Havent been here in like 11 years? wow. Still have my 2000 blazer which has given me almost zero issues since 2006. but now have run into a really strange brake issue.

pedal will go to floor with truck OFF
No resistance at all when truck running.
Calipers do not compress (visual)
No brake dash brake light on
no check engine light on
all bleeder valves slightly bleed with no air.

what happened:
Lost a brake line due to rust, repaired it. broke another one during bleeding, repaired that. Broke another a few days later, Repaired, all sides bled fine pedal would never "pump"
gave up

Month later:
New upper control arms, installed fine, why not fix brakes too?

brake pedal goes to floor with truck off. no resistance when truck running.
No leaks anywhere
no brake light
no check engine light

can only suck through one end of check valve.
no holes or cracks in check valve tube

only going by what "online" says about failing boosters, but pedal is not hard at all. can travel to floor by hand with truck off.
seems pressure is not getting to calipers at all and i find it hard to believe all 4 calipers seized at the same time.

Also, when truck is "off"
push brake pedal down, halfway down feel slight "thump" in pedal before it goes to the floor

no brakes whatsoever when truck is running not even a little.

Any insight or suggestions that i haven't tried would be greatly appreciated.
not an everyday driver but would still like it in working order

thank you

 

Welcome back!

I'm going to guess that you might still have air in the master cylinder and/or ABS system, but...see my last comment... You should be getting resistance at the pedal and pressure to the calipers by pressing the pedal with the truck off and you are not. This points directly to an issue with the hydraulic side of the braking system, not the power assist side that the booster is on.

Air in the brake hydraulic system can be a MAJOR pain to get out properly. Start at the master cylinder and work your way out to the calipers.

For the MC, bleed with made up lines bent into the reservoir. The key here is to keep the lines submerged in fluid and watch for bubbles coming out of the lines. Once you stop seeing bubbles, pump the MC an additional 10-20 times (this is not a rapid pumping of the brake pedal mind you, just a slow push down, hold, then release). Make sure to NOT allow aerated fluid low enough in the reservoir to re-enter the cylinder. If you see bubbles starting to sink in the reservoir, stop and wait for them to float up and pop/disperse.

For the ABS system, you'll need to find a way to activate the ABS bleed procedure once you've properly bled the MC. A scantool will be required to do this, but if the ABS did not activate during any of your rusty line events, you may not have to do this. I'm just putting it in here in case you continue to have issues after doing the rest of what I consider required stuff (MC & main-line bleeding).

My preferred sequence of bleeding the calipers is to start at the passenger rear, then driver rear, passenger front, and finally driver front so as to work from the longest brake line to the shortest.

If at any time the brake fluid reservoir runs low during any of these procedures, you have to start all over again, obviously.

If that is all said and done and you still have a soft or non-existent pedal, then my first shot at a parts replacement would be the MC. The thump does make it sound like it might be a bad seal in the MC, but air could do similar things which is why I waited until the end to mention this. Once you have the MC bled properly, you could test it before moving along the rest of the system by capping off the front & back ports and pressing the brake pedal. If it isn't firm at that point, then it will never be firm and should be replaced. If you get resistance with the ports on the MC capped off, then the MC is good and you can move on with bleeding the rest of the system.

Good luck!

 

Severe leak. It's drawn WET air into the system. MUST flush it.

 

Heyy Swartlkk i was wonderin if you wan still around here! yes it certainly seems to be in the hydraulic side. the only side that hasnt been bled was the passenger front, i stopped the brake work to get the control arms in. bleeding the brakes has even been weird since impossible to "pump" up the pedal as it only goes to the floor, but even doing that, very little fluid comes out of the valve. it would be great if all it was is air in the system, and now that i think of it... not sure if this would matter, but when the second line broke, the one on drivers side above the frame, the truck sat with the broken line for almost a week due to bad weather.
there is also slight dampness around the check valve in the booster and the 2 bolts to the master cylinder, but i dont know it could be from a spill during all of the brake fluid filling ect... also when i removed the check valve to test it i got a big woosh of air from the booster.
but ill try bleeding the mc and hopefully get some sort of indication even if i get the slightest resistance. thanks ill let you know how it turns out. daveca thanks for your reply too

 

just letting thread know that bleeding the mc solved the issue. thanks