Brakes won’t bleed, help!!!

[tophat36]

I have tried bleeding the front and the rear and I cannot reset the proportioning valve physically or thru pedal action. I had to replace the front passenger caliper and hose. While I was at it I changed the hard lines coming out of the master cylinder. Neither the front nor the rears really will bleed. The front some but not like it should. The rear is less but fluid does come out. I’m at a loss and have no brakes to get my truck out of the garage. Please help!

1980 gmc c2500

 

[Chevy 88]

Do you have significant experience bleeding brakes? I'm only asking, so that we don't overlook the basics and go strait to advanced troubleshooting.

As for alternate bleeding options - Amazon has inexpensive next day delivery tools. Some create a vacuum at the wheel cylinder using a hand pump, others create vacuum with compressed air. Then you have an option to reverse bleed, forcing fluid into the bleeder.

Then there is the gravity bleed method.

 

[Ricko1966]

Do you have significant experience bleeding brakes? I'm only asking, so that we don't overlook the basics and go strait to advanced troubleshooting.

As for alternate bleeding options - Amazon has inexpensive next day delivery tools. Some create a vacuum at the wheel cylinder using a hand pump, others create vacuum with compressed air. Then you have an option to reverse bleed, forcing fluid into the bleeder.

Then there is the gravity bleed method.

The shuttle in the combination valve gets off center. It's nothing like bleeding most brakes.

 

[fast 99]

The shuttle in the combination valve gets off center. It's nothing like bleeding most brakes.

People here seem to have a lot of issues with these valves. Can't remember the last time I did. Kind of curious if you have any idea why?

 

[Ricko1966]

Did you empty the master cylinder reservoirs while you were doing your repairs. If the reservoirs ran empty you will need to bench bleed the master. That's mostly just a term you can bleed the master on the car but read up on bench bleeding and bench bleed but use the pedal instead of a screwdriver,and don't push the pedal all the way to the floor. You are going to need to bleed your lines from the master to the combination valve by bleeding them at the combination valve fittings. Then you need to pump the pedal then hold the shuttle valve will recenter. If it doesn't have a friend pump and hold the pedal while you brake a bleeder on which ever brake circuit is getting pressure. If the fronts are getting pressure when you pump the pedal crack a bleeder fitting while a friend maintains pedal pressure,the shuttle should recenter. If the rears will get pressure pumped up crack a rear bleeder and the shuttle will recenter. I use a tool that screws into the combination valve to hold the shuttle centered,makes bleeding so much easier.

 

[Ricko1966]

People here seem to have a lot of issues with these valves. Can't remember the last time I did. Kind of curious if you have any idea why?

I don't know why,it's a luck of the draw thing,I've only had one mess with me,and it was in my 86C10,maybe a batch of the truck centering shuttles came out of the factory a little looser,IDK,but it was a,SOB,A giant PITA. I bought a centering tool and it was amazing.

 

[tophat36]

Do you have significant experience bleeding brakes? I'm only asking, so that we don't overlook the basics and go strait to advanced troubleshooting.

As for alternate bleeding options - Amazon has inexpensive next day delivery tools. Some create a vacuum at the wheel cylinder using a hand pump, others create vacuum with compressed air. Then you have an option to reverse bleed, forcing fluid into the bleeder.

Then there is the gravity bleed method.

I either do the two person method or with a water bottle with some fluid in it and tubing. I got the fronts bled eventually. We pushed the pedal hard 5 times and held it, then cracked the bleeders. Did this until it was free of air. I did the rears first but just never saw much flow. Worked well enough to get the truck out of the garage.

 

[tophat36]

Did you empty the master cylinder reservoirs while you were doing your repairs. If the reservoirs ran empty you will need to bench bleed the master. That's mostly just a term you can bleed the master on the car but read up on bench bleeding and bench bleed but use the pedal instead of a screwdriver,and don't push the pedal all the way to the floor. You are going to need to bleed your lines from the master to the combination valve by bleeding them at the combination valve fittings. Then you need to pump the pedal then hold the shuttle valve will recenter. If it doesn't have a friend pump and hold the pedal while you brake a bleeder on which ever brake circuit is getting pressure. If the fronts are getting pressure when you pump the pedal crack a bleeder fitting while a friend maintains pedal pressure,the shuttle should recenter. If the rears will get pressure pumped up crack a rear bleeder and the shuttle will recenter. I use a tool that screws into the combination valve to hold the shuttle centered,makes bleeding so much easier.

