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73-87 Chevy _ GMC Trucks => Brakes, Frame, Steering & Suspension => Brakes and Braking Systems => Topic started by: mdennison on November 06, 2015, 03:26:09 pm
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77 C10, been sitting for several years. Working on the brakes at this point. I've replaced the MC and the power booster. Did a good bench-bleed on the MC. Now I have bled every corner several times. Here's the kicker: I get VERY little fluid output on the right rear or left front corners while bleeding. Other two corners seem strong. While the brake light is finally out, those two (RR,LF) corners are not braking much, I suspect because they are not getting enough hydraulic pressure. Also, the pedal is slow to return and the brakes are dragging (not releasing very quickly). Is the combination valve the next thing to replace, or is it possible the the lines to those two corners are blocked in some way? I still will probably overhaul each wheel (still has drums in the back), but with insufficient hydraulic pressure, it won't matter how good they are. Hoping not to have to replace all the lines!
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It does sound like a blockage or a leak along the way. Nothing else should stop the fluid from squirting out. Especially since you already changed the mc and booster.
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Thanks! Being that the poor pressure is from opposite corners (left front disc, right rear drum), I doubt the combination valve is the culprit. Is this a generally valid thought? The metal lines all look good on the outside, but of course I cannot see if there is rust on the inside. I've read where the rubber lines can get soft and collapse over time. Do you think these are the more likely causes of the restricted pressure?
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That is my opinion, hopefully we'll get a second opinion. Are there any visible puddles on the ground after pumping pedal?
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ive always heard rubber lines can break down and collapse but i never seen this. what i have seen with my own eyes. is the metal bracket on the brake lines rusting and this squeezes the rubber line almost shut. this will allow fluid pressure to slowly build up and slowly be released (a hanging brake can be caused by this). the rear is kind of a mystery i would take the bleeder all the way out and see what happens inspect the metal lines to see if someone crushed it while wrapping a chain around it to put it on a trailer
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Bleed it at the line before the hose. If you have pressure there then you need to replace the hose.
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Great comments and ideas. There is no evidence of leaking anywhere. I will try the bleeding of the metal line before it connects to the rubber line and see if it makes any difference. It is now cold and rainy and all I have is a carport, so I may not get back to it for a while. The truck has 41K original miles, but it sat for about 4-5 years before I bought it from a neighbor this past summer. It has only ever been in a carport (one family owned since new) - lots of surface rust underneath. Got the engine and tranny going well and I could drive it on down the road now except for the brakes. Even the AC works.
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On one truck I've had that sat for many years, the fluid in the brake cylinders had gummed up. A honing and brake cylinder kit got it working again.