Between 45 and 50 it shifts constantly but if I pushed the overdrive button off it stops. My suv is a 2004 Expedition with 130,000 miles on it. I am a 66 year old cleaning lady so I can't afford a transmission overhaul. Do I need to trade this or could it be something simple?

 

I believe that is the speed where the trans shifts into overdrive normally. If you can't keep a constant speed 45 or over it will do this.If you drop below 40 or so it will drop out of overdrive. As I see it, you have the choice of keeping it under 40 or over 45, OR keep it from going into overdrive at all, but MPG may begin to fall.

 

I really appreciate your answer but I need a little more information. Is this a sign I am about to encounter a expensive transmission repair? I have always gotten very good advice on here so thank you.

 

From the info provided, I don't believe there is any problem unless this situation just started.

 

Are you sure it's not an ignition misfire? I've heard this so much where when you're in 4th gear going between 40-45 MPH under a good load, the engine will misfire, which causes a 'bump' feeling when driving. It's been described as a TOrque convertor shudder, but it's really just a performance problem.
Usually, transmission problems become very easily reproducable under certain driving styles.

 

I don't know. I don't hear anything that sounds like a backfire. Just when the speed limit is 45 and I try to stay at that it keeps shifting unless I take the o/d off. I have cancer in both lungs and neck and toncil cancer so my chances of getting a second job to pay for a transmission overhaul are not there. I appreciate the piece of mind I have gotten on here so far. Thank you for your advice

 

Depending on far you have to drive, leaving the overdrive off will not hurt anything if it makes it more comfortable for you to drive.

 

"Just when the speed limit is 45 and I try to stay at that it keeps shifting"...

The following may or may not help, but...

Have you been driving at this speed for quite some time (as in a few years)?

If so, then I would suspect that you just may gave a DEAD spot in your TPS (Throttle Position Sensor). The TPS is a variable resistor and is a wear item. The DEAD spot provides 0 resistants and this tells the injectors to NOT inject fuel. This can causes a BUCKING feeling or the In & Out of Over Drive feeling.

By turning off the OD, you are changing the position on the TPS away from the DEAD spot to maintain your speed.

Ran into this same senario back in 1987 on my 1983 Mid-Size LTD. Seen this same issue over the years from vehicles driven at the same speed for years (Mainly city driving).

A TPS should be about a $70 part thru the Ford Dealer Network (FORDPARTS.COM), or you may be able to get one cheaper elsewhere (reliability factor).

 

Mine did this also. It was the spark plugs. One was bad.

 

I had a 94 F-150 XLT that would constantly shift in and out of overdrive depending on the speed or if I pressed the gas pedal a little more like climbing a hill most of the time it would be out of that gear and it caused the gas mileage to suffer as well. being that I didn't like the engine I sold that truck as soon as I could