Author Topic: Sway bar issue? (Read 9341 times)

Andres G · « **on:** May 18, 2009, 21:32:04 »

Hello All,

I have encountered a strange occurrence with the car's roadholding/attitude that I'll try to describe... I am pretty puzzled about it and would like to hear some opinions from other forum members.

This happened just yesterday, after done with the refurbishing of the shifter mechanism, I took the car out for a spin to get a feel for the seemingly "new" gearbox. I was driving at about 80 Kph when I went over a small bridge where the road drops right after passing said bridge. Right then, the suspension extended and the car swerved to the right requiring me to correct a to avoid going into the ditch... it seemed as if the geometry of the steering had changed with the suspension extended.

I was caught somehow off guard by this and I wasn't entirely sure there were no other factors affecting the car's behavior, so I decided to turn around and drive the same road again. Once more, when coming off the bridge and extending the suspension travel, the car swerved to the right and required me to correct to stay on the tarmac.

Here go my questions: Is there a sway bar or an anti-roll bar that I need to be checking? What could possibly be causing this?

I never felt the SL had a very firm and sporty suspension to begin with, but this type of occurrence, combined with such a soft suspension are a recipe for disaster...

Andres G

waqas · « **Reply #1 on:** May 18, 2009, 21:38:38 »

Are you sure the directional change was caused by the front axle extending and not the rear? That swing axle can do some funny things during sudden extension/contraction.

Also, when you experienced the directional change, was the steering absolutely straight, or was there a slight bend in the road? Directional changes whilst one side (right or left) of the front suspension is loaded more that the other may indicate idler arm wear.

mdsalemi · « **Reply #2 on:** May 18, 2009, 22:06:02 »

Andres,

While I have never pushed the limits of the suspension (intentionally or otherwise) and never felt as if I were headed into a ditch, there is a stretch of road near me with precisely the road layout you describe: a short bridge (over a small stream, no more than 30m in length) that is a bit "higher" than the approach or exit.

My car has always felt as you describe when going over this, though not nearly as bad. I do know that after I changed my tires some years ago (see Tire Nirvana thread from the beginning) the feeling diminished but is most certainly still there.

Without being a suspension engineer, I might agree with Waqas--it's the swing axle.

Andres G · « **Reply #3 on:** May 18, 2009, 22:46:46 »

Ok, I guess the surprise factor of the occurence lead me to believe I was actually headed for the ditch... I admit I was exagerating a little bit, I was not headed there but probably felt like it as I was caught somewhat off-guard.

Wagas, to your question, the road was absolutely straight, no bend whatsoever... but now that you mention it, it could have been the rear axle extending, rather than the front.

I will review the topic suggested by Michael and definitely research on harder springs, as I get the feeling the car has more body roll than it should, at least compared to other pagodas I've driven.

Thanks for your feedback guys.

Regards,
Andres G

JimVillers · « **Reply #4 on:** May 19, 2009, 12:25:52 »

It sounds to me like a bad shock absorber. As the car comes down, one front wheel can compress faster because of the bad shock and that could cause the the tendency to swerve. Installing a set of Koni adjustable shocks will allow you to stiffen your ride a little and that might improve your handling. My preference for the Konis is 1/2 turn from soft.

waltklatt · « **Reply #5 on:** May 19, 2009, 14:03:16 »

Andres,
Would think Jim is on the spot as the weight is not being spread evenly when the car comes down again from the high.
Try it again with a buddy sitting next to you in the passenger seat. Maybe that will have some correction.
Check the usual rubbers and shocks.
Waqas could be right if the rear axle has a bad bushing or so to cause it to twist in a "crabbing" way.
Mike Salemi, could be right if a tire was out of alignment.
But I would do the trick as I mentioned above to rule out the weight issue. Then check the rubbers in the suspension, all of them.
Walter
1967 220SL-diesel

Shvegel · « **Reply #6 on:** May 19, 2009, 22:46:11 »

Tire pressure being too low can also cause you to feel disconnected from the road. It seems the swing axle tends to exaggerate it. I have found a huge difference in handling between properly filled and under filled tires.

Andres G · « **Reply #7 on:** May 20, 2009, 00:43:00 »

Been thinking about all this mentioned here...

First, the weight distribution. I only had one passenger in the car at the time, I'm 200 lbs (90 kilos). Not sure this was a significant factor but I trust Walter's judgement and will try again with a courageous buddy sitting on the passenger seat. I will also check the bushes and rubber underneath.

Second, shocks. Have 4 new bilsteins that were put on the car less than 4000 kms ago... doubt their are in less than optimal shape, but could be getting "older" due to time being on the car (installed in Dec.03)? I will look into Konis, I like adjustable shocks as I've used them in my off road rig in the past. Definitely would benefit from a stiffer ride.

I doubt it would be an alignment issue, as we've had the car aligned when we got it.

