Aside from popping off the drums to look closer at the rear I cant find anything that is wrong that stands out at the wheels, there are no leaks, no major change in fluid level, vacuum line to booster appears to be in good shape. The front brakes were done about a year ago with HPS pads(blue box), and Bendix rotors, same as I did about 5 yrs prior, that combo seems to stop very well. The rears I have not touched yet since owning the truck, I know they are worn but that's not whats causing this issue. I was a mechanic for a few years, have a few ase certs, and even did a 4 yr stint at an auto zone lol, but its been a few years and I'm a bit rusty at diagnosing it seems.

Thinking of throwing a new MC at it and see if that fixes it..

Appreciate your help very much, any other suggestions?

 

Think I would look inside the drums first.... see what things there look like, and also the rear brake line, just for giggles. If you can find anything else, M/C seems like a good bet.

 

Still struggling with this problem, I'm lost on it, dunno what to try next..

I put a new master in, bench bled it and bled the system and there was no change, I went out and got drums from AZ and pulled the rears apart. On both sides one of the springs were broken, pads had some life left for sure but obviously old/cracked, so I did the rears all new but did not change the adjusters, left them same as they came out. Bled the system best I could and had bad pedal, bled again and it was better but still way off. I go searching all over again and found a small leak at the driver rear line where it meets the new wheel cyl., tried tightening it more(maybe scored it when removing I'm thinking), no luck and I ran out of time at this point and had to leave town for work, but wife wanted to go camping "soon" so I said screw it and took the truck to a shop before I left(my company uses them for our work vehicles, has always been decent service and no real issues that I know of).

I only asked them to replace the line and put it on the bleed machine, they call me the next day and say its ready, I drive it about 2 blocks and can tell its the same as I dropped it off, and they didn't replace the leaky line. I go back and speak to the owner again, and leave the truck there. He calls a day later and thinks my new MC is maybe bad, wants to replace it and the wheel cyl where the leak is, ok whatever, could be I guess, they replace the MC twice cause he thought maybe the 1st reman he put in was bad also, he replaces the line also but cant get the pedal right still and wants to replace the booster(I'm out of town at this point), so I tell him sure, do it.

I pick up the truck the day after they say its ready and its still no good, drive about 5 miles and the new rears are starting to smell, pedal feels like crap, feels like the brakes are sticking as well sometimes, and while turning into the driveway the pedal goes way down near the floor, as I'm getting out of the truck I see the trailer brake controller light is lit, I pull the pedal forward and it goes off, but the lights musta been on alot while I was driving home. I looked around again for any leaks and couldn't find any. I'm guessing he adjusted the rears too much trying to get some pedal back, and didn't get the brake switch adjusted correctly after the booster install?.. But I cant figure out why the pedal is still soft/inconsistent and randomly will go way down near the floor still.

Going back to 1996 I haven't taken a vehicle in for work since 2010 and that was some warranty work. I totally regret taking the truck somewhere, what a waste of time and money it was.

I don't mind throwing more parts at it, but I'm not sure what to try next. Any help is greatly appreciated.

Edit:
The only thing that seems to maybe be repeatable to make the pedal way soft and travel further is a low speed left hand turn, I have not tried to do it, but it has done it several times under that condition. Pulling into parking space, 3 point u turn, pulling into driveway type situations.

 

See if you can get it to do its trick sitting still, turn the wheels to the left, step on the brake, turn 'em a little further, and try again. If you can find a spot where the pedal gets soft, stop there, and take a look at what is happening under the truck.

 

I just had pretty much the same issue on my 2001 6 cyl. I had soft pedal and since the fluid was full, I replaced the master cylinder. Bench bled it and when I went to bleed the wheels, found a weeping lh rear cylinder and a frozen bleed screw on the pass side front. Replaced cyl and caliper. It took forever to bleed and then only when I cracked the lines at the abs module and proportioning valve starting closest to the MC and then re-bleeding the wheels did I get a good pedal. Now, on the first two brake applications of the day, I hear a noise from the rear brakes, almost like they're locking up momentarily. No lights. If I pump the pedal in the morning before I leave, it doesn't happen. I'm going to look at the wheel where I changed the cylinder to make sure I don't have a broken spring or something and if all good, I'm going to change the proportioning valve. I think it may be bleeding back.

 

Have you ever checked with a bore scope to see if your calipers are rusted in the piston cylinder? that can cause a soft pedal.

 

check your caliper pistons cylinders for rust with a bore scope, that can cause a soft pedal.

 

It seems to have fixed itself. I think there must have been dirt in the proportioning valve.

 

Not unheard of. So long as it is working properly, that's all that really matters.

 

Well, everything else is new that I can think to change.. I think I may as well try calipers and new hoses, 196k, why not anyway. Thanks very much for posting.

Any recommendations on caliper brand, place to purchase from?

A quick search lead me to thinking about the raybestos calipers from summit.