Yeah I replaced the two lines that come out of the MC and the front right hose. I was trying to do all of them at the same time but couldn’t get the 2 front lines off the proportioning valve. I think I have the front bled but the brakes feel very spongy. Good enough to get the truck out of the garage but not long term. Do I still need to bend bleed the MC?

 

[Chevy 88]

Just keep at it. Keep trying different things. You will got it sorted out.

 

[fast 99]

I don't know why,it's a luck of the draw thing,I've only had one mess with me,and it was in my 86C10,maybe a batch of the truck centering shuttles came out of the factory a little looser,IDK,but it was a,SOB,A giant PITA. I bought a centering tool and it was amazing.

In the shop when I finish a corner or axle I open the bleeders and let them gravity bleed. When finished installing brakes only one corner remains. Works a majority of the time and doesn't move the valve. ABS systems, that's another story for another day.

Will add on PU and larger brake systems most times I drive around the block and hit every bump I could find. Then re-bled all 4 corners. Was rare not to see additional air. Gravity bleeding didn't always work, especially on systems run dry.

 

[Sad Sack]

Not sure but aren't there certain proportioning valves that require little doodad tools to properly bleed the system. Memory is foggy but seems to me there were instances that require a little clip tool or a screw in bleeder valve doohickey.

 

[tophat36]

Just keep at it. Keep trying different things. You will got it sorted out.

That’s exactly what we did. I have never bled brakes for pretty much an entire day before. I’m just grateful that I was able to get it out of the garage and into the street without needing a tow truck. Once the front were bled I didn’t reattempt the rear. Will probably wait until I do the rears drums in a few weeks. That way I can verify the wheel cylinders at the same time.

 

[tophat36]

I don't know why,it's a luck of the draw thing,I've only had one mess with me,and it was in my 86C10,maybe a batch of the truck centering shuttles came out of the factory a little looser,IDK,but it was a,SOB,A giant PITA. I bought a centering tool and it was amazing.

The centering tool only helps you prior to tripping the valve though right? Not after? I’d really like to take the valve off and look at it up close and be able to see the inside better. I’ll have to invest the $5-10 for the future. Add this to the list of lessons learned.

 

[Ricko1966]

The centering tool only helps you prior to tripping the valve though right? Not after? I’d really like to take the valve off and look at it up close and be able to see the inside better. I’ll have to invest the $5-10 for the future. Add this to the list of lessons learned.

Yes the centering tool only holds the shuttle valve centered. To center it you need to get the hydraulics good enough to center it or manually center it with a small screw driver through the broken warning switch hole. You don't need to bench bleed the master,if you didn't run the reservoirs close to empty. I would still bleed the rear line at the combination valve fitting.If After that,center the shuttle valve with the pedal,and then vacuum bleed the rears or get a centering tool and pedal bleed the rears. After the shuttle is centered,you can try gravity bleeding the whole system,it is/was never my go to, for a few reasons,but some say they've had good luck on a square so try it at your own risk.

 

[tophat36]

Yes the centering tool only holds the shuttle valve centered. To center it you need to get the hydraulics good enough to center it or manually center it with a small screw driver through the broken warning switch hole. You don't need to bench bleed the master,if you didn't run the reservoirs close to empty. I would still bleed the rear line at the combination valve fitting.If After that,center the shuttle valve with the pedal,and then vacuum bleed the rears or get a centering tool and pedal bleed the rears. After the shuttle is centered,you can try gravity bleeding the whole system,it is/was never my go to, for a few reasons,but some say they've had good luck on a square so try it at your own risk.

The reservoir was empty after changing the lines coming out of it. I can try to bleed the MC using the pedal and crack the fittings on the 2 connected lines.

What do you mean bleed the rear line at the combination valve? If you mean to disconnect the hardline that goes to the rear brakes, then that has proven impossible for me. I tried to take that off for a few hours, even tried heat. No dice.

How do you center the shuttle using the pedal?