6.9 Handling

[TJ 450]

On the weekend, I drove my 6.9 a few hundred kilometres and confirmed a potentially dangerous handling phenomena whilst cornering on some surfaces at 110kph.

I had previously only experienced this on a particular undulating road surface in Perth, that is a diagonal weaving motion as the car traverses these undulations.

When I start working on the 6.9 next, I would really like to get to the bottom of this, and I'm really just wondering what other people's experiences are with this, and general 6.9 handling traits.

Tim

[nathan]

i found this early on with the mohican before i replaced the spheres. after that, problem 'solvered'!

[TJ 450]

Good to hear (well sort of)... I have been thinking that my new spheres may not be so new anymore, in the front at least. The front just seems too firm as well.

BTW, I also confirmed for certain that the engine no longer pings, it's just that I believe I have retarded the timing a little too much. That's easily fixed.

Tim

[nathan]

i forgot you had new spheres. they wouldnt have aged that quick. miner were replaced in 2003-4 (?) and are fine. i know the supposed lifespan is 7 years but i think this relates more to km's than years.
maybe something else is astray?

[TJ 450]

Quite possibly. Even though I tried to flush the system out, I think MT's ISO68 may still be wreaking havoc too. In cold weather, the suspension only damps the lower frequencies... it is rock hard over small bumps like catseyes etc.

When I decide to do the work, I'll make sure all is checked anyway.

Tim

[rbpeirce]

BTW, I also confirmed for certain that the engine no longer pings, it's just that I believe I have retarded the timing a little too much. That's easily fixed.

Check for a vacuum leak.  Several years ago mine would ping unless I ran it on higher octane fuel than usual.  My mechanic eventually traced the problem to a vacuum line down in the V between the cylinder banks.  That may not be your problem, but there are so damn many vacuum lines on these cars that it could be.

[Big_Richard]

I prefer the firmer suspension offered by iso68 and thats the only reason i use it. You used it at the time because you couldn't get anything else, it was your choice to use it and i resent the fact that your referring to it as mine.

standard mb hydraulic oil offers a wallowy ride as precise as a hearse.

I have every wear and tear component in my cars drive-line/suspension/brakes new as your aware and i still wasn't impressed. I think you'll find this "phenomenon" is just normal, every 6.9 Ive ever been in exhibits the same behavior.

[TJ 450]

MT, I'm not saying it wasn't my choice to use the ISO68, but IMO it's not suitable and that's why I decided to use the standard oil again. This is my opinion...you're entitled to yours obviously.

Mercedes would never produce a car that handles like this from the factory and I'm convinced something is wrong.

Rbpeirce, I thought about the vacuum leak scenario... that's still a possibility, but it's running OK at the moment.

Tim

[koan]

There must be something wrong somewhere, old or mismatched (as in age) front/rear spheres.

In the early days I had reservations about ride and handling, one particular bit of road that had been scarified across ways prior to relaying shook the hell out of the car at just about any speed.

Mentioned this before I think, quick steering corrections mid corner would induce oversteer needing a quick correction the other way which could get out of hand. Think body roll was the cause.

Over the years I've replace most of the suspension joints, rubbers, spheres (twice) and front shocks. Haven't noticed any surface problems and the oversteer seems to have gone, either that or I've adapted too it.

koan

[WGB]

On the weekend, I drove my 6.9 a few hundred kilometres and confirmed a potentially dangerous handling phenomena whilst cornering on some surfaces at 110kph.

I had previously only experienced this on a particular undulating road surface in Perth, that is a diagonal weaving motion as the car traverses these undulations.

When I start working on the 6.9 next, I would really like to get to the bottom of this, and I'm really just wondering what other people's experiences are with this, and general 6.9 handling traits.

Tim

If you read the original road tests when the car was new this was reported as being a problem by at least one tester.

I am sure it will be exagerated with wear and age.

Bill

[TJ 450]

Interesting stuff indeed.

It's almost as if the suspension system has been caught out. It does snap into an aggressive oversteer mode as well, after the said event.

In any case, I've got a bit of work to do, so I'll keep all this info in mind. I'm also aware that both height valves are leaking, and I'm sure that if they don't respond quickly enough there will be issues. These will need to be rebuilt if possible.

Front suspension bushes/balljoints will be the first port of call.

Tim

[s class]

.....Mentioned this before I think, quick steering corrections mid corner would induce oversteer needing a quick correction the other way which could get out of hand. Think body roll was the cause.....

......It's almost as if the suspension system has been caught out. It does snap into an aggressive oversteer mode as well, after the said event......

These two comments describe my trusty rusty exactly.  It has 4 new struts, 5 new spheres, rebuilt valves and new MB fluid.  In fact, I would say that the handling of my car is treacherous in mountain passes, for instance.  I have tried a fed different sets of quality tyres (I have other cars to 'borrow' off), but this doesn't seem to make much of a difference.  I'm sure that trusty rusty could benefit from new suspension bushes/joints etc, and I really hope that this would improve the situation.

The bit of hope I have is that my red 6.9 (also with new spheres, same brand as in trusty rusty) handles much, much better and more stable. 

The dark blue project car has new spheres in front, and all new suspension bushes in front (not at the rear), but it has crappy tyres, and it is just as terrifying as trusty rusty. 

I think another important aspect is ride height.  Especially the rear, if too high, can lead to negative camber especially when rolling in corners.  I gave this a lot of thought before getting an alignment on the dark blue car.  I measured up both my 6.9's and my 280SE on a good level surface, to see the fender lip height at all 4 arches.  I found that trusty rusty was sitting much higher than the red car, especially at the rear.  My 280SE (with handling I like) had similar ride heights to the red car.  I set up the dark blue car to match these better handling ones. 

[TJ 450]

Actually, now that you mention it, I do recall you mentioning something along those lines when you went on that long drive of yours, S class.

Treacherous is indeed very descriptive of the handling. Hopefully the cause will be pinpointed eventually.

For those who know the area, it was along the Brookton Hwy, the heavily forrested area in the Darling Ranges. There are some really challenging corners for a 6.9, so beware.

As a comparison, my 450 isn't hair raising through there at all, even when pushed hard.

Tim

[WGB]

The leveling valves really only set the ride height and my 6.9 and my ML500 both control their height at about the same rate e.g. The rate of the front rising after a rapid stop.

Not sure the diagonal pitching and lateral roll would involve the leveling valves to any great extent but does use the side to side flow and the damping ports in the struts.

It is possible to tighten up the car considerably by pulling the dashboard control knob into the central position and this has an effect similar to using the sport setting in my ML500.

It appears to also effectively isolate each wheel so that roll and pitch are both tightened up considerably.

Not sure the hydraulics would take the pressure for long and presumably the car would slowly sink as you drove but my car was left in this position after a trip to the a/c repairer and the drive home was better than expected.

[SELfor50]

Unfortunately I can't offer absolutely any input into advice / experience on the air suspension.

But I can say that on 2 W116's now I've replaced every bushing front and rear.. control arms, subframe mounts, ball joints, tie rod ends, damper... steering couplings etc etc....
And on each car, it's un-comparable how much tighter and snug it feels after it.

If you've exhausted your investigation on the air suspension and already have new parts installed.. I'd suggest doing a re-build of the front end to start then go rear subframe mounts / bushing etc...

Could quite easily be rear drive if the rear subframe mounts have gone and it's moving on the undulated corners and pushing from behind with each opposite rear wheel etc...

Best I got sorry.

Cam.