SL-Class (R231) 2013 on: Discussion on the SL550

SL/R231: Lower control arm replacement, how to.

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Old May 28, 2023 | 08:22 AM
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R231 SL500
Lower control arm replacement, how to.

Whilst at a charity event in the UK I took advantage of having my SL checked over by PCS (Prestige Car Services, a well respected independent Mercedes garage near Portsmouth) for free and they gave it a clean bill of health apart from the lower left control arm had some movement and needed changing. So I checked the price of the part from my local dealer and also some ebay shops and the price would be £307 for the part. I had already checked on WIS about fitting it and it didn’t seem too hard a job although PCS did say that they often broke ball joint splitters when doing the job. I checked on ASRA which stated that the job should take just over an hour so I decided to do the job myself…….
I arrived at my mate’s workshop at midday and tried to get the car on the two poster lift. I knew that the car was too low for the standard pads to fit under but PCS had advised me to lift the back up at the jacking point and slide the front lift pad under, then remove the jack and slide under the rear pad then do the same the other side and voila, the car was up in the air.
So the order of business is to take off the wheel, then both front engine covers, remove the control arm, refit then covers back on, wheel on and off we go. Once the covers were off I realised it would be easier for me if the rear wheel arch cover was also removed for access so that came off too. First nut to come off was holding the drop link onto the arm, then the nut and bolt holding the spring carrier was removed, then the ball joint nut and it split with ease, fortunately, and finally the nut and bolt holding the control arm to the car and the arm dropped off nicely. Quick check with the new arm to ensure it was identical (something I always do to be sure) and I was onto refitting. Firstly ball joint into its hole then manoeuvre the arm up through the spring holder and into its position in the body, put the bolt through and nut, then nut on the ball joint, bolt and nut through the spring carrier then fit the drop link and nut. Now for the tightening, I put some large blocks of wood on the floor and lowered the car onto them so I could crawl under the car to tighten all bolts at ride height. For info the inner bolt which attaches the arm to the car is rated at 100nm then 180 degrees, the ball joint is 250nm, spring carrier 110nm and 90 degrees and the drop link at 130nm (according to WIS). Finally all covers back on, wheel on and lower the car to the ground and reverse the action of using the jack to get the car off the lift pads. All in it took me 1 hour 45 mins but a lot of that was getting the car on and off the lift.
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