Strut mount wear - how to test?
 

With our '91 190E 2.3, I notice that although the ride is smooth on most surfaces, the impacts become harsher as the surface imperfections become more sudden. This is more noticeable in the front - initial impact - than from the rear suspension.

The strut mount design seems to allow a degree of flexibility to absorb this, but I suspect the mount halves are 'bottoming' against each other (metal-to-metal) sooner than would be expected if they were new. I am wondering if there is a trick test for resting clearance to determine their condition - as there is for the motor mounts.

As for visible condition, there are small spot cracks that have developed in the rubber, but not close to separation yet. Thanks for any input.

Steve

Steve,

I've not heard it thought out this way before, so I'm not sure if there's good or bad logic here. I've always thought there relatively little difference until the rubber between the center of the mount and the outside cracks. Coudl it be the struts themselves causing your problem?

Don't think so. When pushing repeatedly down on the fender to get the suspension working - hood open - you can see the inside part of the mount moving up and down relative to the outside. I believe this is normal to some extent, and there is no sign of separation just some surface cracking - the rubber part of the mount appears to be 'flexing'. Also, using the picture on FastLane as a guide to the mount's design, it appears to be designed with 'bump stops' underneath to limit travel.

I suspect that when new, these stops would rarely connect. I'm wondering if the increased harshness is a sign that the rubber has deteriorated enough to bottom out routinely. If others haven't noticed this movement, perhaps it shouldn't be enough that I would have either?

Steve

Steve,

I don't have a problem with the ride of my '90 190E 2.3 Sportline, although I too have noticed a few cracks in the rubber at the top strut mount on the left hand side (passenger side in Oz which get more bumps at edge of road). On the weekend I will check for the movement you mention.

Greg

'Ride quality' is a pretty subjective thing, so understand that I still classify the ride of our 190E as 'very good'. I just think it is less refined under some circumstances than it was new- such as broken pavement - and am trying to improve that with a maximum effect from a minimum expenditure.

Steve

Having inspected several with very high mileage, I would rate those things as being quite durable.
Those small cracks you describe do not seem significant when you pull the mounts out and look at them closely.
In order for the halves to actually strike each other, I would expect the visual condition would have to be much worse than that.

On the other hand, they are not particularly expensive or tough to replace.

$.02

Did you check the steering shock?
 

That may be your problem...then again, I would check the whole front end.:(

Thanks for the input, guys. I am partly trying to differentiate as to whether the noise I notice is due to strut wear or the worn rubber. I am certain there IS some strut wear because I can feel a minute amount of vertical play in the front wheels when shaking them while the suspension is under load. However, I also feel they are working fairly normally, else I wouldn't likely see the strut mount movement I do when I bounce the fender ( i.e. there is resistance to small displacement - no freeplay from leakage).

If I can think of a better test, I'll try it, and report back.

Steve

How many miles are on your car?

About 105k, all in SoCal.

Steve

Steve,

On the weekend I had a look at the strut mounts in both my 190E and 300TE. As I mentioned previously, the passenger side mount on the 190E is cracked. The crack appears to be right through for half the mount and does open and close slightly when pushing down on the front of the car. Guess I had better replace that one. The other mount on the 190E and both on the 300TE look fine. They do still show some movement though, probably only about 1mm when firmly "bouncing" the front suspension.

For some time now on the 300TE I have also noticed a slight knock in the front struts when cold. I have been told that this is common when they get a bit of age on them. It goes away when they warm up and does not seem to affect their damping.

For reference, the 190E is a 7/90 build and has covered 212,000km and the 300TE an 8/90 build with 173,000km.

Greg, if you really replace just the one mount, I'd be interested in whether the new one behaves similar to the remaining 'good' one. In particular, when measuring the top of the strut nut to the top of the tower, will you get the same measurement on both sides? Do you also get noticeable deflection of the new mount?

Steve

Steve

That crashing sound could also be worn ball joints. Remarkably the Mercedes ball joints don't seem to offer a lot of protest until well into being worn out, often only revealed while driving over rough, hard small bumps.

My $.02 -

Keep us posted,

Haasman

Steve,

Cost will determine whether I replace one or both. Logic suggests that ideally both should be replaced. In that event though I will still do the cracked one first and then compare it with the other old one. Due to time constraints this might not happen for a couple of weeks. Despite being cracked, the amount of movement does not seem unreasonable to me and I am not concerned that the mount is about to let go completely. It strikes me that the amount of movement I am seeing (and you are probably also seeing) is quite normal. I expect that these rubber mounts are designed to be resilient to isolate road noise and shock loads from reaching the body.

Greg

Greg, I await your experience with patience.

Haasman, ball joints are a possibility, but my past experience with other vehicles indicates shimmy, or vague steering, as the most likely indicator. I don't recall if I did a ball joint test for wear when doing my first round of diagnostics, but I know I examined all joint boots up front and found nothing amiss. I'll keep the possibility in mind though.

Steve