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.

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

I will keep Karps in mind, I may need them. I just got back from the local NAPA store. They told me that Nugeon Brake Calipers are "special order". They said they could ship the calipers for in store pick-up. Great. I have to prepay because it is a special order.

Once the calipers arrive at the NAPA store, they call me. I then take the original calipers off the car to the store to compare to see if the Nugeon calipers will fit. They told me if the Nugeon calipers do NOT fit, I will NOT get my money back!

I am SO disappointed in NAPA.....they have been going downhill for the past ten years. I am going to try to call the Nugeon company directly to find out if their rear brake calipers for the 1991 560SEL have the lug for connecting to the Mercedes Acceleration Skid Control system.

Since they aren't overly easy to source it may be worth seeing if you need them. The binding spot is often at the metal edges of the pad. It isn't always a stuck piston.

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

Maybe send only the back calipers out for rebuilding. Solves the problem of potential fit.

true that; I would need to pay shipping out to california though. I am currently checking out the local O'Reilly and Autozone stores, they carry the Nugeon brand.

you have a 126 with asr. paying shipping is not a bad thing. i really doubt you can find them otherwise. just do the r and r.

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!!