I have a 1998m Grand Marquis gs. The transmission stutters when it changes gears every once in a while. It makes the whole car vibrate, and seems like your driving on a rumble strip usually at the 50 mph range. It gets worse when the AC is on. It doesn't do it so bad when i manually turn overdrive off. No lights are illuminated on the dash...
Transmission stutters when changing gears usually in higher mph range. on 1998 Mercury Grand Marquis
by JohnHenry in Killeen, TX on February 21, 2011
ANSWER by DaveJHM on February 21, 2011
By describing it as feeling like a rumble strip, I can definitely say that this is a classic torque converter shudder. Change the fluid and filter. All the fluid. Use a fluid exchange machine if necessary. Make sure to use Mercon V. Give it 100 miles or so - and hopefully the shudder will dissipate. If it does not, it almost certainly will need a torque converter replacement. See a qualified transmission shop or the dealer to get a good diagnosis.