OK, The 2003 MCS has thumping sounds that appear to be in the rear and directly related to a bearing and tire issue. However here is the story, I replaced brakes on all four corners, wheel bearings on left rear (this one was bad) and right front, Half shaft/CV joint on the right front, realiened the wheels, new tires on all four corners, double checked the runout of the tires and wheels (which was OK), and checked the bearings on all 4 with no apparent problems, and it still goes down the road thumping. The thumping starts at about 20 mph and increases and decreases with speed. It is there with the cluch in or out, under acceleration and deceleration.

Any great ideas? What did I miss? Thanks in advance. MiniGSport

 

When you checked the rear wheels, did they get re-balanced?
Any signs of any rubbing....look around...are you running stock tire sizes? Is the car lowered? More info would be useful.

 

Zip,

Thanks the car's suppention, wheels and road hieght is stock with stock sized tires, and a fresh balance with the new tires (new continental run flats) (less than 100 miles) and check of the balance with the check of the run out (after the new tires).

MiniGSport

 

Zip and all,

Also it is a 2003 MCS with the standard wheel size of 195/16. Sorry forgot that there were 2 stock sizes on the MCS that year.

Thanks, MiniGSport

 

A bad shock would be my guess, or possibly a bad control arm bushing or sway bar bushing - but I'd bet on a shock.