ildd

Background info-
I was going 90 MPH on a very good highway. It wasn't the road quality.
I've gone 90 mph many other times with no vibrations whatsoever(and faster, for that matter)

My idea of causes-
4 months ago, I had the inside part of the bumper(the part that covers windshield wiper fluids) become undone and I had to tear it off( see here). This was the 2nd time that I had gone such speeds without the cover. The first time I had no problems AND I had 2 other friends inside the car with me. For now i'm ruling that out.
My suspension is going to s**t...shocks? struts?

Does anyone have any info on what was happening? Sunny day... not a spec of water... I glanced at all the wheels and tires when I reached my destination and it all looked fine(i'm not going to check pressure when tires are hot).
For reference, I've gone 87-88 MPH countless times since then and never had a problem at all. I watched the speedometer, too. 85 mph? perfect. 87 mph? perfect. 89 mph? great. 90 mph? OH f*** what is happening!?
Thanks in advance.

edit- I can't really describe the vibrations as that was the first time I've experienced the problem. The most accurate thing I can compare it to is going over the shoulders rumble strips... but if they were more spaced out. And if they poked above the surface...

jkowtko

well, sounds like something in your car that moves in a speed dependent way hit a resonant frequency that is either an off-balance or underdampened component.

If you are thinking it's just a flapping body panel, then have someone drive in front of you and look.

If you suspect a mechanical component ...

* balance tires?
* struts/shocks are a big one
* in the front, control arms (bushing or ball joint end) or upper strut mount
* flex disks on both ends of the drive shaft

The simplest one is tire balance.

I would also suggest checking those flex disks immediately ... if they are excessively worn and the driveshaft is starting to wobble, you are in for a major accident and auto repair if one of those gives out.

How many miles on the car, and what has been replaced already?

And another option ... don't drive 90 mph!

SunnyRayToronto

Also check for bent rim.

What`s the speed limit,.....

VVF

I vote for wheel balancing.
Had a slight hint of vibrations starting at 75 (74 was ok).
Then at 80 it's like driving on a wash board.
Rear tires were just a bit off balance

Also, if the steering wheel is vibrating, it's the front tires/shocks/whatever.
If you feel vibrations under your butt, it's something in the rear.

Boom vang

I vote for a seized parking brake lever arm that is under the seat above the prop shaft. That will make the worst vibrations at speed, sounds and feels like the car is going to explode at the rear.

The brake lever arm is exposed to dirt, spray, salt etc and eventually the arm gets stiff and does not return when the brakes are released. The culprit is the rivet bushing with is a very poor design.

I free'd mine up a couple of years ago first by using some PB Blaster to free it then using anti-seize as a lubricant - use a lot of it and coat it, grease will only be a short term fix as I found out the first time I tackled the problem a year before.

I am now on to 5 years without an issue

go check out these related posts:
https://mbworld.org/forums/c-class-w...l-bearing.html
https://mbworld.org/forums/c-class-w...on-rumble.html

ildd

The car is an 02 c240 with a little under 60500 miles. I will look into the flex disks when I get a chance; I have a full Thursday schedule but I might have just enough light near the end of the day. The tires themselves have about 30k miles since 2007 or so. As to what has been replaced... I didn't get my license until Spring of 2012, so the only maintenance that I've been able to go through the car with was an oil change. I've told my parents that the brakes need replacing but they don't want to pay for it...I don't have a job and I don't plan on getting one until I can prove to myself that I can juggle a job and college at the same time. I think the pads were last replaced in 2010(about 7k miles). Other than that... I really have no idea.

Rims have a few scuffs but otherwise fine. Speed limit is 65 mph but I've never seen the flow of traffic go under 73 mph.

The steering wheel had very minimal shaking and vibrations compared to normal(similar to rumble strips). It felt like they were mostly concentrated towards the rear


Thanks to all for the responses...at least now I have an idea of what to inspect(and research as I have nearly no idea what a flex disc is). I just found it weird, though, because I go 80 mph every day and never had this problem and today I just so happened to leave my foot down a little longer than usual

Boom vang

easiest check is to remove the back seat, undo the hatch, disconnect the parking brake cable and see if that arm moves freely. If it is stiff or does not return to its resting place then I am willing to bet 100% that this is where your problem lies. This should take you about 20min and easier than the other suggestions to check out first to verify that this is not the issue, this issue has affected me and 3 other people I know the fix I suggest solve the vibration. Incidentally this vibration would only show up at highway speeds.

The arm in question:

VVF

I think your brakes should be fine with 7k.
Maybe a brake fluid flush is in order, especially driving above the limit

So you have been driving for about a year +- ?
I kinda suggest that you slow down a bit

ildd

1 1/2 years. I know it sounds stupid to say, but I have really good depth perception and instincts. Still, you're probably right. I know from here on out I will slow down until I can get whatever that is wrong fixed.

jkowtko

If the sound is coming from the rear, then I suggest check the flex disks and the rear shocks.

Also make sure that one of your under-chassis cover panels isn't loose and vibrating.