Vertical Loops in Brake Line OK?
 

I've put about 4 quarts of DOT 3 fluid through by brake system and still have a bubble someplace. Master Cylinder was "bench bled" in place using the plastic screw-in fittings and "U" shaped clear plastic tubes that dumps the fluid back into each resevoir. I've gone over all connections and tightened them to the limit allowed by a 3/8" line wrench. So, now I'm wonder if the two vertical loops are allowing air pockets. They are both down low along the left frame rail. One is the line from the master cylinder that bends upward, then down, like an upside down "U" before going into a tee. The tee is oriented with its openings at 12, 3 and 6 o'clock. 12 is the inlet, while 3 sends a line to the Left Front caliper. The line exiting at 6'oclock heads down, then quickly bends upward to the midpoint of the tee before turning downward and running horisontally along the frame rail. Both front lines run horizontally parallel before bending upward to clear the front cross member on their way to the calipers. I might br grasping at straws here, but I've followed every bit of advice on brake bleeding found in this forum: fittings tightened as hard as possible, calipers tilted backwards to put the bleed hole at 12 o'clock, tapping the calipers with a hammer, rasing the front end a few degrees, pushing slow and realeasing slow on the brake pedal. Thanks for any opinions or additional thoughts you may have.

The only other step that you might want to take is try using a pressure bleeder.

I don't know what type of brake calipers you have, but make sure the "bleed valves" are in the up or top position, not on the bottom side of the calipers facing down. I had mine backwards and I couldn't get a good bleed. Also use a pressure set up to make sure you don't have any trapped air. I don't think the brake tubing really cares what position it's in..up, down, looped or just hanging out there, it's all hydraulic...just make sure they are all secured to something.

Good Luck, Bill

Question?: What type of rear calibers are you using? If GM the pads may not be adjusted out right thus traveling to far for good contact with the rear rotors, giving the brake pedal the same feeling as a poorly bled system. Also not having info on your car-right MC for the type of brakes? Disc/drum, 4 way discs? If you have rear drums-same as above, the back shoes may not be adjusted out far enough. That brings up the proportioning valve. Is it adjusted properly or is this option N/A?

Lot of "if's" involved with 4 qts of brake fluid!
DV

Double Venom: I've had the posibility you just mentioned at the back of my head for a while. All four calipers were "rocked back" to put their internal bleed holes at the 12 o'clock position, leaving very little contact of the pads with the rotors. (I popped the piston out of one of the front calipers to verify and probed one of the rears.) This might make the brake pedal feel soft. However, when I still push on the brake pedal after the system has set for a few hours, it goes right to the floor. If I give it 3 or 4 quick pumps, I now have pedal resistance where it normally should start, but the pedal is still mushy, not hard and firm. I believe this is the classic indication of a bubble someplace in the hydraulic system.
Any more thoughts?

The loops in the lines shouldn`t trap air as the bleeding process will push the air out of the lines as it goes through . I didn`t see in your post if the front calipers are two piston . i.e. one on the inside and one on the outside . If so , there is a sequence that must be followed or you won`t get all the air out . Bleed the inside first and then the outside . If you use a pressure bleeder , be careful about too much pressure .... you can rupture a reservoir ( that old pesky hydraulics formula F = P X A ) . You might try bleeding in reverse ... from the calipers to the reservoir , being careful you don`t overfill the reservoir .
I gravity bled my brakes and other than taking a lot of time , have a good pedal .
When you "pump" your brakes .... SLOW is the operative word . When you go fast , you get air entrained in the oil and it takes about 12 hours for it to separate . That`s why I pushed down on my pedal to a slow count of 20 and released the same way . I also paused at the bottom before coming back up and the same at the top . Did that about five times and then checked my pedal .
What you are doing is sometimes there is a small amount of air in the MC and slow actuation allows this to escape back into the reservoir instead of mixing with the fluid .
I can tell you that after 30 years of being in the hydraulics industry ... getting air out of a system can be a real pain .
Good luck .
Bob

Just thought of something else . In talking to Tilton on my Hydraulic Throwout Bearing , they said that it was best to tilt the clutch master cyl. at about a 45 degree angle ( rear/bleeder pointed up ) to get the air out . Being curious , I took a spare master cylinder apart and looked at the design . The seals are positioned on the piston in such a manner that it is almost impossible to get all the air out if the M.C. is horizontal . I tilted the M.C. and then got three or four good size air bubbles out .... and the clutch is perfect .

Bob