Auto Repair Help
LANCE’S CORNER – AUTO REPAIR HELP

DIAGNOSE – THE BRAKE PEDAL GOES TO THE FLOOR WHEN I STEP ON IT
by Lance Wright


SYMPTOM SUMMARY

The brake pedal goes to the floor when pressed. There may be little or no braking action when the pedal is depressed. The Red Brake Warning Lamp may be illuminated indicating a system failure.

USUAL CAUSEbrake_pedal
Very low brake fluid or a defective Master Cylinder is the usual cause of this symptom. The master cylinder pressurizes the brake system when the pedal is depressed and provides hydraulic fluid to each of the wheels to apply the brakes. The braking system is designed to illuminate the Red Brake Warning lamp when a hydraulic failure is present.

DIAGNOSIS
If you have just performed other brake work on the vehicle and the hydraulic system was opened, the most probable cause is air in the system. The system will need to be bled according to manufacturers recomendations. The first step in diagnosing this symptom is to inspect the brake fluid level at the master cylinder. If the fluid level is low, the system will need to be inspected for leaks. The calipers, wheel cylinders (on drum brakes) will need to be inspected. Brake pads that are completely worn can cause low fluid level. This is a result of the caliper pistons being completely extended, causing most of the brake fluid to reside in the calipers. The brake pads and shoes (if equipped) should be inspected for signs of brake fluid contamination indicating a leak. Inspect the calipers for leaks at the rubber dust boot around the pistons. The dust boot on the wheel cylinder will have to be pulled off slightly to inspect for leaks. Check the hydraulic lines, proportioning valve and flexible hoses for leaks. Inspect the master cylinder where it mounts on the brake booster for signs of leaks. Loosening the master cylinder retaining bolts and pulling it back slightly, will usually result in detection of a leak if present. If leaking, the fluid will run out of the mating surfaces. In this case, the master cylinder will require replacement. If there are no fluid leaks present or the fluid level is normal and the brake pads and shoes (if equipped) are in good condition, the most probable cause of the symptom is a defective master cylinder.

CORRECTIVE ACTION
Determining the cause of the failure will dictate what corrective action is necessary. If the hydraulic system needs to be serviced, as with replacement of the master cylinder, it will need to be bled of all the air once it has been resealed. Refer to the manufacturers specific bleeding procedures.

PRECAUTIONS, TIPS, and NOTES
If the vehicle is equipped with ABS, certain ABS components can cause this symptom. In this case, the system should be serviced according to manufacturers recommendations. If servicing the hydraulic system, use caution not to contaminate the system with dirt, debris or water. Always use the recommended brake fluid DOT rating. This information can be obtained from your owners manual or off the cap on the master cylinder.

(Lance owned his own auto repair shop for 30 years before retiring in 2006.)

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12 Comments on "Brake Pedal Goes To The Floor When Pressed"

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roger
3 years 7 months ago

hello, 2006 f150 5.4 …change the calipiers,brake hose, booster was leaking when pedal was pressed,new master cylinder was replaced twice thinking it was a bad master cylinder from auto zone. bleed the brakes using the scanner.but the pedal still sinks slowly to the floor.can it be the adjusting rod in the brake booster going to the master cylinder when brake pedal is pressed.

2 years 6 months ago

I have the same problem, Is there any recall for

a lexus 2001 LS 430 brake problem or any mark levenson

radio volume problem.

roger
3 years 7 months ago

replaced the booster also

john
1 year 10 months ago

I had my master cylinder replaced and it costed be $500. They said its my break booster causing my break pedal to depress and make a whislte sound when i press the breaks. But that would have costed me another $200. How do i know whats causing the problem?

Louis S Coniglio
11 months 1 day ago

I replaced the plugs, wires, and ignition coil today. When I started her up, I had no brakes. What did I do to cause this?

John
9 months 10 days ago

Check to make sure you didn’t unplug the vacuum line leading to your brake booster

7 months 20 days ago

I have a 1988 Ford f 150 I have replaced the rabs unit the master cylinder the booster calipers And the rubber brake line going from calipers to brake lines while truck is turned off i get pressure and kinda hard break pedal when I start truck my pedal sinks what’s wrong please help I’ve been working for a week on this and still can’t get positive results I’ve bleed the brakes for hours at a time help

6 months 18 days ago

any luck? I seem to be having the same problem.

Jaci
7 months 18 days ago

I have a 97 licoln town car signiture series i changed master cylinder and my brakes still go to the floor and brake fluid is fine

7 months 12 days ago

I have replaced this master cylinder twice now … I went to the wrecker and got 2 units now. I could understand one being bad but not twice. They both lasted about two month and the exact same thing happens. All of a sudden one morning I start the van and go to drive the petal goes to the floor and it was great the day prior. Then after during for a while is if fine then as I step on it lightly to starts to lose pressure and goes right to the floor. After a few days it is completely to the floor all the time.

Sedalia
4 months 12 days ago

Hello. I drove to work just fine and parked my car. At lunch I noticed the break light was on. Before pulling Off I pump the breaks a little and the light goes off. I drive off and down to the light, when trying to stop the brakes went all the way to the floor causing me to almost wreck. What could have happened here??

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