intermittent overdrive

[fordmerc]

R9 overdrive is intermittent: sometimes it works perfectly. Other times it won't go into overdrive until after I hit a pothole (!) and then it works fine for a while. Another bump may stop the car from going into overdrive. I would appreciate comments and suggestions about prevention and cure.

[K8096]

My dad had 1948 Custom series many years ago that had similar symptoms.  I think there's a solonoid somewhere in the wiring of the O/D system that was working intermittently.  Once that was replaced the problem was solved.

[fordmerc]

I was concerned  about that so I will pursue that issue. Any other suggestins will be  welcomed.

[billorn]

What you describe definitely sounds like a wiring issue or electrical. Is there a loose wire somewhere that jiggles when you hit the bumps? 

[HH56]

Also check the lockout switch on the back of the lockout knob bracket under the dash.  If the plastic switch plunger has a groove worn in the end the switch can be right at the edge of turning on or off and vibration can cause it to make or break the connection intermittently.  If there is a groove and the serrated lockwasher is still in position, removing the switch and taking out the lockwasher will allow the switch to sit in farther and probably work for many years to come.  If the lockwasher has already been removed then I don't know of any repair that will last very long and replacing the switch with one less worn is the option.