Brake pedal has little pressure

Tiny
DSIEBERT120478
  • MEMBER
  • 1999 TOYOTA AVALON
  • 3.0L
  • V6
  • 2WD
  • AUTOMATIC
  • 211,420 MILES
Brake pedal had weak pressure. Replaced brake master after bench bleeding car still has weak pressure on rear port closes to booster, but somewhat good pressure on front port even after bench bleeding and tried to vacuum bleed with no success. I am wondering if the prop valve could be bad. Please help me!
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Thursday, October 15th, 2020 AT 7:10 AM

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Tiny
ASEMASTER6371
  • EXPERT
Good morning,

It sounds like you have air in the system.

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

There is no proportioning valve in the system since you have ABS.

I would rent a pressure bleeder as having someone push the pedal does not move enough air.

The vacuum bleeder does not pull enough to get all the air out.

With a pressure bleeder, it forces the air through the system and out at the bleeder screws.

Roy

BLEEDING

HINT: If any work is done on the brake system or if air in the brake lines is suspected, bleed the air from the system.

NOTICE: Do not let brake fluid remain on a painted surface. Wash it off immediately.

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1. FILL BRAKE RESERVOIR WITH BRAKE FLUID
Check the fluid level in the reservoir after bleeding each wheel. Add fluid, if necessary.
Fluid: SAE J1703 or FMVSS No. 116 DOT3
2. BLEED MASTER CYLINDER

HINT: If the master cylinder has been disassembled or if the reservoir becomes empty, bleed the air from the master cylinder.

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a. Disconnect the brake lines from the master cylinder.
b. Slowly depress the brake pedal and hold it.

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c. Block off the outlet plugs with your fingers, and release the brake pedal.
d. Repeat (b) and (c) 3 or 4 times.

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3. CONNECT VINYL TUBE TO BRAKE CALIPER BLEEDER PLUG
Insert other end of the tube in a half-full container of brake fluid.

NOTICE: Bleed air of the rear brake first. If front brake is bled first, rear brake air cannot be bled.

4. BLEED BRAKE LINE
a. Slowly depress the brake pedal several times.
b. While an assistant depresses the pedal, loosen the bleeder plug until fluid starts to run out. Then tighten the bleeder plug.
c. Repeat this procedure until there are no more air bubbles in the fluid.
Bleeder plug tightening torque: 8.3 Nm (85 kgf-cm, 74 inch lbs.)
5. REPEAT PROCEDURE FOR EACH WHEEL
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Thursday, October 15th, 2020 AT 9:13 AM

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