Bled brakes, still mushy and weak--what now?

[Dakota]

I an not a brake expert. This is a new build (has been sitting for a couple years in the process), with new MC+booster, new proportioning valve, new lines, etc. Everything appeared to work fine for a time, now the brakes are mushy and weak.

I bled the lines out, still mush. Full of fluid. Perhaps slight leak in MC gasket--could that be the culrpit?

Otherwise, what could it be: bad vacuum, bad proportioning valve...?

Help is appreciated from any of you experts out there. Thanks!

 

[oh2bnok]

If you haven't already done so you should bench bleed the master cylinder.

 

[chuck]

Does the line nearest the booster feed the front brakes? Be Sure. Did you use chevy front discs? If you double check to be sure that the caliper does not hit the knuckle. Are the bleeders up? Adjust the rear brakes.