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Mushy / squishy brakes are usually caused by the brake master cylinder seals failing. You can buy a rebuild kit or a re-built replacement master cylinder. I would recommend the rebuilt master cylinder as all the detail work has already been accomplished and it is not a huge expense. The key is to make sure that your use a bleeder kit to "Pre-bleed" the master kit before installation. Your making sure that the master cylinder is free of air before installation. If you instal it with air in the system it wil take you the better part of a quart of brake fluid to bleed the whole brake system via the wheel cylinders. What will happen is after you install the master cylinder the brakes would still be mushy and until you got the residual air out of all of the lines it would appear and act just like it did before you changed the master cylinder.
REMOVING Removing the master cylinder is really simple, only requiring a few steps. Keep in mind that brake fluid will eat the paint of the car. So use a plastic or vinyl type fender cover to protect the vehicle's paint. Brake fluid is water soluble so if you should get some on the paint, wash it off with plenty of water as quickly as possible.
Using a siphon, an old turkey baster works great, empty the master cylinder reservoir and dispose of the old brake fluid in the proper manner.
Disconnect the wire connector for the brake fluid level and/or brake pressure-warning switch, if your vehicle is so equipped.
Disconnect the brake lines from the master cylinder with a line wrench. A line wrench is specially designed to remove and install hydraluic fittings without rounding them off.
Remove the master cylinder mounting nuts, then the master cylinder.
On non-power brake vehicles, disconnect the master cylinder linkage from the brake pedal underneath the dash.
On models with separate fluid reservoirs, remove the reservoir.
REPLACING
Before installing the new master cylinder on the vehicle, it must first be bled using a specialized bleeder kit. The master-cylinder bleeder kit comes with tubing, clips and multiple adapters. Most new or rebuilt master cylinders come with a bleeder kit for that particular master cylinder.
Begin by removing the cap.
Follow the directions that come with the kit to select the suitable adapters, and then connect the adapters and tubes to the ports on the cylinder. The other ends of the tube extend down into the master cylinder, and are held in place by a plastic clip. Figure 2.
With the bleeder kit installed, fill the master cylinder about halfway with new brake fluid. Use a large screwdriver to depress the valve assembly inside the master cylinder. If you do not have a vise you can mount the master cylinder on the vacuum brake booster and bleed the master cylinder.
Small bubbles will appear in the fluid. Continue working the valve assembly until no more bubbles appear. This indicates that the cylinder has been thoroughly bled.Reverse the removal procedure to install the master cylinder, noting the following Refer to your service manual for any Master Cylinder Push Rod Adjustment procedures if your vehicle requires it.Bleed brakes as described under Brake Bleeding.Operate the brakes several times and check for external hydraulic leaks.This is fairly straightforward job. Replacing a master cylinder should take you about 1 to 2 hours, depending on the make and model of car. If you are rebuilding the master cylinder, add about another hour or so.
master cylinder fault,to brake pedal make sure there is freeplay at the master cylinder to brake peddle rod, if that is ok the bucket in the master cylinder is swollen and covering the oil return port. fit a new kit.
There are seals in the master cylinder that may be bad.
Try bench bleeding the master (there are cheap tubing kits for this) and see if fluid comes out of the ports. If no fluid after bench bleeding, replaced the master cylinder (usually come with a cheap bleeder kit anyway)
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