Brake pedal is hard while car is off but soft while car is on booster?

PLEASE HELPME

MEMBER
2008 TOYOTA COROLLA
1.8L
AUTOMATIC
160,000 MILES

Brakes softish while car is on but will engage. Brake pedal hard while car is off, brakes rotors and drums/shoes were replaced and fluid flushed. Also heard hissing sound when pumping brakes during flushing.

Thursday, July 30th, 2020 AT 6:27 AM

4 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good morning,

The hissing may be a leak in a line. Double check the system and look for any leaks.

https://www.2carpros.com/articles/how-to-replace-an-abs-wheel-speed-sensor

It sounds like you either have air in the lines, a bad master cylinder or a leak in one of the brake lines.

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

The ABS requires a scan tool for bleeding. Air could be trapped in the unit. I post the procedure below.

Roy

(b)Procedure B
(1)Depress the brake pedal several times, then loosen the bleeder plug with the pedal depressed.
(2)When fluid stops coming out, tighten the bleeder plug, then release the brake pedal.
(c)Repeat procedure B until all the air in the fluid is completely bled out.
(d)Tighten the bleeder plug completely.
Front brake - Torque: 8.3 Nm (85 kgf-cm, 74 in-lbf)
Rear brake - Torque: 8.3 Nm (85 kgf-cm, 74 in-lbf)
(e)Repeat the above procedures for each wheel to bleed the air out of the brake line.
4. BLEED ABS & TRACTION ACTUATOR ASSEMBLY (w/ VSC)

NOTE: After bleeding the air from the brake system, if the height or feel of the brake pedal cannot be obtained, perform air bleeding in the brake actuator assembly with Techstream by following the procedures below.

(a)Depress the brake pedal more than 20 times with the engine off.

HINT: Let the vacuum pressure out from the brake booster assembly.

(b)Connect Techstream to the DLC3, and turn the ignition switch to the ON position.

NOTE: Do not start the engine.

(c)Select "AIR BLEEDING" on Techstream.

HINT: Please refer to the Techstream operator's manual for further details.

(d)Bleed the air out of the brake line as usual when "Step 1: Increase" appears on the Techstream display.

NOTICE:
Bleed the air by following the steps displayed on Techstream.
Make sure that the brake fluid in the master cylinder reservoir tank does not become empty.

(1)Connect the vinyl tube to either one of the bleeder plugs.