Torque converter lock-up continually disengages

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Roger Teague

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2008, V8, Sport Trac, 114k, 2-wheel drive. The transmission torque converter lock-up continually disengages and immediately reengages. This only occurs at very low throttle and between 30 and 50mph and about 3 times in a 10 second period. After reaching approx. 50mhp the transmission functions normally.

The filter and fluid have been changed. This greatly helped the shifting. It shifts very smooth. Now the disengagement of the torque converter can only be slightly felt. However, by watching the tachometer an increase of a couple of hundred rpm can still be seen, so it is still happening.

This continual disengagement and engagement of the lock-up clutch can't be healthy for the transmission. Anyone have any experience or ideas

 
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When Im @ 42mph. The slightest push or lift of the accelerator. Mine will go in and out of lock up. If Im @ 40-41mph it stays out of lockup. Or @ 43mph and above it take a good push on the throttle to unlock. Mine is the 5speed auto.



What speed did yours use to steady stabilize at? To my understanding 42mph is fords sweet spot of the program,for most of their automatics lockup. That is what trans folks have told me.
 
Verify your transmission fluid level is correct. Your transmission has a "hidden" dipstick. Take your Trac to dealership for transmission program check/update.
 
Is this the "hidden" dipstick Vic?

Video: 6R60 & 6R80 Fluid Level Fill & Adjustment



I agree. Take to dealer for TCM/PCM update. From what I understand there have been many for the Gen2 ST's. There should be a sticker on the PCM with a code on it (4 digit maybe?) if it has ever been updated. If there is a sticker, call the dealer with the code to verify if you have the latest update. Also, from what I understand. Disconnecting the battery in Gen2's will not reset the TCM/PCM (KAM)for a re-learn.
 
Just found this video: How To Clear your PCM'S Memory on a Ford after Repairs

I may try this on my Father's '07 ST:) His transmission is always a little "quirky"
 
Here is info on the PCM Software Revision sticker.

I never did take my Father's in to update though. Shame on me. I definitely should have after replacing his cracked radiator this summer.

Update should be an hour of shop time.

 
Maybe a little off topic. But, my Father's '07 has this kind of "dipstick". I assume it's 6R60? not sure. But, this is how I checked his level after a local shop dip his pan drop and filter. (it was over-filled btw)
 
Are you sure everything feels fine when you are going faster because the converter isn't locking up at all?



The ONLY thing that can be done is to have this diagnosed ASAP. It Will need a factory scan tool to be diagnosed properly. One needs to look and see if the TCC (torque converter clutch) is being commanded on and off or not. If it is being commanded to kick in and out then you need to find out why. If it is not being commanded on and off then 1 of 4 things is happening.



1) Bad wire between the pcm and TCC solenoid

2) Bad TCC solenoid

3) Faulty PCM

4) Trans needs to be overhauled



It could also have a bad torque converter but if it does and with that amount of miles it falls into caergory #4.
 
l1tech- I agree with your logic. If the computer is not telling the TCC solenoid to open and close, then the trans has major problems or a loose connection.

A little more info. on the problem. When manually operating in 5th gear, the engaging and disengaging still happens, but lower speeds. I have noticed it stops at about the same engine rpm in both 5th and 6th gear (1500rmp).

1.Could there be a issue with hyd. pressure in the transmission? I assume the operating oil pressure increases with engine rpm.

2.Could there be excessive oil leakage in the torque converter lock-up device when it is engaged, causing a drop in pressure which then disengages the lock-up. When disengaged, the pressure increases and the cycle starts again. I know from trouble shooting hyd. oil systems at work, the amount of oil leakage can change when the piston or device operates.

3.Could the TCC solenoid not be opening fully, restricting the oil flow the the lock-up device? This could also cause low oil pressure to the lock-up device.



I have a mechanical background and a auto transmission is the only part of a car that I have not rebuilt, so my knowledge is limited. I have an appointment with a Ford dealer next week, but I hate to pay a dealer to do anything. If you have any other ideas, it would be apprehended.
 
l1teck- I did not answer the 1st part of your reply.

After about 50mph, the lockup stays engaged (the rpms stay steady when slightly modulating the throttle) until enough throttle is applied to cause the computer to un-lock it and change gears. After about 50mph the trans operates normally.
 
When I check for TCC lockup while driving I go about 60 mph on flat gorund at a steady cruise, next while keeping steady pressure on the accelerator I push the brake pedal just enough to turn on the brake lights but not slow down the vehicle, you should be able to see the rpms drop about 200-300 rpm. If you acclerate slowly you may force a downshift that is misinterpreted as the TCC unlocking.



Everything you have listed could be causing the unlocking.



Pressure does not increase or decrease with engine rpm...kind of, it is controlled by a pressure solenoid but will change with engine rpm to a certain extent.



If you did have a system pressure problem I would expect that there would be other shift concerns other than lockup.
 
l1Tech - After keeping the truck overnight, and conferring with "Ford Engineers", the dealer tech thinks the lock-up device needs to be replaced. They think it is slipping. He spent a full day checking the electronics and all of the switches and sensors and could not find a problem. This means replacing the hole torque converter.



The problem is getting worse. Now it will sometimes disengages above 60mph and sometimes there is a vibration when it engages. I told them to order a new converter. It will be installed this week. I will let you know if this corrects the problem.
 
After looking I see there are several trans software updates however without actually being plugged into your vehicle I can't tell you if you have any of the updates. It might be worth a shot to check first though.
 

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