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Brake pedal goes to floor very little resistance

Tiny
CRAIG-H
  • MEMBER
  • 1994 TOYOTA CAMRY
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 222,000 MILES
Brake pedal goes to floor with very little resistance and locks up right front wheel [very poor braking]. Front pads and rear shoes replaced recently and no signs of brake fluid leak, no reduction in master cylinder fluid level. In recent past, car started [cold] the brake pedal would go to floor, however after short period [warm up] brake pedal would return to normal resistance and braking, now no return to normal braking.

Before I go to bleeding the brake system I did some power booster checking suggested in a Haynes repair manual; Haynes Ques.-1. Depress Brake pedal several times with engine off and make sure there’s no change in pedal reserve. Result - 1. No change in pedal, but it goes down a long way.
Haynes Ques.- 2. Depress the pedal and start the engine, if pedal goes down slightly operation is normal. Result – 2. Yes the pedal goes down slightly, but pedal initially goes down a long way.
Haynes Ques. - 3. Start engine and turn off after 1 – 2 minutes then depress the brake pedal slowly several times, if the pedal depress less each time the booster is airtight. Result – 3. After engine is turned off the first pedal depression is easy and deep, subsequent pedal depressions have more resistance and not as deep as first depression.
Haynes Ques. – 4. Depress brake pedal while engine is running then stop engine with pedal depressed. If no change in pedal reserve travel after holding pedal for 30 seconds the booster is airtight. Result – 4. No change in pedal position after 30 seconds, restart engine with pedal still depressed the pedal then goes to the end of its travel.

Any thoughts?

Craig
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Wednesday, December 12th, 2007 AT 5:48 PM

4 Replies

Tiny
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  • MECHANIC
  • 31,937 POSTS
Hi there,

You could have a by-passing master cylinder. This is where the fluid passes from on circuit to the other internally so there is no fluid loss only a poor pedal

First re bleed brakes as a precaution, if no improvement, one test is to pump up pedal to a good high feel and apply pressure not extra heavy, just a constant pressure, if pedal slowly falls away and there is no external leaks, replace the master cyl.

Mark (mhpautos)
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Friday, March 5th, 2021 AT 11:58 AM
Tiny
CRAIG-H
  • MEMBER
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Before I go to bleeding the brake system I did some power booster checking suggested in a Haynes repair manual; Haynes Ques.-1. Depress Brake pedal several times with engine off and make sure there’s no change in pedal reserve. Result - 1. No change in pedal, but it goes down a long way.
Haynes Ques.- 2. Depress the pedal and start the engine, if pedal goes down slightly operation is normal. Result †2. Yes the pedal goes down slightly, but pedal initially goes down a long way.
Haynes Ques. - 3. Start engine and turn off after 1 †2 minutes then depress the brake pedal slowly several times, if the pedal depress less each time the booster is airtight. Result †3. After engine is turned off the first pedal depression is easy and deep, subsequent pedal depressions have more resistance and not as deep as first depression.
Haynes Ques. †4. Depress brake pedal while engine is running then stop engine with pedal depressed. If no change in pedal reserve travel after holding pedal for 30 seconds the booster is airtight. Result †4. No change in pedal position after 30 seconds, restart engine with pedal still depressed the pedal then goes to the end of its travel.

Any thoughts?

Craig
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Friday, March 5th, 2021 AT 11:58 AM
Tiny
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Hi there,

For many years I have used the simple booster test, Basically the same as what you have posted. Engine off pump brakes to evac booster start engine with foot on brakes pedal should suck down a little if so booster servicable. If the booster is faulty you will have a very hard pedal. This has no relationship to how high the pedal is. The booster (using vacuum over air) increases pedal force. The master cylinder creates the braking pressure, if air is in system (air will compress) and a low pedal will resault If drum rear brakes fitted and out of adjustment pedal will be low but will pump up with a few pedal strokes. If Master cyl id by passing, often with little pedal force pedal will fall away as piston in cyl passes fluid past the seal (by-passing) pedal drops with Little brake pressure increase. If you pump the brakes and hold hard pressure pedal may stay high and hard as the seals are forced out and seal better, back off pressure and pedal will slowly fall away. Now this is all in theory, with out actually inspecting the problem first hand there may be other issues involved as well. A bit long winded, but if you need some point explained further please re post or IM me.

Mark (mhpautos)
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Friday, March 5th, 2021 AT 11:58 AM
Tiny
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One extra thing.

Get 3 brake hose clamps and lock off all flex hoses. What is the pedal like then,

Mark (mhpautos)
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Friday, March 5th, 2021 AT 11:58 AM

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