4R100 Piggyback
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More Turbo
Joined: Apr 2008
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From: North East Arkansas.
4R100 Piggyback
I recently rebuilt my 4R100 transmission in my 1999.5 F250 7.3 Powerstroke. It had developed a front seal leak and I decided to repair it myself. But with 333,000 miles if I pull it, I was going all the way. So I ordered a master rebuild kit with the Transgo shift kit from Transmissionbench.com. It had a PWM solenoid pack (f81Z-7G391-CB) and I installed a conversion kit to make it an on/off lock-up This was accomplished with a kit from SHIFT Technology Products which called for a non-PWM solenoid pack (F81Z-7G391-BA). I did not rebuild the cooler bypass. Okay. This truck now shifts through the gears like a well tuned machine. You can tell exactly every gear including when the torque convertor locks-up. But then there is 4th gear. When shifting both in and out of fourth gear, I'm getting an RPM flare. I know mechanically that the transmission is sound. I have no doubts there. I'm not sure electronically, or about fluidly. I have so ideas, but need some input.
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Joined: Sep 2006
Posts: 258
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From: NorCal
That is interesting AJ. I'm sorry to hear 4th is performing like you want it to. I went the all Transgo route to convert TC lockup from PWM to on/off. With the Transgo install, you keep your PWM solenoid pack and only replace the valve in the pump. I'm not sure how it performs yet but hopefully will soon. Another thing could be how large a hole did you make in the Transgo tugger calibration plate for 4th? Maybe you just need to make it a little larger to firm up the shift? I hope you get to the bottom of this soon.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,722
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From: SE Florida
I think the problem may be that your PCM is a modulated lockup, not an on/off. During the 3-4 shift the PCM is trying to control the slip across the torque converter clutch, but it can't because of the modifications to make it an on/off. The control system is probably causing the solenoid to allow the converter to unlock, which will cause an RPM flare.
Why did you want to convert it to on/off? The only reason I can come up with to do this is to install a later PWM transmission in a truck with an on/off control system.
Why did you want to convert it to on/off? The only reason I can come up with to do this is to install a later PWM transmission in a truck with an on/off control system.
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More Turbo
Joined: Apr 2008
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From: North East Arkansas.
I think the problem may be that your PCM is a modulated lockup, not an on/off. During the 3-4 shift the PCM is trying to control the slip across the torque converter clutch, but it can't because of the modifications to make it an on/off. The control system is probably causing the solenoid to allow the converter to unlock, which will cause an RPM flare.
Why did you want to convert it to on/off? The only reason I can come up with to do this is to install a later PWM transmission in a truck with an on/off control system.
Why did you want to convert it to on/off? The only reason I can come up with to do this is to install a later PWM transmission in a truck with an on/off control system.
I'll go back to PWM. I'm not interested in changing out the PCM. I'll buy a new F81Z-7G391-CB solenoid pack, double check all my paperwork, and get this thing right. Thanks Mark. I'll let you guys know how it comes out. These 4R100's are amazing machines.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,722
Likes: 2,648
From: SE Florida
Don't argue with me on the actual transfer of percent on/off to actual clutch capacity. That was an example to explain how it works, not actual numbers, which I don't have.
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More Turbo
Joined: Apr 2008
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From: North East Arkansas.
To Mark. So just like there is a difference in the solenoid packs, there is a difference in the PCM which controls them. My original PWM solenoid pack would not shift through the lowers gears like it should. Its seemed to want to skip the third gear. Maybe it was a tired torque converter. All the ohmic values checked out on the original solenoid. Perhaps that value changes as things heat up to running temperature and one of the solenoids is bad. I'll pull the pan install the original solenoid pack (PWM) and try it again. If that doesn't do it. I'll buy a new PWM. I don't like kicking around a dead duck, but I'm not quitting until this thing shifts like it did 18 years ago.
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Joined: Apr 2008
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From: North East Arkansas.
Ok. That make sense too. If this is the case, I will have to do something about it. (Skipping third?) It would dump somewhere around 1000 RPM's when making this transition. Then the engine would have to pick up the difference. It was embarrassing. I'll pick this back up in about two weeks. I've got an all expense paid trip to Hawaii. Leaving out Saturday.
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Joined: Apr 2008
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From: North East Arkansas.
I appreciate that for sure. This thing shifts so well, I dumped all programs and running everything in stock. One day I would like to completely rebuild the engine.
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