Unsolvable brake issue?!

[7Stepside8]

My 1978 C10 custom dulexe stepside has been sitting in shop for 2 weeks now because the rear axle seals were leaking and it needed brake overhaul. So they have changed the axle seals, front calipers and pads, front brake hoses, have tried 4 master cylinders, proportional valve. Also they changed the brake fluid out cause the morons that had the truck before used oil in it! Whats left is hard brake lines and rear drum assemblies. They say the pedal keeps getting harder every stop and they losen the hoses and they relieve themselves. They don't know whats going on and im clueless as well. They changed everything they belive that could have been the problem but no solution. Please and thank you for help I want my truck back! 

[bd]

1978 C10 custom deluxe stepside... the pedal keeps getting harder every stop and they losen the hoses and they relieve themselves....

Don't quite follow your question.  Is it that the brakes won't fully release after they're applied; or you're losing power assist; or...?  Also, how did the brakes feel before work was performed?

[DnStClr]

When you lose power assist, the brakes get really hard to apply. It does sound like you're losing power assist, like BD suggested. Could there be a vacuum leak in the rubber hose that goes from the engine manifold to the brake booster? The booster is the big round diaphram housing attached to the master cylinder.

[7Stepside8]

They arn't power assisted brakes so there Isn't a vacuum leak. What's going on is the shop says that they drive it the brake pedal gets harder every stop but it relives when they loosen the front hoses to relieve the caliper pistons from dragging and the pedal. They change the parts listed in my first post that could be the issue but it still happens and they know nothing whats going on and I'm clueless.

[thirsty]

Do both front brakes hold pressure and not return? That sounds like a bad rubber line or caliper. I have seen rubber line installed with a twist in them causing the same symptom. The owner did a brake job himself and twisted the line around when he moved the caliper out of the way. Fixed it by unbolting the caliper and untwisting it and reinstalling the caliper. Maybe it could be something as simple as that.

[bd]

In addition to Thirsty's post ^^^^^^, residual pressure in the front brake lines can be caused by the wrong master cylinder: (1) a M/C for drum brakes may incorporate a "residual check valve" that, by design, maintains 3-7 PSI in the line, or (2) the pedal push-rod may be too long for the new M/C, keeping the M/C piston from returning all the way.  Or, there could be a partial blockage (debris) in the line leading to the proportioning/combination valve.

You said they changed the fluid.  Did they also flush the lines with alcohol or other brake system approved solvent to remove all traces of oil?

For us to better help, post a list of the parts the shop changed initially, before they noticed the brakes hanging up.

[bake74]

     2 questions.  #1:  You said it has no power assist.  So all you have is the master cylinder only, no big round thing between the master cylinder and the firewall ?
     #2:  Ask them if they bench bleed the new master cylinder before installing it, new master cylinders have to be bleed before being put into operation.  (I assume they did bleed the master cylinder first, if not I personally would be looking for a different shop to work on my truck, but that is just me.)

[Blazin]

If someone put oil in it the wheel cylinders, calipers, porportioning valve, the master cylinder, and all three rubber lines should be replaced. All the metal lines should be flushed with brake clean, and then compressed air.

[DnStClr]

I can only imagine what the mechanic said when he found the original master cylinder full of motor oil...
 

[Blazin]

 When I bought Yellow Snow way back when. The master cylinder rubber was all ginked up, and swollen outa shape. I looked inside and it had what looked like ATF in it. I asked the previous owner if he had puit ATF in it. He answered YEAH! With the tone of like what else would you put in it! Idiot!

I replaced everything except the hard lines in that the next day. One of the calipers was frozen up, and I couldn't get fluid to the rear of the truck at all!

[7Stepside8]

Well yesterday they said they found the problem. What was occurring was there was a plate on the brake pedal that pushes on the brake indicated and it was bent so far it stopped the pedal from releasing the pedal all the way. All possible parts were changed and lines flushed so it was just mind blowing it was doing it but turns out that plate got bent back which I seen that the previous owner did it to reach the brake switch rather then just screw it out farther. Thanks guys for the help though!

[bake74]

I can only imagine what the mechanic said when he found the original master cylinder full of motor oil...
 

      Just had an image flash, mechanic standing there scratching his head in disbelief   .

[burbboysgc]

Some people have no business trying to fix things. Sounds like the p.o. like to to take allot of short cuts. Common sense isn't very common now days.