Brake issue with my new setup

[wolffcub]

Converted the 52 with a disk kit back in the day and ran drums in the rear. Things appeared to run ok even though the truck was never 100% done and only test driven. Now i changed out my rear end and the new one has disk brakes. The disk disk setup never worked with the other proportioning valve from the disk drum setup so i bought the WILWOOD ADJUSTABLE COMBINATION PROPORTIONING VALVE. After installing that the brakes were always super spongy after bleeding at least half a dozen times.

Went out and bought a new master cylinder today that i know was based on a disk disk setup and im still getting this poor feeling pedal at times. When i say at times i mean this.........when the valve dial is set full counterclockwise (less rear brake) the pedal feels perfect, as i turn in the pedal the spongy feel comes back. To me it does not seem normal this happening when allowing more pressure to the rear

Any ideas?

[OrrieG]

Is there any place in the front lines that can trap air like expansion loops. And if you are using GM calipers are they installed on the correct sides? They will fit either side, but the bleeders have to be at the top to let out the air, other wise you get an air pocket that cannot be bleed out. Do you have the MC mounted in the frame near level or below the calipers? If so you need a check valve to keep the fluid from reducing the pressure and the calipers not fully compressing before you run out of pedal at the mc. That prevents you from getting them fully bleed.

[dwcsr]

If they have a parking brake in the caliper they need to be gravity bleed and then adjust the parking brake before you get a good pedal.

http://static.speedwaymotors.com/pdf/910-31919.pdf

[wolffcub]

have a 2lb installed on the front and rear as the MC is frame mounted. All calipers are installed correctly and bleeders are all up.

[wolffcub]

parking brakes are not part of the rear calipers and are stand alone.

[OrrieG]

Sounds like you have checked off all the obvious boxes. When I first put my truck back together in 85 and this time in 07 for the brakes I had to work really hard to get that last little bit of air out. Ended up using speed bleeders (built in check valve so you can't let air back in) and running a couple of quarts of fluid thru the system. The old man used to make me pump the pedal 100 times anytime we had the brake lines opened up. Post some pics of your installation, we might see something you are overlooking....

[wolffcub]

Found out the issue. The adjustable plunger on the back side of the booster was set way too far based on the old master cylinder i was using so i extended it out so it was only 1/16" shy and now the pedal feels acceptable at all proportion dial settings.

Thanks for the help anyways.