[Shotimes] OT: Grand Marquis

[George Fourchy]

On Sun, 29 May 2005 15:03:41 -0400, Doug Copeland wrote:

> I took it for a drive and under normal braking it
>shook really bad.  I thought the problem seemed to be coming from the
>back, so I took the car back to her house and popped off the back
>wheel, only to find perfect pads again and immaculate rotors.  There's
>plenty of brake fluid and the pedal does not feel spongy.  Does anyone
>have any ideas on what the problem is?

Does the shaking only occur when you are braking?  If so, then it is caused by
warped rotors.  If they aren't too bad, they can be turned on a brake rotor lathe
that will cut down the highs spots.  If they are too bad, they need to be replaced. 
Usually it is the fronts that do most of the warping, but rears can do it too.  Rear
rotor warpage shows up as shaking in the seat and floor, while front warping is felt
in the steering wheel.  You also feel it in the brake pedal.

In a rear drive car, it is harder to check them at home for warping.  FWD makes it
easy, as you can sit there and see the rotor turning and moving side to side as it
rotates.  You can do the rears on your GM at home, but again, the fronts are usually
worse, and easier to spot.  If you do check it at home, do one rear wheel at a time,
and leave the other one on the ground (with the tire mounted).  Tighten the rotor
down with a lug nut put on backwards.  With the car at idle, in gear, watch the
rotor turn through the rotor....you could apply the E brake slightly, just to get
rid of extra clearance between the pad and rotor.  The caliper should wobble in and
out as the rotor turns.

I'd take them all off and have them turned.  You don't say what the mileage is on
the car, but if it hasn't
had brakes yet, it's probably due for new rotors anyway.

George