cmpcpro

Hey guys I have an 06 S55 I have spent about 15k wholesale replacing many things to make this car run and drive the way it did new. One thing I've noticed with this car is when on the freeway hitting a bad bump the car will skip to the side. I rebuilt the front end but haven't touched the rear end as I was told it was good. Keyes MB did claim to do a 4 wheel alignment a couple months ago but I noticed no difference.. This is my fourth S and the only other one that did this was my 08 550. I've been searching for days and have seen the issue crop up a few times but haven't found any solutions. My tech said he took a crowbar to the rear sub bushings and they flexed within spec, but I'm wondering if they should flex at all.. other than the dealer not aligning it correctly I'm at a loss. I'm about to just have the rear end rebuilt to rule it out but would prefer to know and fix the precise issue.

Any help is appreciated!

tusabes

Could be your abc reaction over big bumps , I've noticed my cl will do this

cmpcpro

Hmm what would cause that? I remember my 08 S550 had it too and that was Airmatic then my 2010 S550 was issue free

Welwynnick

Jack up each rear corner in turn, so the wheel is clear of the road.

Grab the wheel and try to shake it up and down hard. It shouldn't move, but I will place a small wager that one of them will move up and down freely a few fractions. That would probably be due to a worn strut top rubber bush. Happens quite a lot. Only solution is to replace the strut I'm afraid, so good luck.

nick

compaddict

iTrader: (1)

That makes a bunch of sense. My old 05 S55 would do that and the PAX front had a torn bush.

cmpcpro

Thanks for the info. I know the rear pass side abc strut was replaced a couple months ago so I assume their struts have new bushings? Which makes me wonder. If they can replace the bushings why can't we? Also would the top bushings make the car skip like that? Also what about those pieces that guys add in?

Welwynnick

That was me.





You can add a rubber washer to the top of the strut top bush to take up the slack caused by the wear of the bush. It's a cheap, quick, easy fix that makes a big difference to an old car, but unfortunately it only works on the front. The rear strut top bushes are quite different, and you can't do anything with the bush. Tragic.

Nick

cmpcpro

Thanks Nick I just called Arnotts asking if their rebuilt struts have new top mounts and they have to contact their engineers and let me know. I assume they must be as they couldn't sell them bad but the fact they can't be replaced yet they sell rebuild struts confuses me. As for the fronts, is that a decent fix or does that still compromise ride quality? Do you think this is probably the cause for this skipping to the side? I've searched for this issue and have only found one or two cases across multiple boards which surprises me. Thanks again!

cmpcpro

Just thought I'd give you an update guys.. when you buy an Arnotts strut you are getting a USED upper mount!! In other words buy from the dealer if you want it right/to last...

Astro14

Whaaaat?

YGTBKM!!

cmpcpro

Yup.. Arnotts messaged their engineers and they said "at this time" they are using the best cores they have.......

cmpcpro

Hey Nick,

Do you think it could be from the front struts too? Those spacers you use to stop the play on the front struts does that make the ride as good as struts with no issues? Is it an easy job? I just had the dealer align it will it need to be done again? Thanks for all your help!!

ItalianJoe1

Both of my CLs have done this, and it's from the upper rear strut mounts. I have lived with it, as the cost of replacing two complete, otherwise good working struts is too much just to eliminate that sideways kick over uneven surfaces.

cmpcpro

Wow that's good to know. I have a new Arnotts on the pass side rear only a couple months old but now that we know they are used that's iffy.. but maybe I just need one

JohnnyV12

I recently noticed this on my CL, too. I was a bit unsure what to think about it. I'll try the mentioned method next time I change the tires.

cmpcpro

Hey Nick,

I took the car out on the freeway tonight and noticed a few things.. yes it happens over bumps but it seems worse when I hit cracks in the road or certain road that walks the car.. once even the steering wheel turned pretty quick on its own when it happened. Those time there really wasn't any bumps, yet sometimes I can hit good bumps and have no side to side feel.. also keep in mind I just had the front end rebuilt with all new OEM parts and the dealer re leveled and four wheel aligned it.. would the strut mounts still be the cause? I'm thinking whatever this is is in the front and the back too. Thanks for your help because I'm lost!! This makes the car kind of scary on the freeway.

Welwynnick

Hi Chris

Bad strut bushes can have a profound effect on the car's ride and handling, though it does depend on the circumstances. Strut bushes have little effect when going slowly, or when the road is smooth, or when the bumps are long, or when the surface isn't broken with cracks and pot-holes, or if you have tires with tall sidewalls. In other words, when the suspension isn't doing much.

Strut bushes have more effect on short length, small-amplitude, high-frequency bumps because the damper becomes stiff when the wheel moves quickly, and the bumps tend to by-pass the spring /damper, and get absorbed by the bush instead (and the tire of course).

These are the sorts of bumps that tend to excite a resonance/oscillation in the suspension's unsprung mass. The sprung mass is the car itself, while the unsprumg mass is the wheels, tyres, brakes and suspension. Just as the sprung mass bounces up and down on the springs and dampers at a frequency of roughly one hertz, the unsprung mass is also excited by higher frequency bumps, more like ten hertz.

