1993 Toyota 4Runner Intermittent brake peddle to the floor

EHX482

MEMBER
1993 TOYOTA 4RUNNER

Brakes problem
1993 Toyota 4Runner 6 cyl Four Wheel Drive Automatic

Hello, I have been experiencing my brake peddle intermittently pushing down to just above the floor and automatically returning under pressure until the car comes to a stop.
I have replaced the master-cylinder/brake booster twice using one rebuild and one factory. I have also replaced the anti-lock brake system's speed sensor. There are no fluid leaks. Brake pads/rotors are fresh. There are no lights on the dash panel. Do you have any ideas? Thank you, Mark.

3 Replies

KHLOW2008

MECHANIC
41,814 POSTS

Hi ehx482,

Thank you for the donation.

Do you mean the first initial depression of the brake pedal results in it being low and subsequent depressing of the pedal would hold the pressure?

Was this the reason for replacing the master cylinder?
Did you bleed all the 4 wheels after repair job?
Is the pedal to booster push rod clearance correct?
Did you check the calipers pistons for sticking?
Were the rear brake slave cylinders checked?
Is the braking efficiency very bad when the problem occurs?

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Sunday, March 21st, 2010 AT 1:50 AM

EHX482

MEMBER
1 POST

Hello, yes I measured the booster arm length on both replacement master cylinders and it is at the factory setting for length. I also bled at all for wheels. No sticking slave cylinders. Yes the parts that have been replaced is all for this problem. Like I say this is an intermittent problem. The peddle will depress to the floor without pressure felt in the driver's foot and as soon as I realize this (under-pressurized situation) I will "release peddle pressure" to "regain peddle pressure" and the pressure regains so well that the brakes are sensitive enough that they can easily lock. I hope that this helps for which way I need to go next. Thank you, Mark.

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Monday, March 22nd, 2010 AT 5:56 PM

KHLOW2008

MECHANIC
41,814 POSTS

The push rod measurement I meant is between the pedal and booster. If there is insufficient clearance, it can cause the problem described.

If you have not checked the brake calipers, ensure the slider bolts are not stuck and pistons move freely.

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Tuesday, March 23rd, 2010 AT 8:01 AM