 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 CAUSE
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.) |
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.
I have the same problem, Is there any recall for
a lexus 2001 LS 430 brake problem or any mark levenson
radio volume problem.
replaced the booster also
Posted to BAT Auto.
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?
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?
Check to make sure you didn’t unplug the vacuum line leading to your brake booster
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
any luck? I seem to be having the same problem.
I had the same problem with an older Lincoln the actuator rod from the master cylinder through the booster was misaligned causing it to be depressed all the time
What did you find out? I hv the exact same problem
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
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.
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??
I HAVE A 1998 CHEVROLET 1500 4X4. BRAKE PEDAL GOES TO FLOOR. HAVE EVERYTHING NEW.FT CALIPERS,PADS, HUBS,BRAKE HOSES, BRAKE VALVE, 2 MASTER CYLINDERS, BRAKE BOOSTER, I BLED THE
BRAKES AND STILL GOES TO FLOOR. NEXT STEP IS TO REPLACE WHEEL CYLINDERS IN BACK. I HAVE DONE PUT $1600.00 DOLLARS IN THIS TRUCK ANY SUGGESTIONS.
Check out the ABS module system
hi, changed the pads on my car now I have no bakes
My opel Monza 2L when idleng, brake pedal goes to the floor and lightly brakes, when off lightly hard.
Last year my son replaced front pads and have had no problems since. Last week was driving home and brake pedal went to floor. He put in a new master cylinder and now there’s a rubbing scraping loud noise when driving. It seems the brakes are ok but don’t want to drive with the noise which gets louder when as you drive. He’s talking about transmission trouble but have no symptoms of that. Could it be possible to tie the two together. I have always had my work done the car by a mechanic so now don’t know what to do. He said the noise can’t be heard outside of the car, just inside. Any suggestions?
Could be hub bearings if it growls and the pads are good, have him kick up the front wheels, spin and shake them side to side and see if there’s any play or noise
Hello, I’m currently working on a 2015 Ford F-250 and the pedal goes to the floor every now and then so I replace the master, booster, hcu and the LR caliper and did a brake flush and still it sinks to the floor and it seem like it only for it when I make a hard right or left turn. The I choked the left front brake line and the problem when away . Idk what to think should I replace the right front caliper or not . What will fix my problem
WHAT FIXED IT
i just replaced every brake line on my 99 chevy silverado 4×4 and now i cant get a brake pedal ? ive tried bleeding every thing n no go
I have a 2003 chevy malibu that I took to the garage too have new brake pads put on. They put new pads rotors , wheel bearings and a new master cylinder and my peddal is still going too the floor. Any ideals
I have replaced the master cylinder two calipers the ABS. I have brakes when engine shut off, but when I start the car I don’t have any brakes, need help
I’ve got 03 gmc Sonoma 2w drive auto..has front disc,rear drum..Brake pedal is good with eng off ,goes to floor with eng on..have replaced padss and shoes.new master cylinder was bled.all wheels bled..abs autobleed was done.still no change..I was thinking maybe the abs module but I’m at best an amateur at auto mechanic work..please help..also this truck has been sitting in my daughter’s back yard for appx 5yrs..thanks in advance