4L60E tuning in $0D

[Roadknee]

I'm seeking insight into how the following tables under 4L60E line pressure parameters affect transmission operation in $0D:

Pressure ramp delay time vs tps vs shift (sec)
Extended ramping pressure time vs tps vs shift (sec)
Initial ramping pressure vs tps vs shift (psi/sec)
Ramping pressure vs tps vs shift (psi/sec)
Post shift ramp time vs tps vs shift (sec)

In the stock bin for my 1995 K1500, these tables are mostly unpopulated. There are some negative values (psi/sec) in the ramping pressure vs tps vs shift for the 1-2 shift. There is also a 0.5 second value in the corresponding cells in the pressure ramp delay time vs tps vs shift.

I assume these tables modify line pressure during the line pressure modulation time during an upshift, but don't understand exactly how they function. I'd appreciate any guidance.

[Roadknee]

I looked through several of the $0D bins. In general the V8 bins are similar and the 4.3 V6 bins are similar to one another. Unfortunately there was not a performance application that used $0D for me to try and learn from. I spent a little bit of time experimenting with the above tables, but not enough to draw any conclusions. More on that later.

I've made several changes to upshift/downshift mph vs tps vs gear tables and the TCC lock and unlock tables. I have it rev a little higher before upshift, downshift sooner, engage TCC later and disengage TCC sooner for a more performance oriented feel. Much of this is personal preference.

The biggest improvement was locking the TCC in third gear. With the stock BJYL tune, the trans upshifts to 4th at 29 mph under light throttle and never locks the TCC in third. The TC slips considerably when running around town at 35 mph in fourth gear. I delayed upshift to 4th under light throttle to 44 mph and engage TCC in third at 32 mph. It feels a lot better now and takes considerably less throttle running around town.

I also set the Lower Low Speed TPS and Upper Low Speed TPS to Prevent TCC Cycling to 0% to keep the TCC locked on deceleration at 0% TPS. As long as MPH is below the MPH for Using Low Speed TPS Thresholds the TCC will remain locked. I temporarily set the Low MPH to 84 and high MPH to 86 for a test. The TCC would remain locked on deceleration in fourth gear, and it behaves like a manual trans. In third gear, the TCC appears to remain locked, but the trans shifts to 4th at 0% TPS. It loses a little rpm on deceleration. As soon as I touch the throttle it returns to 3rd gear TCC locked rpm. If I pull the shift lever into third gear, it stays in third and the TCC stays locked on deceleration, and it behaves like a manual trans. I searched through the BIN, but couldn't find any way to keep the trans in 3rd gear during deceleration with the selector in fourth gear.

There are a second set of parameters, High Speed TPS to Prevent Repeated TCC Cycling. As long as these are populated with positive numbers, the TCC will disengage on deceleration when the actual vehicle speed is above the Upper and Lower MPH for Using Low Speed TPS thresholds. I set these to 46 and 44 mph, respectively. Thus, in 4th gear and above 46 mph, the TCC unlocks on deceleration. I didn't care for the feel with it locked in fourth during DFCO. It really slows the truck down.

[billygraves]

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[Roadknee]

I zero'd the negative numbers in the 1-2 ramping pressure tables. It was inconclusive whether it made any difference. So I turned to the 0-64 mph and 64-128 mph pressure tables. I compared these to the 1994 Cadillac V4P which is said to shift pretty well. My K1500 pressures were higher below 50% TPS and the V4P tables were higher 50% and above. I copied the V4P values 50% TPS and above into my K1500 tables. The top several rows in the V4P tables go to 90 psi where my K1500 pressures peak at 59 psi.

What a difference. The WOT 1-2 shift is firm. It doesn't bang; just a nice firm shift. The 2-3 shift actually hit a little too hard, so I reduced the pressures either side of 60 mph in the proximity of the WOT 2-3 shift to 78 psi. This made the 2-3 shift feel like the 1-2 shift. When datalogging, the WOT shift times are about 0.3 seconds, compared to 0.5 seconds with the stock K1500 tables. Downshifts feel a lot better too. Nothing hits hard; just feels like a daily driven performance trans should.

Earlier I modified the appropriate table to lock the TCC in third gear. One thing I did not like was the way it unlocked prior to the 3-4 shift. Prior to the shift it would unlock and the motor would rev up for several seconds, then shift with an rpm drop. Not a big deal; just kinda annoying. I unchecked a flag to unlock TSS during upshift. I was a bit nervous about this thinking the shift would bang with the TCC locked, but its fine. The 3-4 shift now feels similar to how the TCC locks in OD. One interesting observation about the code is that in order for the TCC to remain locked during upshift, the 4th gear TCC release speed must be less than the 3-4 upshift speed. If the 4th gear TCC release speed is higher than the 3-4 shift speed, the TCC will unlock prior to upshift.

I haven't had a chance to feel a 3-4 upshift with the TCC locked at higher speed (say 75 mph) and higher TPS. I'll have to see if it hits too hard. I did program the shift points to prevent 3-4 shifts above 50% TPS so I think it will be fine since the shift pressures are relatively low. Will report back if its an issue.

[billygraves]

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[Roadknee]

All I can tell you is Good Luck and if you cook a set of clutches, I hope you don't mind pulling it out to overhaul it. It usually gets expensive. If I had an L60 all I would change is the steady state pressure to increase it, increase the upshift pressures and really add some PTS to the TCC ON in 4th.
If you think the 10 pack of the 3-4 clutch is a good set up, you are mistaken. The clutch design was NOT THOUGHLY thought out. This is why GM ran test after test on all of these and did NOT change to them. They seem like a good idea but do not hold up with any HEAT. The clutches are very thin and will NOT tolerate HEAT and there is not enough capacity in the steels to carry the heat from the shift to the oil without going over the temp of the clutch material or bonding agents. I would use the OEM 7 cl 3-4 set up thickness. Never tow or run a L60 in 4th with TCC on at low Engine RPM. It will burn the 3-4 cl. Best of luck to ya.

Thanks for the feedback Billy. I post (1) to share my observations with others and (2) obtain feedback if something in my tuning methodology may cause issues. I won't even pretend to have a thorough understanding of the mechanics of the 4L60E. Thus, for the benefit of myself and others that may read this, could you please describe what specifically in my tune puts the 3-4 clutches at risk? Also, does my OEM 1995 trans have the 10-clutch 3-4 pack? Thanks.

[billygraves]

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