speed sensor causing abs problem?
 

I have a 1995 fleetwood brougham 5.7 350ci. the warning light for ABS is on... and the brakes grab when pedal is pressed. put it up in the air, started the car put it in drive and hit the brakes and the rear wheels grabbed HARD. looked at the front and the pads and rotors look good. did not look at the rear brakes yet tho. took it to dealer and asked them to check it out. returned and they said your front left speed sensor needs to be replaced... i asked them what about the rear brakes grabbing, they said the speed sensor probably has something to do with it as it is part of the abs system. wondering if they are correct? it still stops but the brakes are grabbing even at light pedal pressure. also anyone know if i can scavange the sensors from any other model or year?