Brake Advice Needed
 

I've made some modifications to the brake system and ended up with a bubble someplace that I can't get out after running 3 quarts of DOT 3 through all four calipers. Initially, the brake pedal will go to the floor with ease. Three or four quick pumps brings it up a lot higher to I stop the car reasonably. However, the pedal is still mushy. This tells me I've got a bubble.

1. In Front, I replaced Mustang II 9" rotors and caliper with 11' rotors and
80's GM single piston, slide pin calipers. I've found where the bleed hole is inside the piston and have rotated the top of the caliper back about 10 degrees to put the bleed hole at 12 o'clock.

2. Removed the factory brakeline junction box, replacing it with a Tee for the two front lines and putting an adjustible proportioning valve in the line to the rear calipers. Totally split system.

3. Installed a new Master Cylinder and "bench" bled it with the plastic adapters and tubes supplied. No bubbles from either piston.

4. I've checked the bleed hole on the rear axle, and it's on top. It's supposed to be from a Lincoln Versaille, which had a narrow axle perfect for the track width of a Cobra replica. I'm assuming the rear calipers with parking brake feature are the ones originally on the axle, and so the bleed hole should be on
top.

I've got speed bleeders on all four calipers so I can pump the peddle myself; however, I can't tell if any bubbles are coming out with the fluid. Maybe I should try my vacuum bleeder with some teflon tape around the bleeder valve?

I had two problem areas in making these changes. The hard line to the left front flex hose would not loosen with a line wrench, so I ended up using a vice grip and re-tightening with vice grip because flats destroyed. The hard line comming out of the front of the MC that goes to the rear brakes also wouldn't loosen with a line wrench, so it was vice gripped to disconnect and reconnect. Is it possible to have air leakage at these connections without dripping any Dot 3? I'm thinking of replacing both these lines. Also, is orientaion of the proportioning valve important. The knob is on top at a 45 deg angle for easy access.

Any and all suggestions and recommendations will be greatly appreciated.

I believe it is and I would suggest picking us some new brake line and then gravity bleeding your brakes to get the air out. Then slowly pump the brakes so as not to airiate your fluid and once you have bleed your calipers release the pedal even slower than you depressed.

Clois

I just replaced all the lines on this car I am rebuilding and I chased two leaks where apparently air could get in but fluid was not seeping out. Both were at new flares that I didn't get "just" right. In one instance, I had to re-make the line 3 times to get it right.

You might try taking a ball peen hammer and taping on the calipers to shock them a little and see if a bubble comes loose.
Get a helper so you can watch what is coming out of the bleeder. Use a clear hose. Are you starting with the right rear, left rear, right front and left front last?
Good luck,
Steve

To expand some on Clois and Seagull`s comments .... if your bleeders on the calipers aren`t completely vertical , you can trap an air bubble and it will drive you crazy . On mine , I had to place a 4x4 on the jack and then jack to front of the car way up to get the bleeders completely vertical . Tapping on the master cylinder and the calipers as you bleed them is also a good idea . We did that on hydraulic sysems that had runs of up 100 feet to help get the air out .
Look at how your master cylinder is mounted . On mine , I had to take it off the mount and tilt it at a 45 degree angle to get the bleeder screw at the highest point and then got 3-4 good size air bubbles out of it .
What Clois is talking about is a good tip . If you move the pedal too fast , you get air in the oil ... and then you have to wait about 12 hours for the air to separate from the oil . I slowly push the pedal down after all bleeders are closed until it won`t go any further , hold it for about 5 seconds and then very slowly come back up . I do this about 5 to 6 times .... and my pedal is rock hard now .
Good luck.

Thanks for the tips guys. I crawled under the car yesterday to look at the porportioning valve and found the side that has the inlet to be wet with brake fluid. However, this side is on top, and if it had air inside, it should bleed out like the fluid does. It's very diificult if not impossible to get a wrench between the frame and the oil pan to tighten fittings, so I'll probably replace the whole line from the master cylinder, tighten the fittings when they are below the frame, then push everything up leaving the MC end free. I'll also replace the line from the tee to the left front caliper as I think this is where I lost a hard pedal. I keep checking the connection to the rubber caliper hose and find not wetness.

It also helps to start bleeding brakes at the wheel furthest away from the master cylinder and work your way closer.

I also find it easier to bleed brakes if the fluid is warm.

Scott S

GreensnakeDoc,

When I rebuild an entire system or replace big pieces of line, I have the best luck by pressure bleeding from the calipers back towards the m/c. I use a big plastic syringe and some Tygon tubing.
It seems to be the easiest way to get the big air pockets out.

Jason