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Discussion Starter #1
Hello (again).

It happens at speeds like ~100km/h but the faster I go it does not get worse as I first expected. As a matter of fact, sometimes this even makes it disappear.

I balanced tires weight and alignment (if I get those names right) but it didn't solve it. The service guy says it's the rear tires as they got uneven before the alignment (they are like one year old now too but passed the inspection unlike the other two that I had to replace) and the mechanic found that the steering shock absorber is a little internally loose due to age.

Are there other reasons for it?
 

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Discussion Starter #3
The front tires are brand new with no deformity on them. But if the rims make a difference (even tho they are clean) then that could be it. I'll give it a try.
 

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If the shaking happens in a narrow speed range, it is generally the tire balancing.
Steering wheel shake= front tires. Seat= rear tires.

Rotate the tires as suggested. See if the shake changes orientation.
 

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If you find that tires make no change to the situation i would look at the drive shaft - gearbox to final drive like the propshaft rubber mounting as its called for splits .
 

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Discussion Starter #7
The shake is not close to a real problem really in my driving conditions specially that it disappears on higher speeds hat I don't do much anymore and if I do I don't go more than 130km/h. Right now I need to confirm the rear two tires are not the problem by rotating the four in different arrangements. The tires are 205/65R15 and speed rated H. I remember checking the specifications and they were acceptable but I forgot. I'll have another look. But are there really any H speed 205/65R15 Yokohama and Hankook tires with less specs for a 300E W124? Still gonna have a look, tho. Gonna see to other suggestions after the above.
 

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Load rating and speed rating are 2 completely separate things. Load ratings are identified by a 2 or 3 digit number. For example, my W140 requires tires with a 100 load rating. Using the proper size and speed rated tire but with a subpar load rating (even 99), is a automatic fail at the annual inspection.

Important: Don't confuse treadwear rating with load rating, even though both use a 3 digit system.


When it comes to MBs, I stick with Michelin pretty much exclusive, with Pirelli and Continental as alternates.

These cars ride the best with Michelins and give the longest tire life, period.
 

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Discussion Starter #9 (Edited)
Okay, here's what I found. Was in a rush (I'm under lots of pressure today) and found that the front (Hankook) are speed rated 94H with a load rating of 680kg (load index 94) and the rear (Yokohama) are speed rated V and I believe they are not less than the Hankook in specs. According to the user's manual the gross weight of 300E is 1890kg. Dividing that by 4 it is 472.5kg (load index 82) so I presume I'm safe at least with the front tires?

EDIT: actually, it's not divided by 4. Allowed front axle load is 905kg and for the rear it is 985kg. Still does not change the conclusion.

Will check the rest soon. The rear are of higher quality and rating, although more worn out, and price tag as I remember when I compared the two a while back.

I'm familiar with some of the tire specs; weight load, treadwear, speed rating, etc. but I thought some specs logically relate to each other since a car that can safely go 210km/h (and other specs like the size) seemed to me it should be heavy in the first place. Guess I was wrong. I don't drive more than 130km/h anyway (can't here) anyway, and only if I do. Only 100km/h is what I do now.

But the picture will be clearer when I confirm all the specs. Gonna do that soon. Tire manufacturer can wait for a little longer.
 

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It is highly highly highly improper to divide the mass of the car by the number of tires and extrapolate that X tire is acceptable because the car weighs less than the combined stated load capacity of the four tires (In your case, both should be fine if the load index is 94 as you've said.)

This is because of weight transfer; the weight is not a static thing. When you accelerate, the weight is "transferred" to the rear tires. Front if you brake. Left if you turn right. Right if you turn left.
On a steep downhill left turn, the right front tire will have a lot of weight on it if you're driving at high speed, braking into the corner and initiating your turn. (Also an easy way to exceed traction capabilities of a tire in extreme circumstances. A tire can only offer so much traction, and when you ask it to brake, or turn, you effectively reduce its traction capability. Some of that can be attributed to the weight transfer we just mentioned.)

The W124 is blessed with near 50/ 50 weight distribution, fortunately.
 

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Discussion Starter #11
Okay, all tires are load rated 94, rear treadwear 300, fronts are speed rated H and rear are V. Can't find the treadwear for the fronts. Am I in trouble?
 

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Have you rotated the tires yet? If not, try that first. Otherwise, you'll just be chasing your tail
 

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before rotating the tires, spin each wheel and eyeball the rim to see thats its not visibly bent I've never had this happen with alloys, but with steel wheels (on non benzes), in the past I've had a bent wheel or two, that caused the wheel to wobble side to side as it turned, this causes all kinda funky shimmy at highway speeds, and if ignored, will eventually shake your ball joints and/or suspension bushings apart.
 

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Discussion Starter #14
I did fix one of the rims before an replaced another completely. Ever since there were no shaking. But I'll have a look at it too. I can do both tasks (along with the rotation). And I don't wanna drive in circles attempting to see the rear plate number indeed.
 

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What do you mean by "FIX one of the rims"???

Sounds like you have damaged or misbalanced wheels.

Alloy wheels do not lend themselves too much to fixes, other than curb rash and repainting. Welding, patching alloy wheels is a huge no no.
 

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Discussion Starter #16
Wait, now I remember. I took a serious bump once (a pavement, ehm) and had the front right rim broken. Dunno how the rear right survived. It was long ago.

The ones I fixed were for the old Crown Victoria. Not welded or patched, fixed/bent back somehow. I don't remember the view.
 

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Discussion Starter #17
Okay, I didn't have time to even scratch my head, so I changed the rear tires air pressure (apparently that's easier than scratching my head) just as the car parked at home. It was 40 psi (what I always do) so I reduced it to 35 since less tire air pressure means softer tires and more surface coverage to test the theory of the uneven tire surface the service center guy mentioned. Does that prove anything other than just the worn tires?
 

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Softening the tire pressure allows the sideway to absorb more than it would at higher pressure. You could mask a balance issue with low pressure but that is not a good long term solution. I was thinking the same as LeftCoastGeek that a bent rim is at play here. Usually a good mechanic will see the runout of a bad wheel when he is balancing it.
 

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Discussion Starter #19
Yes, that's why I did it within specs. which say rear tires pressure is 34-42 psi (if I remember correctly) depending on speed and weight. I'm still considering the other instruction in this thread, of course.
 

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I still suspect you are dealing with wheels and/or tires that are out of round or a driveshaft imbalanc, although I am leaning primarily towards wheels&tires.

Easy enough to verify when you have your car on a 4 post lift or on jacks. Put the car in Drive and bring the car up to 100 km/h. Repeat by swapping in the remaining 3 at the driven wheel.
 
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