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Discussion Starter #1
Alright, the deal is i got my old cat and i'm losing pressure in my brakes when i hold the pedal. I replaced the master cylinder cause it looked like **** and a new one was like 20 bucks, plus i get a core refund. So i got the new master cylinder in today, and bled the brakes, so that made a huge difference. The brakes lock up about 3/4 of the way in and stay there when the car is off. Once i start it, that slip comes back, and i can feel the pedal slowly go to the floor. It holds long enough for stoplights and everything, but it'd be nice to fix it. Any ideas?
 

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The booster is helping apply more pressure, which is forcing out fluid where your foot cannot do it alone. Lots of possibilities too. Check all of the brake lines and connections for damp spots. Pay close attention to the distribution block and proportioning valve. It will only be a damp spot, any more and the car would run out of fluid. You should also pull the brake drums to see if the wheel cylinders are leaking. I had a similar problem, I ended up spraying all of my lines with carb cleaner, wiping them down, and then watching them until I found the problem, an improperly flared line at the distribution block.
 

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Discussion Starter #3
I'll try that, thanks Bruce.
 

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Ian,
Let me get this straight you pump the breaks and bled them or used a power bleeder i assume you also started at the rear right and went around left rear then right front ending in the left front during the bleed. Now without vacuum the pedal is hard as a rock it shouldnt go 3/4 travel at this time it should be only half or less but be very firm. you start the engine and the pedal foes soft when vacuum is applied? But the breaks hold. Check all the places also stated but i have to ask did you replace the master cylinder or just the booster? it sounds like you may have a leak in the master as a posible cause as fluid may be slipping into the booster from suction through the rear of the master cylinder. check there if you dont find a leak anywher else in the lines or metering block.
 

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sinking feeling

Greg, I'm not too sure about your master cylinder response. I doubt it'd be a new master Cyl, considering that was just replaced.

Ian69cat- does the pedal feel firm all the way down? Either way, you're going to need a brake job. They should lock at 2/3 max. 3/4 is out of spec. I suggest looking at all the lines and the wheel cyls/ caliper pistons (not sure if 69's had front discs). It may be a little costly, but I suggest that you check the booster and replace all the rubber. If, in the off chance, you've still got original rubber in your brake system, it's time for an overhaul.
 

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OOPs i thought i read he replace the booster my bust but new parts have been known to be bad so as last resort i would still check there after everywhere else.
 

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It'll be monday before I can ask my professor about it. He'd know... I know we saw a video on it, but there were so many problem areas it was hard to remember where it began...

Could you describe the problem a little more in detail....
 

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I went through this same thing. Was totally going crazy. Rebuilt master cylinder, new wheel cylinders, new seals on the discs. No leaks. Still the pedal would go away after a while. Finally I figured it had to be a bad master cylinder. So I bought a new one - not rebuilt. It was junk. Returned it - got a new master cylinder. This time it worked perfectly.

So if you don't see leaks anywhere it's the master cylinder despite it being newly rebuilt.
 

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Yeah, I'd be tempted to also blame the master cylinder...every time I've had such complaints about my kitty (once) or my old El Camino (around 12 !!!), or my '46 ford - - - it's always been the master cylinder.

MHO, based on the description and previous work done...

And trust me on this, I pretty much know everything about everything...ask my mommy!!! ;)
 

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Discussion Starter #10
Long time since i read this, thanks for all the advice, but it turns out my brakes do hold, and i guess i was tripped out from having bad brakes. The only thing is that they go down a little low, and i'm assuming that's from warn pads and drums.

Thanks guys
 

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Don't forget rotors and linings:D And remember to bleed them when you're done.
 
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