haoz129

Guys,

Finally I finished this one, as important information for ABC owners which could help increase the ABC reliability and reduce the owning cost:
https://mbworld.org/forums/5749055-post173.html

I told myself I have to gather those information to help/benefit ABC owners when I see ABC issues continue to trouble us.

Thanks.

Howard

ibeforreal

Very much appreciated Howard. This information is very useful. Since my car does have the ABC setup I am constantly concerned even when the slightest thing goes wrong because I know how expensive the repairs are.

Maybe Warren (Skylaw) can put this in the encyclopedia.

haoz129

Thanks John.

It is a great idea to make these information easy to be accessed, so they can reach every ABC owners.

Regards.

Howard

shardul

iTrader: (1)

nice write up! thank you

Welwynnick

Great stuff as always, Howard!

My impression is because ABC is so unfamiliar to most people, even mechanics fight shy of it ("if it ain't broke, don't fix it") just as I did with my first two ABC cars. My first was a five year old S600 NA that really caused me no problem at all. It did have a slight wiggle from the rear end over single, large bumps, which I thought was down to suspension or subframe bushes. I even asked the dealer to investigate, but they found nothing. I wondered if I was imagining things, but I now know I wasn't. That car had 225/55 tyres on 17" wheels, and they weren't enough to give the ABC any work to do.

My second car was much older by the time I bought it, but had the great advantage of 245/45/18 tyres. That was the sweet spot for the chassis, it had a magic carpet ride and unbelievable handling; there was real, physics-defying talent there.

My third is the 155k mile S600 TT, which has been much more of a challenge. Its had at least one ABC pump, two rear struts and three ABC hoses. It has 265/40/18 rear tyres (and is much worse for it) and it wriggled and shook itself down every bumpy road, like the first car, but worse. Again, I presumed it had bad subframe or suspension bushes, but they all semed OK, so I dug deeper, and I think I found another underlying ABC problem that I haven't heard people talking about.

ABC struts have a ball joint at the bottom, and a large rubber bush at the top. Both of them wear out, but its not very apparent even with the wheels in the air - as always you have to disconnect the suspension strut before find out what makes the suspension tick (or clank). The bushes on the suspension links are pre-loaded so that their natural position is normal ride height. With the car jacked up and the wheels in the air, the bushes are pushing the wheel upwards quite firmly - more then enough to lift the wheel and brake, and push the strut upwards into its mounting. This keeps the upper bush in compression, so any bush damage isn't apparent when you inspect. When you go over sharp bumps at speed, the unsprung weight tends to oscillate fast against the compliance of the tyre, but the damper damps this out. However, if the bush is degraded, the damper can't pull on the bush and it just comes away, so the wheel is completely undamped, and it bounces against the tyre.

Depending on the degree of degradation of the bush, this is horrible. It was subtle on my first car and severe on the current one. On smooth surfaces its fine, but as soon as the suspension has to do any real work, it fall to pieces. The afflicted end of the car bump steers all over the road, and it shakes over any sharp bump, especially when you're going fast. Because the suspension keeps the bush in compression in the static condition, this is difficult to diagnose by inspection, but there is a way.

Jack up the car so the wheel is off the ground, then push the wheel down hard with your foot. It shouldn't move, but if the top bush is worn, you'll find that the whole wheel/brake/suspension unit may move downwards relatively freely, once you overcome the suspension's natural upwards pre-load. That's what mine did, so I replaced a rear strut with a good used one, and for a few hour's work the problem entirely went away.

I think its something everyone should be aware of. Unfortunately you can't get the bushes on the their own (Mercedes what were you thinking of?) but used or re-manufactured struts aren't that expensive, nor difficult to replace. I've got some description and pictures for what I did, which I'll post up next weekend.

Nick

haoz129

Thanks Shardul.

Thanks Nick. The way you replace the ABC hose really benefit us.

And yes, the strut bushing investigation you have done will be appreciated too. I will keep that in mind.
Waiting for your next write-up.

Howard