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Discussion Starter #1
I have a 2003 F350 SRW, 7.3L PSD, Crew Cab, Auto, with 4x4 and adjustable pedals.

I have a problem with weak rear brakes, recurring. The rears aren't doing enough work. I bled the brakes back there and for the immediate time, they were better, however within about a week, the brakes were back to how they were.

I am wondering if anyone has seen this before.

I have 188K miles on the truck. The front calipers are new, the rears are not.

The rear calipers are original, but don't seem to be sticking. Wondering if air is possibly leaking in, although I don't know that this would make sense because the brake calipers are usually under a slight positive pressure from the head of the fluid from the master cylinder.

Is there something that could go wrong with the master cylinder that could cause this? The truck also seems to have trouble stopping on a dime when necessary, so I'm wondering if all of the brakes may be weak and if i need a master cylinder.

I have also heard something about some kind of failure inside the ABS unit on these trucks that causes a soft brake pedal.

Any ideas or suggestions are greatly appreciated. Thanks for your time.
 

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Do the calipers slide properly? How do the rubber lines look-cracked and corroded? When you bled the brakes, did you flush all the old fluid? Brake fluid is anhydrous (containing no water) but also hygroscopic (has a tendency to attract moisture from the air). As it gets older, it absorbs moisture and as such lowers the boiling point. This results in brake fade, and otherwise sub-par braking performance. Make sure the rear calipers slide properly, the pistons move in and out freely, none of the brake lines are bent/kinked, and finally bleed the brakes until the master is nearly empty, refill, and repeat until the brake fluid coming out of the bleeders is new and clean. Does wonders.
 

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Discussion Starter #3
Would you agree that I could eliminate calipers as sticking by having an immediate improvement that lasted a few days after bleeding brakes?

Thanks for the sound advice. I inspected the lines and felt for deformation with brake pressure applied. I think I will try the mass bleeding next.
 

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How have you determined the rear brakes are not doing enough work?
 

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Discussion Starter #5
The pedal feels low but somewhat firm. The front brakes have got hot to the point that the shims have moved. I can't make an immediate stop from high speed if I literally put my back against the seat and stand on the pedal.
 
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