s.i.f.i.

Under hard accel my car acted a bit like this. We traced it down to a 700 buck pair of links in the rear suspension that passed the prybar check perfectly when it was on the lift. But when the bushings get soft they allow toeout. Toeout is bad. Thing is, they aren't the toe control links. IIRC, they are almost C shaped up high and slightly ahead of the wheels but would have to check my paperwork to make sure. Basically, that reaer suspension is tricky enough to hide worn components from prying bars.
How is ypur tire wear? The big improvement for my car beyond tracking like a laser, is a set of rears lasts 3x longer than before. They used to wear inside shoulders first... like negative camber. They wear flat now. Lemme know if you want better info on what links got replaced.

brmn1987

Thanks, man. I think i know what links you are talking about, but if you can give me exact name, that would help. Tires wear fine, which makes sense because car drives good unless you really crack on it going fast. Ill update when lower CA bushinhs are replaced.

StarvingArtist

Please show us exactly which links. My car is over 100k and I like to fix things ahead of failure.

s.i.f.i.

Dammit, who has a parts diagram? I can't find one anywhere. I think it's called the upper control arm, not the upper toe control link. It's the upper arm that runs east-west in the car, 90 degrees to the direction of travel, not the angled one.

ikrazyfoo

My car has the same exact issue. If I go over 65~70 it feels like I'm towing something in alot of wind. I found that both rear wheel bearings are bad and a front inner tie rod is bad. Once I do the repairs I'll report if the issue has been cured or not.

StarvingArtist

That's a good enough description, thank you!

EvoTechnik

I bet its those nankang front tires causing the car to float. I would suggest borrowing a different set of wheels from someone and taking a test drive.

wellshii

Old thread,but did you ever find the issue?
This is typical of bad wheel bearings.

wellshii

Yep. Did it resolve your issue?

rogerthedodgerr

Has anyone ever found the issue for this? I am having the exact same issue, except I have pss9 on mine. Same exact thing, everything in the front replaced, Subframe bushings replaced, c shaped arm bushings replaced. I've narrowed it down to either bad UPD toe links, or a bad pss9 shock still didnt change rear bearings

06cls55amg

My issue was tires, was suffering from bump steer. slapped on a set of all seasons. car is solid.

hachiroku

if you have coilovers there are only a few items that could cause this...bushings, sway bars, shocks. i would inspect items in that order.

also inspect your rear cross member bolts...those fail, there is a thread about that topic around here somewhere.

15SL550

My issue sounds identical to the one you were having. I just took my car in for a full inspection and am feeling a bit nervous.

I have a 2015 SL550 with 70k. Do you think suspension parts would go bad at that age and mileage? I am considering just changing to all season tires as well.

Tomsti

Hi 550From the thread above we can see there are many things that may lead to all of us complaining the car having a sway from the rear. This thread also nailed the problem my CLS had. My car felt like the suspension was lose or falling off under hard acceleration. Hitting hard bumps in road id get a side to side motion, hard to describe its how it felt.. I had some older Michelin Super Sport tires on it, had tread and didn’t look bad. I replaced with Michelin 4S and like OP noted, the problem went away. I assume in my case just putting new tires of any kind may have helped. So its something to look at on your car, how old or worn are the tires?

Something to think about if the dealer comes back with no other issues found. Usually dealers will find 'something'

15SL550

The tires are in great shape with about 70% Tread left. They are sumitomo tires. I purchased the car used recently and just noticed the issue.

I told the dealer to do a “ Pre Purchase Inspection” so hopefully they will give me the truth, I do have my suspicions about these stealer ships adding unnecessary issues.

thank you for your reply!

Tomsti

Look at the date code on the tires, my tires appeared to have good tread also. The date code may also be an indicator.

Just something else to check.

Sam Bunz

which accelerator sensors did you replace? i have the same sway on my 2007 R230 hard left to right sway only under hard acceleration.

Sam Bunz

2007 R230 SL550 under hard acceleration, huge sway left to right at any speed. only under acceleration, already did alignment. front set to .10 toe, and .12 rear toe. thanks in advance if you have suggestions, i have 305/25/20 mich pilot sport cups. no codes in suspension system. im thinking acceleration sensors?

bobgodd

If you have access to Xentry there's a test for acceleration sensors. If not, I would find a friend who has access, it's a quick and easy test, and can rule them out as a possibility. They're quite expensive.

hachiroku

could be because you don't have an LSD is my assumption. if you do have an LSD i'd look into bushings. bad bushings and ball joints could attribute to some vehicle tracking issues.

feeshta

OP, I've seen several suggestions that you should check your rear subframe bolts and mounts, but so far if you have mentioned that they were checked and/or changed, I must have missed it.

These cars are known for destroying rear subframe mounts and breaking rear subframe bolts, either of which could cause exactly the kind of issues you are experiencing. My own car started exhibiting symptoms like this, particularly over uneven transitions at speed, with the front end staying planted and the rear end feeling all over the place despite no loss of traction. I replaced the rear subframe mounts (with creative steel poly mounts in my case) and the problem was completely solved.

I would highly suggest you look into that if you have not already.

ctravis595

I replaced two rear tires on my 211 wagon today and now I am experiencing the same issues, feels like the rear subframe isn’t even connected to the chassis anymore, at first I believed I left a wheel loose but that was not the case. It would have been my first time leaving a wheel loose in the thousands of cars I’ve worked on, or at least to my knowledge

I immediately went back in the shop and put the car in the air, was surprised to not find any control arms or bushings loose.. seems maybe there was some extra space between the rear subframe and the frame, but I did not have a “before and after” to compare it to

I’m 100% sure this only started after lifting the car off the ground and lowering it back down to do tires.. which is another thing that makes me thing of the rear subframe

Sulaco

Some 211's have broken a rear subframe bolt in the past. It's mechanically totaled cars before but it's definitely not that bad for a competent shop; involves cutting a hole in the unibody in the rear wheel wells to access the broken bolt.

Double check that immediately.

Craig32935

I have a 2010 C300 (not a 4-Matic) that I recently had new tires put on the rear to get rid of road noise. The car was solid on the highway before that. Now the faster I go, the more it sways in the back. Feels like if I were to do a deliberate swerve at speed to avoid an object the car would spin out or pit itself into the median! The following are the tires being used and the staggered size front to rear that is called for. The care rode solid before this, just with bad tire noise which is gone now. It kind of feels like what you would expect if the rear tires were severely underinflated but they are not. All suspension components are solid. Thoughts? BTW the tread pattern of the two brands is near identical and neither are directional.

Front: 225-45-17 Mich Pilot S

Rear: 245-40-17 Kumho Solis

kevm14

Can you properly spell out the exact model of both tires? If those Kumhos are what I think they are, they are the problem as those are, at best, sort of a grand touring tire and nothing approaching performance.