I do believe tire pressure may be a factor, as I believe we've not aired them up properly. Anyone have a suggested pressure for the 205/70R14s?

As a matter of fact, I think this may be a combination of all factors mentioned above (aside from alignment), probably exaggerated by my lack of experience behind the wheel of a 113.

I'll let you guys know what I find.
Andres G

ja17 · « **Reply #8 on:** May 20, 2009, 22:56:12 »

Hello,

This is not a typical condition. You have something not right in the suspension. Could be a bad front or rear rubber suspension mount also.

Rick · « **Reply #9 on:** May 21, 2009, 17:56:18 »

A seperated front subframe mount can cause extreme suspension geometry changes during major suspension motion.

Andres G · « **Reply #10 on:** May 29, 2009, 16:26:58 »

Guys, thanks for the added suggestions. I checked the suspension mounts on the bottom and they are fine (attached). I ran the car again with a friend on the passenger seat and there was a significant difference in behavior... I also was more expectant of what might occur when driving over the bridge, that I probably didn't feel i was caught off guard like the time before.

I think in fact, that the key must have been the tire pressure. I aired them up adecuately as I had found they were way below ideal pressure... also, one of them had 18 psi while the one on the opposite side had 29 psi.

I am having the car checked by a local mercedes shop (Shuler Autohaus - Fayetteville) and I'm going to ask him to pay close attention to all the suspension components.

Thanks,
Andres G

waltklatt · « **Reply #11 on:** May 29, 2009, 17:31:21 »

That extreme difference in the tire pressure will most certainly cause strange behavior in the suspension.
So you caught it and hopefully the quirky charactor is nothing that is un-pagoda like after the checkout.
I have yet to get used to my diesel 220SL as the engine weight is so much different from the original. The front seems to be too high.
I'm still going through the various pieces and correcting them to return the original stance.
Put a hydropneumatic compensator in the rear in order to raise the rear up more. Tried to rotate the rubber pads and spring to no avail. But the compensator works well, buit it's a very tight fit. Whew.
Nut all that's going for naught as i'm going to change the rear axle to a lower ratio 3:27 soon.
Need to head to the junkyard for the brake lines and retrofit them to match the rusty originals.
Also waiting for the parking brake cables.

Peter, I am currently doing the heat/AC combo box retrofit and will put together a writeup of the progress for anyone who is brave enough to venture into the unknown.
Walter
1967 220SL-diesel

Andres G · « **Reply #12 on:** May 30, 2009, 15:45:58 »

Update! - I took the car in yesterday afternoon and had them put it up on the lift. Inmediately, we found that the bushings on driver side the trailing arm were worn, I think that's what they are called... I'm reffering to the two longitudinal arms that run from the subframe to the axle and have a big round bushing on the front end.

Well, it turns out that the bushing on the front end of this arm was really dry and loose. The whole arm could be easily moved around with a pry-bar and not much effort at all. I had to take the car back home as they were not able to get to it until next week, but I will have these replaced on both sides and on both ends.

Here's a picture I stole from www.motoringinvestments.com where you can see these arms:

Any other bushing you guys suggest checking? I'm sure the front end is pretty solid, but just in case I will double-check on wherever you guys may suggest.

Thanks,
Andres G

Benz Dr. · « **Reply #13 on:** May 30, 2009, 16:40:55 »

A couple of questions in no particular order:

Was the bridge level or was it more like it was in a small valley?

Did it feel like it was the front of the car that was steering off road or the back?

Which way did the car turn?

Normally the car sits upon all the suspension componets as designed. A very sudden lifting and falling dip-de-do can make every loose bushing and joints do a high or low speed wobble or even worse.

If your car tends to push one way with on/off throttle that's rear axel.
If it dives sideways at the front under braking that's more like brakes.
Turning right onto an on ramp ( or similar ) with constant steering correction is more like idler arm bushing.
A general loose feeling in the sterring is any and all front end parts.

When shocks go bad they generally make a light thumping noise. There's nothing wrong with Bilstien shocks - they're pretty much all I use.

I run my tires at 32 PSI. This covers almost all types of driving conditions without being to hard or giving up tire wear.

psmith · « **Reply #14 on:** June 01, 2009, 20:21:11 »

Also check the differential mount while you are at it.

JimVillers · « **Reply #15 on:** June 02, 2009, 12:36:15 »

Dan .... Good comment on the idler arm bushing, a common problem but normally overlooked.

Andres G · « **Reply #16 on:** June 03, 2009, 21:27:34 »

Guys,

Thanks for the replies and suggestions. I'm not sure of all the answers to Dan's comments, but since I'm in Hong Kong until friday, I will only be able to check this next week.
I'm sure I will be able to find some additional components that are collaborating to deteriorate the performance of the suspension, but I probably have to get the M3 performance out of my mind

Andres G

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