Soft Brake Pedal and the parts cannon is out of ammo

Tallishyeti27

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Howdy Everyone.
My brake nightmare started a couple months ago when I replaced my pads, rotors, and soft lines with braided steel lines and Power Stop pads/drilled and slotted rotors. During the process, the master cylinder went dry. I pulled it off and bench bled it as well as bled all the calipers and still had a pedal issue. When I say bled, I mean I've sucked no less than 2 gallons of brake fluid through the system by the use of a vacuum bleeder and the trusty two-person method. I even bought a scan tool that can do the ABS bleed. Ran the ABS motor several times and then bled each caliper again but only got one bubble out of one of the calipers. The pedal is hard if you pump it with the engine off, but once you start the engine, it travels softly through 80% of its travel before getting firm and activating the brakes in the last 20% of travel.
I double checked to make sure all the pads are seated in the calipers correctly and checked for leaks at all of the connections I made. I though the issue might be something to do with the booster or master cylinder so I replaced both of those with brand new replacements from American Muscle. I also checked the vacuum line from the intake to the booster and there are no vacuum leaks. When I disconnect the vacuum line with the engine running, the pedal stays firm like it does when the engine is off. I'm going to replace the check valve on the booster in the morning to eliminate that possibility also but I don't have much faith that will fix the issue.
I've looked through some other threads tonight and it seems like the only thing I haven't done is pump the clutch pedal while bleeding the brakes, or use pressure at the reservoir to force the fluid through the lines. Someone else recommended hooking vacuum up to the reservoir to suck the air out of the top. Any Suggestions on any of these methods would be appreciated.
I'm really beating my head up against the wall here. About to throw in the towel and take it to a shop.
 

RoushedGT

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Try a Motive power bleeder. Once I tried it I never went back. Since our cars don’t have a bleeder on the trans id slowly pump the clutch with the system under pressure.
 

GriffX

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The pedal is hard if you pump it with the engine off, but once you start the engine, it travels softly through 80% of its travel before getting firm and activating the brakes in the last 20% of travel.
I would expect that. When the vacuum kicks in the pedal will travel some inch.

My Mercedes has low engine vacuum during cold start. The first stop sign in the morning is 200 m away, when I stand at the sign, the normal vacuum after startup gets in and the brake pedal travels down with my foot on the brake.
 

86GT351

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Vac bleed is not the answer. If the master went dry you have air in the system. You need to use a pressure bleeder and that should help.
 

Juice

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Good pedal without boost, but soft pedal with boost tells me:
no air in system. But likely an assembly error at one or more calipers/pads. If you didnt line up the rear caliper piston slot, with the nub on the pad, (piston on top of nub) will cause what you are describing. Or even a frozen/rusted caliper slide.
 

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