2005 Explorer 5R55S Loss of 2nd Gear

[jmpreiks]

Hi,
I have 2005 Explorer XLT 4.0 4WD with a 5R55S transmission that just lost 2nd gear and presumably 5th but haven't tested at that high speed. I am hoping you guys might be able to help me diagnose the issue. It has around 150k miles on it.

Background and Symptoms:

1. My wife was driving one day and said it wouldn't let her drive faster than ~20mph or so (all of a sudden). It was flashing the O/D Off light and she said it said to service the transmission on the display. It hasn't flashed the light or message in my subsequent test drives. The only transmission issues prior to that were some harsh shifts into reverse, and my wife says there might have been a few delayed shifts recently but can't really remember.
2. There is only one code I could read, P0775, which the service manual says is "PCB solenoid or circuit fault --- PCB functional fault — low pressure --- Incorrect shift pattern indicating mechanical or hydraulic failure of the transmission. Will turn on MIL." The MIL is NOT on.
3. Torque Lite said that it was a "pending fault" and not a "logged fault", though I don't know what that means.
4. I did some driving tests and manual 1st and 3rd work perfectly fine. D gets to around 20mph and falls flat when trying to shift to 2nd and then returns to 1st and keeps going in that cycle. Shifting to 2nd while driving results in really slowing down and heading toward what feels like a stall before I shift back to 3 or 1. Starting from stop in 2nd feels like the brakes are on and the car does not move.
5. I bought a pressure gauge and did a line pressure test at idle and close to WOT:
   1. IDLE (psi)
      
      1. N: Service Manual Range: 90-120; Measured: 120-150
      2. R: Service Manual Range: 100-140; Measured: 240-270
      3. D, 3, 2, 1: Service Manual Range: 90-110; Measured: 170-180
   2. WOT (psi)
      1. R: Service Manual Range: 282-380; Measured: 360
      2. D, 3, 2, 1: Service Manual Range: 228-263; Measured: ~270, lots of needle bouncing
   3. Pressure drops to around 60-90 psi while shifting.
6. The line pressures at idle are significantly higher than the service manual specs. Is that a concern or a clue? I have not checked the PC C pressures yet, but I'll try that tomorrow night, hopefully.

I am aware of the servo bore issue that plague these transmissions, but since this was all of a sudden I'm thinking that is not the issue here. But let me know if you think otherwise.

Any guidance on this would be GREATLY appreciated, my wife is due with our 3rd child in 2 weeks and we really need this car back in action. I am really hoping to not remove the tranny to fix it, but think I can pull that off if I really have to. I think any internal repairs are out of my league right now given I have a short time frame and basic tools.

The service manual says to do some diagnostic "Trans-Bench Mode" where you can send control signals and measure the results to help diagnose, but I don't have access to a tool that can do that. What electronics can I test with just home tools (i.e. a multimeter)?

Thanks in advance for any guidance or tips!
Justin

 

[JK080]

2nd and 5th gears are applied using the overdrive band, the band is controlled by the overdrive servo piston. Either the servo is broken and you might be able to fix it by replacing the servo or the overdrive band is broken and would require the transmission to be rebuilt.

Use the adjuster for the overdrive band to determine if the band is broken by seeing how many turns in the adjuster will go before it gets tight. More than three turns in the band is most likely broken, if it tightens down less than three turns back out two turns and remove the overdrive servo.

 

[jmpreiks]

Thanks for the help. Tonight I managed to back off the lock nut on the adjuster after much frustration and then tighten down the overdrive band. It seemed to tighten up just fine, though I only had a tiny wrench that fit the adjuster so I could not apply very much force. I guess this means that it is pretty unlikely that the band is broken (thankfully)?

Just to be sure I also measured the resistance on all the solenoids from the PCM connector and they were all right in the middle of the desired range.

So does this 100% narrow it down to the overdrive servo piston? Or are there still other things I need to worry about and check? Nothing in the valve body could be the culprit?

Now I just need to figure out how to remove the servo piston in that confined space. I have read the snap ring might need a modified set of pliers and some way to compress the piston spring?

Thanks again!
Justin

 

[JK080]

It is possible to have a valve body problem causing this but it is unlikely just based on my experience with this issue with this transmission.

You could drop the pan and remove the valve body and air check the servo, you should be able to tell if the band is being applied during the air check. If it does apply then you could remove the plate and check the valve trains in the valve body, I can help you identify whats what if you get to this point. If the servo wont apply the band then that would be a pretty good indication that the servo has failed.

This is a overdrive servo piston failure we had not so long ago

 

[jmpreiks]

So after several hours of cursing to myself I finally got out the O/D servo piston... and it looks fine to me. See the photos below. When I push the back end of a drill bit in the bore I can feel something that feels like a pretty light spring that I can bottom out. I assume that is the connection to the O/D band. Should it be stiffer to push on? It does gently spring back at me (the adjuster is 2 turns looser than normal to aid in removal/installation).

What's next?? I'm getting a bit frustrated and my wife is about to lose it LOL.

 

[JK080]

Were you able to air check it before removing the servo?

The servo looks good and if you are able to feel the band through the servo bore I would reinstall the servo air check the band adjustment and air check it. You should be able to tell that it is functioning correctly, use the other one for comparison. If it air checks then look in the valve body.

Air check at the 4th gear location it applies the overdrive servo.

 

[jmpreiks]

I did not do the air check yet since I didn't want to drop the pan if I didn't have to. Don't I need a special test plate to do the air test?

P.S. This is what the ATF looks like. It is 2.5 years old, does it look too dark for that age?

Thanks again

 

[jmpreiks]

So it looks like I can stop troubleshooting... I took the valve body off and a bunch of metal bits fell out. Thanks for your help but it looks like this one is screwed.

 

[JK080]

Yep its got bigger problems.