Low Brake Pedal- finding resolution

[Reega]

2000 K25 350 JB7 .I started with some nasty fluid and weeping wheel cylinders. Cleaned that up and thought I would firm up the pedal. Also replace the rear soft line before changing the wheel cylinders since a lot of bleeding was to come. 1.5 gallons later, with 3 abs bleeds, pedal was still garbage. I was convinced it was the drums since based upon my inspection they were past the wear limit-I didn’t measure and just adjusted way out. My fear is it was upstream of that and in the combo valve or the Kelsey Hayes unit. Well, I just clamped the rear soft line…still crappy, left front….still crappy….right front….a nice normal brake pedal!!!!!

So square cut seal??? I just lubed the slides as part of diagnosis as the PO or whoever only lubed the bolt itself and not the outer sleeve. I had to force them out with a screw driver and they were dry. There is no noticeable leakage from the caliper. The wheel cylinders were trash-full of brake mud. POs obviously were not **** about systems as myself-hate finding that out.
I have rebuild kits for both front and new lines, I guess it could be the line as well, below where I clamped it. Any thoughts? Best practices? I’m pumped its not in the combo or Kelsey Hayes unit.

Pick below is after about a gallon of fluid, front left. Still one tiny bubble coming out. @Schurkey is correct, plan on a gallon. And now I have more to do.

 

[Reega]

Is this done?

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[Schurkey]

WHAT VEHICLE? WHAT BRAKE OPTION NUMBER?

Wild guess with no evidence: JB/JN3, 5, or 6. Low-drag calipers, and the right front is sticking but not completely seized.

Second Guess: sticking caliper slider pins. Given that you lubed them already, this seems unlikely.

Good chance that pulling the caliper apart, cleaning everything, and putting it back together will take care of the sticking, whether it's the piston or the mounting pins. If not, time for a replacement caliper or a proper rebuild using new rubber parts.

 

[Reega]

My apologies. It’s JB7. There is a wonderful thread Schurkey had a few years back on caliper rebuild. I Jumped over there and he responded about a cleaning the piston and checking the piston and checking the square cut seal and did dust cover/boot….and more cleaning.

So, today I broke down the calipers/wheel bearing&hub. Not too bad , 4 15mm holding the hub/bearing came loose fairly easily. I spent the most time cleaning. Where the hub meets the rotor and the backing plates.
One rotor is trashed, please lube your slide pin’s properly!

So now, new brakes for both front wheels. One of my caliper dust boots had a gash though.

 

[Reega]

Rebuilding the calipers with Schurkey’s expertise was spot on, replacing the slide pin bushings and seating the slide pins was a mess for some reason. Took way longer than expected. The hub/wheel bearing took a good while to clean(wanted to minimize any potential runout). With a new bearing/hub, it would have been pretty easy. Tomorrow, I plan to paint the backing plates and reinstall.

 

[Reega]

Check out my “Raybestos” brake hose…means the AC Delco would be the same

 

[df2x4]

Check out my “Raybestos” brake hose…means the AC Delco would be the same

Someone else here recently informed me that Sunsong is a current GM hose/line supplier, I want to say it was @L31MaxExpress. I used a power steering pressure hose from them on my red truck based on that recommendation and I have no complaints. Seems to be well made as far as Chinese products go.

Interesting that Raybestos is using them too. Kind of makes sense though as @MrPink confirmed that Raybestos is a current GM brake parts supplier.

 

[Reega]

Yeah, seems decent quality. I’m just a little agitated Sunsong is like $6 on RockAuto and I paid $17 a piece for Raybestos. I would like my dollars to go to better quality, not a shinier box. Sure it’ll be fine, until it isn’t.

 

[Reega]

Okay, so back in the same boat…maybe a marginally better pedal. Line lock the front right and it’s way better. What am I missing? I don’t think it’s air, but obviously could be wrong. I took the caliper off while gravity bleeding and held it in several different orientations and still didn’t get anymore air. Two man bleeding the same. Can a caliper fatigue? I mean with 200k and heavy use? What about hardness of brake pads? Checked the slides again they are fine. Thoughts? Ideas?

 

[1998_K1500_Sub]

Line lock the front right and it’s way better. What am I missing? I don’t think it’s air, but obviously could be wrong.

Did you already say: Was the right-side hose replaced?

Another tack:

@Schurkey may frown on this, but on occasion I've pumped fluid UP, from the caliper to the MC, to aid in purging air bubbles. Air wants to rise... so push the fluid in bottom-up.

I'm not saying this'll fix you, but...

And all your lines have clean fluid in them already, so pumping backwards doesn't sound so bad (does it?).

I used a "ZEP" sprayer bottle from Home Depot, removed the "twisty" blue spray nozzle and jammed a length of hose over the end of what remained. Tie-wrapped it on. Filled the bottle full of brake fluid, purged both the sprayer's pump and the hose I attached so they're full of fluid, then attached the end of the hose to the brake bleeder on the caliper / wheel cylinder.

Use your head and it can be done.

As you pump the ZEP handle, watch for air in the hose. If you get air, stop; remove hose from bleedr, re-purge, re-attach to bleeder and then slow your action on the hand pump.

And maybe this is a $h!t idea, but AFAIK it's never caused a problem for me. Then again, I've only done it maybe half-a-dozen times in the last 20yrs.

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