This is what the inside of your brake system looks like...

[Yamaben]

My 1990 C3500 had a brake light that I couldn't seem to make go out. After some reading, I figure that maybe the RWAL brake solenoid is causing the problem. I also figure the brake system might need an overhaul after 25 years.

 

[Yamaben]

I wanted to simply take apart the RWAL and clean it, but I broke 2 pieces trying to get it apart. Very crusty and corroded inside. Auto Zone sells a rebuilt one of these for $125. I bought it.

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[Yamaben]

The master cylinder was pretty scummy inside. I have rebuilt hundreds of master cylinders on motorcycles, but a whole new (not reman) M/C assembly complete with a new plastic reservoir and lid was only $53 from NAPA. The rebuild kit was $39. I bought the new one.

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[Yamaben]

The calipers both had sludge build up inside. They are both pitted from corrosion too, but I think they are ok to reuse. Guess I'll find out when I go smashing through a building.

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[Yamaben]

The pistons were gross too

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[Yamaben]

Calipers cleaned with new seal kits installed. That rust pitting wont hurt a thing. These will work fine

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[Yamaben]

I put the pistons in the ultra sonic cleaner at work, and then polished them on the lathe

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[Yamaben]

The proportioning valve had lots of sludge inside, but this picture is after I cleaned it.

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[Yamaben]

I've always liked laying out the new parts and looking at them. It just makes me feel good to see it all lined up like that. It's just a weird, kind of obsessive thing I do, I guess.

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[skylark]

You address a big problem on our trucks, age + a lack of maintenance. I flush every fluid every 5 years without fail.