The strut bushes have little bearing on the primary resonance, but they play a much greater effect on the unsprung resonance, especially on modern cars which tend to have soft bushes, and they have to control this high frequency resonance. If the bushes wear, they don't control it effectively, and the wheel can shake up and down as the unsprung mass bounces up and down against the compliance of the tires and the bushes.

The thing with a resonance like this is the energy is alternately stored in kinetic energy as the wheel moves up and down, and in potential energy as the bushes are compressed, which is typical of oscillating systems. When a wheel hits a sharp bump, the bush is compressed, and the stored energy is released as the bush relaxes. If the bush is worn and slightly collapsed, it can relax far enough to go slack, and then it's no longer controlling the unsprung mass. It hardly controls it at all.

When you drive down a bad road at speed, that is full of small, short, sharp bumps, the wheels can bounce up and down at high frequency, without either the damper of the bushes controlling it properly. That makes the car feel crashy and shaky, but it also makes the suspension feel like a blur, like you've got a horrible, rough ride, but you're also disconnected from the wheels. It's horrible, but again not something that you're really aware of on very smooth roads.

The first time I encountered this I thought my subframe bushes or suspension arm bushes were worn, but they were all fine. It was difficult to pin, but it all became clear once I started experimenting adding spacers to the front bushes, which you can tackle relatively easily.

No, you don't have to have alignment re-set.

Regards, Nick

cmpcpro

Thanks for the info Nick! What threw me was going over the road with a long crack and how it felt like the car was on a long rail all of a sudden following this road.. it just didn't seem like it was bumping at all but I figured it could be at the wheel without me knowing as the strut isn't pushing the wheel down like it should. I tried searching for the directions on how to install the spacers but maybe I'm not using the right keywords. Do you know the link? Also if memory serves me didn't you or someone else discover where the spacers could be bought instead of made? Thanks again!!

Welwynnick

I think most well-used W215's and W220's will suffer from this problem, and it can be easily fixed. The improvement to the ride and handling is really worthwhile on broken surfaces.

On the rear strut, the bush appears to be bonded to the metal mounting. I don't think this causes problems as readily as the front, but the bush can come free due to corrosion or bonding failure. The only solution I found was to replace the strut. Buy a good used one off ebay, and its not too expensive or difficult (as long as the so-called quick-release connector isn't seized).

I cut some small doughnuts out of a 10mm rubber sheet and put them under the top bush nuts. You need a stout 35mm pin spanner. Don't even need to lift the car up - in fact its better if you don't.

The ride is much better now. You can't do the same trick with rear struts unfortunately.




Its an angle grinder type of spanner that you need; not a C spanner.

You can't use adjustable ones; they're not up to the job. Ask me how etc.

You use the spanner to undo the large flat nut on the top of the front strut, in the centre. You remove the electrical connector first.

Don't jack the car up - you need the weight on the wheel to stop the rest of the strut from spinning round (which may damage the hydraulic pipe).



I'm afraid that getting the strut off is often difficult. You have to remove the electrical connector at the top, plus the hydraulic connector at the side, plus the mechanical bits. The worst bit is that the hex grub nuts at the bottom of the strut are often corroded and seized. Heat helps, otherwise just remove the transverse control arm.

The easiest way to get a rubber bush/spacer is by searching for an M20 rubber washer on ebay. Check the diameter of the bush itself, and you should be able to find something 3mm thick quite cheaply and easily.

Nick

cmpcpro

Thanks Nick! I am not sure I understand I am not familiar with how the struts look. So you take the top nut off with the spanner and then you mentioned taking the strut off. So does the car have to be jacked up then to remove the strut? Also, those M20 washers, do you think those are as good as the ones you made? Thanks again for your help! Also I'm almost positive my front mounts are bad but is there an easy way to check them? Thanks!

cmpcpro

Look at this on eBay http://www.ebay.co.uk/itm/360582863882

Here are some that say 3mm

Welwynnick

Sorry, I was trying to remember what I did, which was indeed to take the struts off. It's absolutely not necessary, it's just that I usually do things the hard way before I find the easy way.

You just have to remove the top washer/bush, and it's best if you don't jack the car, as that keeps the weight on the strut and helps to stop it spinning when you undo the top nut.

Best to drill out the blind holes so that the pin spanner pins can go in deep and engage properly. Even with a proper, non-adjustable spanner, it's still quite difficult.

Make sure you don't turn the strut when to undo the washer, so that you don't damage the ABC hydraulic hose connection.

Nick

cmpcpro

Thanks Nick. Is there a way to confirm they are indeed bad by looking at them?

Welwynnick

With weight on wheels, if you can see a gap between the washer bush, and the wheel arch pressing that it sits against, then I guess you could just go ahead an fit an additional rubber washer. It's not a guaranteed method though.


Nick

cmpcpro

Hey there I am still not sure I understand where the problem is.. I found this picture. Do the bushings go under that puck looking thing? What if we were to cut them and stuff them in and then epoxy the cut? I'm not sure I am completely clear on taking it apart.