Bleeding brakes

Tried to bleed brakes yesterday and only get a trickle coming out of the rears. Moved to the front and they bleed and work fine. Have new cylinders in the rears as well. Would it be the proportioning valve or brake boost?


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Definitely not the booster. Try bleeding the air before the proportioning valve.
Remember that the volume of fluid going to the back is much smaller, so it may take a few more minutes to get fluid back there.
Joe

Yep for sure booster has nothing to do with it. All it does is assist you in applying the brakes. If the booster is totally out or truck off without any vacuum your brakes still work you just have to press harder.maybe just crack the lines and keep the master full and let gravity run the fluid down to them. When the leak, if they don't already keep bleeding. Are you sure your rear rubber line is not collapsing or bulging out? How old is it?

How I do it.
That is a piece of flat aluminum stock with a piece of rubber glued to the bottom.1 hole drilled and tapped with an air hose fitting screwed into it.A piece of hardware store tubing some flat washers all thread and some nuts.The exhaust springs shown weren't in use that time but are a nice addition.Thats a 5.00, Dollar General sprayer.I just use it for air over brake fluid I don't put fluid in it.I don't, because brake fluid absorbs moisture from air so I use small bottles of brake fluid directly in the reservoir . I like it better than my Snap on pressure bleeder, but it is at least 30 years old.

Thanks for the info guys. I’ll give this stuff a try tomorrow. Original rubber lines in the back so like you said, one of those could be collapsed I guess.


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Had exactly this same issue twice now on the 77 K10. For me, and very possibly for you, the issue is the prop valve. The prop piston in the valve is more than likely moved over (fail safe mode) to block fluid to the rears. The first time this happened I was able to open the front bleeders, stomp on the pedal once really hard and get the prop valve piston to pop back to center (you can hear it pop). Then I was able to go back to the rears and bleed them. The second time this happened, this time with a new prop valve (the other 'new' one was leaking), I could not get the valve to come back to center. It got stuck. So I ended up pulling the warning light sensor and manually pulling the valve back to center with a pick. Then I invested in one of these -



Screw it in where the sensor goes and it holds the prop valve centered. You can then easily bleed the rears. Easy peasy.