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P0756 and P0761 no OD

LouieD

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First and foremost I'd like to thank Glacier991 and BrooklynBay as well as others in helping me get as far as I have with this issue. It may be time to dig into the VB, but I wanted to make sure I hadn't missed anything before doing so.

Vehicle: 1996 Explorer 4.0 4wd 225k. Trans appears to be untouched, short of fluid changes. Pan was externally clean.
CEL on: P0761
OD indicator light: not flashing, but functioning.
Trans shifted very well, but would slip into neutral during deceleration. Would not engage OD during test drive.

OD fuse#26: OK

Fluid was not dark, did not smell burned. No trans leaks, fluid level correct.

Internal harness missing insulation at every connector. Exposed wires throughout.

All solenoids OHM tested ok.

Replaced internal harness with Ford part. Replaced filter, cleaned pan, added drain plug and refilled.

OD band out of adjustment. Took care of that as well. Could not get to the intermediate band. (Someone put a selector switch in the way :rolleyes:)

Test drove: same issue.

Tested harness: Unplugged main (104) harness at PCM and tested for resistance. All solenoids tested withing spec through harness leading me to believe no broken wires or bent pins at main harness to trans harness.

Tapped into main harness and attached DVOM to make sure PCM was sending 12v signal to SSC. Began test drive and noticed CEL turned off. No stored code or pending on scan tool, but I had not cleared it. Huh?
Continued with test drive and voltage registered when PCM sent signal to solenoid C. Surprised to see 14.5v, I thought it would be regulated to something less.

Continued with test drive. New pending code pops up on scan tool: P0756, quickly becomes stored code, check engine light pops on. Trans slips into "Limp" mode and I struggle to get home in 2nd.

I assume that the deteriorated internal harness was responsible for solenoid C not actuating, and now that it is getting a signal, moving fluid has dislodged crud and this is now causing compound problems. Regardless of cause now I have two problems and even worse performance than when I started.

I have read that these codes typically point to electrical issues, but at this point I'm thinking VB. what say ye 'o wizards? I don't know much about transmissions so I need a bit of guidance here. Have I exhausted all possibilities? Should I delve into the valve body?

Thanks in advance for your time and help on this.
 



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LouieD

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Well I pulled the VB out hoping to find a blown out gasket or something that would lead me to believe the VB is the culprit, but nothing. I did find that the spring has already been removed from the rear servo, so someone has been in here before I got to it. I have an updated VB with bonded gaskets + solenoids coming. I hope this will take care of these issues.

Side note: So much nicer to drain the fluid before dropping the pan. Drain plug FTW.
 






LouieD

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Installed the reman valve body today and initially got the 2-3 flare (which the trans had not previously demonstrated) but after a few miles it went away. I still do not have OD :mad: with the exception that if I'm cruising at 45mph and I turn off the OD the RPM's increase about 300rpm, but no effect above those speeds. It still will not engage 2nd or 1st during decel, even if manually selected.

What am I missing? Anyone have any suggestions?
 






truckerb1

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what happens if you shift manually during acceleration,can you feel each gear?
 






truckerb1

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what happens if you manually select gears
 






BrooklynBay

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Try to adjust the intermediate band even though the shift selector/range sensor is there. You could remove this part, but remember to make a mark on this part, and the case to ensure its alignment. There is no spring on the low/reverse servo on this transmission.
 






LouieD

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what happens if you shift manually during acceleration,can you feel each gear?
Yeah, shifting up, no problems.

what happens if you manually select gears
No engine braking. The moment I let go of the throttle RPM's drop to just over 1k and shifting from D to 2nd or 1st has no effect at all.
 






LouieD

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Try to adjust the intermediate band even though the shift selector/range sensor is there. You could remove this part, but remember to make a mark on this part, and the case to ensure its alignment. There is no spring on the low/reverse servo on this transmission.

Ok on the spring. I will adjust the intermediate band and hope for the best.
 












truckerb1

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Follow BB's advice on adjusting the intermediate band, but you could also be having trouble with the torque converter itself, or possibly a fracture in the od planetary
 






LouieD

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LouieD

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The VB re-builder is sending out another valve body. I thought about the broken OD planetary, but then I would get nothing right? I can cancel the OD via the switch and it will kick up the RPMs, but it's only effective under or around 45mph. I will try the 2nd VB and adjust the intermediate band and see what happens.
 






LouieD

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Received the second VB from re-builder. This one looks much better than the first one. The previous one had clearly been installed as the separator plate gasket had been compressed. I adjusted the intermediate band and installed the 2nd VB. Sorry to report that although it shifts silky smooth I still have no OD.:(

I spoke with a local trans shop and he is confident that with all the steps I have taken, it's an internal mechanical problem. Band could be worn/broken/cracked or the OD drum or even the planetary could be at fault. He will pull trans Monday and inspect.

I will post results in hopes of helping others.
 






LouieD

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UPDATE

I stopped by the trans shop as the trans was being taken apart. The OD drum was toast as other associated parts. Long story short, it's back together and it shifts beautifully. IMO I spent a reasonable amount of $$ and according to the trans man the transmission has a long life ahead of it. Let's hope. Here's some pics of the carnage.

Well worn thrust washer
thrustwasher.jpg


my two piece OD drum :rolleyes: For those who don't know the part in the following pic should be welded to the part in the next pic.

inner
ODdrum4.jpg


outer
ODdrum2.jpg


ODdrum1.jpg


...and the planetary. I couldn't believe when Wally the trans guy showed me the new "un-grooved parts.
DSCF9309.jpg


So to recap; if everything electrical checks out when you get these codes, and your valve body is ok, don't be surprised to find this kind of damage.
 






BrooklynBay

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LouieD

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It's been a while now since the trans was repaired and I thought I would update the thread with a bit of knowledge I have recently gained. A week ago the trans started acting up again. No 2nd gear... would go from 1st to 3rd and of course flashing OD light would follow and subsequent CEL. Same shift solenoid code, but overdrive was working just fine. Well about a week later the battery went completely dead. So I popped in a new battery and as added bonus, no more trans problems.

My assumption is the solenoid were not getting a full voltage signal. This would make sense as I remember that when I was tracing down the original problem, I realized that the PCM sends out battery voltage to the solenoid(s). I remember measuring 14v during shifts. So even though the truck would start and run fine, when it came time to shift, there wasn't enough juice in the battery to make it happen. This was specific to 2nd gear. No other problems were noted.

Anyway I hope that this helps others... make sure you have properly functioning battery/charging system when tracking down shift solenoid problems.
 






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