More and More Brake Problems

[aiyana7.3]

I have been having a lot of problems with the brake system on my truck. So far I have replaced the following:
Brake Booster
Master Cylinder (twice)
Both Calipers
Both Rotors
All Pads
Both Drums
All Shoes
Both Slave Cylinders
Brake drum hardware kit for both sides

At one point of time, after replacing and adjusting the brake drums, the brakes worked perfectly. They had a ton of grab to them and they didn't feel spongy in the slightest. The truck then sat around for awhile while I was doing some interior work on it-around 5 or 6 months. After the interior was done, the brakes felt spongy, they didn't stop very well and the "Brake in Park" light was on. The ABS light also flashes if I stop too hard. If I stop REALLY hard then the back brakes lock up. I took my truck into a shop to have them bled and adjusted but I am now being told that after bleeding the system several times the pedal still has low pressure. I'm not sure whether or not they have adjusted the shoes yet but due to the back brakes locking up, I'm not sure if that will help.
Does anyone have any idea what is going on with my truck? Thanks for all the help!!

 

[79jasper]

Maybe the RABS valve.

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[aiyana7.3]

Would a bad RABS valve trigger the ABS light? Because only the Brake in Park light is on.

 

[OLDBULL8]

There are two reasons that the brake light is ON. 1st is that the master cylinder is low on brake fluid. 2nd is that the park brake has not released all the way. If you have applied the park brake at some time, the cables get rusty and won't release, the RAB's light will flash if one side is not releasing. You will have to observe if that's the case. Climb under the truck and have some one apply the parking brake and then release it, watch to see if the cables release all the way, the the equilizer, where the two cables connect should be straight. Jack up the rear wheel one at a time and make sure they turn easy, if one turns hard, that side cable may be stuck (not releasing).

 

[aiyana7.3]

Ok I will have to check on that. As far as getting some pressure in the pedal and increasing the stopping power, it sounds like the ABS valves might be the problem. It is one of the things I haven't replaced. I've seen some posts about a bypass for the RABS. what do you all think?

 

[aiyana7.3]

Also, I misremembered - the ABS light was the one that was on... Sorry!