Transmission does not go into overdrive

If OD is the only thing not operating and the OD light is not flashing, the most common thing I have found is the servo itself fails. Usually the seal on the piston fails and doesn't hold pressure to apply the bands properly.

Again, if OD is the only issue and the fluid is good, you don't need a rebuild. Also, have you checked for codes yet? There is normally a DTC that goes along with a failure to engage OD.

Let me know if you have codes and we can go from there.

Hi and thanks for starting a new thread. It's appreciated.

Have you had the computer scanned to identify trouble codes? I ask because it can be a few different things.

What I am starting to see more often is the OD servo clip is breaking. To access it, you have to remove the transmission pan and then the valve body. I found two great pics that show where and what. Now, I can't be certain this is the issue, that is why we should have the computer scanned. If there are codes, I will be better able to determine if this could be it. However, I will tell you that I have now seen this issue three times. When the vehicle should shift to OD, it goes to neutral.

Here are the directions for removal and replacement of the servo. If you need the directions for removal and replacement of the pan and valve body, let me know. This component is on the underside of the valve body. Of course they couldn't make it simple. LOL The remaining pics correlate with the directions.

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2006 Ford Truck Expedition 2WD V8-5.4L VIN 5
Overdrive Servo
Vehicle Transmission and Drivetrain Automatic Transmission/Transaxle Band Apply Servo Service and Repair Procedures Overdrive Servo
OVERDRIVE SERVO
4R70E/4R75E Automatic Transmission
Overdrive Servo

Special Tools
pic 3


Removal
1. With the vehicle in NEUTRAL, position it on a hoist.
2. Remove the main control valve body.


pic 4


3. NOTE: If the tool is not available, extreme care must be taken. Spring pressure will force overdrive servo piston assembly out of case. Case bore damage may result from trying to pry on overdrive servo internal retaining ring.

Using the special tool, compress the servo spring to remove the overdrive servo retaining ring.


pic 5


4. Remove the overdrive servo piston and return spring.

Installation

pic 6


1. Install the overdrive servo piston assembly.
1 Install the overdrive servo piston return spring.
2 Install the overdrive servo piston assembly.


pic 7


2. Use the special tool to install the overdrive servo piston retaining ring.

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If possible, let me know if you can have the computer scanned. I don't want to put you through this if it isn't necessary.



Let me know.
Joe

Check engine light has not turned on. Would it still show codes? Servo clips are all intact.

There could be a code with no light but it is unlikely in this case.

The way overdrive works is the servo is applied in 4th gear (turned on) and it presses in on a band that wraps around a drum. This causes a gear ratio change and achieves overdrive.

This means if you don't have overdrive, that you probably have one of two issues. First, the servo is being applied but is not moving to apply the band. The other is the servo is applying the band but it is slipping and not holding the drum to achieve the gear ratio change.

Clearly it is speculation until we do an air pressure check to see if the servo can be applied. Basically the attached test uses air pressure in place of fluid pressure so that we can see if there is a leak in the hydraulic circuit.

Clearly an air check is not the easiest but it sounds like you are capable of performing it. Let us know if you have questions.

Appreciate the help. Replaced solenoids and servo piston and still doing same thing.

Ugh. I hate to say it but I think the next thing would be to pull down the transmission and replace the band as it is probably slipping.

Have you actually checked for codes? If there are no codes then a mechanical issue like a smoked band would be the likely cause. If there are codes then that could take us in a different direction even though I know you said there is no light.

Going to order a master rebuild kit and hopefully rebuild it next weekend. Can you change just the band?

You can but you kind of said what I would recommend. If you are going to open it up, why not just rebuild the whole unit with a master kit which includes seals, clutches and bands. By that point it is not much more work.

Let us know how it turns out and if you run into issues in the process. Thanks

Ordering the whole kit. Hopefully all goes well this will be a first for me. Thanks again for the help.

Sounds great. If this is the first one here are some exploded views of the major systems. Let me know if you need more info and we can provide it. Its not a difficult one so I am sure you will be fine. If it includes new clutches, make sure you soak them in transmission fluid for about an hour before you install them. It will cut down on chattering at first engagements. Thanks