schematics and diagrams: excessive brake pedal

The Problem Started After replacing brake pads.Now the Brake pedal just falls to the floor.

The pedal is very loose and has no pressure.

As per the problem,it clears that problem is with master cylinder or brake calipers.

But before we assume either caliper or master cylinder damage, we need to do a couple of basic checks.

This basic inspection test will help to confirm the exact cause of problem.
For this test / inspection procedure.
Pull the wheels, check that the brake hoses are not twisted. If ok, check that the pads are seated flush and engage the rotors flushly when someone pushes the brake pedal. If ok, check the calipers are not bolted up cocked at an angle.

But if all basic possibilities are getting checked ok, then you have to do a brake line clamp test. Use vise grips to lightly clamp in place about halfway up all the flexible brake hoses. Check the brake pedal. It should be firm. If not, then when you pushed the calipers in the master cylinder got damaged by the force of the backpressure or from sediment being pushed up into it. Replace the master cylinder.

If pedal is firm, then remove one clamp at a time and retest pedal. At whichever wheel you remove the clamp and brake pedal drops, that is the one that caliper is bad and needs to be replaced.

This tests and details will help.
Thanks.

Users Who Viewed This Problem Also Viewed:

How to fill Brake line antifreeze on freightliner classic?

http://technoanswers.blogspot.com/2012/01/how-to-fill-brake-line-antifreeze-on.html

Engine accelerates when brake is applied?

http://technoanswers.blogspot.in/2012/02/engine-accelerates-when-brake-is.html

Dodge RAM Cab: Brake pedal loose after replacing Brake Calipers?

http://repairhelpcenter.blogspot.in/2012/05/dodge-ram-cab-brake-pedal-loose-after.html

1996 Dodge Grand Caravan: Parking Brake Cable Broken?

http://schematicsdiagram.blogspot.in/2012/05/1996-dodge-grand-caravan-parking-brake.html

2007 Cadillac CTS: Brake System Locking up?

http://howtobyme.blogspot.in/2012/05/2007-cadillac-cts-brake-system-locking.html

Brake Pads Inspection on Acura Integra?

http://repairhelpcenter.blogspot.in/2011/11/brake-pads-inspection-on-acura-integra.html

How to remove Brake Pads on Acura Integra?

http://repairhelpcenter.blogspot.in/2011/11/how-to-remove-brake-pads-on-acura.html

How to remove Brake Disc Rotor on Acura Integra?

http://repairhelpcenter.blogspot.in/2011/11/how-to-remove-brake-disc-rotor-on-acura.html

Brake Caliper OVERHAUL on Acura Integra?

http://repairhelpcenter.blogspot.in/2011/11/brake-caliper-overhaul-on-acura-integra.html

How to remove Brake Caliper on Acura Integra?

http://repairhelpcenter.blogspot.in/2011/11/how-to-remove-brake-caliper-on-acura.html

How to remove Brake Disc Rotor on Acura Integra?

http://repairhelpcenter.blogspot.in/2011/11/how-to-remove-brake-disc-rotor-on-acura.html

How to remove Parking Brake shoes on Acura Integra?

http://repairhelpcenter.blogspot.in/2011/11/how-to-remove-parking-brake-shoes-on.html

How to remove Parking Brake Cable on Acura Integra?

http://repairhelpcenter.blogspot.in/2011/11/how-to-remove-parking-brake-cable-on.html

For All types of Car models and brands help
Go to Newly Launched

FREE Car repair guide?
http://technoanswers.blogspot.in/2012/03/car-repair-guide.html

&
Complete Car repair Help FREE?

http://repairhelpcenter.blogspot.in/2012/03/complete-car-repair-help.html

This problem is noticed many a times.
The brake pedal travels excessively when brakes are applied.
This problem is called.
Excessive Brake Pedal Travel.

This problems occurs due to many possibilities.

The details below will help you.

A worn brake linings front or rear (or both), misadjusted drum brakes, or air in the brake lines.Can cause such problems.

