4L80E & 2nd Gear TCC Lock

[JayTheCPA]

So the next thing is to determine what your stall speed is and guesstimate peak tq rpm.

My stall is likely OE, but for grins will find out later.

Get tranny to temp, then at a stop hold full break and throttle.

That was the method that I had previously known about as well.

 

[FellowTraveler]

I never heard the 2mph thing for stall. I see how that could work but you can't test a lot of vehicles that way, they just spin the wheels.

Get tranny to temp, then at a stop hold full break and throttle. The engine will go up to the stall speed and can not accelerate beyond because the brakes are stalling the rpm via the TC. Never do this for more than 30 seconds- it gets fluid temps up quick. Drive the vehicle afterwards easy for a few minutes to cool down the temps.

How about boost when doing power braking rev does it rise up to full boost or?

 

[3500_6.5]

More curious than anything, but what are you hauling behind you that has you drop all the way from overdrive with converter locked up speed to 2 (or 1st) gear by the time you make it up the hill? I live in Ohio where the mountains are few and far between (or maybe none at all.....) and we don't have miles and miles of steep grades, but we do have some hills. And they can be steep and relatively long (maybe a mile or two at most that I've been on with a trailer). With my current setup, at most my converter unlocks and I can stay at speed for as long as necessary. In stock form, the lowest I have ever dropped is 3rd gear. I did have my old duramax loaded down pretty good before and was in some steep and very curvy terrain before where I was forced to drive slower and tranny temps would get a little warm. But all it did to help fix that was lock the converter up earlier and longer in 3rd gear.

I currently have a 700 that has an issue with the converter locking up from the time the truck shifts into 2nd all the way into 4th. Unless you have a lot of torque, you won't like locking the converter up when your trying to pull a load up a hill. You'll lose all your power. This truck with the lock up problem can't even hardly pull itself down a level road with the converter locked up, let alone pull a trailer. This is a gas truck though, with an engine rated at 275hp and maybe 300 ft lbs torque?? (Lt1 out of a 93 z28).


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[FellowTraveler]

When towing anything past peak torque rpm is a waste as the tq quick drops off from there even though HP increases, then there is engine and transmission heat load increase which the cooling system must be able to control....

 

[3500_6.5]

When towing anything past peak torque rpm is a waste as the tq quick drops off from there even though HP increases, then there is engine and transmission heat load increase which the cooling system must be able to control....

That's not entirely true. But I get what you're saying.


I understand the heat concern. But I get the feeling that the idea is to make the automatic more like a manual. So you have a mechanical link between the engine and tranny so you aren't getting that dreaded power loss through the evil automatic. But if you are wanting to run lock up in all gears, you are going to have to be running higher than 2200 rpms otherwise you will continue to lose speed. You are trying to run a transmission that is geared higher like a manual that is geared lower. There is a reason that manuals generally have to be tached out higher than their automatic counterparts while also requiring lower gearing to do the same work as an automatic: they don't put down as much power. Period. There is a reason drag racers use automatics. There is a reason formula one switched to automatics. There is a reason that circle track switched to automatics. There is a reason why (other than dodge owners) you run automatics when pulling a sled (or at least you should). There is a reason semis are even trying to switch to automatics. It's because automatics put more power to the ground, are stronger, and all around better. I know, it goes against everything everyone hears, and I argue with people all the time about it. But it's true....

Now there is a time when you get more power from locking up the converter than you do slipping the torque converter, but I guarantee you that at 2200 rpm in second gear with the converter locked up, you are not putting down more power than at that same speed in second gear with the converter unlocked. Especially if you are running anything bigger than the stock turbo (I can't see your signature on Tapatalk).

If you are pulling something heavy enough that you lose enough speed to warrant dropping all the way to second gear and are still losing speed, you may want to invest in a newer more powerful diesel truck, or swap to a turbo that puts out more power at the 2200 rpms you are wanting to stay at. Or, if you are running a large turbo, tach that engine out!

