Brake Problems
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New User
Joined: May 2010
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Brake Problems
I own a 1975 ford f100. It has problems with the drum brakes, both cylinders in the drum brakes are leaking. But that's not the real problem, the real problem is, when I bleed the brakes, air is coming from somewhere. it never comes out in a clear stream, even after i filled the reservoir five times. The experienced mechanic I was working with told me it was the pressure differential valve. could this be it?
Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
Did you mean the positioning valve? Did you fix all the leaks? If the front cylinders are leaking it could suck in air there too. If the positioning valve is bad it would leak or you would not get fluid in my experience. I have a 75 F-100 4x4 also. I feel you pain. Went through fun with the drum brakes too. I converted to disc brakes back about 5 or 6 years ago. Wasn't cheap but will stop now. But the drums will work if you get everything sealed up. Welcome to FTE.
Junior User
Joined: Feb 2010
Posts: 60
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If your wheel cylinders are leaking like you say they are, they are going to suck air into the line everytime you press, than release your brakes... Making it so you can't bleed them... The air in the lines is coming from the leak .. You won't be able to bleed them until you replace th bad wheel cylinders, and you won't have the problem anymore
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
I completely agree with DansBBF250. If brake fluid can get out, then air can most definitely get in. Only until the braking system is completely sealed and free of leaks can you begin to purge it of air. What's the point of bleeding the brakes if the wheel cylinders leak anyway? Surely you weren't going to put this truck on the road...
Junior User
Joined: Feb 2010
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Yes it is VERY dangerous! The leak will only get worse to the point where they will fail... Be sure to replace the brake shoes as well if they have any brake fluid on them. Don't try to clean the brake shoes with brake cleaner it won't work.. Brake fluid is corrosive and will eat away the padding on the shoes. If possible, park it untill you can fix it, and borrow someones car or rent a car untill they are fixed if you don't have another rig. You really don't want to put your life, and other drivers in danger... I'm Not sure why that mechanic told you that, but if you replace your wheel cylinders, and replace your bake shoes, and resurface your drums, and bleed the brakes, all your problems will be gone...
Post Fiend
Joined: Apr 2008
Posts: 8,261
Likes: 15
From: Big Sky Country
Ditto what the others have said, why not just replace the wheel cylinders they're like 10 bucks each, if not brake fluid will eventually find it's way onto the brake shoes (if it hasn't done so already) then you'll be into the job for the cost of new shoes as well.
Cargo Master
Joined: Dec 2006
Posts: 2,511
Likes: 8
From: hinckley ohio
if you have 4 wheel drums you wouldn't have a preasure differental valve or proportioning valve.There on front disc, rear drum to balance them out.
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
That is not correct 4 wheel drums still have a proportioning valve. My 75 has one also. I put in a different one when I put the front disc on. The master cylinder has 2 chambers also.
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
It's on the frame below the master cylinder and behind the cross member. There is a metal piece that sticks up that kind of protects the steering shaft it is right below that. I am running a wild horses one on my truck. I think I paid $98 for it but that was like 5 or 6 years ago.
Elder User
Joined: Sep 2004
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It's on the frame below the master cylinder and behind the cross member. There is a metal piece that sticks up that kind of protects the steering shaft it is right below that. I am running a wild horses one on my truck. I think I paid $98 for it but that was like 5 or 6 years ago.
Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
I got mine at wildhorses4x4.com It's a bronco site. I bought the whole front disc brake kit from them. I looked and they have a proportioning valve for the drum/drum set up also. According to them it is the same as the disc/ disc setup. It is item number 3037 and the price is $94.99. They changed some of the ways to get around the site. I just typed brakes in the search and it was on the first page. The one I got from them leaked after about 8 months on my truck, but I talked to them and sent them the bad one. They sent out a new one for no charge. That one has been fine for many years.
Freshman User
Joined: Jun 2010
Posts: 42
Likes: 0
Seconded my 75 f250 has all drums and it does indeed have a 2 chamber master and a proportioning valve. witch is failing (as far as I can tell).
Did you say that they had one for DRUM/DRUM or just DISC/DISC?
Thanks.
Did you say that they had one for DRUM/DRUM or just DISC/DISC?
Thanks.
Post Fiend
Joined: Apr 2008
Posts: 8,261
Likes: 15
From: Big Sky Country
Drum/drum brake setups do not use a proportioning valve per se, instead they use only a pressure differential valve, disc/drum brake setups use a pressure differential valve as well but also use a metering valve and/or proportioning valve within the same valve body i.e. a combination valve.
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