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spowel4

2001 4R70W slips in first gear but not in manual first

Question

Like the title says, I have a 2001 Expedition, 2WD, 4.6L engine, with a 4R70W. When in Drive, the tranny slips when starting out from a dead stop. However if I put it into manual first gear, no slippage. Any suggestions on what might be going on?

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In Drive 1 only the FORWARD clutch is applied. In manual 1, the LOW/REVERSE band is applied as well as the FORWARD clutch, but all it does is make it so the OWC can't free wheel on coast. There are several potential causes.

 

1. EPC solenoid is getting lazy and not following the increase in throttle pressure.

2. Forward clutch circuit is failing or clutch itself is.

3. Bolt backout in the valve body.

4. Several potential internal valve body issues.

 

That being said, are you 100% sure the PCM is commanding and achieving first gear and not actually in a higher gear? Any codes? IS the T/R sensor adjusted right and operating properly? Does it make all 3 shifts and lockup the converter? For example, if SSA is stuck off, you wont get first or fourth. If SSB is stuck on you won't have first or 2nd. Starting in a higher gear can seem like its slipping.

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