Torque converter unlocking
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Mountain Pass
Joined: Mar 2018
Posts: 176
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From: Syracuse NY
Torque converter unlocking
Is it normal for the torque converter to lock, then unlock, only to lock back up again? All this happens when it is full throttle on flat roads. Also no bumps being hit because I know it can unlock when you are pushing it and you hit a bump to induce slip. It locks up mid third gear then unlocks at the top of third again. It will shift into fourth unlocked and lock back up when it runs out of rpms at the top of fourth. After it locks up in fourth it'll take longer than normal to shift into fifth. After it unlocks it'll stay above 3200rmp until it locks back up in fourth. Is all this functioning as designed? Seems like tranny slippage but hope not. I still have to check for codes on forscan as well.
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Mountain Pass
Joined: Mar 2018
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From: Syracuse NY
These are just observations from driving. My cts insight (not cts2) doesn't show tcl. I am assuming you'd be able to see commands through torque app as well? Yes under full throttle unloaded. I'll try it loaded (14k) next week as well and report back.
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Mountain Pass
Joined: Mar 2018
Posts: 176
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From: Syracuse NY
OK I looked to see if any codes where in forscan related to the transmission. None. Also towing there weren't any issues but I didn't beat on it loaded either because of of some loose cargo. I also did a trans reset/relearn with no change. But I am still getting the strange downshift into 3rd. Then unlocking the torque converter, shifting into 4th and 5th unlocked and finally relocking in 5th. This is happens consistently if I am doing 35mph and stomp on it. Anyone else's truck do this?
Senior User
Joined: Sep 2009
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OK I looked to see if any codes where in forscan related to the transmission. None. Also towing there weren't any issues but I didn't beat on it loaded either because of of some loose cargo. I also did a trans reset/relearn with no change. But I am still getting the strange downshift into 3rd. Then unlocking the torque converter, shifting into 4th and 5th unlocked and finally relocking in 5th. This is happens consistently if I am doing 35mph and stomp on it. Anyone else's truck do this?
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Mountain Pass
Joined: Mar 2018
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From: Syracuse NY
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Cargo Master
Joined: Dec 2003
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From: Saint Augustine, FL
OK. The OE shift strategy is to lock the converter after the shift to 3rd. It should always be locked in 4th, 5th and 6th. However, it might unlock at wide open throttle. I'll have to try that in my truck to see.
Its important to note that the converter clutch doesn't say locked on the upshift. The clutch cycles off/on during the upshift. If it didn't the shift would be a massive bang as the next gear is engaged. But that cycling of the TCC should be seamless.
It would be important to know of the ECU is commanding the TCC to do what you are observing. I suspect it is because you said there are no codes and a TCC slipping or failing to engage is certainly set one.
Its important to note that the converter clutch doesn't say locked on the upshift. The clutch cycles off/on during the upshift. If it didn't the shift would be a massive bang as the next gear is engaged. But that cycling of the TCC should be seamless.
It would be important to know of the ECU is commanding the TCC to do what you are observing. I suspect it is because you said there are no codes and a TCC slipping or failing to engage is certainly set one.
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Thread Starter
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Mountain Pass
Joined: Mar 2018
Posts: 176
Likes: 1
From: Syracuse NY
I am going to try it w/ 4wd engaged sometime too to see if it's a wheel slippage strategy that the trans has built in. I am on new snow tires too. I am making a run down to FL for Christmas and will put the a/t's on for the trip. I am not well versed in psd and torqshift but if the Allison in my previous denali slipped from hitting an expansion bump (wheel hop), under heavy power it would let go of the tcl in a heart beat, drop a gear and relock. Is there a way to check in forscan gauges for commanded tcl and status?
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Mountain Pass
Joined: Mar 2018
Posts: 176
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From: Syracuse NY
OK so the torque converter unlocking is totally a traction control strategy. I don't know if it's a function of ambient Temps or the tall lugs on the new snow tires that are causing the traction control/converter unlocking but, I held the traction control button until advanctrac off and it locked up real fast (3rd) and stayed locked all the way up through 5th. OK now I can stop beating the **** out of my truck to see if a CEL gets tripped by a possible slipping trans.
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