Question about 1988 Chevrolet C1500

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Brakes (rear) Previous owner (1 month ago) changed the left rear brake cylinder. Pedal felt spongy when I bought the truck, so I bled the right rear, then the left rear brake cylinders. I'm 99.99% positive that I had no air left in those cylinders, and the master cylinder was kept topped-off the whole time. However, now the BRAKE light comes on whenever I press the brake pedal. What did I do wrong, or is there something else I should look at?

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  • Dean Phillips Mar 12, 2009

    Good call, xsvector! The right rear cylinder had a 1/8-inch hole in the forward boot, and there was brake fluid all over the inside of the drum, and all over both shoes. Luckily, the previous owner had told me he bought a second new cylinder but hadn't installed it yet (it was still in the wrapper under the seat). I cleaned up the drum and brake components, then replaced the wheel cylinder and bled the rear brakes again. However, I still have the BRAKE light coming on, and the pedal still goes to the floor and feels really mushy. I'm going to recheck the rear cylinders for air again tonight, and if they're okay, I'll try bleeding the front wheels. If that doesn't resolve the problem, since I don't appear to have any leaking brake fluid anywhere, I'll probably try the master cylinder and/or the proportioning valve next.

  • Dean Phillips Mar 23, 2009

    Follow-up: After replacing the RR wheel cylinder, I replaced the master cylinder with a reman unit. However, I still had the same soft-pedal problem. I still could find no leaks. Reluctantly, I took it into the shop. They found broken brake springs in the LR wheel and replaced them at no charge. Both rear drums and brake shoes were "saturated with brake fluid", so they replaced those (NOT at no charge). They recommended replacing master cylinder again with a brand-new (not reman) unit. At this point, they thought they had the problem licked, and told me I could pick up the truck that evening (second day) but when they road-tested the truck the brakes faded out on them again. They couldn't find any leaks either. Finally (evening of the third day, working 3+ hours past closing time) they replaced the ABS modulator and dump valve. They bled the entire system one more time, and now (four days and $1000+ later) I have good pedal and stopping performance. My wife says that, after this expense, further restoration efforts will have to be delayed for a while, but at least now my truck stops on a dime instead of a dollar!

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I would look at the othe rear wheel cylinder it is most likely leaking

Posted on Mar 10, 2009

  • xsvector
    xsvector Mar 10, 2009

    i would look at the othe rear wheel cylinder it is most likely leaking

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1997 mercury sable gs 3.0l replaced master brake, still having brake pedal feeling spongy and slowly traveling down. i bench bled master brake and bled brake right rear left rear right then front.


If the master cylinder is replaced, care must be taken to prime the new master cylinder by removing all of the air and completely filling it with brake fluid. The spongy feeling is air that is still in the circuits. You will need to bleed the back brakes as well as the front ones again. The order that you bled them seems correct, but perhaps there remained some air in the main trunk lines.

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Most of the brake fluid can be reused, but not the darker portion at the bottom of the jar.

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