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Discussion Starter #1 (Edited by Moderator)
My '08 280 Edition 10 continues to act like all 4 wheels are out of balance right at 30 MPH in any gear including neutral otherwise it is dead smooth right up to 100 MPH. The roughness seems to be worse at times under the same driving and road conditions.

I've checked motor and transmission mounts and wheel lugs.


The previous owner put front tires on the car that are out of size specs. It is supposed to have 225/45 R17 on the front. However 225/40 R17 are installed on the front. The rear tires are in spec with 245/40 R17 installed.


The difference in circumference is 2.7 inches which will will result in a 3.7% increase in calculated rotational speed being sent to the stability control computer systems.

Could this be confusing the stability control systems and causing them to kick in because of generating out of spec wheel rotational speeds?
 

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Administrator - Founding Member since 2006
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we might have mentioned it before

Have you had a 4 wheel alignment done?
Have you had all 4 wheels balanced.
is the tire pressure correct in the tires?
 

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@Dave2302
@Turdo2

I know the 170 is more your thing but I reckon your input is worth a shot.

+1 on starting with tyre pressures, condition, alignment.

What makes are they? some do not mix.

The size may/may not matter with the difference you have.
 

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Another thought, I used to have a Jag that did the same sort of thing...it would shake around 40-45 mph then smooth out...found a rim that was out of true (bent) actually found a couple of bent rims.its worth a look

Sent from my SM-T550 using Tapatalk
 

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Discussion Starter #5
Reply to posts to my shaking problem

The tires are Continental Extreme Contact Sport Plus with about 40% tread left.

I have not done a 4 wheel alignment and balance as of this writing. It is in my plans but getting the time to do it is difficult now with my wife's health issues.

Every balance problem I've seen in my 62 years of driving has been a smooth ride up to 45 mph or so then the out of balance shimmy would kick in.

The tire pressures are to spec.

I was just wondering if others ever had had a similar problem. I do need to check the rims for run-out.

Thanks for the input, if and when I solve this I will share the cure.

Dennis
 

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Bent wheel is the first thing I think of also. Front wheel bearing or bad tires are other possibilities. The speedo system can be thrown off by incorrect tire sizes, but it will end up using a correct sized one before an error is thrown. Your rear left tire is probably the one it is using right now for speed. If the yellow triangle isn't lit up on the dash then you should be ok.
 

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Discussion Starter #7
Thanks to all for the suggestions and feedback.

It appears like my problem is solved. - Yesterday, I decided to check the run-out on the wheels and in the process I rotated them from left to right etc.



The lugs on the left front reluctantly gave up to my electric impact wrench - 250fp - but the rest would not. So I got out my 600fp impact wrench which loosened the right front and left rear. The right rear lugs would not budge. At that time I said what the "#*%&" and put a 4 ft pipe on my 2 foot breaker bar, thinking they will either break or come loose. They fought back but finally gave up with a loud crack. The lug bolts were somewhat rusted and were tightened way beyond their torque requirementson all four wheels.



Once the lugs were out the wheels would not come off. I had to get out my 4 lb rawhide mallot and hit them on one side a number of times while rotating the wheel and pulling on the opposit side. There was rust build up between the wheel centering surface and the rotor hub causing them to be stuck.


The two front wheels had 0.045" and 0.022" run-out respectively, the rear ones had none. I did not recheck them after re-installing. That is in my plans just for curiosity sake.



After cleaning up the rust, applying some antiseize and putting things back together I took the car out for a spin and the vibration/shuddering at 30mph was gone. Drove it some again today and no vibration is present.



My take on this is that the extreme tightness of the lug bolts was pulling things out of shape and causing the problem.


Dennis
 

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Discussion Starter #8
30 ph Shudder Up-Date

Hi All,

Decided to see if returning the front tires to their original positions would prove that the problem was over tightened lug bolts.
To my surprise the 30 mph shudder came back immediately so I swapped them again and it is gone once more.
I have an appointment for 4 wheel alignment and balance on Monday, both fronts are showing wear on inside of tread.
I'll return the front wheels/tires to their original position before the alignment/balance.
If the problem returns once more I'll replace the front tires with the correct aspect ratio of 45 instead of the 40's that are on the car now.
At least to this point I have isolated the problem to the front tires/wheels.

Dennis
 

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Discussion Starter #9
Balance and Alignment did not help

Hi Again,
The balance and alignment did not stop the shuddering with the wheels in their original position. The balance was dead on and did not require any additional weights.

The alignment did make a slight difference in handling and the position of the steering wheel while driving in straight line.

The shuddering continues to leave when the front wheels are swapped side to side.

Next on the agenda is to get the bent wheel straightened.
Dennis
 

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Bent wheels are the bane if smooth rides...repair generally works until you hit a pothole etc. Then replacement is the real fix

Sent from my SM-T550 using Tapatalk
 
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