I ran the ATT for a while and learned after pulling a few times , and with the help of some on here, that that low of rpms isn't going to cut it with that turbo when pulling any kind of weight. The engine needed to be tached out for it to work the way it was supposed to. After I learned that, it did much better. I didn't like that, so I adjusted accordingly. Now my truck cruises right along in the 2000rpm range and has plenty of power in that range to do everything I've needed it to do thus far.




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[WarWagon]

I don't think you would want to shift from 2nd-3rd with the TCC locked. The ECM unlocks during a shift, probably for a good reason.

The input shaft of the 4L80E is said to be a touch weak and prone to snapping when you shift with the TCC locked. Never broken one myself so I can't verify that are that weak per say.

Overall, excellent information and just makes me want to ditch the 4L80E even more


For clarity though . . .

Am *not* thinking about locking the TCC in 2'nd for daily driving.

Question *is* about locking the TCC in 2'nd while pulling hard.


Scenario:
> Pulling a trailer.
> Enter grade (5%+) at speed and apply power. Depending on the length of grade, I do not go WOT as the cooling stack is not going to dump the heat by the time I crest. If I hold the power according to EGT's, the motor will stay within desirable temps.
> Immediately drop to 3'rd with TCC locked.
> Speed decreases due to load even though applying power.
> Gears drop due to decrease in speed. Power remains heavy.
> TCC at some point in 2'nd unlocks do to further drop in speed.
> If necessary, drop to 1'st which is always TCC unlocked.

Currently (in the above scenario) I manually control the RPM's to keep them above 2,200 as the ECM will let them drop to about 1,650 (presuming a 3.73 rear and OE tires) before downshifting which is too low for my preferences. Seeing as I am not the only driver of the truck, I want the ECM to do a better job of managing gears while climbing so that others can simply drive it and not have to work it.

Toward the end result, am looking to have the ECM keep the RPM's above 2,200 in the above scenario for maximum cooling. Also want to keep the TCC locked as much as possible, but at some point I will have to just let it unlock if the load drops the RPM's too much in 2'nd. Naturally, 1'st will run unlocked.

And by the way, I picked +/- 2,200 RPM's as the downshift point (depending on gear) as it is a fairly good transition point to not over-rev on the lower gear.


In the end, if the TCC I have only has a service life of 50K from towing, then it is not likely that moving the shift behavior around (based on the scenario) is going to have much effect on that anyway seeing as it is either going to tow, or it is going to tow


In re-reading my original post, I was not clear enough, left out too much detail, and apologize. So, back to the original question . . .
Can 2'nd gear handle getting locked-in while pulling hard?
.

That changes the question bigtime. You are expending all this energy looking at the transmission control and TCC options to fit the above situation.

First off the 4l80E really isn't all that bad for what I did to it including mis-plumbed cooler that ran the fluid at 220 degrees. With a better TCC clutch and fluid changes every 25K miles I can't really complain. I have owned worse transmissions that only lasted a week towing...

To me it looks like you are lugging the engine on the grades. Even a 2008 Duramax with a massive 25" cooling fan will burn 350 degree sustained aftermarket oil cooler hoses clean off because the folks at GM decided to lug the engine in double overdrive (6th) on grades that do not require heavy to wide open throttle. This resulted in oil that went out of grade from heat stress, 2 sets of oil cooler hoses, low oil pressure stop engine alarms, heater hoses and a passenger side battery boiled dry from the extreme lugging heat and "normal" ECT of 235 degrees F. We took to manually shifting to 5th on these grades.

I assume your cooling system has been upgraded. You may need a faster reaction fan clutch or a low temp clutch. Anything under 210 is good and frankly ignore EGT. EGT will tell you when your turbo blanket is on fire or where the turbine wheel melts down... a 6.2 with uncoated pistons can sustain 1550 EGT. The Turbo blanket and paint under the passenger floor near the exhaust not so much.

