I HAVE A 99 TAHOE WITH A VERY SPONGEY BRAKE PEDAL.I CHANGE MASTER CYLINER,FRONT CALIPERS ,REAR WHEEL CYCLINERS,BLEED ALL THE ABS AND ALL WHEELS.PUT GAUGES AT MASTER CYCLINER PORTS AND HAVE 1500PSI DEAD HEADED.WHY DO I STILL HAVE A SPONGEY PEDAL.
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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.
Some vehicles have an odd way of bleeding them. My Chysler is one of them. Typically, you start from the wheel furthest from the master cylinder and complete one axle at a time, ending with the front wheel closest the master cylinder. On vehicles where the brake line is a tandem design, this is not the procedure. The brakes are bled diagonally beginning with the rear wheel closest the master cylinder and going diagonally to the front wheel, and then to the other rear wheel and then diagonally to the final front wheel, closest the master cylinder. Failure to follow the correct bleed protocol may leave some air in the lines, leading to a spongey pedal., depending on what type of brake line routing your vehicle has. Check your brake lines for leaks.
Bleeding brakes is easiest done with a helper to push the brake pedal.
If the master cylinder was empty, top it up. Have the helper push gently down the pedal while you crack the line fitting on the master cylinder enough that it allows air to come out. Generally it is a 1/2 to a 3/4 turn off the seat. Close the fitting when the pedal is down and then release the pedal. Continue this until no air is evident. Then do the other line fitting on the master. This operation will get the air out of the master and is easier than pushing air all the way through the system.
Make sure you keep the fluid topped up! If it goes dry you will need to start over. And use approved brake fluid only! Anything else will ruin the complete system.
Next proceed to bleed the remainder of the system as described below.
If the master cylinder maintained fluid then you will need to go to the bleed screws on the wheel cylinders or calipers. Front brakes will have calipers, rear could be wheel cylinders or calipers, depending on how it was equipped. Each one will have a screw with a hole in the center. this is the bleed screw. They are usually close to where the main line is attached.
Start at the right rear bleed screw and bleed the same as the master-------crack....push...close...release. Then go to left front bleeder and do the same. Then to left rear, right front.
Have the helper push the pedal hard after you are done bleeding to verify the fittings that were loosened do not leak.
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The brake system bleeding procedure differs for ABS and non-ABS
vehicles. The following procedure pertains only to non-ABS vehicles. For
details on bleeding ABS equipped vehicles, refer to the ABS procedures
later in this section.
Make sure the master cylinder contains clean DOT 3 brake fluid at all times during the procedure.
The master cylinder must be bled first if it is suspected of containing air. Bleed the master cylinder as follows:
Position a container under the master cylinder to catch the brake fluid.
Loosen the left front brake line (front upper port) at the master cylinder and allow the fluid to flow from the front port.
Connect the line and tighten to 24 ft. lbs. (32 Nm).
Have an assistant depress the brake pedal slowly one time and hold
it down, while you loosen the front line to expel air from the master
cylinder. Tighten the line, then release the brake pedal. Repeat until
all air is removed from the master cylinder.
Tighten the brake line to 24 ft. lbs. (32 Nm) when finished.
Repeat these steps for the right front brake line (rear upper port) at the master cylinder.
Do not allow brake fluid to spill on or come in contact with the
vehicle' finish, as it will remove the paint. In case of a spill,
immediately flush the area with water.
If a single line or fitting was the only hydraulic line
disconnected, then only the caliper(s) or wheel cylinder(s) affected by
that line must be bled. If the master cylinder required bleeding, then
all calipers and wheel cylinders must be bled in the proper sequence:
Bleed the individual calipers or wheel cylinders as follows:
Place a suitable wrench over the bleeder screw and attach a clear plastic hose over the screw end.
Submerge the other end in a transparent container of brake fluid.
Loosen the bleed screw, then have an assistant apply the brake
pedal slowly and hold it down. Close the bleed screw, then release the
brake pedal. Repeat the sequence until all air is expelled from the
caliper or cylinder.
When finished, tighten the bleed screw to 97 inch lbs. (11 Nm) for the front, or 66 inch lbs. (7.5 Nm) for the rear.
Check the pedal for a hard feeling with the engine not running. If
the pedal is soft, repeat the bleeding procedure until a firm pedal is
Fig. 1: Loosen the front brake line in order to bleed the master cylinder
Fig. 2: Connect a bleed hose from the bleed valve on the front caliper to a jar of brake fluid
Fig. 3: Always follow the lettered sequence when bleeding the hydraulic brake system
Hope this helps to solve it; remember to rate this answer.
there is air there somewhere. try manual bleeding the brakes. do the farthest wheel first. if they are calipers all the way around, when you bleed them tap them gently to remove any air that can still be inside the chambers.
A bad brake booster will result in a hard brake pedal, stiff and more effort required to stop the truck. Here are my questions to you, first, you said you replaced the master cylinder, did you bench bleed it before you installed it? If not, there IS still air in it, regardless of how much you bleed the brakes at the wheels. Second, when you bled the brakes, after changing the calipers and master cyl., did you also bleed the proportioning valve? Sometimes air can get trapped in the valve, and its almost impossible to get it out bleeding just the wheels. And lastly, when the brake light comes on, does the abs light also come on with it? Air can also get trapped in the abs control module too.
Try having the dealer flush and bleed your system. It is very hard to bleed ABS systems yourself and have safe brakes that still work afterward. Bleeding non-ABS brakes yourself is easy not the same for ABS brakes. Valving, sensors and what-not require a tech and the correct equipment in my opinion. You do it wrong and you could ruin your ABS system. Do that and see if they firm up. I replaced my brake shoes/pads at the same time all new everything in back, drums/springs everything and new rotors up front. then I had the chevy dealer flush, refill and bleed system. Stiffer pedal and brakes work better. Keep in mind the brakes on 99 Tahoes are inaedequate, require new rotors often, heat up and fade/glaze pads regularly. I replace my pads long before they wear down because they glaze up and start fading early. I'll rough em up once maybe, next time, new ones. Every two brake jobs, new rotors for me. Just how it is. They will stiffen a bit and work better but they will never be awesome brakes. Just how it is on 99 and earlier Tahoes. Hope it helps. Very important to bleed correctly though. I'll bleed my 83 Toyota 4x4 myself but not the Tahoe.
i try to help you, firts refill brake fluid container,open purge valve in one wheel front only,wait few minutes when drops fluid, close this valve and open other wheel, same procedure, finally repeat this in each 4 wheels