On the W126, the lower ball joints, regardless of brand, need a press to install them. IIRC, someone here on the forum made the press from an auto parts store work. But it was with a little finagling and using it "backwards". Another, purchased a mandrel with a special cut out.

Personally, I took mine to an indy who had the press. Cost ~$10 and 5 min. of time.

Also, I think a ball joint press is available in the forum tool rental program.

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Sam

84 300SD 350K+ miles ( Blue Belle )