The Buick Reatta brake system is the Teves Mark II ABS system. It uses a pressure accumulator, (shown in the photo on the right), to store a reserve of brake fluid pressure so there is still braking power when the brake booster pump is not running.
The Buick Reatta accumulator is a hollow steel chamber that contains a rubber bladder. The rubber bladder is pre-charged with about 750 psi of an inert gas. The rubber bladder separates the inert gas charge from the brake fluid.The bladder works much like a spring to keep constant pressure on the brake fluid in the system.
When the pump runs it compresses the bladder with up to 2600 psi before the pump shuts off. The system has a pressure switch that monitors the pressure in the system. When the pressure in the system drops to about 2000 psi the pressure switch will close and the brake pump will start again to rebuild the pressure in side the Reatta accumulator. If for some reason the pump fails to run the pressure stored in the accumulator will give you several pumps on the brake pedal with enough pressure to safely stop the car.
When the bladder inside the Buick Reatta accumulator ruptures the accumulator will lose the inert gas charge. If the accumulator bladder is broken, the brake pump will still apply pressure to the accumulator and the rest of the brake system but the system will no longer have the reserve pressure that it did with a good bladder in the accumulator. The result can be a flashing red brake warning light and the pump starting each time you hit the brakes. The pump running so often puts an extra load on the pump that could result in failure of the pump. A good accumulator is an important part of the Teves brake system.