#1  
Old 09-12-2020, 05:12 PM
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Birdman1437 Birdman1437 is offline
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Default My Brake problem

I have searched and searched for an answer to this brake problem with no luck. Hopefully someone here can help.
68 Firebird- Manual Drum brakes front and back. About 10 yrs ago I replaced the master cylinder (leaking) and all wheel cylinders. I flushed the lines and everything worked great. Since then every 3 yrs I have replace the fluid by pumping thru until I see clean and then bleeding the system. Always gave me good results. THIS year I flushed and bled the system and now- periodically I have no brakes! The pedal is hard and low. Pumping the pedal gives my braking back but not at all strong as before. The brake work fair for maybe a day, or couple hours and then suddenly no brakes. Pushing the pedal really, really hard will draw the back brakes when this occurs. I’m not sure where to start. I have bled the system twice sine this occurred hoping it was just air but I think the hard pedal is telling me something else is wrong.Any ideas? Thanks in advance for your help.

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Old 09-12-2020, 05:34 PM
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400 Lemans 400 Lemans is offline
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Could be the rubber brake lines. They will start to swell shut if there old.

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Old 09-12-2020, 05:52 PM
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Birdman1437 Birdman1437 is offline
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I forgot to mention that I replaced the rubber lines to the front brakes and just the hard line that goes across the rear axle because it was looking in bad shape

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Old 09-12-2020, 07:24 PM
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67drake 67drake is offline
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I’ve had master cylinders go bad over the years that would act like that. Rare, but it happens.

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Old 09-12-2020, 09:20 PM
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LATECH LATECH is offline
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X2 on the master. Classic symptom.

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Old 09-13-2020, 03:24 AM
Geoff Geoff is offline
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With Detroit in love with cast iron, the wonder metal, rust is the eternal enemy. It is likely that stroking the pedal to bleed the brakes has dislodged rust in the m/cl & cut the seal[s]. If you intend to keep the car for many years, might be wise to have the m/cl s/steel lined & avoid this problem in the future.

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Old 09-13-2020, 08:59 PM
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Thanks for the replies. I too wondered if I dislodged some rust or crud that is mucking things up. I have ordered a new, Cast Iron, Master cylinder and distribution block. I already have new wheel cyls but really don't think I'll need them. After install I'll see if the lines flush clear and if not proceed to replace the lines.

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