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Old September 1st, 2009, 09:44 PM   #1
bnmarlatt2004
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Default Brake issues, need help......

Me and my father in law have gone over everything we can think of and we can not figure out why the brakes are still soft. we have blead the brakes, checked all vacumn hoses and we have plenty of vacumn. Just can't figure out why they aren't working well. Let me know if you have any ideas on what could be causeing the soft brakes. I have a 79 ford f-150 shortbox, 429 big block, stock brakes.
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Old September 1st, 2009, 10:23 PM   #2
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Have you adjusted the rear brakes?
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Old September 1st, 2009, 11:36 PM   #3
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Yeah, make sure the rears are adjusted first.

You can pinch off the rubber hoses with some pinch off plyers and see what that does, if the pedal is high and firm remove them one at a time to find out where the problem is.

If it is still poor then it is either air or a bad MC. You can check the MC by removing lines and blocking off the ports with something. if the pedal gets high and firm it's not the MC.

I have seen calipers with bad orings that pull the piston back when you let off the pedal giving you a soft and low pedal. Also if the calipers have the bleeder on the side I have seen air get trapped in there. You can take the caliper off adn put a block of wood between the pads so you can tilt the bleeder up while bleeding

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Old September 2nd, 2009, 06:11 PM   #4
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ok, we have allready adjusted the rear brakes and blead the brakes very well too so I will check your suggestions. thanks.

any other ideas please let me know.
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Old September 3rd, 2009, 03:02 AM   #5
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Are you using silicone based fluid? Silicone fluid has a spongy pedal feel because it is more compressible than ordinary brake fluid. The pedal will also have more travel before the brakes are fully applied.
To check the system for air have someone apply the brakes about 10 times, holding it the last time. With the master cylinder cap removed watch the movement of the fluid while the pedal is released. A heavy surge from the compensating port indicates air in the system. Note which chamber has the high fluid surge. This is the side that has the trapped air.
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Old September 3rd, 2009, 03:19 PM   #6
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my 79 bronco had a pin in the proportining valve that had to be pulled out while bleeding
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Old September 3rd, 2009, 03:32 PM   #7
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Are you still running the original rubber lines? Try replacing those. A guy I work with was just going through the same thing. Kept bleading the lines and bench bled the master, then ended up replacing the master cylinder. He got to the point where the only thing left was the soft lines and replaced those and everything worked perfect.
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Old September 3rd, 2009, 03:37 PM   #8
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I just had the same problem on my blazer and i replaced the master w/ a 1ton master w/ a bigger bore and now it stops a lot better.
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Old September 3rd, 2009, 04:34 PM   #9
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I'm gonna try a new master cylinder tomaroow and see if that works. If not I will try some more things. Thanks for the help.
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Old September 3rd, 2009, 04:44 PM   #10
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Check the prices and if theres a upgrade master you can do. All the ones for my blazer and ones for a 1ton truck were right around the same price. Ask about the bore side too, if you can get a bigger bore one go for it!!
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Old September 4th, 2009, 04:38 PM   #11
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thanks again. just put thenew mc in and it worked. Much better. thanks again to everyone.
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Old September 4th, 2009, 06:41 PM   #12
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Did you get a bigger bore one or just a stock replacement one?
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Old September 5th, 2009, 04:25 PM   #13
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stock replacement and it works great now.
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