'77 High Sierra Brake problems

My '77 has had brake problems since I bought it. I have replaced every thing in the system and I still have problems. Yesterday, I installed a new proportioning valve and I am having trouble bleeding the system. I get good pressure to the rear brakes but next to none to the front. I have tried to re center the valve by opening the rear bleeders and pump the brakes to center the valve, but when I go to do a full bleed, I run into the same problem again. Any help would be greatly appreciated.:banghead:

i just had some pretty serious brake problems myself on my '91 sierra and i ended up replacing my entire brake system.......down to the brake lines themselves. i changed the master cylinder 3 times, proportioning valve, rear wheel cylinders, shoes, drums and spring kits, front calipers, pads and rotors but nothing helped. my brakes were always sluggish and wouldn't stop good. not long ago my right front wheel was grabbing all the time without using the brakes. after i replaced the front calipers, pads and rotors, whenever i used the brakes it would pull hard to the left so i decided to change out the front flex hoses to the calipers and ended up changing the hard lines too. problem solved. my brakes have never been better. who knew a little thing like the flex line would cause such a big problem. maybe that is causing your bleed problems. i know that those lines are known to get destroyed on the inside and get all clogged up. hope this helps.

My '77 has had brake problems since I bought it. I have replaced every thing in the system and I still have problems. Yesterday, I installed a new proportioning valve and I am having trouble bleeding the system. I get good pressure to the rear brakes but next to none to the front. I have tried to re center the valve by opening the rear bleeders and pump the brakes to center the valve, but when I go to do a full bleed, I run into the same problem again. Any help would be greatly appreciated.:banghead:

I also change the flex lines. The ones that I replaced were dated Sept '76. I think I just have a massive ammount of air in the system and I just have to keep at it untill I get a full bleed. Thanks for the reply.