I have front brakes but no rears this is on a saab 9000cdturbo withaccumulator boosted master cylinder

If you have checked round the rest of the vehicle for brake fluid leaks and you are unable to pinpoint a leak. Eg calipers, brake flexible hoses, brake pipes. The next step would be to check the brake master cylinder by removing from the servo to check the rear seals.

Bill:

Check your master cylinder. It could be a piece of junk lodged in the fluid port for the rear brake lines, or in the brake line its self. The fact that both rear wheels spin tells me that if it is a clogged line, it is between the two manifolds, (one next to the master cylinder, and the other where the rear brake line splits into two... one for each rear hub. Or it could be that the piston in the master cylinder needs to be replaced. I would disconnect one brake line at one rear wheel and disconnect the rear brake line at the manifold (near the master cylinder)and blow that line out with air pressure. . do not leave the rear brake line connected to the master cylinder as you blow air through the lines as you may damage the master cylinder piston packings. You'll have to bleed the brakes when you are done.

Does the brake pedal go to the floor? Or does it stay up, and is hard to push...? Did you bleed the master cylinder? Also, you will need to bleed all 4 wheels connection to the brake wheel cylinders...you must start with the rear, farthest from the master cylinder, then other rear, then front farthest from the master cylinder, then other front...the bleeding of each line is a must, since you switched the master cylinder.

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

The rear seal of the master cylinder plunger is leaking, you must replace the master cylinder to correct this.

It sounds as though where the rear brake lines meet up with the master cylinder; there is probably a piece of dirt in the lines that could be blocking any fluid from getting in. To test this, I would remove the brake lines from the master cylinder and then remove the master cylinder. Once done, have the master cylinder cleaned inside out. This will remove the dirt particles that are clogging your lines.

A booster cannot cause a low pedal. (unless it is boosting too good...which will put your face through the windshield - LOL!) If you have replaced all that stuff, you probably have lots of air in your lines. Many times, "normal" bleeding will not remove this air. The best way to cure this is to do a "Radical" bleed. You need to start at the right rear wheel. Make sure that your master cylinder is full. Open the bleeder screw at the right rear wheel and pump the pedal about 15 times. DO NOT close the bleeder screw while doing this. Be careful to watch the master cylinder so you do not run it out of fluid. (If you run it out of fluid you will have to start over) Leaving the bleeder open, refill the master cylinder and allow the right rear to gravity bleed (just let it drip) for about 1 minute, then close the bleeder screw. Repeat this process next with the left rear, then the right front, and lastly with the left front. Top-off the master cylinder again and pump the pedal HARD. Then open the bleeder at the right rear and close it again as with "Normal" bleeding. Do this at least twice or until it stops spitting air, whichever comes first. Repeat this process also with the left rear, right front and left front. Top-off the master cylinder ... the problem should be fixed.

check vacumn and\or connections to the vacumn boost cannister.

You have a Master Cylinder/Vacum problem. The Master Cylinder Utilizes Vacum to provided Boost, if your vacum system is not working properly your brakes will malfunction. If the issue is a rear brake locking up double check your brake assembly on the rears. They are spring and Caliper combination and if the emergency brake cable is routed wrong or getting snagged it will activate the brakes and cause them teo lock up.

start with wheel furthest from master cylinder,then 2nd furthest,etc.,closest wheel last.