I have no brake pressure. The rear calipers and master cylinder are new. There are no apparent leaks in the lines, and yet there is still no pressure in the brake system. The pedal just sinks to the floor. The car was working wonderfully until I noticed the rear brakes were in bad shape. That's when I changed the pads and rear calipers in my garage. But when I bled the system there was no pressure. Then I replaced the master cylinder and bled that too. That's where I am now. What else could I try?

Fix the leak
then use a vacuum on the furthest bleeder to pull the brake fluid
keep the brake fluid filled
do that on all four
if that does not work, good chance you need to replace the seals on the master cylinder.
also check the linkage from brake pedal to master to insure that is ok

Does the car have ABS ? And does it have an equalizer block for the 4 wheels ?
It sounds like the ABS has been affected, or there is an equalizer block that is stuck on the front wheels only.
Can you open the bleeder or the rear line on the master cyl and get fluid to come out by depressing the pedal ?

Hello Patricia,

Have you checked the master brake cylinder reservoir for brake fluid loss?

I don't suspect the master cylinder as you have replaced it... but am more suspect of a leaking brake line or fitting which should have
been discovered when you had the system bled.

The only time I ever had a rear brake problem with a 2500 series Chevrolet was due to seized rear brake caliper guide pins...as your calipers are also new that is not your problem.

If your brake pedal feels spongy and travels to the floor board you have air in the system, a brake fluid leak or a failure in the power steering system, such as a broken hose, broken power steering pump drive belt, or failed pump, would result in a loss of pressure to both the hydro-boost and steering.

Find more information here:

. Hydro Boost Power Assist Systems Operation Diagnosis and Repair

Hi bradrolader
check on abs distributor if the car has, or a tee joint.that links rear right
break hose to the banjo bolt on the caliper bleeding nipple for blockage.
Raymond

Check for brake leaks. Make sure that the resevore is full. With the engine off pump the brakes then check for leaks. If there is no leaks then bleed the brakes start with the right rear and work clock wise around the truck. If there is no air that comes out of the lines and the fluid looks clean your master cylinder went bad and it is a easy replacement. To replace the master cylinder you'll need a 14 mm for the lines and a 15 mm for the booster. Thanks!

usually an indicator of either a loss of pressure due to low fluid and/or air in the system (brake fluid leak) or extremely worn rear brakes (if drum brakes in rear). possible causes include master cylinder (internal fluid pressure leak), external fluid leaks (calipers, lines, wheel cylinders), rear drum brakes extremely worn down or severely out of adjustment. normally worn disc brakes may reduce pedal height SOME, but seldom "to floor". but the "mushy" quote combined with the "floor" quote suggests a hydrolic fluid pressure problem.

possible leak in brake system. if not then you have a bad master cylinder. have to replace it.

Sounds like an internal leak in the master cylinder, an external brake fluid leak (such as a leaking brake line), or extreme misadjustment or binding of the calipers or drums. Any could be the case, and you can eliminate the last 2 rather easily. Do you see any sign of fluid coming from any of the brake lines? If not, move to adjustments. Check the calipers for bound up caliper pins and if equiped with rear drum brakes, the adjustment and condition of the rear shoes. After that, go right for the throat and replace the master cylinder. Be sure to bench bleed it before you install it, and if you have ABS, make sure you also bleed the ABS system, OR if you can't bleed the ABS system have the new master cylinder ready to install, and remove the brake lines as quickly as possible from the old master and have a friend hold thier fingers over the ends of the lines. I do this quite a bit at my shop, and it's VERY rare that I actualy need to bleed the ABS after replacing a master cylinder if little to no air gets in the brake lines.

no they are inverted flare fittings no seals check all lines and calipers/wheel cylinders if all are dry remove the vacuum hose from the booster if there is brake fluid in the hose the master cylinder is bad

The master cylinder supplies the pressure to the brake fluid that travels between the maste brake cylinder resevoir and the brake caliper pistons (through the brake lines. If the master cylinder fails there will be insufficient compression of the brake fluid to make the calipers operate as designed. Leaks in the brake lines and/or cylinders is a possibility, and unrelated to functionality of the master cylinder. Also, pistons located in the brake calipers can form a corrosion ring on their inside walls if there is breakdown in the brake fluid or moisture that gets into the lines. Operating the vehicle when there is insufficient brake fluid in the master cylinder resevoir can also lead to air getting into the brake lines, causing bad working brakes. Air compresses more than brake fluid, and the master cylinder isn't designed to compress air in the brake lines. Sounds like a bad case of "lack of maintenance", as opposed to bad advice from the mechanics. That said, there's no excuse for bad installation. But, it's tough to improperly install a brake line since they are nothing more than hollow metal tubes. There should be no rubber connectors installed in the brake lines. When bleeding the brake lines one must remove all of the trapped air before you will see any fluid appear. If the valves in the master cylinder are not properly operating the master cylinder will not allow the brake fluid to get into the brake lines.

Hope this helps.