I need to get the brakes in working order so I can sell the car. I have installed new brake rotors and have new brake pads to install along with new brake hoses. Of course the brake fluid needs to be replaced along with new brake fluid.

I have brake caliper rebuild kits for the front Bendix calipers and the rear ATE calipers.

Question; what are signs the calipers need to be rebuilt? How can I tell if a piston is seized?

If they leak, or the piston binds/seizes they need to be rebuilt. Binding pistons may be detected when pushing the piston back in to replace the pads, if the car pulls during braking or if a wheel overheats. Hoses can also cause these problems.

Start soaking the bleeder screws repeatedly if you plan on doing hydraulic repairs to the brakes.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

what should I soak the bleeder screws with?

Any good penetrating oil e.g., Liquid Wrench or the like.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

OK, I found the Nugeon brand reman brake calipers on the Napa website. The front calipers show to be Bendix which is the brand that is on the car now. The Nugeon's for the rear calipers do not show the brand. The Napa website says their calipers are "guaranteed to fit".

On the 1991 560SEL, the rear ATE brake calipers have a lug to which a cable attaches. This cable feeds to the throttle and controls something Mercedes calls "Acceleration Skid Control" a precursor to traction control. The important thing is the rear calipers MUST have this lug so the cable can attach.

Since Napa says "guaranteed fitment", I guess I could order the calipers and if they do not fit, send them back for a refund. Their Nugeon brand is about $200 less per caliper than the genuine ATE brake calipers which would save me some money......

Karps in CA can rebuild your calipers if you run into fitment problems.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

The lug on the rear calipers is for mounting the plug to which the brake pad wear sensors connect. The sensors are installed to disable the ASR when the pads are too worn.
Standard rear calipers can be installed with the loss of only the ASR disable function (assuming that ASR is still functional!).

Trust Frank Reiner; I think this is a no brainer.

never having worked on an asr car;126 or otherwise; this is news. the pad wear sensor light comes on and the asr is disabled? alldata is down so i can't look at asr. thanks.

After digging through the ASR test program, it may be that the wear sensors only turn on the light; they do not appear in the test program, and indeed may not be used by the ASR controller.

pf: Count not having worked on ASR as a plus!!