This is not a reply you want . If you are actually trying to fix someone else’s brakes and have theories instead of actual knowledge then you should tell the person they should have a shop fix their brakes.
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Volvo_V70, I’m not interested in your negativity. He’s allowing me to learn from his brakes. If I can’t solve the problem, then we’ll go to a mechanic. If I go to a mechanic I learn nothing. If I study theory and then do some actual testing on a vehicle, then I can learn. I get tired of people like you who automatically think I’m stupid. You don’t know what my experience is. I don’t have much experience with brakes but I have experience at other things.
One other thing: Mechanics aren’t always so smart either. Last summer I went to a mechanic and had the rack and pinion changed in my chevy venture. The symptoms were noisy steering pump and steering fluid leaking out passenger side of the rack. After he gave me the van back the pump was noisier than when I brought it to him. He told me he wanted to save me money by not replacing the pump and said I can just live with the noise. A week later, I was driving along and suddenly the power steering didn’t work. I will never go to that mechanic again. That mechanic actually has awards hanging on his office wall honoring him for being such a great mechanic. I took the steering pump apart and discovered that the spline that connects to the rotor was partially stripped so the pump wasn’t spinning to build up a pressure. I changed the pump.
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I posted this thread almost 2 years ago but I ended up being too busy with other things, but I did get back to this project a few days ago and I did solve the problem. The symptoms that I mentioned in the original post aren’t exactly right. it was my understanding that there was a loss of brake fluid, but I found out there wasn’t. The owner of the vehicle told me that he used the truck for about a month and has never had to add any brake fluid. The brakes worked normal for the most part. The problem is when he’s sitting there in traffic with the brakes on (such as at a red light), the brake pedal would slowly sink to the floor and he’d have to pump it to get the pedal back up (Yes I did tell him not to drive it like that). I spent some time on it 2 years ago and wasn’t able to find any external leaks and I bled at all 4 wheels. After several hours of reading articles and watching videos again, I became very sure that the problem was that the fact the pedal sinks to the floor means there’s a leak. 2 years ago I couldn’t find an external leak, so I figured there must be an internal leak in the master cylinder. I didn’t understand this idea 2 years ago but I realized this time that if the seals are bad in the master cylinder, the brake fluid will just flow past them when the pedal is pressed. So when sitting in traffic and holding the brakes down, the fluid would slowly leak past the seals causing the brake pedal to sink as the pressure is going away. I changed the master cylinder and the brakes are good now. I did a bench bleeding of the master cylinder, bled the two outlet ports of the master cylinder after installation and bled at all 4 wheels.
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