Ironing out Ford 5R55N/S/W clunks and bumps

The design of the OD planetary gear set (Figure 1) in the 5R55N, S and W transmissions allows for a 1:1 ratio from the Input Shaft to the Center Shaft until the Overdrive Band comes on and holds the sun gear. When this happens, the Input Shaft will spin slower than the Center Shaft.

Ford Motor Company’s 5R55 W/S & N Transmissions Theory and Operation manual provides the following gear ratio information:

5R55W                        5R55S                         5R55N

1st gear:  3.22:1           1st gear:  3.22:1           1st gear:  3.22:1

2nd gear: 2:41:1           2nd gear: 2.29:1           2nd gear: 2.41:1 (early)  2.29:1 (later)

3rd gear:  1:54:1          3rd gear: 1.54:1           3rd gear: 1.54:1

4th gear:  1:00:1          4th gear: 1.00:1           4th gear: 1.00:1

5th gear:  0.75:1          5th gear: 0.71:1           5th gear: 0.75:1 (early)   0.71:1 (later)

By looking at these ratios the main difference occurs in both 2nd and 5th gears. This is when the Overdrive Band applies causing the OD planet from being locked at 1:1 to overdriving at either 0.71:1 or 0.75:1.

There are two different OD Planetary assemblies. They are as follows:

Set 1                                                    Set 2

Overdrive Ring Gear: 94                    Overdrive Ring Gear: 72

Overdrive Sun Gear:   38                    Overdrive Sun Gear:   24

Overdrive Pinion/Carrier: 28              Overdrive Pinion/Carrier: 25

To determine which Overdrive Planetary Assembly provides the 0.71 or 0.75 ratio, the Ring Gear teeth count will need to be divided by the Ring Gear teeth count added to the Sun Gear teeth count (Figure 2).

Set 1: 94  /  (94 + 38) = 0.71

Set 2: 72  /   (72 + 24) = 0.75

Lubrication problems are known to destroy this planetary assembly requiring the need to replace it. Incorrectly interchanging these two assemblies can cause a variety of issues. The Lincoln LS for example was originally equipped with a 5R55N and was changed to a 5R55S around 2003. It seems that the computer strategy in the Lincoln has a tight window on ratio tolerance causing it to be very sensitive to variations. Should the wrong ratio OD planets be used, gear ratio error codes are produced followed by harsh shifting.

Otherwise, the vehicle could develop a harsh 1-2 up-shift and/or 2-3 shift the longer the vehicle is driven and may not have any codes present. Other times gear ratio error codes such as P0732 and P0735 may accompany the complaint. May also have coast downshift clunks.

In the cases of Mountaineers and Explorers, they seem to be less sensitive. In fact anything earlier than 2004 doesn’t seem to be an issue. Starting around 2004 and later we have noticed an increase in the sensitivity of ratio tolerances which may explain why in some models there are no apparent side affects while in others there are.

What makes these a bit more elusive is that in many cases a harsh or bumpy 1-2 up shift occurs the warmer it gets yet there are no codes. Sometimes it is the 2-3 shift that gets harsh. Downshift clunks and bumps may also be present. Yet, no codes. Sometimes there will be codes and servo bores and valve bodies are blamed yet it's the wrong OD planet ratio.

One way to determine if the wrong OD planetary ratio has been used is to first erase the Keep Alive Memory with a scanner. Then perform the following garage shift relearn procedure:

1. Ensure that the transmission fluid level is correct.

2. Install diagnostic equipment and monitor TFT.

3. Warm the transmission fluid to 54°C (130°F) as  indicated by the TFT.

4. Perform 5 engagements from Park to Reverse.  Each engagement must be five seconds apart.

5. Perform 5 engagements from Drive to Reverse. Each engagement must be five seconds apart.

6. Perform 5 engagements from Reverse to Drive. Each engagement must be five seconds apart.

7. Perform 5 engagements from Neutral to Drive. Each engagement must be five seconds apart.

Then perform the following drive learn procedure:

8. With the shifter in the (D) or (D5) position, moderately accelerate from a stop to 80 km/h (50 mph). This allows the transmission to shift into 5th gear. Hold vehicle speed and throttle position steady for a minimum of 15 seconds.

9. With transmission in 5th gear and with steady speed and throttle position, lightly apply and release the brake pedal to operate the stop lamps. Then, hold steady the vehicle speed and throttle position for a minimum of 5 seconds.

10. Brake to a stop and remained stopped for a minimum of 20 seconds.

11. Repeats steps 8 through 10 at least 5 times.

Usually the 38 tooth sun gear is the most prone to destroying the OD planet set causing the need for replacement. But if you are not sure what originally belongs in the vehicle, the most inexpensive and sure way of knowing is to call the dealer and with the vehicle’s VIN, order the washer/adapter that spline onto the OD Sun Gear and locks it to the Coast Clutch Drum (Figure 2). The basic part number for this piece is 7660. If the washer fits the sun gear you have the correct OD planet system. If it does not, the right assembly will need to be acquired and installed.