I was looking in the brake bleeding area of the W123 Chassis FSM and there was this notation: "Attention!
The 4 piston fixed Caliper, Installed in September of 1985, has one vent screw inside and one vent screw outside. For venting the brake system or replacing the fluid, remove the front wheels so that the outer pressure chamber can be vented."

Is that The 4 piston fixed Caliper part of the Cars equipped with the ABS system or is it an error in the Manual? Or what?

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84 300D, 82 Volvo 244Gl Diesel

September 1985 is VERY late in the W123 production life. I think the last US spec cars were built in August 1985 and some wagons were built until January 1986.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

But, do you know if there is actually a thing as 4 piston front calipers for a W123? And do you know if they are only on models with ABS?

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84 300D, 82 Volvo 244Gl Diesel

I don't know, but ISPPI/EPC should be able to tell you.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

There was. It was offered in some AMG tuned cars but gave way to the big brake upgrade.

Something tells me and always did there was a COTS solution which AMG seized upon

Thanks.

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84 300D, 82 Volvo 244Gl Diesel

YW. I have never seen them, but I have heard folks talk about them a lot regarding the pre-merger cars. I suspect they were either Volvo or BMW applications which either bolted right on, OR reguired very little modification so that it was a simple fit without any engineering or any real effort. Over on STD.com there was tons of chatter about them around a decade ago; however, nothing ever materialized. Something tells me if a set would surface, then their true ID would surface. Then, it would be a rush on the remaining stocks.