Brake Problems
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New User
Joined: Feb 2016
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Brake Problems
I'm having an issue with my brakes on my 76 F150 where I have a lot of free play with my brake pedal. The pedal goes a good 6" before you can feel the brakes engage. Also, sometimes (not very often) I completely lose my brakes where the pedal goes to the floor with no resistance at all. I have to release the pedal and the pressure comes back. I was wondering what part would be the issue, power booster, master cylinder, proportioning valve or what? PS I did replace the rear drums, shoes, etc.. about a month ago where it didn't help the problem at all. Any help will be great thanks.
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New User
Joined: Feb 2016
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Yeah I recent bought this money pit. The guy that sold it to me said he redid the brakes about a year ago. But once in a while the brakes needed bled. Needless to say I was trying to bleed them and found that one of the rear wheel cylinders was bad. I opened up the drum and the shoes were completely to the metal. That is where I replaced everything except the lines going to each rear wheel. Sorry to ramble. Do you think it is worth it to replace the MC and Brake Booster all together or just replace the MC?
Mountain Pass
Joined: Feb 2003
Posts: 185
Likes: 3
From: Fargo
From my experiences.
When a booster goes bad, the pedal gets rock hard.
Usually when they go bad you have symptoms of a massive air leak, you can test it by pinching off the vacuum feed line (rubber from motor to booster).
Yours really sounds like a master cylinder problem.
When a booster goes bad, the pedal gets rock hard.
Usually when they go bad you have symptoms of a massive air leak, you can test it by pinching off the vacuum feed line (rubber from motor to booster).
Yours really sounds like a master cylinder problem.
Elder User
Joined: Jan 2003
Posts: 759
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From: North Dakota
Double check your rear brake adjustment first, then I would get a new master cylinder.
One thing I have learned on older vehicles is that the brake system turns into a cascade of failures... once I replaced everything I finally had good brakes again.
One thing I have learned on older vehicles is that the brake system turns into a cascade of failures... once I replaced everything I finally had good brakes again.
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Lead Driver
Joined: Apr 2011
Posts: 6,399
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From: El Dorado, Arkansas
Sounds like the MC may be internally by-passing or, it may be leaking out the back end where it bolts up to the booster.
Look on the face of the booster to see if it's wet with brake fluid. You may have to loosen the nuts holding the MC to the booster and slide the MC forward enough to get a good look at the back of the MC.
IF the MC is leaking out the back end (where the output rod of the booster goes into the MC), and IF the brake fluid has leaked over into the booster, the booster will also have to be replaced since brake fluid will destroy the booster's rubber diaphragm.
Look on the face of the booster to see if it's wet with brake fluid. You may have to loosen the nuts holding the MC to the booster and slide the MC forward enough to get a good look at the back of the MC.
IF the MC is leaking out the back end (where the output rod of the booster goes into the MC), and IF the brake fluid has leaked over into the booster, the booster will also have to be replaced since brake fluid will destroy the booster's rubber diaphragm.
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Lead Driver
Joined: Apr 2011
Posts: 6,399
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From: El Dorado, Arkansas
Unless something really crazy happened, there shouldn't be anything wrong with the brake valve --other than the pressure differential valve spool MAY have shifted. It will just have to be recentered, if it has shifted.
Moderator & parts slinger
Joined: Feb 2007
Posts: 50,096
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From: S/W Missouri, Polk county
Once you get the new m/s and booster on and get a good brake bleed done, you should be ok. And not have to replace the pro valve. Did you push or pull the pin on the pro valve afterwards?
Lead Driver
Joined: Apr 2011
Posts: 6,399
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From: El Dorado, Arkansas
If you have the brass brake valve, (made by Weatherhead for trucks over 6,800 lbs), the metering bleed pin is pushed inwards.
Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
Sometimes this works. Other times it doesn't. If it doesn't, you'll have to open a bleeder opposite of the circuit that tripped the warning light, mash down on the pedal until sufficient pressure builds up on the side that failed, in order to push the spool back over to recenter it and turn the warning light off.
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