Inspect Brake Pad/Shoe-Front and rear both: Worn or Damaged Brake Pad/Shoes can cause this problem.
Inspect Brake line: If Pressure Air in Hydraulic System or Fluid Loss is noticed then brake line has to bleed.
Inspect Master Cylinder (For Brake System): Faulty Brake Master Cylinder can cause such problems.
Inspect Brake Caliper: Air in Hydraulic System or Fluid Loss can also cause such problems.
Inspect Brake Drum : Excessively Worn Brake Drum can be one reason for this problem.
Inspect Wheel Bearing-Front and Rear: Incorrectly Tightened or Installed Wheel Bearing can cause this excessive brake pedal travel problem.

In some cases this problem is noticed after changing the master cylinder and bleeding the brakes.

AT our garage one of out regular client noticed this same problem on is Light duty ford truck.

I suggest you to go through this detail to understand this problem.

A common problem is the rear wheel anti lock brake valve,they by pass internally and give you a a low, sinking pedal.

The valve is located in the rearbrake line circuit.

Symptom/Problem: Brake pedal fade, low pedal. The problem is an internal leak in RABS valve.

Background: A common complaint on Ford light duty trucks with the rear anti-lock brake system is that the brake pedal will fade while under steady pressure. In a conventional brake system this would point to an external fluid leak or an internal leak (bypass) in the master cylinder. Generally, one and usually two master cylinders have been replaced already, leaving one very frustrated technician. In this system there is one other possibility - the rear anti-lock brake valve. This valve is the electro-hydraulic proportioning valve located on the left-hand frame rail between the master cylinder and the rear brakes. This valve controls the brake fluid during an anti-lock stop by restricting or bleeding off rear wheel cylinder pressure.

To better understand what's happening, let's take a quick look at system operation. The RABS module continuously monitors rear wheel speed by means of a sensor installed in the rear differential. When the sensor signal to the module shows a rapid decrease in speed - indicating rear wheel lockup will occur - it energizes the isolation solenoid in the RABS valve. By doing this, the normally open valve is now closed, blocking off the line to prevent further brake fluid from entering the rear wheel cylinders. If there is still too great a decrease in rear wheel speed, the module will then energize the dump solenoid in the RABS valve. This solenoid is normally closed and, when energized, will open a port to the accumulator and bleed off some of the pressure to prevent lockup. This fluid is then stored until normal brake functions are resumed and the fluid is returned to the master cylinder.

If rear wheel speed is now OK, the module de-energizes these solenoids to resume normal braking. If speed decreases too rapidly again, it resumes anti-lock control. The module will alternate between the two solenoids and normal braking until there is no further chance of locking up or vehicle speed is now under 5 mph.

The focus is on this dump portion of the RABS valve. Occasionally the seat between the solenoid and the accumulator will leak, causing the pedal to fade during normal pedal applications. This sinking pedal has no other abnormal braking characteristics and is usually not noticed (depending on severity) unless it sits for an extended amount of time with constant pressure applied. It may be due to physical damage or a buildup of contaminants in the hydraulic system, but the results are the same.

Some customers report that the brakes were just fine until a hydraulic component was replaced or repaired and the brakes were bled. Then the pedal started fading. Quite possibly this is due to a new problem that is created by "moving" some of the contaminated fluid into the valve. To diagnose this system, like all brake systems, first verify that there are no external fluid leaks. If visual inspection is OK, disconnect the brake lines at the master cylinder and plug the outlets in the cylinder. When the master cylinder is plugged, if a fade is still experienced, the master is at fault.

If, however, there is no fade, determine if it is coming from the front or rear brakes by blocking one port at a time at the master cylinder. If there is no longer a fading pedal when blocking the port to the rear line, go one step further and build a short brake line to splice between the inlet and outlet lines at the RABS valve to temporarily bypass the valve.

After bleeding the rear brakes and verifying there is a solid pedal, it's a good bet that the problem is in the valve itself. The next step is to replace and bleed the valve (if equipped with a bleeder) and the rear wheel cylinders. Verify the repair and road test.

See below diagram shown below :----