Drive Wheels: longitudinal front-engine/rear-wheel drive

Hi,

was all models from 1990 - 1993 rear wheel drive?

I have an 1990 LX Standard V6.

Yes.
In fact, all 1989-1997 Thunderbirds/Cougars are rear wheel drive.

Ok thx for fast answer, so i must change the oil for rear axle?

When yes, where can i check the oil? Or how can i change it?

theres a bolt in the rearend cover loosen it with a ratchet like any other rear drive vehicle to check and add to drain it is a lil more involved you have to remove all the bolts mounting the rear pan on the center center section and then (personal preferance) either remove the final 2 bolts on the crossmember to take it completly off or just make a gap so it can drain out.