I would suggest revving the engine before the grade and keep the RPM up. Even with an upgraded cooling system lugging and RPM too low can heat things up. Even Patch would lug with lighter throttle and touch 210 with all the cooling system goodies, but, hit the same grade at WOT and the peak ECT would be lower than the 210 mark. More coolant flow and faster fan kick on with more RPM.

Past peak torque...
2200 RPM is peak torque with a stock GM3. 62 MPH on Patch with 4.10's. This is the balls to the wall WOT speed with a trailer from Lake Havasu. Other grades slow me down to 33 MPH.

Chuck GM turbo for ATT. Wind it up. 70 MPH with ease and 55 MPH on the 33 MPH grades. This is wound up past 2200 RPM. Basically down shifting a few hundred RPM below redline. At this load and temps the TCC was locked so it's out of the picture for torque multiplication.

 

[FellowTraveler]

OK, can someone please explain how is driving past any given maximum torque rpm is a good thing while towing or hauling a heavy load?

I do understand that once the max tq rpm is reached the tq output drops off quickly.
Converter reaching stall speed before max tq rpm is a requirement, or?

 

[Will L.]

FT: on the reaching boost level compared to stall speed while power braking...That can change from one truck to another. The stall speed of the TC doesn't match boosting point in just about any street driven rig. Also my center mount gm6 w/ chocked exhaust will light sooner than side mounted 4" exhaust.

You could set it up that way for quickest acceleration, if that's is your #1 priority. Just keep in mind the 3 legged barstool: peak burn efficiency(best mpg),peak horse power (higher speed at distance), peak torque (quickest acceleration).

While peak torque is normally the desired shift point when racing or towing, it is the hardest on the drivetrain. It also is the lowest point in burn efficiency. That's why from the factory they are never set up to align with peak boost.

The idea of shifting at peak torque for climbing a hill is great, but would perform best if peak boost was at the rpm where the engine falls to after the shift to accelerate it back up the quickest as to not loose momentum. But that will not be the same when empty on flat ground.

Peak mpg would have the lowest lockup available, with a long slow boost matching peak before max torque. Then 0 boost at cruise speed on hiway with the rpm as low as possible, while being just after the power band.

 

[WarWagon]

OK, can someone please explain how is driving past any given maximum torque rpm is a good thing while towing or hauling a heavy load?

I do understand that once the max tq rpm is reached the tq output drops off quickly.
Converter reaching stall speed before max tq rpm is a requirement, or?

The engine with a better turbo like you have simply has more HP and cooling system to use it. The GMx falls over and dies above 2200 literally slowing you down if it shifts to higher RPM. (God I hated shifts with it pulling grades.) With the larger turbo the engine is able to make power in the higher RPMs over the stock setup. Night and day improvement.

So in grade climbing experiments with a trailer I had to wind the engine up for max HP, found near redline, vs. max torque around 2200 for the old setup. The difference here is the improvement in power at higher RPM the better turbo gives us along with less exhaust restriction/cooling system load. (I wasn't able to lug the engine that much in 4th or 3rd as the auto simply downshifts at WOT. Only less than WOT would leave it in higher gears and resulted in ECT spikes as noted above.)

You wouldn't be entirely wrong to assume that torque gets things moving and that horsepower keeps it that way.

So to maintain speed on a grade you need high RPM horsepower vs. the low RPM peak torque number.

Although the grades were long enough to rule this out for me as temps would lock the converter quick on the grades that go for miles I will explain the converter stall advantage.

Converters when unlocked make more torque. For example the 400 lb ft 6.2 burb engine I had would put down 1000 Ft Lbs on the dyno at the rear wheels going through the unlocked converter and gears. Patch would squeel the wheels on the rollers even with a scrap big block Pontiac engine in the bed to weigh it down. This isn't engine power numbers so not bragging rights, but, illustrates what an unlocked converter does. Further high stall eliminates the need for lower gears in the transmission with a trade off of heat.

