weird brake problem
 

I have a 1993 w250 auto. No engine mods. 265/75-16 tires. Has the 3 inch wide brake shoes but wheel cylinders for the 2.5 inch shoes (stock)
Noticed my brake pedal was squishy-er than normal this spring and checked master as 1st step. Front chamber was low and about to start sucking air. Rear chamber was full to top and spilling over when I pulled cap off. Truck has a history of sucking air in the rear wheel cylinders after sitting all winter when I don't drive it if its snowy from January to March.

I gravity bled the brakes and noted that the passenger side caliper bleeder screw was leaking and I replaced it with a new screw- no more leak. Also tightened the rear brake adjuster 4 clicks on each side and tightened up slack in parking brake adjuster cable to rear

After a hard driver around town on a 87 degree day with 500 lbs of steel in the back, the front brakes read at 190 F and the rears read at 145 on pass side drum and 135 on drivers side .

I still got squishy brakes after this and fluid is still accumulating in the rear chamber. master is one of the last US made Bendix ones. Its 7 years old and has 9.5k miles on it.

I'm going to bleed the system one more time with pressure- but any more ideas? bad master or bad ABS valve?

This is a common problem on these trucks. The first thing that you need to do is adjust the rears correctly. NJTman posted this:

I know you guys all have your hearts set on the idea of the shoes having a "Slight drag" on the drums, but after all the years of dealing with these trucks, I found that no drag at all is best for me.

Your mileage, may vary, we all can at least agree on this.

When I was allowing the brakes to drag sufficiently, or so I thought, i was actually allowing them to get hot, ultimately warping the drums and destroying shoes (glazing them over) on my truck. After going through a couple sets of shoes, cutting drums, and eventually purchasing new drums and installing, this time, I did it a bit differently, and I haven't had any issue since.

Put everything together, spin the tire while adjusting the star wheel, till I hear a "scrape" on the drum with the shoes starting to contact. I go back to the cab, start the engine, pump the brakes a few times to "re-seat" the shoes, turn the truck off , and go back to adjusting.

When I get back under there, since the shoes re-centered themselves by pumping the brakes with the truck running, the shoes are no longer scraping / contacting the drum, as the assembly has found it's new center. I adjust the starwheel till I just start to (again) get a scraping noise, and go back to the cab to start / pump / shut off again. It puts me back into the shoes self centered position, and no contact between the shoe and drum.

I did this process a couple of times until I felt that the shoes were just scraping and continuing to just scrape the drums after the start the engine/ pump / turn off process. I then backed off the star wheel till there was NO scraping at all..... Usually just a few clicks.

This prevents the drums from overheating, as there is no "slight drag" at all. The shoes are at the location where they work best, the pedal is as high as it's ever going to get, and the brakes continue to work fine, as their break in process is no longer being affected by overheating drums.

At about 6 months of driving, I had to manually re-adjust the star wheels, but that only required a couple clicks outwards to the shoes barely touched again, backing them off till the drum spun freely.

I've had ZERO issues since I've done this process. It's what I will continue to do until proven otherwise that it's not effective at keeping the parts in their best (un-warped or damaged) condition.

Again, your mileage may vary.

https://www.dieseltruckresource.com/...-321344/page7/

...Mark