My dryer does not stop automatically.

@johnzechnersr, without the model number of your dryer we can't be specific, but the times when I've seen this situation it's been due to the timer motor dying. The timer operates with a motor that rotates the dial very slowly, and when that motor craps out, you get this situation - everything works as long as you advance the timer by hand.

I've been able to test it by taking the timer switch out and manually wiring the timer motor up to 110V. Obviously you'll want to verify that's the correct voltage for yours before doing that. Take a marking pen and mark any random position on the timer dial, then leave the timer connected up to power for like 15 minutes. If the mark hasn't moved, you need a new timer motor.

It's a crapshoot as to whether you're going to be able to buy just the motor itself, or you'll end up having to replace the whole timer; it all depends on which model you have, since Sears used several manufacturers to build their Series 80 dryers. Again, the model information is critical for finding the right parts.