The high stall converter I have of 2400 RPM does something else. From a stoplight or brake stand the engine will NOT reach 2400 RPM. It simply doesn't have enough power to hit 2400 RPM without the turbo. If I stand on the throttle in reverse with a trailer and front wheels hung up on the driveway curb the turbo will light in a moment as the engine stalls up to 2000 RPM without the turbo. After the turbo lights the rear wheels break loose. So I can't get a good brake stall number due to turbo light off and inability to keep the rear wheels from turning.

Another way to look at a high stall converter is peak torque with HP. HP climbs with engine RPM the peak being just before the engine runs out of air/fuel at max RPM. Torque climbs and lets say peaks at 2200 then falls off. So low RPM is low torque and HP till 2200 RPM then it is less than peak TQ with the HP to back it up. This is why high RPM is better: you have the HP to back up the lower than peak TQ. A low stall keeps you at low torque and low HP with no way to overcome either. Modern HP War diesels have enough power to overcome this, but, our IDI's don't and simply are stuck at low RPM needing another gear.

After things are moving and you are near the TQ you need you can lock the converter and forget about it using gears instead.

The above is simply climbing a grade w/o economy or any other consideration.

 

[FellowTraveler]

FT: on the reaching boost level compared to stall speed while power braking...That can change from one truck to another. The stall speed of the TC doesn't match boosting point in just about any street driven rig. Also my center mount gm6 w/ chocked exhaust will light sooner than side mounted 4" exhaust.

You could set it up that way for quickest acceleration, if that's is your #1 priority. Just keep in mind the 3 legged barstool: peak burn efficiency(best mpg),peak horse power (higher speed at distance), peak torque (quickest acceleration).

While peak torque is normally the desired shift point when racing or towing, it is the hardest on the drivetrain. It also is the lowest point in burn efficiency. That's why from the factory they are never set up to align with peak boost.

The idea of shifting at peak torque for climbing a hill is great, but would perform best if peak boost was at the rpm where the engine falls to after the shift to accelerate it back up the quickest as to not loose momentum. But that will not be the same when empty on flat ground.

Peak mpg would have the lowest lockup available, with a long slow boost matching peak before max torque. Then 0 boost at cruise speed on hiway with the rpm as low as possible, while being just after the power band.

When I stand on it from a stop I'm looking at a 1.8k average stall speed and 100% load at 2.6k @ 18 mph and 2.5 pressure ratio from here it accelerates very quickly then the pressure ratio drops to 2.0 or lower there is "lots of black smoke from stop or when I stomp on it at any speed to pass other vehicles big bellowing cloud. I suspect over fueling and lack of fuel at top of rpm band. So changing anything at this point would probably cause lag with the big turbo I have. I'm reluctant to allow more boost as 2.5 pressure ratio is already pushing it IMHO, any thoughts?

I'm having trouble right now trying to determine what rpm it makes peak tq.

 

[3500_6.5]

You do not ideally shift at peak torque for towing or racing. You shift just after peak power. Will explain later, but looks like WW pretty much summed it up with his explanation.


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[FellowTraveler]

You do not ideally shift at peak torque for towing or racing. You shift just after peak power. Will explain later, but looks like WW pretty much summed it up with his explanation.


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Thanks I'm just trying to get a better handle on this.

 

[WarWagon]

Another thing high stall converters do:
Reduce 1/4 mile track times around 0.5 seconds in some rides.

It does this by allowing the engine to instantly come up to peak torque when the vehicle isn't moving. It then allows the HP to climb as TQ falls off. This is vs. waiting for TQ and HP to come up as the vehicle starts moving. The torque coming out of the higher stall converter is also higher than stock - like a lower gear. So you have full engine power and RPM a few hundred feet before a stock stall converter would allow full engine power.

