i got a 2004 F150 that won't go into reverse. All other gears work, including 4 wheel drive. I checked the linkage and it is working. Any suggestions? thanks

 

The number one reason for no reverse with that trans is a broken sun gear shell, but when this happens you will also have no 2nd and 4th. You said all the other gears work fine, do you mean that you can shift into them with the shifter or you have all the forward gears when you drive the vehicle?

Other reasons for just no reverse can be a failed reverse servo or its snap ring or a broken reverse band.