I dont understand..

[SS66]

I just replaced ALL of my brake lines and hoses. I was bleeding the brakes with the truck off and I built up good pressure and figured all was well. When I turned the truck on and pushed the brake pedal it was soft and went to the floor and wont build up pressure. But when I turn it off again and pump it.. it gets stiff. Anyone know what the problem is?

Thanks

 

[Pvt. Maggot]

You have air in the lines, bleed at the master cylinder, before starting at the brake farthest from the master cylinder. Make sure all your lines are tight, and the fittings arn't leaking.

 

[onetonbb74]

sounds like a booster, do you have vacuum brakes, or hydro boost brakes? rear disc?

 

[SS66]

sounds like a booster, do you have vacuum brakes, or hydro boost brakes? rear disc?

I dont know. I didnt see that big black ball thing some brakes have which I think is vacuum? I have two lines that go to the proportioning valve then from there they branch out to the individual lines.

I'll have to go check if the rear is a disc tomorrow, Im cleaned up and in for the night. Though its an 88 K5 so It probably is.

I didnt bleed at the master cylinder.. I was unaware that I had to. Do I bleed where the lines meet the proportioning valve to do the master cylinder?

It worked fine before I blew a brake line.

Oh and I have no leaks...not anymore at least

 

[Hogback Fabrication]

I dont know. I didnt see that big black ball thing some brakes have which I think is vacuum? I have two lines that go to the proportioning valve then from there they branch out to the individual lines.

I'll have to go check if the rear is a disc tomorrow, Im cleaned up and in for the night. Though its an 88 K5 so It probably is.

I didnt bleed at the master cylinder.. I was unaware that I had to. Do I bleed where the lines meet the proportioning valve to do the master cylinder?

It worked fine before I blew a brake line.

Oh and I have no leaks...not anymore at least

K5's never had discs in the rear. Diesel and 1 ton trucks had hydroboost brakes, so if you have a gas powered K5 you have vacuum brakes.

I agree that you probably haven't got the air out of the lines yet.

 

[SS66]

Looks like I will be doing more bleeding tomorrow.

To bleed the master cylinder do I do it where the lines go into the proportioning valve? I didnt know I even had to bleed it there. I thought the air would end up pushed to the wheel cylinders and I could extract it there.

Also, not that it matters a lot but I'd like to know the reason why its stiff when the truck is off but soft and spongy when its running. Anyone want to explain in laymans terms?

Oh and is it OK to bleed it with the truck off? I prefer to because its loud due to an exhaust leak but will run it if need be.

THANKS CK5!

 

[Chevy305]

yes, bleed with the engine off. The reason your pedal gets mushy when the engine is running is because the engine is producing vacuum, thus powering the brakes. When the engine is first shut off, there is some residual vacuum left but after that is used up, the pedal becomes stiff because there is nothing to power the brakes other than your foot.

Also if you blew a brake line and just replaced the damaged section, then there is a huge amount of air in the lines. Your only realistic option is to power bleed the system and/or gravity bleed. Also, if at any point the master cylinder ran dry then you have to bleed the master cylinder.

 

[Cowboy_80]

by gravity bleeding he is referring to hooking up a hose to the wheel cylinders and opening the bleeder screw. Stick the other end of the hose into a cup of brake fluid though to keep it from sucking air. It's the easiest way ever to bleed brakes. It also takes forever. One thing that you need to pay attention to while you're bleeding the wheel cylinders is the fluid level in the master cylinder. if it gets too low and sucks air, you've pretty well wasted your time and money...

 

[dyeager535]

My dad just did a rear disk swap, we did the gravity bleed method on the rears.

Just watch the fluid coming out of the wheel cylinder, when the bubbles stop, let it go a bit longer and then seal it.

It does take awhile, but it's fast enough, and easy.

In my experience on this truck, bleeding by pumping the pedal then opening the bleeder with the pedal down was unnecessary, got the same results by pushing the pedal down once and holding, then bleeding.

 

[SS66]

All of my bleeder screws are busted or rounded off so Ive been loosening the screw ( fitting at the end of the brake line) where the line runs into the cylinder to let fluid out, then I tighten it before my helper lets off the pedal to avoid sucking in more air. I know this isnt the best way and leaves some air in still but right now its my only option till I can afford new cylinders. I replaced ALL the lines so there is probably a huge amount of air in there.

Thanks for the help guys.

 

[Chevy305]

All of my bleeder screws are busted or rounded off so Ive been loosening the screw ( fitting at the end of the brake line) where the line runs into the cylinder to let fluid out, then I tighten it before my helper lets off the pedal to avoid sucking in more air. I know this isnt the best way and leaves some air in still but right now its my only option till I can afford new cylinders. I replaced ALL the lines so there is probably a huge amount of air in there.

Thanks for the help guys.

Thats your problem, you will never get all teh air out by doing the two person method. Since you're not a member here, google gravity bleeding and pressure/power bleeding. I replaced the rear lines from the proportioning valve back and I had a vacuum bleeder and there was no way I could get enough air out to even make the truck remotely drivable.