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73-87 Chevy _ GMC Trucks => Brakes, Frame, Steering & Suspension => Brakes and Braking Systems => Topic started by: Ben_Greenberg on September 30, 2014, 08:20:29 pm
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Hey guys,
I've been struggling with my rear brakes and finally got everything tidied up. This is on my 78 c15 with power brakes.
Now I'm trying to bleed the brakes so that I know there isn't any air in the system. Is there anywhere I can look for a good tutorial on how to bleed my brakes. Im used to abs systems on newer vehicles.
I was hoping just turning the bleeder valve at the drum and having my wife pump the brakes would do the trick but it doesn't seem to be enough. Any and all help is appreciated guys! Also, do I need to have the truck on or running to bleed the brakes?
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You do not have to have the truck running to bleed the brakes. I usually open one of the brake bleeders on either wheel and let it gravity bleed until it starts dripping out the bleeder and again on the opposite side. This at least gets the fluid down to the bleeder and most of the air out of the system. Don't forget to keep the master cylinder full. When this is accomplished I would then have somebody help and bleed them again and check how the pedal feels. If nothing is working you may have a problem with your brake valve on the front cross member. You may already know when a brake line fails this shuts off the fluid to that particular line and has to be reset. A light in the cab usually lights up when this happens unless your bulb is burned out or harness is not connected at the brake valve. Just my opinion. Hope it helps.
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ive always done just like illiniosk said. i crack the left rear bleeder and was away then once it starts to more than dribble ill close it and crack the left rear.
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Thanks for the replies guys.
I did not know that the brake valve shuts off. How do I reset this?
One of my wheel cylinders fell apart and so I had to replace it. In the mean time it just dribbled all the brake fluid out. I will gravity bleed the brakes and once I've got fluid moving I'll have my wife come pump the brake pedal.
Any special instruction as far as pumping? On my other vehicles I just pump until I don't see bubbles and I shut off the valve. Same idea?
Also, I've been searching around for the answer to this, but the two reservoirs under the cover. Is one for the rear and one for the front? What's the purpose of these?
Sorry for all the new questions. Thanks guys!
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I always left the truck off. Here are the steps that I use to bleed the brakes with a helper:
Helper pumps the brake and keeps pressure on the brake. Helper then says OK.
You open the bleeder valve, the pedal should go to the floor. Helper then says "its on the floor"
You tighten up the bleeder valve while the helper still has their foot down on the floor. The helper maintains pressure the entire time. After the bleeder valve is tight then you say "OK pump it". Then you repeat the process until you see no air bubbles.
If your helper pumps the brake while the bleeder screw is open then air will go back into the line and you have wasted your time. You will have to start over and it will take longer. Hope this helps.
The two reservoirs are for the front brake and the rear brake. I have always thought that it was done as a safety feature so that you would always have some brakes in case of a failure.
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Don,
Thanks for the info. Any idea on the brake shutoff? Is that a valve or something? I haven't been able to crawl around to look for it.
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Idk for sure but the two reservoirs could be because disk use more pressure than drums. But the ideal about not losing both front and rear also is possible. If you follow the lines off the master cylinder it goes to the front cross member. That's where the proportioning valve is at it should have a button on it and that is supposed to trip when you lose pressure
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The dual MC is for safety
I gravity bleed em then have a helper in the cab
I say "down "
Helper mashes pedal and after its down helper says "down"
I crack the bleeder and watch
Then close bleeder and say "up!"
Helper releases pedal and after they do , helper says "up"
Repeat about 100 times
Also if your MC is not brand new
Place a block of wood or something on the floor so the pedal can't go down beyond what it's normal travel is
If you pump it all the way to the bottom a lot sometimes it will damage the o rings inside the MC
Start at the right resr then do Left rear
Right front and left front
Then repeat it at least once more
If this doesn't work you may have to use a pressure bleeder and if that doesn't work you have a bad MC or prop valve or swollen rubber flex lines
The flex lines on Squarebodies are notorious for swelling closed on the inside when they get old
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Thanks for all the info! I will try this out and post an update!
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Like roundhouse said,sometimes pumping and to much pressure makes tiny bubbles out of big ones.Fluid will start to foam,makes it harder to get all the air out
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Got everything set! Worked great! Thanks for all the help guys!
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I take my hand held vacuum pump with a bleeder cup in the line , fill the master , apply vacuum and suck the fluid through the lines. works great and you can do it without a wife or helper 8)