Brake Bleeding. Need some help

So I'm at the stage if bleeding the brakes and I'm running into an issue I cannot for the life of me fix. I replaced my front lines on my CJ past the union T (hard lines, brake hose, etc.) When I press on the brake pedal to get pressure built up in the lines, instead of fluid going in and pressurizing the air in the line, the air comes back from the line out of the master cylinder.

I have already bled my rear brakes and have a dual MC. I checked the lines to see if I have and leaks or kinks. None to be found. Also replaced the rubber parts in my front passenger wheel cylinder.

Ideas?

 

Check the bleeder valves and see if they are plugged. If not then most likely a m/c issue.


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Stuck the little brake clean nozzle into both of them, no dice

 

Did you bench bleed the master cylinder? Even if it's not a new MC, if you run them completely dry, they will get air in the bore and you'll need to bench bleed. It's possible that the air you're seeing is that air in the bore.

 

I don't know where you live,but here,I have to run a drill bit in the bleeder screws to get them clear.

 

Well there wasnt much gunk in them to begin with, so brake cleaner went straight through. The jeep has lived in Idaho its whole life.

 

Anybody every have that issue before?

 

I don't think so. Every one that I've ever installed out of the box has required bench bleeding.

 

If its a frame mounted m/c it won't gravity bleed. Might remove the line(s) from the m/c and bench bleed in the vehicle then re-bleed the system and see if that helps. Are you using dot3 or dot 4 fluid? If using dot 5 silicone that can create issues as well.


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the simplest answer is usually the correct one. sounds like a clog in the lines. unscrew lines and blow some compressed air through them.

 

Well its still on the frame and I dont think that gravity bleeding will really help....I've heard tale that it may be the proportioning valve that is the issue. When I first took my lines off the front I didnt think to bleed my brakes. And I've heard that if the brakes had a sudden blow out on either end (front or rear) that the proportioning valve would keep fluid from going in the side that has the blow out. Am I wrong on this?

The symptoms when I try to bleed the front brake: When pressing the pedal fluid comes out of the top of the cylinder, when letting the brake pedal rest after pumping fluid comes back into the reservoir. When I take the soft lines off the "s"-line and pump the brake fluid goes through the line. But when connected to the "s"-line it does that bubbling thing and fluid wont go into the wheel cylinder even with the bleed screw open....Totally confused at what is going on here with all of these problems at once.

 

Are you actually seeing air bubbling back up into the M/C reservoir or is it actually fluid? Either way, this is a problem with the M/C. The fluid in the M/C should only go one way which is out to the lines.

 

Yes it will.
Maybe not by gravity, but by siphon.
DAMHIK.

 

It could be fluid coming back out, but it looks like air.

 

When the piston travels back to the rest position it then sucks the fluid into the piston area and the piston will push some fluid back up thru the reservoir until it passes the inlet port. Once the piston passes the input port then you should not have any fluid bubbling back up into the reservoir. The amount of fluid returned is dependent on how much your piston return travel is adjusted for. If bubbling is occurring during the full piston travel, then you need to re-kit the M/C with good cleaning and bore inspection.

 

I just came across a similar issue when I was bleeding my all new brake system. Not sure what front axle you have. I have a D30 front axle with disc brakes and a D44 with 11" drums.
With a new dual reservoir m/c that I bench bleed; I was not getting a firm pedal and I was getting air bubbling back into the m/c. The solution....I had the front calipers switched. The calipers are not clearly marked and I mixed them up. With the calipers on the wrong side, the bleeder screws were too low. Once I swapped the calipers and bleed the front again, all was well.

Another trick is to use needle nose pliers and pinch off the front brake hoses. This should eliminate any mechanical or air problems in the system. This test will show if the front is the culprit and you will have a firm pedal for the rear system. You can also pinch off the rear hose and test the front. HTH, Jonah

 

Sounds like a plan. It may as well just be that issue you speak of. Because not a single bit of fluid is making its way into the front line anymore....could it be that air is just trapped in the piston area? (Not a brake guy, so if my questions seem dumb, they probably are :| )