Hi All,

I'm a longtime lurker (student) of this forum and I'm hoping someone can help me out a bit.... I know there's a wealth of intelligence and experience that's shared here.

THE TRUCK:
1975 F-250 4x4 Crew-Cab Cummins Conversion

THE DRIVETRAIN:
’95 12 valve motor
’95 47RH 2wd transmission (TCC & OD controlled w/ switches on steering wheel)
Original Ford NP205 divorced transfer case (relocated approx. 12” rearward)

THE PROBLEM:
Overdrive (OD) engages normally, but at times will not disengage when the OD control switch is shut off. The overdrive WILL disengage when the truck is shifted to neutral and back to drive again. I *think* the overdrive piston must be receiving hydraulic pressure when it is not supposed to (or not releasing pressure when it should). I also *think* that mechanically (clutches and gear set), the OD unit is OK.

The transmission shifts normally through 1-2-3 and the TCC engages/disengages normally. The OD control switch, OD solenoid, connections and wiring check out OK. The valve body has been swapped out with a known good part. There are no external fluid leaks and the fluid and pan are clean.

I suspect that an unaddressed shudder in the driveline when accelerating from a stop may have damaged something in the transmission. I have since found and corrected the source of the driveline shudder (loose transfer case mounts). I’m kicking myself for driving the truck around with the driveline vibes if it caused some damage to my transmission.

Are there any tranny gurus out there that can point me in the right direction? I plan to pull the OD unit off and closely inspect the OD piston and retainer this weekend. I’ve got the ATSG manual for the 47RH, but my firsthand experience with this tranny is limited.

Thanks,

Jeff

 

can u lock up the converter in every gear?

 

You have a 95 in it and that has a TPS. Known to get flakey and cause shift problems. Do a search here and read up on TPS. Several trouble shoot discussions are in the archive. You can also just delete the TPS with a linear rheostat that can be picked up cheap. No more TPS probs.

 

He doesent have a TPS because it is on manual switches.

If im not mistaken, the signal wire for overdrive uses a ground to make it come in, just like TCC lockup, correct?

If that is the case, I would look really hard at the wire that you have and make sure it isnt worn through somewhere and still making a partial ground or something similar. It sounds to me like it should just be a wiring problem of some sort. I would definately inspect that before going on with pulling the tailhousing off.

Let us know if you have any luck with it.

Eric

 

Missed that. Sounds like you may be on track with a wire problem. Bad switch??

 

Thanks for the the input guys. I ended up pulling the tranny and tearing it down for a once over. I'd never had a 47rh/re apart before; it's surprisingly easy to tear down with hand tools, a pry bar and snap ring pliers! I found a small screen missing from the bottom passage on the OD piston retainer. I don't know if the builder knocked it out intentionally as part of the rebuild or if it became dislodged and stuck somewhere in the valve body.

I installed a new OD piston retainer and replaced the valve body yet again. The tranny is back up and running fine now. I can't say for sure which component I changed out was causing the problem, but it's sure nice to have a trans that does what you tell it to again!

Jeff

 

Thanks for letting us know what you found.