So this gets you going. Once going the triple disc TC Clutch can lock in and not slip. Short bursts of unlocked TCC action on short grades are really fun. I imagine you have short grades out east and can trade MPG for converter heat while keeping MPH up to the speed limit. Even the short time after a downshift can perhaps bring MPH and engine RPM high enough to maintain speed when heat numbers lock the TCC back up.

 

[JayTheCPA]

Am glad to see that the conversation is at least roughly heading in the direction of the scenario that I am working

So far, what I am gathering is that nobody really knows whether 2'nd is stout enough for locking the TCC while RPM's are 'up' and pulling hard, and am sensing that it probably is. But real the issue is starting to look less like a gear issue and more like a TCC issue. If the question truly lies with the TCC's ability to handle lock-up in any gear (and not just 2'nd) while pulling hard, then that is the weak link. Seeing as TCC lock is going to (and does natively) happen, doing it in 2'nd should not really change the calculus much.

Toward what looks like thoughts about keeping the TCC unlocked in 2'nd at all RPM's when pulling, am not convinced that a ~1,500 RPM stall on my TCC is allowing the 4L80E to get any significant torque multiplication by letting it remain unlocked above 2,200 RPM's. Given that at 2,200 RPMs the motor is above the range of where the 6.5's HP and torque curves commonly intersect, keeping the TCC unlocked just to let the motor spin a little faster is really not going to get much of a multiplication effect and hence why I am looking to lock the TCC and cut down on heat generation.

And just as a minor point, for the grades that I am climbing, when empty I just set the cruise control at the speed limit, smile as the Burb goes whizzing by a Prius, rarely will the tranny drop out of 4'th, do not recall the TCC unlocking except for the very rare downshift, and ECT barely budges. With the 6,500# RV in tow, it is a completely different game.


Am suspecting that my statement of downshifts at 2,200 RPM's is getting interpreted as a desire to keep them low in the towing scenario. Just for clarity, the purpose is to keep RPM's as *high* as possible during the climb and 2,200 is a low-end shift point to the next lower gear to deliberately keep the RPM's as high as possible.

Toward management of the RPMs, am not convinced that a low-end range of 2,200 RPM's when asking for heavy power is lugging the motor. Besides, from what I can tell, GM thought this was Ok. Even if 2,200 RPM's does qualify as lugging, a 3 ==> 2 shift at 2,200 RPM's lands the Burb just below redline for 2'nd. If I land in 2'nd over redline, either the ECM will de-fuel until RPM's drop to 3,300 (which is not what I want when pulling hard) or possibly just wait to do the downshift.


Here is how *I* manage the system in the pulling scenario:
> Manually shift 4 ==> 3 just ahead of the hill to start cooling everything.
> As the climb starts and speed drops, work the throttle based on the EGT I want (more on this in a moment) which is dependent on the grade and length of the climb. This is from experience as WOT will generate too much heat on the pulls and the Burb will crest with ECT's (as measured at the thermostat housing) above what I want.
> When RPM's in 3'rd drop to 2,200, manually shift 3 ==> 2.
> When RPM's in 2'nd drop to 2,200, manually shift 2 ==> 1.

Reasoning for downshifting *no lower* than 2,200 is:
> downshifts at higher than 2,200 runs the risk of de-fuel from over-rev when landing on the lower gear (not worried about over-revving during the transition as the ECM will just de-fuel).
> improved cooling.
> avoid higher EGT's that occur at lower RPM's.
> with the Hayden severe duty fan clutch (for the Kodiak) and the A/C 'On', I have learned that the longer 5% - 6% grades (5+ miles worth) call for a throttle that sets EGT's just under 1,000* F, doing this will keep ECT / tranny temps in the range that I want.
> Keeping the amount of time between power strokes as short as possible.

Passengers (mostly the wife) are not overly fond of climbing hills as the way I control the truck is far from running it quietly, but I'd rather get guff for noise than from sitting on the side of the road waiting for a tow when it blows from an overheat.

