What I seem to have is weak overall pedal. I can stand on them and get no protesting or noise from the tires or ABS. No ABS lights or Codes. At 1st I thought I may have air in the ABS and have done several automated bleeds with a Foxwell NT630 Plus. Bleed, automated bleed, bleed again and so on. I have done many. No change.
When I do these automated bleeds and then pressure bleed I see NO bubbles and I give them every chance to show by letting a good amount of fluid go to the bottles.

I read an article saying this weak pedal can be a sign of the ABS Modulator with over time the brakes becoming more and more harder to operate or say take more effort. The article didn't really go into detail if its the valve or module. These are not cheap.

I posted a thread about no rear brakes but removing the ABS fuse proved different, they will lock up if I want them too but the truck still has only half the braking force it should, maybe less. I thought not having rears was overworking the fronts. The fronts get no better with the fuse removed. Bo the the Brake and ABS dash lights are on during the test.

I have new master and wheel cylinders, drums and shoes.
In recent weeks of trying to find out the issue I have cooked my rotors to a nice gun barrel blue, the pads are Raybestos Police black nasty semi metallic dusting grabby pads. I'm replacing them and the pads this weekend just in case. Everything will have been replaced but the ABS control and Module and Modulator Valve.
I know these pads to be very good performers that resist fade very well. Some RV users swear by them especially on the mountain down hills.

If by some chance the new rotors and pads prove to be the issue great but I'm not optimistic. All new wheel components will be my process of elimination. The rotors will be StopTech Slotted with PowerStop Z37 Top Cop Pads.

So my question in the title is does anyone have the process for testing the ABS modulator and/or Valve?

 

The pictures of your truck show that you have a vacuum brake booster. Did you test it?

 

There likely referring to the mechanical Valve and not the electrical module on top.

Usually if the Electrical module goes bad , it will throw codes.

 

Yes I have.

Thanks

 

Hi Guys, Well I don't know how I overlooked the booster check & fail because I researched this before I posted here.
Being I was asked here I did the pump and hold the pedal with engine off (after driving a while), and it goes almost to the floor instead of the 1/4-1/2". It goes close enough to the floor I can make it touch.
I shot some carb cleaner around the check valve and master cylinder flange with no changes in idle.
My boost/vacuum pillar gauge shows 18.5 idling.

Mercy!

 

Hi Guys, I finally got my pedal back while basically refurbishing my brake system in the process. I admit its has been a Keystone Cop Episode in which I played a starring role.

I have no idea how air got into the system in the first place but long story short - Bleeding a Master Cylinder (MC) can be a PITA!
I have read and viewed many pages and videos on the process, some bogus, some generic, but did benefit here and there.

I bench bled the original MC a few times always followed by an install, brief gravity bleed, pedal bleed, ABS Automated Bleed, pedal bleed but still had a low soft pedal and weak rear brake response.
Needing new shoes @105k miles with front caliper piston dust boots crumbling I decided to refurb it all, new vacuum booster, master & wheel cylinders, drums, shoes & hardware, rebuilt the front calipers, new StopTech slotted cryo rotors, Power Stop Top Cop Z37 pads.

OK, My bench bleed skipping all the previous blunders & mistakes. After contacting LEED Brakes about something else we talked about MC bench bleeding.
I have read about short stroking and not bottoming the piston, he said go all the way. With an old one if you are worried about crud or pushing the seal into an unfinished bore end, maybe the MC needs to be replaced.

Putting the cylinder in the vice and pushing the piston I found the first stage to not be primed. So I did short stroke it until I had no air in the line returning to the reservoir and could feel resistance.
I then did no less than 20 controlled full strokes non-stop getting a little cardio workout. The air stopped showing in the return lines about stroke 6.
I then took a screwdriver handle to the unit rapping it several times where ever I could, and while doing so looking into the filler opening I was seeing bubbles trailing out of the first stage intake port! Very small trails. I mean tiny.

So I started short stroking the first stage again and on every stroke a BB sized bubble would l rise out of the port. Damn! Maybe 20 times at least until they stopped, I then did 20 more full strokes stopping every five to rap and tap.
I took the lines out, put the cap on, took it out of the vice and tipped it up and down rolling it a little side to side while tapping on it and remounted it in the vice stroking it again and seen no bubbles. IF I had a soft low pedal after this and the system bleed process I was thinking trade in. Geesh.

I now have a factory pedal. Lke new brakes. In 2005 they reworked these truck's brakes and they were impressive. I got them back.

Long story shorter:
When you pull an MC, and even capping the lines off there is still air in them.
After bench bleeding when you uncap the lines and MC ports to connect there is air there.
Some have a person lightly press the pedal and crack the lines one at a time to spit the air out. When they release the pedal the air in the next line is pulled into the cylinder. And if you missed any in one you spit it pulls it into the cylinder.
Not saying its my way or the highway but I skip that and just open the right rear bleeder and let it gravity bleed maybe an ounce and the same for the RF.
I then pressure bleed with a Motive Bleeder kit.
After this the pedal is great and I then do some stops that activate the ABS and they get a little better.

Thanks for your help and listening. I hope this helps others.