I did the early (81-85) W126 brake upgrade and yes, it is a bolt-on operation. The car stopped marginally better, and the brake discs would not overheat and warp like the solid ones. People have swapped the second generation, double-piston W126 calipers (plus larger ventilated discs) in the W123 with success and a strong difference in performance –I do believe they just need to replace the dust shield, but I would install the upgraded booster and master cylinder.

Keep in mind: if you go for this upgrade, you will need 15'' wheels as MINIMUM, so you will not be able to revert to the good ol' bundts.

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[GONE] - 1995 Mercedes E300 Diesel - 130k miles - Smoke Silver (702) over Mushroom leather (265) - Bladder blasting, coast-to-coast work machine.