If there is a better way to manage the scenario, I remain open to suggestion and will give it a try at the next opportunity.


If I left the ECM alone in the scenario (based on the shift patterns I have (which I am presuming are GM's design)), it would:
> Drop ~5 MPH while it figured out what was going on.
> Almost immediately shift 4 ==> 3 with the TCC unlocking just for the shift.
> Run 3'rd gear with the TCC locked.
> At 44 mph (~1,900 RPM's), unlock the TCC in 3'rd and TCC remains unlocked all the way down.
> At 39 - 41 mph, shift 3 ==> 2 (3'rd is probably turning 2,100 - 2,400 RPM's, but not exactly sure as the TCC is unlocked at this point).
> At 22 - 23 mph, shift 2 ==> 1 (2'nd is probably turning 2K - 2,300 RPM's, but again not exactly sure as the TCC is unlocked).

In terms of the Burb's current setup, agree that the cooling stack will benefit from more aggressive cooling. Toward that, I am likely going to install Hayden's EV fan clutch by next towing season. In terms of speeds dropping due to grade and load, IIRC, Leroy's truck (with the exception of remote mounted coolers, a modified exhaust manifold, and 3.42's) is pretty much the same as my Burb and even his truck wanted to build heat and drop speed when climbing with a load. Point is, am not alone in this ;-)

There is a reason . . . {X, Y, and Z} use automatics.

Not sold that other vehicle classes that are moving to a slush box and away from the stick merely due to torque multiplication. There are many more factors at play (actually, IIRC torque multiplication is not among the sales points in current marketing literature). They are from a mix of technology advancements that allow more gears, better TCC lock-up (Yes, from what I am reading, this also applies to the big rigs and buses) for fuel efficiency, better integrated computer control of the powertrain, better component efficiency than their earlier generations, and quicker shifts (way faster than what a human can do (which is critical to a racing machine)). Another significant factor in using today's slush box is that it reduces load on the driver which in the case of racing allows for more focus on the surroundings and in the case of big rigs / buses it significantly reduces driver fatigue.

And NO, I do not want out of the 4L80E just 'cause it is a slush box. I want out as this dog won't hunt for how I want it to, unless I put way more money in it than what a conversion to a sick will do And as a side benefit, getting more power to the wheels for less heat generation and better fuel economy are just side benefits A third order of benefit is that it is a theft deterrent as fewer people take the time to learn how to drive a stick

 

[FellowTraveler]

Not sure if the stock program will allow manual shifts up/down at any rpm w/o damage to the transmission it's been so long since I had stock program I don't remember.

The TransGO HD-2 reprogram kit allows for up/down shift and hold @ any rpm it controls pressure too so case does not crack...

I've mentioned this several times in other posts sealing area around cooling stack greatly improves flow through coolers, condenser and radiator eliminating need for anything more than the med duty fan clutch you already have.

Westers has some 1998 6.5td tuned maps that show peak tq rpm @ 2500 rpm on F and 2750 rpm on S.

 

[JayTheCPA]

Given that the OE tune does allow for shifts, and from observation it seems to unlock the TCC during shift, out of curiosity what damage could occur? Besides, it is highly likely that a pure OE setup had to allow shifts that managed the TCC.

And good point about sealing the gaps around the radiator. Will tackle that when I redo the fan clutch. In any event, at 30 - 40 mph when pulling hard, something is telling me that the fan is going to pull more air than the ram-air would flow. But in any event, sealing the gaps will assure one path for the air versus multiple paths of least resistance.

 

[FellowTraveler]

Remove the upper fan shroud see all the gaps sides and top of radiator OK for stock 6.5td not so good for any modified 6.5td.

IMHO, when modifying the diesel for performance direct clutch can burn up easier, high transmission pressure spikes can break the case and drum. You did say you had all the updates installed at last build so more likely than not these things will not happen.

