brake problems.....

hello to all i have a 95 astro cargo van with 4 wheel abs .i went to adjust the rear brakes today and found that i have no brake fluid to the rear cylinders bleeders..i have not had time to mess with the rear brake line at the wheel due to the line being frozen together.but i took off the line at the master cyl. and there is presure but again the lines where frozen at the juction before the abs controle mod and i just could not get to the control mod...so i disconectedthe wire harness to it and no change....:screwy: ne one have ne ideas or help that would be great..thankyou for your time ahead of time....

The front brake hydraulic system is a true anti-lock system. Each wheel has its own speed sensor and its own hydraulic line and is controlled independently of each other in the event one or both wheels lock up. The rear brakes however, utilize one hydraulic line, and one sensor to cover both wheels. If either wheel locks up during braking, the ABS system controls pressure simultaneously to both rear wheels.

If during braking, hydraulic pressure is not supplied to the rear brakes, the red, and possibly the orange ABS, warning lamp(s) on the dash will be illuminated, along with a low brake pedal. If there are no lights illuminated, try removing the bleeder screws and make sure the passage is clear in each of the screws. Be certain the master cylinder is full, and remains full while the screws are out, and do not push on the brake pedal. When you are sure the bleeders are clear, reinstall them and bleed the system.

The two most common problems encountered with this style rear brake system are that the pistons in the wheel cylinders will seize in the bore, end result, no rear brakes. Secondly, the backing plates wear if they are not lubricated regularly. This will allow the pistons, if not seized, to slip off of the brake shoe and exit the wheel cylinder causing a major fluid leak, and a total loss of rear brakes. Many times the cylinder is replaced only to happen again due to the backing plate being the CAUSE of the cylinder coming apart. Hope this helps.

thankyou for all who replied...i found the peoblem it was the preportioning valve....was a easy fix ..but the rear cylinders ended up too dry from no fluid so as soon as i put presure to them they blew up so for ten dollars each i fixed that now all is better...have a good xmas all.