Brake issues

[thepatriot2705]

GM vehicle. Early 2000s.
4 wheel ABS.

Replace calipers and master cylinder. Bled everything except abs module. Pedal is firm with engine off. Goes to floor with car on. Any ideas?

[eightmillimeter]

Air leak between master cylinder and vacuum booster or within the booster be my guess

[Gabriel556]

Just enough vehicle info to elicit guesses that will have you racking your brain. More detailed vehicle information is needed.

[Pressingonward]

You'll need to bleed the ABS module.

A slowly sinking pedal indicates a small leak, a soft pedal that goes to the floor indicates air in the system still - probably in the ABS module, but could also be somewhere else. Did you bench bleed the master before installing? Did you adjust the length of the actuating rod in the booster?

A bad new master is always a possibility too, but I'd start by bleeding the ABS (and rebleeding the entire system according to the specific procedure for your vehicle).

Did you replace the rubber brake hoses? If your pedal was bad before you replaced the master, it could be a bad hose that is bulging, but again, I'd start with bleeding the ABS since you had the entire system open

[utahjeepr]

Rent a bleeder bomb and bleed the entire system.

[Pressingonward]

One other comment, it's pretty normal for the pedal to feel good with the engine off, but soft with it on, when you have air in the system. With it off you can't develop much pressure in the hydraulic system relative to when the engine is on and the brake booster is "boosting" your effort.

With the engine on the pressure in the brake lines is much higher and will compress the air bubbles to a much smaller volume, giving you more pedal travel and a soft squishy pedal

[czgunner]

Many scan tools will allow you to run the automated bleed procedure. Not sure you can do it manually.

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