1996 dodge ram 1500 4x4 Brake pedal depresses to floor when making a full left turn or right turn. Replaced master cylinder 4 times, brake booster, brake proportioning valve. all master brake cylinders was bench bleed, the entire brake system was purged each time. Had 4 mechanics work on it, still same problem.

Michael:

You must start bleeding the brakes at the wheel farthest from the master cylinder (usually the right rear), then the next farthest from the master cylinder, then the next, then the closest. If your master cylinder is at the left front of the car, start with the right rear, then the left rear, then the right front, then the left front. If you don't bleed the brakes in the correct order, you are just shifting the air in the lines from one line to another. Make sure that you close the bleeder before letting the brake pedal up, and the engine should not be running when you bleed the brakes... Make sure that the emergency brake is off. Make sure that the master cylinder does not run out of brake fluid at any time that you are bleeding the brakes.

The master cylinder in your Dodge Caravan is responsible for forcing fluid pressure to the four wheels when you apply the brakes. The master cylinder is also the main storage vessel for brake fluid. If the seals inside your master cylinder develop leaks, you will lose brake pressure internally. This could cause problems for the brake booster, as well as causing the brake pedal to sink to the floor when you press the pedal. The master cylinder can be replaced in about 30 minutes.

• 1 Press the brake pedal a few times until you have a firm pedal.
  
• 2 Open the hood and prop it up with the hood support rod. Locate the master cylinder, which is mounted to the brake booster on the bulkhead between the engine and passenger compartments, just in front of the driver. Spray the top area of the master cylinder liberally with brake cleaner. Push down lightly on the master cylinder filler tube and turn it counterclockwise to remove it.
  
• 3 Locate the fluid-level sensor connector(s). There may be one or two sensors on your vehicle and they appear as wires, in a plastic housing, plugged into the side of the master cylinder. Remove each connector by depressing the locking clip and pulling straight out from the master cylinder.
  
• 4 Remove the brake lines from the master cylinder by turning the fittings counterclockwise with the flare nut wrench. Gently pull the brake lines away from the master cylinder.
  
• 5 Remove the bolts securing the master cylinder to the brake booster by turning the nuts counterclockwise with a socket and ratchet. Pull the master cylinder straight out, being careful to avoid spilling brake fluid on your vehicle's painted surfaces.
  
• 6 Verify that the rubber O-ring seal is in place on the new master cylinder and then slide the master cylinder in place over the mounting studs. Thread the nuts onto the studs by turning them clockwise. Tighten the nuts to 18 foot-pounds. You may have to hold the booster actuator rod in position as you install the master cylinder.
  
• 7 Fill the master cylinder with new brake fluid and thread the bleeder fittings into the brake line ports by turning them clockwise by hand. Install the rubber tubes onto the fittings and secure the tube ends in the master cylinder filler opening. Make sure the ends of the tubes are completely submerged.
  
• 8 Depress the brake pedal a number of times, slowly and evenly, while a helper watches to ensure that no more air escapes from the bleeder tubes. Remove the bleeder fittings by turning them counterclockwise and carefully set them aside. Reconnect the electrical fittings by firmly pushing straight in until they click.
  
• 9 Thread the brake lines into the proper ports by turning them clockwise by hand. Tighten the fittings to approximately 13 foot-pounds with the flare nut wrench. Have your helper press the brake pedal slowly and evenly five times and then hold it. Slowly crack open the front fitting by turning it a quarter-turn with the flare nut wrench and allow the brake pedal to fall to the floor. Have your helper hold the pedal on the floor as you tighten the fitting. Repeat this process until no more air bubbles appear. Repeat this process on the rear port.
  Retighten the fittings to 13 foot-pounds. Install the filler tube by placing it on the filler opening and turning it clockwise. Refill the master cylinder to the "Fill" mark or 1/4-inch from the top
  

1. Check the fluid level in the reservoir after bleeding each wheel. Add DOT3 fluid, if necessary.
2. If the master cylinder was disassembled or if the reservoir becomes empty, bleed the air from the master cylinder as follows:
   1. Disconnect the brake lines from the master cylinder.
   2. Slowly depress the brake pedal and hold it.
   3. Block off the outlet plug with your finger, and release the brake pedal.
   4. Repeat 3 or 4 times.
   
   
3. Bleed the brake starting with the one furthest from the reservoir and then the next furthest, etc.
   
4. Depress the brake pedal several times, then loosen the bleeder plug with the pedal held down.
5. At the point when fluid stops coming out, tighten the bleeder plug to 11 Nm (8 ft. lbs.), then release the brake pedal.
6. Repeat until all the air in the fluid has been bled out.
7. Repeat the procedure to bleed the air out of brake line for each wheel.
8. Check the fluid level and add DOT3 fluid if necessary.

