Good day FTE. Posting over here for the first time, long time poster on PSN. Veteran 6.0 owner and amateur mech. I've rebuilt 6.0 and 5R110s over the past few years. Happy to help where I can.
Conversation for Mark and other trans gurus... In tow/haul specifically, why is the downshift sequence from o/d and converter locked, then it's first move when pulling a grade (power on) when additional thrust required is to release the converter and hold the o/d, instead of releasing the o/d and applying the direct and holding on to the converter? Basic terms for anyone else. The stock tuning goes 6/locked---6/unlocked---5/unlocked. If you're power off (coastdown), it goes 6/locked---5/locked, which I like better. The question is why the different sequence power on and power off? Is it for shock loading of the trans under power, or was this for drivability/comfort? Personnally, when my 05 pulls a grade and goes from 6/locked to 6/unlocked, the RPMs go to about 3k and slips the converter up to about 8-900 RPM for quite a while until it slows down to the point where it will apply the direct, 5/unlocked. During that time I see very high MGP and the VGT locks at 15 in an effort to slow down the turbine. If I can trick the truck initially into going into 5/unlock and then let off a bit above 54 mph to allow converter lock and pull the grades in 5/lock, the truck digs in much nicer and pulls with much less screaming with the MGP and vgts at a reasonable level. So again question is, is it a shock-loading or other mechanical issue as to why the PCM/TCM decides to unlock first before a downshift while under power, and would Mark and others approve of a tune that swapped that sequence under load? Truck sure pulls grades nicer with 5/locked than 6/unlock.

 

It is for driveability. I proved that unlocking the converter in 6th would almost always result in less torque to the wheels than 5th locked. This all but guaranteed that after the unlock there was going to be a downshift. But higher ups prevailed and we stuck with what you have. They felt people would think it was too aggressive to go right to 5th locked.

I sure preferred the 5th locked to 6th unlocked. It will not hurt the trans in any way to do that.

 

Thanks Mark. Additionally, I misspoke in my initial post in regards to the coast down sequence. My converter stays locked only because it’s tuned to hold it locked at closed throttle down to 45mph. If original tuning, the converter will unlock at CT, my mistake.

 

In addition to driveability, was any of the rationale for the 6/lock to 6/unlock sequence due to a concern with holding power of the converter? Was the converter verified to withstand lockup at max gcwr and high load % without slipping? After a lot of trial and error, I’ve created a tune file in T/H mode that sequences the power-on downshift from 6/lock to 5/lock, and boy does it tow up the grades so much better. MGP is in check and the vgt no longer goes full open to slow the turbine. I know there’s some that believe that holding the converter locked through a shift is bad news, and perhaps for a synchronous shift like the 3-5/5-3 and 2-3/3-2 that would be true, but the 6-5/5-6 is non-synchronous and is simply the apply/release of the OD clutch, one that I feel is not really a hazard to hold the converter.

 

No, it was purely subjective opinion.
Yes, it was.