Are you saying the trans will hold 1st, 2nd or 3rd at any rpm or?
The transmission can be manually shifted up/down at any rpm, or?
I thought those two features required a reprogram of valve body via a kit like the TransGo HD2 or other aftermarket kit.....I could be wrong though.

 

[FellowTraveler]

The stock 4L80e is a good transmission for stock applications IMHO it is when you throw more tq/hp or repeated reverse like when plowing snow you run into troubles.

Tweaking the OEM code to your requirements maybe a good thing but as you know aftermarket has this cornered with better control...

I've had simple parts fail on various 4L80's like manifold pressure sensor fail and trans would go into a frenzy of destruction you'd think OEM would have included some fail safe to prevent the destruction, failed servo (reverse?) went to billet, burnt out TCC, cracked case. In the end I spent big to have a build that can hold up to my expectations and beyond then I have run it on the cool side since then, however I do have to use a cover over radiator area of trans coolers during extreme cold weather.

I suggest you tinker some if you feel you can improve the code to your requirements.

 

[JayTheCPA]

Are you saying the trans will hold 1st, 2nd or 3rd at any rpm or?

At the moment I know much less about the physical side (tranny) than I do about the logical side (ECM).

Do not have tuning software at the moment (for seeing everything that the ECM controls), but do have a few screen shots of the tables. The ECM does have tables for locking the TCC in 2'nd, 3'rd, and 4'th (but not 1'st). Even though 2'nd has a set of variables for when to lock the TCC, GM basically made it not happen by setting the lock speeds *way* over the truck's max possible speed. Only exception to the not locking 2'nd is when TFT is Hot, GM's code locked the TCC at 23 - 25 mph and up.

The transmission can be manually shifted up/down at any rpm, or?
I thought those two features required a reprogram of valve body via a kit like the TransGo HD2 or other aftermarket kit.....I could be wrong though.

I regularly manually shift the tranny, so yes it will do it, and gracefully at that. I have not tried to downshift into a gear that will result in an over-rev (ex dropping into 1'st at 55 mph) as I do not care to experiment with this one aspect. On the converse, I am not too concerned about over-revving on upshifts as the ECM will de-fuel at 100 RPM's before the P-400's rated redline.


In terms of my current tranny, while I was not given the parts list that went into the rebuild:
> it was comparably expensive (more than what WW typically pays for a rebuild).
> I talked directly with the rebuilder and he was aware that it *must* tow.
> the rebuilder told me that he corrected all of the 4L80E's OE issues.
> it does seem rather solid in that TFT temps when pulling hard do not go over ECT (actually they stay just a tad cooler than ECT) and suspect that the radiator is actually heating the tranny fluid more than the tranny is heating the fluid.


To bring the topic full circle, I know that the ECM is capable of locking the TCC in 2'nd (and with TFT Hot will actually do it), I know that the tranny can lock the TCC in 2'nd, but I also have read that there are physical differences in 2'nd versus 3'rd & 4'th gears (ex: the overrun clutch) which is why I am looking to find out if 2'nd can actually handle getting locked when pulling hard. So far, it seems that I have stumped the experts

Longer term goal remains simply to pass knowledge to the community as to whether this works (or not) and get out of the 4L80E. Also it is a matter of economics. For the all-in costs that I will have to spend on making the 4L80E meet my towing expectations, it will cost much less for conversion to either a NV4500 or ZF6 with an add-on of either a gear splitter or driveline retarder.

 

[FellowTraveler]

OK, you it down pact the only thing I see now is the cooling stack air gaps and perhaps adding an additional or larger aux trans cooler use AMSOIL synthetic and you already have the EVENS then your good to go IMHO.
Most heat is generated by torque converter when unlocked followed by working the trans hard.
I run my trans on the cool side and 300 deg f out of converter is not uncommon so it's the last place the fluid flows before radiator trans cooler then on to the aux cooler if you have the heavy tow package.....OH and do you have an aux engine oil cooler, or?