Since new, the wiper arms loosen up with the slightest bit of snow or frost on the windshield. One will work while the other remains in the park position. I have tightened the nut under the plastic trim cap on the arm when this happens and the wipers will work fine for a while. Is there a specific torque that this nut must be tightened to? Has anyone else encountered this problem and is there a permanent solution to this problem?

Thanks

 

you need to take off the arm and check the threads
to see if they are stripped.
try scraping the threads a little bit so you get a better bite
from the arm

Sniper
2000 Expy
5.4 4x4;-)

 

You have to walk a tightrope when tightening this nut. Too loose, and the problem you indicate; Too tight and the wiper arm won't slip under heavy loads (as designed), transferring the overload to the rest of the system. $$$$.

It's possible that the splines have bored the wiper arm mounting hole out too much during prior slipping events. A new arm is about $16-$17 from Ford. Be sure to specify which arm you need as the driver's side arm is different than the passenger side.

But try cleaning the splines and the wiper arm mounting hole first.