM
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I've been told by more than one mechanic about the vacuum line sucking in brake fluid from the back of a leaking MC. I know it's true, because it cured my main seal leak, and adding brake fluid to your oil was one of the possible solutions to fixing a main seal leak I found on the net. Tnx for the link, I'll check it out.
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Old 05-04-2004, 08:09 PM
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How would sucking brake fluid into the intake manifold stop a leaking rear main seal? If the fluid was being sucked out of the M/C by the vacuum hose, it would go into the cyls and be burned. It is quite a distance for it to get to the rear main seal.

I believe that you would have to have both a bad M/C and booster for you to be able to get brake fluid into the engine that way.
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Old 05-05-2004, 11:15 AM
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Well, the booster passes the start engine after depressing brake pedal 5-6 times test, so I'm hoping it's OK. I'll have to check where the vacuum line is attached. Why would the booster being bad inject brake fluid into the engine oil, but not just the vacuum line sucking it up ? Wouldn't the path of fluid be thru the vacuum hose in both cases ?
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Old 05-05-2004, 07:01 PM
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It is extremely doubtfull that the brake fluid stopped a rear main seal leak by being sucked out of the M/C. If your rear main seal stopped leaking, it was just a coincidence. I would take to hose from the booster loose on one end or the other and look inside. If there is brake fluid going thru there, you should be able to see some inside.
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