It looks like you're screwing down on the lock nut, and that won't get you anywhere. (The lower small one). You need to turn the top one (acorn) while holding the large nut at the bottom (spring collar) still. If you can't hold that bottom nut (the really big one) with a screwdriver, then you'll need the special third wrench. Many people have done this many times without the third wrench, including me. But when you need it you really need it and there is no substitute. Leathermang found that out the hard way. You can get the spring collar wrench at Performance Products or at a Mercedes dealer.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References