SL500 swerves when brakes applied
 

Hi all, a couple days ago I set off to drive home from work. The first time I applied the brakes, I felt an unsettled swerving motion from the rear end. I got out and checked to see if the lug nuts were lose (they weren't) or a tire was flat (they were all fine). Next I took the car up to about 30mph and hit the brakes. The car started to yaw around it vertical axis fairly violently - it even briefly threw an ESP message. After turning the ignition off and on again, the error message was cleared and did not re appear although the problem remained. I decided to limp the car home on side roads which gave me more time to try and get a feel for what's going on. The best way I can describe the feeling is that it's as if the brakes are only being applied to one side. However since This happens even at very low speeds I would be surprised if uneven braking (in the rear) would be enough to cause this.

Once home I ran a scan with STAR diagnostics. The SBC system shows no faults, nor were there any other remarkable codes - although in fairness I may just not be looking for the right thing. I also jacked up the car and did a visual inspection of the wheel - everything seems normal and tight.

I'm really just looking for some ideas for trouble shooting. Not sure where to start and wondering if anyone has ever experienced this?

Thanks,

Matt

Get up under the rear of the car and check the joints on the subframe in the picture below for any cracks.

https://cimg9.ibsrv.net/gimg/www.mbw...7a2c95cb72.jpg

Thanks, will do.

Found the problem
 

https://cimg5.ibsrv.net/gimg/www.mbw...d5241b09fb.jpg
https://cimg6.ibsrv.net/gimg/www.mbw...a1bc944f69.jpg
https://cimg7.ibsrv.net/gimg/www.mbw...bb1cabf649.jpg
Well, I'm pretty sure I've identified the culprit: The rear passenger side lower control arm broke clean off. I'm not sure how this happened - I figure I would have noticed a hit violent enough to do that kind of damage. My best guess after talking to a neighbor who used to drive a tow truck for a living is that this was caused by someone using the control arm as tie down points on a flat deck or to winch the car onto a trailer. The part is thin and really light so it is obviously designed to only be strong in a specific direction. Anyway I just wanted to get back with a resolution>

Now for the follow up question: The part number on the LCA is R 2303520205, but when I search for it I get results for mid 2000s E-class cars. Obviously it's possible that the same part is used on both cars. I was wondering if anyone can confirm this part number for use on a 2003 SL500 or provide a link to a site where I can get a definitive answer before I order.

Thanks everyone for views and suggestions,

Cheers

Matt

Glad you found the problem. That is the correct part number. If you're going used, this outfit in Florida has all 5 control arms on Ebay for $35 + $20 shipping = $50. Control Arm Set

And you'll need to get an alignment after installation.

Thanks, I ended up ordering a Lemfoerder OEM unit from AutohausAZ. After seeing how thinly built they are, I would not personally trust a used one - especially after experiencing what happens to the cars handling when it breaks. I'm curious though as to why you would assume that an alignment needs to be done? Assuming the old and new parts have the same dimensions I don't see why. There is nothing adjustable about it, just two bolts.

Those 5 rear suspension links are under a pretty good degree of tension and to get one part reinstalled generally requires loosening, at least, all of the bolts on one side of the link(s) so you can manuever the link into it's seat and fit a bolt through it. Doing so disrupts the alighment and failure to reset alignment leaves a high likelihood of finding the toe off and then you end up with the "inside tire wear" that this model is famous for. In it's natural state, the particular link that's broken on your car, when attaching the side closest to the differential 1st, the side that attaches to the hub sits almost an inch away from it's final resting spot, and when all the links are detached from the hub and fully torqued to spec, they are NOT "floppy" as one might imagine. Each of them are stiff and require force to articulate and if you attach just one, none of the others naturally meet the hub in their final resting place. That's gives an idea of the degree of tension you're dealing with. I just completed replacement of all 5 rear links 5 weeks ago. 4 hours of cursing and thinking I was going to finally have to swallow my pride and see a mechanic for the 1st time in 32 years.

If you take a look at the 1st of the 2 pics you posted, you can see just how far offset the portion that's still attached to the hub is from the natural trajectory of the remainder of the link.

Why did you decide to replace them? Any symptoms? Or just a preventive maintenance?

Yeah, it's hard to tell from the picks what shape the bushings are in. Still, since the Lemfoerder piece is around $93 alone, it might be worth it if you had to replace all of the links. I doubt all the bushings would be bad. Plus, the seller advertises that they are in good condition. I wouldn't consider a bad bushing as being good.

During our rare big snow event here in Seattle back in March, a woman was hesitant to stop as she came to the crest of a hill for fear of losing traction, so she continued out into the road I was on and I had about a second to decide to either T-Bone her, or swerve to miss her and on a snow covered ice slick road, that sent me into a curb resulting in the rear wheel being bent under the car at about a 50 degree angle. Upon getting home, inspection showed that at the very least, the lower control arm was bent into a "L" shape. Since I couldn't be certain if any of the other links had been damaged just by visual inspection, I decided the best course of action was to purchase and replace all 5 links. Amazingly, all the bushings on the links I removed seemed to be in remarkably good condition, and when measured against their replacement, none other than the lower control arm seemed to be damaged. After getting everything back together, I noticed the same symptoms the OP described, then and upon closer inspection, I could see a crack on the subframe bracket holding the same link that was damaged on the OP's car- that's how I had an inkling that it might be the cause of the OP's swerving issue. So I had the subframe welded by a buddy and had him add in a couple of gussets for additional strength. When I finally get the car back home to Hawaii, I've a complete drivetrain and subframe that I'll be swapping over from my wrecked SL55, so I wanted to avoid replacing the subframe if I could help it.

Sorry to hear that. Any help from insurance, or you just ate the cost of repair? And I would say that bent rear wheel definitely is a symptom. Congratulations on getting the OP problem figured out.

P.S. My SL was safely in the garage this winter, AWD only.

The driver of the other car was in tears when she was explaining the situation to her husband, and as I'd suspected by her reaction I later found out they didn't have insurance. I could have filed an uninsured motorist claim, but instead tried to show a bit of compassion and let them pay for the parts and $200 for my sweat equity. Sadly this town is UBER expensive,and a lot of working folks are barely making it by every month, so 4 crappy hours of my time doing the repairs myself was a small price compared to the headache it would have caused their young family..

Fair deal.

Wow, here in Alabama, "uninsured motorist" only covers bodily injury. Damage to the car is covered by the collision policy. Also, if the other car does not make any physical contact with your car, then the other driver cannot be held at fault. So, even if a crazy person is trying to run you off the road and you do so to avoid a crash, the resulting damage is consider your fault - no matter what. I once had a guy pull out in front of me at 1mph on a 45mph highway. I swerved to miss him and crashed. He even told the police it was his fault for pulling out and offered to let his insurance cover it, but the police could only list him as a witness and his insurance said no since he was not "involved".

If I was someplace where that was the law, then I would have just T-Boned her. Honestly, I would have even accelerated to punish her for her "Legal": stupidity.

My guess is that you would have steered away from doing harm, in a reflex. Sometimes our reflexes are kinder than our premeditated thoughts, like when it comes to avoiding injury.