Hi all,

I've replaced everything in the brake system except the booster, lines, and lsvp.

My pedal still goes to the floor, all the way down, to really brake. It does brake, just all the way down, feels like air, but I've bled the damn thing plenty of times. Yes, I bench bled the MC and have bled it all correctly. When bleeding brakes and press down pedal completely, idle goes down. From what I understand that may be normal.

Is it possible that the booster is bad and causing this? Any way to check / test before I order one?

 

Brake pedal should not have an effect on the idle. Disconnect the booster from vacuum, cap the vacuum port on the intake and test again. If it still happens it's either completely unrelated or an electronic issue (load on alternator/battery)

I've never heard of anyone trying to bleed brakes while the vacuum assist is active (engine running), you should probably try that in "the normal way" without the boost.

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If you get air in the bleed tube keep pumping, it's not bled yet. Any of the connectors could be leaking from the bleed valve all the way back to the cylinder. Leaking bleed cocks are pretty common.

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There have been a few instances of upside down calipers, or bleeders installed in the wrong position (they are supposed to be the higher location).

PS. If you have oversized and/or heavy tires it doesn't help.

 

I'll try although it doesn't always happen... only when I'm bleeding, and not all the time? i've actually read a lot of threads that say that the idle does respond to brake as the ecu reduces it on purpose, but is only noticeable when you're idle is too high to begin with, but that's not my case. i mean.. technically, wouldn't the idle go up if there was a vacuum leak, and if the brake booster is vacuum actuated, and leaking, that would cause the idle to go up. but in my case it idles down when i press down all the way while bleeding, so shouldn't be caused by a leak.

really? i've read around some people to say it with the truck running. although I can't really imagine it making much a difference technically, it should only make it easier to pump. anyways, i have tried both ways.
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i don't get air in the tube, looks good.
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i replaced them myself, bleeders on top front and back

31s but i'm pedal to metal every time to come to a stop

 

Is the pedal soft and spongy or just have a lot of travel? If it has a lot of travel and the brakes work you may need to adjust the rear brakes. You can also test the booster by pressing the pedal with the engine off and starting the engine. If the pedal goes down it is most likely working.

 

Lots of travel, and soft. What's the difference? It travels a lot till it begins braking, then it brakes ok, but softly. It can fully lock up, but hardly, and after pressing all the way down. When the truck is off, it takes a couple pumps for the pedal to be rigid. Then, turn on the engine, and the pedal sinks.

Anybody have input to my original question? Can a brake booster, even hypothetically, make your brake spongy / lot of travel?

 

Yes, a bigger booster (pretty common upgrade) will make it easier to mash the brake pedal.

There was a good point above regarding the travel. You don't get pedal pressure untill there is resistance pushing back against the pads. Pop the inspection port open on the rears and check the resting position of the pads (spec is in the FSM, from memory its something like two or three MM)

 

I know this is super old but I have the exact same symptoms as you (albeit on a completely different vehicle). Have also changed MC, flex lines, calipers, cycled the ABS module, bled the systems soooo many times. Did you ever figure out what your culprit was? I’ve been leaning towards my issue being the brake booster but it’s a huge pain to replace so I’d like more confidence that’s my problem.

 

An older thread, if you don't get responses try poasting anew.
Anyway there is also a proceedure in FSM (don't have in front of me) to check and adjust the pedal freeplay and travel. Thats probably a good place to start at this point.
Good luck