Are There Special Procedures For Adding Fluid to And Bleeding ABS Brake Systems?
 

My roommate has a 1991 W126 350SDL with ABS, so it has the big module box setting on the inner fender. We are going to be replacing the brake hoses and calipers (as well as the shoes, rotors, and bearings). Obviously the brake fluid will be drained out during the process and it will need to be replenished and bled.

I am familiar with bleeding brakes on older vehicles. Are there special precautions to take on this W126 with ABS? I think I remember seeing a bleed screw on the ABS module.

It's the same as any other car.

The only trick is that the fluid reservoir has two compartments, and the rear compartment only begins to fill when the front is above the partition. That means you can run out of fluid in the rear while the reservoir appears full. So when I bleed the rear, I try to keep the reservoir filled to the brim. Other than that trick, it's straightforward.

Oh, okay. That seems similar to any dual-circuit system, then.

The ABS pump is passive when not needing to provide assist. The fluid just flows right through. I would highly recommend a Motive (or home made) Power Bleeder for this job. It makes it so much easier.

Using a power bleeder also prevents the master cylinder from getting over stroked which can harm the seals.

The one you have to be careful with is the SBS system on 2005 and 2006 W211s.

Bosch ABS2, which is what your car has, doesn't need any special bleeding procedure. Virtually every other ABS system does.

-J

Power Bleeder
 

I'm about to replace the brake hoses in my SDL. Put together a home made power bleeder with Lowes parts for about $18. Took about 20 minutes to put together.

Why? Because even though I've been bleeding brakes from time to time for 45 years, I really don't want to "over stroke the master cylinder" and end up having to add that to the project.

Good, good. It looks like the biggest hangup is going to be grinding down the ceramic pads a couple mm on each side because they are too thick for the ATE calipers. Or, we might have to exchange the rebuilt ATE calipers for Bendix so the pads will drop right in. That is probably a better idea.

to prevent brake fluid from draining out - push the pedal down about 1 or 2 inch and somehow lock it there. This prevents the brake fluid from draining.

disconnect the battery - if you want everything off, MB brake lamps are only powered up when the key is on though. I usually disconnect the battery or remove the brake lamp bulbs on other brands of cars.