Looking to replace the steel rear control arms on my '88 560SEL with the aluminum version (moving the hub/brakes to the "new" arm). The purpose would be to avoid rust on the next set. Looks like the caliper is in the rear on the steel version but in the front of the hub on the aluminum version.

Is this swap possible?

That swap is possible if you have a donor car to get ALL of the needed parts.

I wouldn't waste the time though.

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I've been working on this interchangeability problem for my W123. I think you'll be more successful with a W126. The aluminum trailing arms all seem to come with an anti-dive (EDIT => sorry anti-squat) mechanism:-

http://www.peachparts.com/shopforum/showthread.php?t=289638

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Don't leave that there - I'll take it to bits!

I thought the 560s came with the aluminum control arms

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Never seen one without them.

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My '88 560 has the same arms as a 420 my '86 560 has the aluminum versions. Calipers are on the trailing side in the '88 and leading side on the '86.

My understanding was that the 86/87 560 has the anti-squat control arms and subsequent models did away with them. Sub frame attachments are the same but there are some differences in brake mountings and other bits. Might have to swap sides on the calipers to get the bleed screws pointing up, etc? Worth a close look to be sure before you get too deep.

Also, make sure that the fulcrums are good, weird noises and clunks will follow if they are sloppy.

Not as straightforward as I was hoping. I will likely replace with the steel version to reduce problems. Thanks for all the replies.