2000 Chevy Impala Still shaking!!!!!

[quote:3cc139a2c4="LSchevy"]Shakes or Wobbles problem
2000 Chevy Impala 6 cyl Front Wheel Drive Automatic 104000 miles
----------------------------------------------------------------
I have a 2000 Impala LS with 104, 000 miles and after a few years of no maintenance other than oil changes, I decided to get the needed repairs done to my car.
A few months ago I started to notice that the car is not as smooth a ride as it once was. I shakes at Hwy speeds staring at about 56 MPH and does not realy smooth out until just below 80 MPH.
Given that my new job requires me to drive 800 miles per week on the Hwy, I cant stand this continued vibration. It seems to be more "under my seat" than in the steering column.
Here is what I have had done to the car in the last month;
All 4 rotors & pads replaced.
All 4 tires replaced with Cooper CS4 80K tires.
Aligned & Ballanced. (twice)
Intermediate stearing shaft replaced.
Left front wheel bearing replaced.
I have gotten the car up to a speed of 90 MPH and slipped the shifter into nuetral and allowed the vehicle to slow down on its own and as it came down through 75 MPH, it started to shake and it smoothed out at about 57 MPH.
The shake is not violent but it is annoying.
Any ideas?
I have two seperate mechanics who scratch their heads over this issue. They do not work at the same ASE shops.
Feedback would be great!
Thanks.[/quote:3cc139a2c4]

if you feel it in your seat bottom its a sign its comming from the rear

I'm aware that the problem most likely is in the rear of the car. I'm not aware of what could be the cause.

[quote:74db44e2dc="LSchevy"]I'm aware that the problem most likely is in the rear of the car. I'm not aware of what could be the cause.[/quote:74db44e2dc]

Its kinda one of those hard things to do if I cant see the car and look at it for myself

checking the rear suspension parts for loosness.

Did you have that 100 dollar ballance done? forget what it is called, oh a force ballance its a special machine for ballancing tires checks for out of roundness and heavy spots, does it matter which tires are on the rear?

The mechanics checked all that was possible without actually disassembling rear components. The tires are brand new and knowing it is possable for a new tire to be bad or out of round. They put the rear tires on the front and asked me to re-drive to see if the shaking went to the front. It did not.
The mechanics in both garages removed the rear tires and looked over the wheel bearings and physically tried to move them.
All this inspecting, ballancing, replacing & rotating leaves us all confused.................
I have not had a $100 dollar ballance done.
Is it some kind of a machine that the car drives on?

[quote:25c5080898="LSchevy"]The mechanics checked all that was possible without actually disassembling rear components. The tires are brand new and knowing it is possible for a new tire to be bad or out of round. They put the rear tires on the front and asked me to re-drive to see if the shaking went to the front. It did not.
The mechanics in both garages removed the rear tires and looked over the wheel bearings and physically tried to move them.
All this inspecting, balancing, replacing & rotating leaves us all confused.................
I have not had a $100 dollar ballance done.
Is it some kind of a machine that the car drives on?[/quote:25c5080898]

no its just a different balancer, not to many car repair places have one of these, there expensive.

another thing to try would be to get a standard set of tires and rims and try that, this would rule out the tires

did you get a print out of the alignment?

Thanks for getting back so soon.
I forgot to mention that this shaking was there before I had the new tires put on. I replaced a set of Bridgestone Potenza G009. These tire were "cupped" due to never having been rotated and the vehicle was mis-alligned.
I received a computer print out of the allignment.
The shop uses a laser set up for this process.
The print out showed a 2.7 degree variance on the front left Camber and a -0.16 variance on the right Toe.
What is the exact name of the procedure you reffer to?
I will need to know what to ask for.
Thanks.

[quote:d51acdd1f0="LSchevy"]Thanks for getting back so soon.
I forgot to mention that this shaking was there before I had the new tires put on. I replaced a set of Bridgestone Potenza G009. These tire were "cupped" due to never having been rotated and the vehicle was mis-alligned.
I received a computer print out of the allignment.
The shop uses a laser set up for this process.
The print out showed a 2.7 degree variance on the front left Camber and a -0.16 variance on the right Toe.
What is the exact name of the procedure you reffer to?
I will need to know what to ask for.
Thanks.[/quote:d51acdd1f0]

what about the rear, did you have a 4 wheel alignment?

Yes it was a 4 wheel alignment.
I took the car to the local Cadillac dealer and a technician drove the car (with me in it) and he said he notices more shake in the front than rear. He also stated that he can regulate the shake by feathering the gas pedal.
He states that when you accellerate, everything tightens up and the shake becomes more noticable then. CV joint?
Cadillac wants $200 to perform a "Force Balance".

have the motor and transmission mounts inspected.
Also make sure the front control arm bushings aren't torn out of the sleeves.