Confirm that it is the boost pump

Replaced brakes, master cylinder, no leaks, but still excess movement in brake pedal The last thing I believe it could be would be the boost pump

 

Sure, it could be the booster, but there's a test for that in the FSM, it's been posted here a few times.

More often than not, it's that people don't fucking realize how critical the parking brake system, specifically the load sensing prop valve and rear drum adjustment is to proper braking. It's so important there's an entire thread on this forum dedicated to it, because people don't want to believe it.

We've had numerous people find your same result using aftermarket master cylinders, parts store brand. I'm assuming it's because of pushrod issues, but ...

We've had numerous people find your same result because they didn't bench bleed the master cylinder before install, or they didn't know they needed to bleed the prop valve, and had air stuck in the system.

We've had people lift their trucks and not realize they needed to also re-jigger the prop valve armature, else it would fugger up the LSPV.

More info from you would help us help you. i.e. was it mushy before, is parking brake assembly intact and adjusted properly, did you dial in the rear brakes properly per the manual because there's so little tolerance on adjustments before shit gets awry, where'd you got your parts, what order you bled, did you bleed using a tool or with someone stomping on pedal.

I'm going to guess it has nothing to do with the MC, more likely to do with rear brake adjustment, and possibly to do with your bleeding job.

 

Brakes bled using a one man bleeding kit having a person watching the air bled in the order RR-lr-rf-Lf drums are set in accordance to the manual E-brake works fine this has been happening since I bought it four months ago just bled the prop valve now gives resistance if I push fast many times while but after I give it a second it goes to floor replaced M/C first having same situation on jeep

 

Test the booster per FSM. If it checks out per FSM, then …

Triple confirm the rear adjustments per the FSM. Confirm the parking brake works to keep the truck stationary while in gear and you let off the brake.

Read the thread on brake adjustment theory and heed the advice in there. Attempt to adjust the LSPV arm per reply 33 in that post.

I suppose it’s always possible the prop valve is fucked.

 

Put a block of wood under your brake pedal while bleeding to prevent it from traveling to the floor.

it should never go all the way to the floor.

 

Goes to the floor while pressed, sounds like it may be a bad master cylinder. Even a bad rebuilt one can happen.

 

Multiple pump required to build up brake stiffness would suggest a leak in the booster, either internal, or external.

 

I replaced the master from Autozone, bench bled then bled once installed then full bleed followed block of wood tip now it is 1in off floor no leaks found no rust still lots of movement still need to pump to get pressure

 

Well, no leaks and not going to floor is a step in the right direction.

You may still have air in the system if you didn't bleed the lspv.

Order is: RR, lspv, LR, RF, LF iirc. (Could also be lr, rr, lspv, rf, lf.)

 

Bled valve then rebled the lines gone through 3/4 gallo of brake fluid remained same

 

It’s a very slim chance, but it could be your rubber brake hoses could be expanding when you’re pressing the brake pedal. It happened to me once way back in the late 90’s on my CJ7. I just installed a Warn XCL coil conversion kit in my jeep, and the brand new rubber brake lines that were included lasted only about two years before they failed. I drove the jeep through the entire Rubicon trail with pretty much non existent brakes. And when i say non existent, i would have to brake about 6’ before i needed to have to brake. So that meant i ended up crashing most of the way through the trail. It took a few months to figure out the problem. One person to press and hold down the brake pedal (with the engine running), and a second person under the vehicle to look for problems.

 

Also curious about something.

You say pushing the pedal down multiple times builds up pressure. How long does it take before you LOSE pressure again?

Have you checked the vacuum line from the manifold to the check valve on the booster? Sprayed soapy water all around it, and around the seal between the MC and the booster, then charged up the brakes by pushing the pedal several times with the engine running to see if there are any bubbles or signs of unexpected inflow/outflow?

 

Have you adjusted your rear shoes like shifty suggested above? I know when the shoes are out of adjustment the pedal acts the way you are describing.

 

(Also, for double cab guys who may read this)

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