It sounds like you have a faulty Electro-Hydraulic Control Unit (EHCU) or a Brake Pressure Modulator Valve (BPMV). Air is trapped in the valve body and air is much harder to get out of the master cylinder than it is the lines. You can try this method to help troubleshoot.

This is out of the Online GMsevice manual for a 2001 Blazer with 4-WD
Use the two-person bleed procedure under the following conditions:

Raise the vehicle in order to access the system bleed screws.
Bleed the system at the right rear wheel first.
Install a clear hose on the bleed screw.
Immerse the opposite end of the hose into a container partially filled with clean DOT 3 brake fluid.
Open the bleed screw 1/2 to one full turn.
Slowly depress the brake pedal. While the pedal is depressed to its full extent, tighten the bleed screw.
Release the brake pedal and wait 10-15 seconds for the master cylinder pistons to return to the home position.
Repeat the previous steps for the remaining wheels. The brake fluid which is present at each bleed screw should be clean and free of air.
This procedure may use more than a pint of fluid per wheel. Check the master cylinder fluid level every four to six strokes of the brake pedal in order to avoid running the system dry.
Press the brake pedal firmly and run the Scan Tool Automated Bleed Procedure . Release the brake pedal between each test.
Bleed all four wheels again using Steps 3-9. This will remove the remaining air from the brake system.
Evaluate the feel of the brake pedal before attempting to drive the vehicle.
Bleed the system as many times as necessary in order to obtain the appropriate feel of the pedal.

Good luck, i hope this helps.

You either have a leak in the the system or your master cylinder is bad and allowing the pedal to push through the cylinder without bulding pressure. Check all the wheels for signs of a leak, if none and the brake fluid resivoir is full then the master cylinder on the back of the firewall is bad. These can be rebuilt very cheaply and you can do this yourself with parts from the parts store.

go in this order-
-make sure the fluid resivoir is full and the cap on
-crack both front bleeders loose and allow them to "gravity bleed"
-once you see fluid constantly dripping out of the bleeder close them
-do the same with the rear
-after you have gravity bled the brakes grab a partner and have them pump the brake 4 to 5 times holding the pedal down on the fifth time
have them say "holding" while you crack the right rear bleeder-once the pedal hits the floor they should say "floor" and hold it there while you tighten the bleeder. repeat until you see nothing but fluid squirt out.
repeat this whole process in this order
right rear
left rear
right front
left front
make sure to continually check the brake fluid level so it doesnt get too low
this should work unless the master cylinder leaked dry from replacing the lines-if this happened you will most likely have to bleed or even replace the master cylinder

The "pedal goes to floor" is a mechanical problem and it more than likely that there is still air in the system and that the bleeding is not complete. Find level ground and start at the back of the truck with the hand brake off, chock the wheels if needed. Fill the brake fluid reservoir. Loosen the bleed screw on the back brake assembly and have a colleague depress the brake. Tighten and release the brake, NEVER allow the brake pedal to rise when the bleed screw is loose as this will **** air back into the system. Undo the bleed screw about half a turn and again depress the brake, tighten off at bottom of stroke and again release the pedal. Every couple of times top up the brake fluid reservoir. Keep pushing fluid through until about half a pint has been expelled from the bleed screw assembly. Tighten off the bleed screw for good. Go the other rear wheel and repeat the process making sure that the reservoir never runs out of fluid. . Now go to the front and repeat with both wheels. There should come a time that your colleague can report that there is increasing resistance when standing on the brake pedal. If after all this the pedal continues to sink to the floor it sounds like the seal on the master cylinder piston is defective or there is a leak in the brake line.

Hello;
Did you bleed the master prior to installation? If not you may have a bunch of air trapped in the system. Start at the master and use a pressure bleeder too get the air out. If you have anti-lock you may have to have the dealer purge the system.
Thanks;
Rich
RPM Northwest

I am a hydraulic technician and I can tell you that air is a killer in the hydraulic system.

Start from the rear and work your way forward. I f you are using the two person method, make sure the second person keeps the master cylinder full. If the fluid level dropped anywhere in between pressing and releasing the brakes....you have a lot of air in the system.

Make sure you are tightening the bleed valve when the brake pedal is full pressed.

Remeber...start from the rear brakes first, then do the front.

this is caused by a defective brake master cylinder, this assumes the system is not low on brake fluid.