If you follow the test procedure on this website and find that your ABS hydraulic accumulator is weak (less than 10 pumps before the ABS pump cycles to restore system pressure), you may need to purchase and install an accumulator.
Before you do that, follow the first section of this procedure up to the point where you have removed the old accumulator. Check to see if a diverter fitting is installed in the base of the accumulator. Without it, you may not get enough brake pedal pumps until the ABS pump starts. If you do not, reinstall your accumulator and contact this site for acquiring the fitting. My Saab was missing the fitting, and installing it fixed the accumulator capacity problem.
Thanks to Steve Corgan for contributing to this FAQ!
Replacing an accumulator is a relatively simple job. Bleeding the brakes afterwards is also simple, but requires accessing the brake cylinder and caliper bleed fittings and having the equipment to bleed the system properly. This will be an ideal time to flush the brake system and install fresh fluid. Whether you are replacing the accumulator or not, this is always an excellent bit of preventative maintenance to perform.
Getting started: First make sure you have a large (32 oz) container of DOT 4 brake fluid, some means to suck the old brake fluid out of the Master Cylinder reservoir (a turkey baster works great), an 8 mm metric allen wrench, a metric box/open end wrench set for the bleed fittings, a brake bleed vacuum pump or at least some clear 3/16th ID clear tubing and a jar. It would also be good to have some ramps or some means to raise the car up to access the fittings.
Saab manual. It worked well for me.
Before beginning, remember that your ABS pump relay should still be pulled, so the pump will not run.
The manual says to bleed the front brakes first, starting with the right front caliper using a pressure or vacuum system. For a long time, I bled my brakes with a "MightyVac" vacuum pump available at most auto parts stores.
Anyway, you may also be able to bleed the front brakes by using the hand vacuum or the old tried and true "have somebody pump the break pedal" method. Be sure and keep the reservoir full during the bleeding process.
Once you have bled the right front (passenger side) then the left front you are ready to bleed the rear brakes. For these, you will actually use the ABS pump.
Plug in the ABS relay and turn the key on. You will hear the pump running, and it will run for about 10 seconds to pressurize the system. Have somebody available to work the brake pedal. Put some clear tubing on the rear brake cylinder fittings that run into a jar.
Be ready to open the bleed fittings, and have the person push down and hold the brake pedal. Carefully crack the bleed fitting open. There will be a lot of pressure and a lot of fluid will come out.
In a very short time, a lot of fluid will be bled out, and most likely some pretty dirty looking stuff. Close the fitting before you tell your helper to let off the pedal. Fill the reservoir again before the next bleeding operation.
Now bleed the other rear wheel using the same process and you are done.
Test the system in using the same procedure mentioned at the start that you used to determine that your accumulator was weak.
Thanks to David Carlson for contributing to this FAQ!
|STEP 1||The accumulator can be very difficult to remove. Note that the twisting effort to remove the accumulator can result in twisting of the of the pressure pump mounts. The hex nut rounded out. I then used a stud extractor|
which twisted the entire nut off the top of the accumulator, so then needed to pull the master cylinder out of the car and remove the accumulator on a bench. That is a tiresome procedure, but the results were very good. I did not swap the diverter, and the new accumulator (GM equivalent) works just fine. I am very happy to have saved the price of an entire ABS master cylinder unit, which was the alternative.