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I recently bought a 2001 F-150. The first time I checked the transmission fluid level, it looked like it was overfilled but the filler tube mount had rusted off and I figured it wasn't accurate.

Last week I bought a new transmission filler tube from a dealer and installed it. When I took off the old filler tube, lots of transmission fluid spilled. I held the old tube against the new tube and they seemed to be the same size and length. I added a quart of transmission fluid and the dipstick seemed to indicate that it was filled. The transmission would still slip when I went up hills so I added another 1/2 pint (once or twice) until it stopped slipping. The dipstick is now in the DO NOT ADD range, but it was also in that range when there wasn't enough fluid in there to function correctly so I just don't trust it. I'm still worried that although there seems to be enough that the transmission is working, that there isn't enough in it yet. I don't want to overfill it either...

The way I check the fluid level is as described in the owners manual.

  1. Warm the transmission fluid by driving 10-20 minutes
  2. Park on a level surface (my garage)
  3. Set the parking brake
  4. Shift through each gear, pausing long enough to allow the gear to engage.
  5. Clean off the dip stick.
  6. Reinsert the dipstick fully
  7. Remove the dipstick and read the level

I have the Ford service manual for this vehicle. According to the Ford workshop manual and my certification label, the transmission is a AODE 4R70W (tr code U). This model is also sometimes outfitted with 4R100.

Here's my dipstick (not representative of the level, just illustrative):

enter image description here enter image description here

The Dipstick part number is XL3P-7A020-CA

Youtube videos referencing the 4R70W seem to have a similar dipstick but one thing that worried me is that the dipstick looks more like the illustration in the workshop manual in the 4R100 section than the one in the 4R70W section. The illustrations aren't great, but I'm just trying to figure out why the dipstick would read full and I'd still have slipping when I go up hills.

manual image for 4r70w dipstick: manual image for 4r70w dipstick manual image for 4R100 dipstick: manual image for 4R100 dipstick

I've thought about dropping the pan and draining the Torque converter but even the specifications say to use the level indicator to refill it.

general specifications

What should I do? Should I add an extra 1/2 pint to be safe? Do you think I have the correct dip stick? I could take a picture of the dipstick sticking out of the old filler tube to show how it indicates levels with respect to the filler tube hole on the transmission if that will help.

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    Its ok to overfill 1qt on adoe transmissions. – Moab May 3 '18 at 19:10
  • You've done a lot of good work here. Slipping is likely from another cause? Other possibilities apart from over or underfilling. – geoO Oct 1 '18 at 16:11
  • I ended up adding another quart of fluid and that fixed it. My guess is the slipping was happening in the torque converter. – Jon Oct 2 '18 at 19:55
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One way to know for sure you have the correct amount is to completely drain the transmission and torque converter (and change the filter), then add the correct amount the manual calls for. But that may not be practical at this time.

One thing you said that worries me is "The transmission would still slip when I went up hills". This may or may not be related to the extra trans fluid. Too much trans fluid can cause foaming and pressure issues. It is also an indicator of other things may be wrong.

My advice to you is to find out exactly which transmission you have, and verify you have the correct dip stick and tube. If both of those are correct, then your next step is to change the fluid and filter. After that, it is time to take it in for a service.

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