Spongy brakes to no end

[HawkDsl]

One of my pet peeves is people blaming the ABS for spongy brakes. 100% of the time, there is air in the lines/ABS modual/master. 100% of the time.

A Zen master once told me, air in liquid floats up. Be the bubble. Where do you want to go? Is the truck pointed down hill? Raising the front up will do wonders for bleeding the ABS and clutch slave.

But anyway, I think your on the right track. Them trucks are long. It can take quite a bit of time to get that system bleed, even with the fancy bleeder tools.

 

[Schurkey]

One of my pet peeves is people blaming the ABS for spongy brakes. 100% of the time, there is air in the lines/ABS modual/master. 100% of the time.

Ehhh. Now 'n' then, you find a defective ABS unit where the solenoid valves leak. If the valve that should close (seal) the accumulator leaks, it acts just like air in the system.

So maybe 99.44% of the time, it's air in the system.

 

[Donald Mitchell]

A drum brake may not be as good as a disc, but if you have a fluid leak or axle seal leaking oil, you need to fix it before you have a wreck or cause someone else to! A proportioning valve would be last on my list to replace.

 

[SasquatchOnDeck]

Meh. Good working drums are just fine. If you have an 8.5" axle though, you are unlikely to have good working drums.

Dana 70, and in my opinion, good working drums are unicorns.

 

[SasquatchOnDeck]

One of my pet peeves is people blaming the ABS for spongy brakes. 100% of the time, there is air in the lines/ABS modual/master. 100% of the time.

A Zen master once told me, air in liquid floats up. Be the bubble. Where do you want to go? Is the truck pointed down hill? Raising the front up will do wonders for bleeding the ABS and clutch slave.

But anyway, I think your on the right track. Them trucks are long. It can take quite a bit of time to get that system bleed, even with the fancy bleeder tools.

I jacked it up one direction and bled through a half gallon or so of cheapy super tech, then the back and did it again, and still got solid fluid through all bleeders after the first couple pumps. and yeay, ext cab, long bed.

 

[Nad_Yvalhosert]

I read through this thread twice. I dont see where you took the drums off to look at the shoes...

Bear with me: Your brakes were OK before applying the parking brake, yes or no?
Then terrible after disengaging them?
So why are you loading up the parts cannon?

K3500, c-clip or full floater? I know it's a pain to tear down a FF 14-bolt, but if the parking brake lever was stuck, you released the pedal but the shoes were still applied due to friction & rust. Then you drove, you likely tore apart the assemby.

Air in the lines caused the pitiful brakes? If the brakes were good before you parked on a hill, how did the air get into the brake lines?

Before you throw more parts at it, diagnose the low pedal. Make sure the mechanical parts are lubed, can move freely, and adjusted properly.

 

[Nad_Yvalhosert]

Wait a minute, you replaced the master in post 1, and in post 7 you have long travel, then great brakes?
You installed the wrong master cylinder. I surmise you have low drag calipers and a master W/O a QTU valve. All the initial pedal travel pushes fluid into the front calipers till they hit the pads to the rotors, then the wheel cylinders till they hit the drums, then and only then (at half travel) do you start to slow down?

You arent mixing 1989 V series and 1989 K series accidentally?

 

[Nad_Yvalhosert]

Based on my reading, tomorrow im gonna get it up around 35 on gravel and lock them up a few times (it will still lock the brakes on pavement if that helps diagnose an ABS problem... lol)

It's a rear only ABS system. Of course it'll lock up the fronts...

 

[SasquatchOnDeck]

I read through this thread twice. I dont see where you took the drums off to look at the shoes...

Bear with me: Your brakes were OK before applying the parking brake, yes or no?
Then terrible after disengaging them?
So why are you loading up the parts cannon?

K3500, c-clip or full floater? I know it's a pain to tear down a FF 14-bolt, but if the parking brake lever was stuck, you released the pedal but the shoes were still applied due to friction & rust. Then you drove, you likely tore apart the assemby.

Air in the lines caused the pitiful brakes? If the brakes were good before you parked on a hill, how did the air get into the brake lines?

Before you throw more parts at it, diagnose the low pedal. Make sure the mechanical parts are lubed, can move freely, and adjusted properly.

The parking brake was the first thing i troubleshot. it still feels the exact same, engages, and disengages 100%.
As for air in the lines, that was a simple suspicion. Possibly coming in as a hose or wheel cylinder ruptured, and i let off the pedal to start down the hill. I'm not a certified GM tech, i'm not required to be right on my first guess every time.

Wait a minute, you replaced the master in post 1, and in post 7 you have long travel, then great brakes?
You installed the wrong master cylinder. I surmise you have low drag calipers and a master W/O a QTU valve. All the initial pedal travel pushes fluid into the front calipers till they hit the pads to the rotors, then the wheel cylinders till they hit the drums, then and only then (at half travel) do you start to slow down?

You arent mixing 1989 V series and 1989 K series accidentally?

I'll be honest, the master is the part number from autozone's website. Never read much into qtu, just know the basics. But it was for a K3500, as much as that can be trusted, as all autopart stores give me the wrong oil filter in their system.

It's a rear only ABS system. Of course it'll lock up the fronts...

It's a dually. i can tell im leaving a scrape four tires wide, not just two.