please help brake issues

[Stevie_Fresh]

I'm gonna drive this thing off a cliff soon. There's no fluid leaking anywhere. Bled the brakes all around. No changes. Bought a master cylinder, bench bled, installed, and bled/flushed all the lines again. Seems as though the pedal is stiffer, but only a little bit. Brakes work sometime just fine. (Haven't taken it out of my driveway, just quick gas and brake in the driveway) seems almost like the anti lock brakes are kicking in. Only sometimes, I can feel something in the pedal, and it basically goes to the floor. Let the pedal up, press again it's fine. I know the sensor in the axle is bad, have a new one just haven't put it in yet. But the main abs fuse in the panel under the hood was pulled, so the system should have been DE activated. Can that sensor cause issues with brakes even with the abs disabled??? I'm going nuts, someone please help!!!!!! Lol

 

[98RedExp]

I would move on to the ABS Module next. You may have air seeping in somewhere. The master cylinder can fail right out of the box too.

 

[FordandPolaris]

Try putting the truck on ramps and bleeding that way. Air is in the lines somewhere. I had the brake line leading from the frame to the front caliper blow out on my truck. The flexible tube is basically two pieces and those blew apart. If you don't see a massive amount of fluid though, then my guess is you still just have air in the lines that is being stubborn. I bled through nearly a full tall bottle (quart maybe?) of brake fluid in my truck. Another thing to check is piston seals in the calipers. Again though you would see fluid leaking if those failed I would think.

Removing the ABS fuse should shut the system down completely. I am not very familiar with the ABS module but I know it operates by opening and closing valves that build and release pressure, creating the pulsing effect. From what I can tell, these valves no longer operate when the fuse is out. Try putting the fuse back in to see if one of the valves blew itself open.

 

[Stevie_Fresh]

I think I finally found the issue. The rubber boot from the brake booster, which is supposed to be connected to the plunger, is completely blown apart. I wish I knew how to post pics on here and I'd post it, but...lol so I zip tied it nice and snug onto the plunger, and the pedal instantly got stiffer. Actually too stiff. Seems as though the booster isn't even working with that boot snuggled up, however the boot isn't as big as it used to be, and it's not in place properly. So looks like I'll be slapping a new booster in. I'm just relieved I figured it out so I can fix it....lol truck has been parked all winter

 

[FordandPolaris]

Very good. Loss of vacuum was a nice catch. Glad you found it.