4R100 shifting oddly

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Mar 19, 2008 | 10:34 PM

ATXZJ

Thread Starter

Junior User

Joined: Feb 2006

Posts: 77

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From: SLC, UT

4R100 shifting oddly

For the last few weeks, my trans has been occasionally flaring about 100 RPM when shifting into OD. It only does it at light throttle, and one out of 20 times. When I hook the trailer to my truck or under 1/2 or more throttle, it's fine. Very strange. No CE or trans lights and my fluid/pan looked good when I did my valvebody Saturday.

I figured upping the pressure with the VB would help? I checked TSBs, and only 7.3s are reported to have this issue. Do you think this an electronic or mechanical issue?

Thanks in advance,
Marcus

1999 V10 F250, 4.56s, stock tires, 160k

Mar 20, 2008 | 01:19 PM

Mark Kovalsky

Frmr Ford Trans Engr

Joined: Aug 1999

Posts: 24,714

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From: SE Florida

It's a bit of both. There is a TSB that describes the changes that are needed to the valve body and a relfash to the PCM. Upping the pressure in the valve body isn't going to help.

The problem is in the calibration of the torque converter clutch. It is supposed to slip just a bit during the 3-4 shift, but it's disengaging completely and then relocking.

Mar 20, 2008 | 02:50 PM

BPofMD

FTE Legend

Joined: Jul 2005

Posts: 65,938

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From: Millersville, MD

Also, have you converted the old Mercon III over to Mercon V yet? If not, it's probably time to do so. The Mercon V is a synthetic and is a better product than is the III. Ford has been recommending the V instead of the III for some time now.

Mar 20, 2008 | 08:12 PM

ATXZJ

Thread Starter

Junior User

Joined: Feb 2006

Posts: 77

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From: SLC, UT

Quote:

Originally Posted by Mark Kovalsky

Well, that makes sense. That is exactly what it seems to be doing. Do you know the TSB# or what needs to be done to the VB? Do you think I can get a custom burned chip or tuner to control the lockup during shifts?

Thanks again. I was worried that the trans was going out since I've been pulling quite a bit of weight with it over the last year.

Marcus

BTW. I (up until recently) always ran motorcraft merconIII/dex and now run valvoline mercon/dex. I've heard horror stories about switching to synthetic or specialized fluid in high mileage trans and was terrified to do so.

Jul 25, 2008 | 07:38 AM

Stone Mathews

Senior User

Joined: Oct 2006

Posts: 215

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From: Allegheny Mountains, VA

Did you ever get the PCM reflashed? Did that fix the problem?

What TSB# was that? I'm trying to hunt down a disengaging/relocking TC myself (I think....I don't know crap about these things....)

Thanks,

Stone