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2006 Ford Explorer XLT w/5R55S Automatic Transmission Slipping In Reverse

The Swamp Fox

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Hello all,

I'm new to both my Ford Explorer and the forums here. I am currently having some transmission trouble, and am hoping to learn from those who have found themselves in my situation before. The vehicle in question is a 2006 Ford Explorer XLT with the 4.0L V6 engine and 5R55S 5-speed automatic transmission.

The engine is running flawlessly and the vehicle is in great shape for the year. I'm trying to ascertain whether the transmission issue is serious enough that it will require a rebuild / replacement, or whether the slipping is caused by a more peripheral issue such as a bad sensor that would be a far less expensive repair.

I'm no rookie under the hood, but have (fortunately) never had transmission issues before and know next to nothing about them. That said, I am eager to learn.

History of Transmission Performance
For several years now, the transmission has slipped slightly in reverse when under a heavy load, such as when backing up a steep incline or when backing up with a loaded trailer. The slipping was usually preceded by a significant mechanical shuddering. However, the Explorer would walk up a hill in reverse no problem when in 4x4 Low. No other slipping or shifting issues ever presented.

Some time ago, the driver side transmission oil cooler fitting at the radiator sprung a slow ATF leak. I successfully fixed this by replacing the two O-rings contained within the fitting. I then carefully followed the Ford Service Manual procedure for topping off the automatic transmission fluid:
  1. Warm up transmission to 80-120° F.
  2. Park on a level surface (verified via level on running board)
  3. With engine running and transmission in Park, loosen drain plug
  4. Pump Mercon V ATF into transmission until it begins draining out
  5. Re-seal drain plug when transmission is no longer draining a steady stream of ATF
The Explorer took almost exactly 3 quarts of Mercon V ATF to become full. I was hopeful that these three quarts would eliminate or reduce the slipping problem in reverse when under load, but it didn't appear to make a difference one way or the other.

A few weeks later, the slipping in reverse worsened. The only thing I can figure is that the 3 quarts of new fluid may have been enough to have the effect of eating away any built-up grime on the clutch plates, contributing to additional slip. This seems plausible given that I don't even know the last time the transmission fluid was flushed or the pan dropped.

Possible Causes

Given the fact that topping off the fluid didn't resolve the slipping in reverse, my first thought as to cause would be a worn reverse band. But if I'm dealing with a worn band, I'm confused as to why Reverse worked flawlessly in 4x4 Low for years under heavy load with no issues. The only theory I've read that could possibly explain this is that the lower gearing of 4x4 Low lowers the torque requirements on the transmission. Does this seem like a valid explanation?

Note that I never experienced an instant loss of Reverse or a loud "bang" that others describe when the band ears break off. One alternative explanation to a worn or broken band that would possibly explain why Reverse worked so well for years in 4x4 Low and not in 2WD is worn gears in the transfer case.

Another possible cause seems to be a broken sprag one-way clutch. Does this seem likely?

Last but not least, the symptoms described here on the forums in a related thread exactly match those of my Explorer. The problem in that case turned out to be the Manual Lever Position Sensor (MLPS) which was failing to properly boost the line pressure in reverse.

Summary
The transmission shifts beautifully under normal 2WD driving, including hard acceleration and heavy load (trailering). The only problem is Reverse.

The only Check Engine Light which is relevant is P0720 — Output Speed Sensor Insufficient Input. It sounds like this error can be triggered when the PCM detects an out-of-range relationship between engine RPM and transmission output rotational speed.

I'm trying to nail down whether I'm looking a worn clutches / bands requiring expensive repairs, or whether it's possible this issue is related to the transfer case or simply a bad sensor like the MLPS which may be a much simpler and less expensive repair. Any and all input as to underlying cause or further tests which I can perform to narrow the list of possible causes would be appreciated.
 


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MotorCityFats13

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I had a 5r55 in my 2nd gen that broke the ear off of the reverse band and lost reverse and because this band is in the tail of the trans just to replace the band the whole thing needs to be torn down making it pretty normal to do a full rebuild you could look into a band adjustment or if the solenoid is bad but with how reverse is not an often abused gear i would rule out clutch pack wear or solenoid bore wear
 




boominXplorer

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^^^^ Broken reverse band
 




The Swamp Fox

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I had a 5r55 in my 2nd gen that broke the ear off of the reverse band and lost reverse and because this band is in the tail of the trans just to replace the band the whole thing needs to be torn down making it pretty normal to do a full rebuild you could look into a band adjustment or if the solenoid is bad but with how reverse is not an often abused gear i would rule out clutch pack wear or solenoid bore wear
Thanks a ton for weighing in. What you're saying corroborates much of what I've read regarding the location of the reverse band basically requiring a full rebuild if that is the problem. And I appreciate the thoughts regarding clutch pack and solenoid bore wear being unlikely culprits.

What were the symptoms on your 2nd Gen that broke the ear off of the reverse band? Did you lose reverse entirely, or just encounter a lot of slippage in reverse? And did your problems in reverse develop slowly over time, or happen all at once overnight?
 




The Swamp Fox

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^^^^ Broken reverse band
Well, the consensus thus far regarding a broken band isn't great news... :(

Would a broken band only cause slipping, or would it completely kill a given gear? And how does the 4x4 Low experience of eliminating the slip (for years, at least) play into the equation if the gear has been broken for some time? As mentioned, I know very little about transmissions, but am trying to understand cause-and-effect logic since the stakes in this case are rather high for me.
 




boominXplorer

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The band cannot tighten on the drum to fully engage the gear, the anchor is broken. It's still in there so it does something when you put it in reverse but will not "grab and hold tight".

4x4 low gives you gear reduction and ease of movement at low rpm. If you hit the gas in 4lo I bet it will also slip but will do more than in just 2wd because of the gear reduction.

Btw the reverse band is the same from like 91-2010 n the v6 transmissions.
 




The Swamp Fox

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The band cannot tighten on the drum to fully engage the gear, the anchor is broken. It's still in there so it does something when you put it in reverse but will not "grab and hold tight".

4x4 low gives you gear reduction and ease of movement at low rpm. If you hit the gas in 4lo I bet it will also slip but will do more than in just 2wd because of the gear reduction.

Btw the reverse band is the same from like 91-2010 n the v6 transmissions.
Thanks a mil for the explanation! I was picturing a broken band no longer forming a circle, and was thus confused how my symptoms of still having *some* reverse could align with such a diagnosis. But if I'm following you correctly, you're saying the "ears" on the band are what form the anchor point that enables the tightening on the drum — so the anchor is sheared / broken, you have no tightening at all.

Your comment explaining how the gear reduction in 4x4 Low would reduce strain / torque requirements on the tranny makes sense and confirms a hypothesis to that effect that I had read elsewhere.

Appreciate the tip regarding reverse band compatibility across models as well. How involved is pulling the transmission, whether for a rebuild or just to swap in a different unit?
 




boominXplorer

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Unfortunately pulling the transmission is the easy part. The entire transmission has to be broken down to get to the band. If you have been driving like this for years I'd suggest a full rebuild as clutch material will be throughout the transmission.
 




MotorCityFats13

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my personal solution that I did for 3 years before I finally junked my 2nd gen was to always pull into a parking spot that I could pull straight out and when needed i had to push the truck backwards I had to be extra cautious in winter that I didnt get it stuck in a way that would require rocking it in reverse.... by the end the trans was reaching 200f on normal drives and 1st was starting to slip and then the engine started pouring out coolant from somewhere in the back of the block and didnt care to find out what let go
 




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