Brake bleed problem

[eaton]

I recently rebuilt all four calipers and replaced the rubber brake lines. And for the life of me, I can't get the air out of the system. I've gravity bled the brakes multiple times. Had my wife help with the pump bleed method. Still only get pedal after one pump.

Any thoughts? Brakes are on the correct side (bleeders up). I did not remove the master cylinder, which worked fine before the work. I did worry that the master cylinder was dry so I bled through the fittings there with wife holding pedal down.

Thanks for any help you can give. Frustrating to say the least.

Joe

[edmayo]

It may be that the pistons haven't come out far enough in the calipers yet. If so remove the pads from one caliper at a time and insert a thickness of metal equal to a worn out pad.Operate brakes until pistons are out to the dummy pads. Now carefully just push pistons back in just far enough to install real pads. Do this at all corners one at a time. See what that does.

[eaton]

Thanks, Ed. I'll give that a try.

Joe

[gled49]

Master cylinders can be corroded and rough down in the bore where the piston and cups haven't operated during normal operation. When bleeding a system like this the cups can be destroyed when they go into this rough unused portion of the master cylinder during bleeding process. It will never bleed properly. You might be looking at a new M/C. Good luck.

[eaton]

Slightly better, but still not great. I did the trick Ed suggested. It didn't help much, but I bled the brakes after and was surprised to see a few more bubbles.

I don't think it's a problem of destroyed master cylinder cups (although who knows?). I didn't resort to the old style pump the pedal bleeding until after gravity bleeding didn't work. The problem was there before the pumping.

I'm thinking about driving it around for a while before bleeding again.

[Merv]

Ed's approach always works for me. I use a thin piece of wood and compress against that first and then open the pistons just enough more with a piston compressor to slide the new pads in. Then re-bleed.

[Ivan Fuller]

Calipers back on the correct side with bleeders at the top? Don't ask how I know.

[RSTarga]

The Motive bleeder is one of the best tools ever. It made it much easier than convincing my wife to sit in the car and pump.
I've never used gravity bleeding, (except unknowingly in an old Jaguar, with disastorous results), and can't imagine how it would get rid of the trapped bubbles.
Are you submerging the purge line into brake fluid? Do you see bubbles coming out of the bleeders. Did you flush your lines with anything else besides brake fluid? What fluid are you using? No Silicone I hope.

[NeunElf]

There's another method for addressing the freshly rebuilt caliper problem Ed Mayo pointed out: get the brakes hot--this may cause the the new seals to release their grip on the pistons. Check PMB Performance's article http://www.pmbperformance.com/bedin.html. Going out and making panic stops (granted, that's not exactly what PMB advises) when the brake pedal goes to the floor until you pump it up isn't the first thing that comes to mind. So, be very careful where and when you try this.

I actually mixed some hard stops and driving around while dragging the brakes and got home with that wonderful smell of cooked brake pads. It worked though. When things cooled down I had a high brake pedal.

Somebody else recommended this, too. I figured one recommendation might just have been somebody trying to get me killed, but I don't have that many enemies so with two recommendations I gave it a try.

[Jay Laifman]

The Motive bleeder is one of the best tools ever. It made it much easier than convincing my wife to sit in the car and pump.
I've never used gravity bleeding, (except unknowingly in an old Jaguar, with disastorous results), and can't imagine how it would get rid of the trapped bubbles.
Are you submerging the purge line into brake fluid? Do you see bubbles coming out of the bleeders. Did you flush your lines with anything else besides brake fluid? What fluid are you using? No Silicone I hope.

EVER!

But why do you think that you have not bled the brakes fully? You say you only get pedal after one pump? Do you mean it goes to the floor? Or just not as high as you think it should be?