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Can't get brakes to bleed (1978 Chevy K10)

I just rebuild the front end (ball joints, tie rods, bearings, etc) including the calipers and rotors and put new rear wheel cylinders on along with about 8 foot worth of rear brake line, rear brake hose and a new master cylinder.

I cannot get the front brakes to bleed the peddle is very, very soft.

I believe the back brakes are OK. I removed the front brake line from the MC and plugged the hole. When I did this the peddle was rock solid. However, with the front line hooked up (along with the back) the peddle goes to the floor.

I have went through about 3 gallons of brake fluid trying to bleed the front brakes. I replaced the bleeder screw just in case those were the culprit but it didn't make a difference. I don't see fluid leaking from anywhere so there is no obvious leek that would be letting air in.

Any ideas on where I should look to find the problem?

Thanks in advance.

Reply to
ngpost1
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this is a vague memory, but some systems have a "shuttle" valve in the system that senses (fluid volume, pressure difference?) between the front and rear circuits, and can cut off the faulty circuit as well as lighting a warning light. Check the brake lines from the master on down and see if there is a valve like thing with a button to press while the brakes are bled.

--Ken

Reply to
dye

Get behind the wheel and hit the brake as fast as you can and hard enough to scare it. I had this happen on a similar vintage vehicle before.. There is a valve in the system (part of the proportioning valve? heck if I remember) that sense the lack of pressure and directs the fluid to the other circuit. They get old and wonky and stick when you bleed the brake.

Steve B.

Reply to
Steve B.

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