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Old 08-13-2010, 01:45 PM   #1 (permalink)
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s.o.s. Strong vibrations at speed over 80 km/h

Since almost two weeks I try to find the solution for a problem that had ruined my holiday.

I was in a new euro-road trip but I got a problem near Vienna and due to that reason I have made the way back home (total of 1300 kms) thinking that I will have a quick and easy repair of my car and I can still make my planned trips.

The problem is a vibration of the whole car ( W126 280SE ) that appears at exactly 80 km/h , aprox. 50 mph, and that vibration getting stronger at 90 km/h is such way that I do not have the nerve to accelerate further that speed.
Over 90 km/h the car seams to disintegrate...The feeling is similar to that of crossing over stairs from a long distance...This is the closest that I can explain to you!

So...What have I done in two weeks:


-change of the tire rod ends ant the central tire rod...the old ones where OK but I have changed them just in case...
-change of the lower ball joint...again, seams OK but changed that too...
-wheel alignment and geometry done
-changing of the front tire with those from the back checking if the front ones are not out of balance...same vibrations
-change of the right side dogbone...(because the bushings into the dogbone seams to have a "play")
-change of the gearbox
-remake of the exhaust system
-change of the tires...inspection of the rims without the tires...all OK
-balance of the wheels...checking the balance of the wheels at an other wheel shop...all OK
-checking of the flex disc from the gearbox/drive shaft...seams good but I will change that too when I will get it ( have to order...)
-checking of the flex disc from the differential/drive shaft...it is good
-checking of the central bearing for the drive shaft...seams good but maybe I will change that too
-checking the engine mounts...seams good but I will change them too

I have made two individual test at two separate locations for the inspection of the suspension of the car and in both places the result were goodand they did not find anything that can be associated with the vibrations that I have described.

After all the thinks that I have made to the car the proble is exactlly the same as before. No improvement at all!


If anyone of you can help me with some advice I will thank you very much!
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Old 08-13-2010, 03:57 PM   #2 (permalink)
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How is the condition of your tires? any broken bands?

Why not take it to a mechanic to have him diagnose it?

Sweeeeet car by the way.
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Old 08-13-2010, 04:24 PM   #3 (permalink)
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There are alot of things that cause such vibration : rings, tires, axles, drive shaft, drive shaft central bearing, flex disc etc......
How did you get this problem, just all of a sudden? or is there some thing went wrong before that? You may not need all what is being done so far.
Most of the vibration comes from the rings and tires, check and/or do tires balancing, also take a look at the diff mounting bolts with its rubbers.
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Old 08-14-2010, 01:14 AM   #4 (permalink)
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Quote:
Originally Posted by Firewater View Post
How is the condition of your tires?
As I said in my first post the tires are new and even the rims were checked...and the balance of the wheel was double checked in two places.

Quote:
Originally Posted by Firewater View Post
...Why not take it to a mechanic to have him diagnose it?
I was with the car at a few mechanics...(I did not made the jobs that I described in my first posts...the mechanics did). I have speak with the representant from Mercedes Romania, the chief engineer of mechanics, but even him did not give me a good tip that resolve this annoying problem.

The car was put to tests in two "stands" and everything was just perfect. I have made the shock`s test and they were all good. At first test the difference between the shocks were 1% in the front and 2% in the back. Just the efficiency was a bit low :50-51% front and 37-39% rear.(I have attached a scan of the test results)
At the second test in a new location the efficiency of the shocks was an average of 75%.

Quote:
Originally Posted by Abdullah2009 View Post
There are a lot of things that cause such vibration : rings, tires, axles, drive shaft, drive shaft central bearing, flex disc etc...
You are right! There can be numerous reasons and I (or the mechanic) have tried all of that: rings, tires, axles, drive shaft, drive shaft central bearing, flex disc...and even more: engine mounts, gearbox mount, shocks, undercarriage, etc.

Just that there is something that is slipping to us or the checks were not good enough to find a problem.


Quote:
Originally Posted by Abdullah2009 View Post
...How did you get this problem, just all of a sudden? or is there some thing went wrong before that?...
To be precise: I have hit a pretty big hole in the road in Hungary at 90-95 km/h the day before...but after that I have made a few hundred kms on the highway without problems. The vibration had started when I have arrived near Vienna and the highway started to get bad, made from concrete and with uneven joining of the surface. It was the place where the vibrations started!

The strange thing is that if I go in bad roads the vibrations are not present, or they are overwhelm by the moving of the car`s body.
In the way back home, in Hungary-where the particularly bad roads are present everywhere, I did have no problem going even with 100 km/h.
Only when the road is smooth the vibration is feeling so strong that the car shake violently.


Quote:
Originally Posted by Abdullah2009 View Post
...Most of the vibration comes from the rings and tires, check and/or do tires balancing, also take a look at the diff mounting bolts with its rubbers.
All of this were checked and declared OK!

Quote:
Originally Posted by Abdullah2009 View Post
You may not need all what is being done so far.
Absolutely right! Nothing has changed since I have made those changes...
Attached Thumbnails
s.o.s. Strong vibrations at speed over 80 km/h-hwscan00111.jpg  

Last edited by dan500se; 08-14-2010 at 01:18 AM.
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Old 08-14-2010, 01:21 AM   #5 (permalink)
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is it possible there is a problem in the steering box? IDK, I'm just putting it out there because you seem to have tried just about everything else....
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Old 08-14-2010, 01:40 AM   #6 (permalink)
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Quote:
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is it possible there is a problem in the steering box?
Steering box was checked and it was find a minor play...but declared unsuficient to cause this kind of problems.

In my search on the Internet I have find a site where somebody had a similar problem and it was recommended to him to make the 9/12 hour test. Maybe you have heard of that...Must grad the steering wheel with left hand at 9 hour and right hand at 12 hour. With the right index finger raised you observe the moving...It the index finger is moving left/right is a problem with the direction system and if is is moving up/down is something unbalanced (wheel in particular...not my case do...) or transmission system...

In my car after that 9/12 test the finger is moving shorth up and down...
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Old 08-14-2010, 01:47 AM   #7 (permalink)
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can you get it onto a dyno and check out more closely where the vibration is coming from under traction conditions (dangerous I know).
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Old 08-14-2010, 02:06 AM   #8 (permalink)
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Quote:
Originally Posted by 420 SE View Post
can you get it onto a dyno and check out more closely where the vibration is coming from under traction conditions (dangerous I know).
Yesterday evening we have made a test...a home made dyno...

We raised the back of the car, rear wheels on the air and accelerated and decelerated...0-60 km/h, 0-80 km/h, 0-90km/h and the last time even to 180 km/h (110 mph) at 6000 rpm. Everything was OK...No vibration whatsoever! The car was raise over a "channel", so we have access under and we can observe everything from there. Drive shaft moving even, flex disc are spinning round without jumps.

Seams like the vibration are present or on the front of the car or they appear only when the car is "in trust" ... or sitting on the road. In the air everything is good!

Last edited by dan500se; 08-14-2010 at 02:09 AM.
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Old 08-14-2010, 02:23 AM   #9 (permalink)
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is it possible, that when you hit the hole, you have broken a part of the chassis and are getting some body flex at speed?
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Old 08-14-2010, 02:31 AM   #10 (permalink)
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Quote:
Originally Posted by 420 SE View Post
...you have broken a part of the chassis and are getting some body flex at speed?
We have checked and nothing seams to be deteriorated... I have received an advice that i should change the left side arm that is maybe bent when I have hit the hole. But I`m assuming that when I have made the geometry this should be coming out from the tests. If it is required I`ll will do that too...
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