4L80E & 2nd Gear TCC Lock

[JayTheCPA]

Lets presume a healthy 4L80E and use for towing.

Remind me please, is 2'nd gear stout enough for locking the TCC while pulling?

From what I recall, the 4L80E does have some minor internal differences across the years, so is there a year range factor to locking the TCC in 2'nd?

Background: Am pondering a shift pattern that locks 2nd gear in higher RPM ranges to help with keeping overall temps down.

 

[WarWagon]

I forget if it's 3rd or 2nd manual select that brings on the weak over run clutch for compression braking. So don't compression brake with the TCC locked. Nothing you can do to cure that.

The TCC itself is the next weak point. IMO it can't take stock or turned up power. 50K miles it it's lifetime before it slips. A better *cough cough* triple disk eliminates this issue. Sure the factory tune will lock the TCC in 3rd gear for temp control at WOT, but, extended WOT trailer pulling grades does it in. YMMV.

 

[JayTheCPA]

From observation (while manually downshifting for braking), 2'nd 'manual' brings in the overrun clutch; 3'rd 'manual' barely does anything and mostly just lets the tranny freewheel. But my focus is not on braking, it is on pulling up grades when applying power despite falling speeds from the load.

If I was going to keep the 4L80E, Yes, I would do it right with a different converter and even one of the '6 speed' 4L80E conversion trannies (plus stand-alone controller) and probably change the rear to 3.42's. But with 'all-in' pricing for an automatic that can handle towing duty (including braking), conversion to a stick continues to look more attractive.

At this point, all I really want is to get better lock-up of the TCC for mitigating heat while pulling hard. Longer term I am building the budget for swapping over to either a NV or ZF.

If consensus is that the 4L80E can handle locking 2'nd while pulling hard, I will play with some shift curves that do it; otherwise, I will leave it un-locked.

 

[Burning oil]

When you going to stick a stick in that thing?

 

[JayTheCPA]

Am probably still at least a year away from the tranny conversion. It depends on how quickly the wallet recovers from the Burb's recent less than graceful motor replacement . . . And prior to sicking-it, I have other projects that are higher in priority now that I am not worried about the Burb going back in the shop for nit-noids.


In the interim, want to holistically tweak the 4L80E's behavior (as opposed to only modifying the shift points) for better heat control when pulling hard. Getting an understanding of how stout 2'nd gear is will help with the approach.

 

[FellowTraveler]

My memory is sketchy at time but I seem to remember the stock converter can't do lockup under 1.7 k rpm's for any lengthy time the clutch is the issue I suspect FERM can chime in on this.
There are custom single to triple clutch converters using high end clutch materials and even billet construction. After reading up on converters for diesel I've decided my next converter will be billet triple clutch w/1.2 k rpm stall speed simply because I don't hot-rod the 6.5 Burb this will also keep the trans temps cooler too.

As the 6 speed 4L80e goes I'd opt for the lower 2.98:1 1st gear and all the stronger 4L85e parts if going to 3.42 gear-sets.

 

[WarWagon]

Again, with a factory converter don't mess with lower lockup RPM's/MPH. The weak clutch simply can't hold any diesel lugging power.

The factory ECM will lock the TCC in 3rd gear at WOT at a specific temperature to keep temps from running away. (Usually the RPM it locks at is above the engine's peak TQ.) The TC Clutch is weak and will only take 50K or less of abuse. I have gone through two rebuilt converters with the TCC override switch I have. At the end of their life they slip and code or have the ECM lock and unlock the converter rapidly due to detected slippage. Lower RPM lockup IMO is too much torque for the TCC and will slip easier for whatever reason. (Low fluid pressure at lower RPM? ECM Tables?)

Regardless the last converter would slip when I attempted to lock it up at 35 MPH and lug (light throttle) a 7% grade with it. Dropped in the Yank triple disk and can climb the same grade at 35 MPH without TCC slippage. The factory converter still held at 75MPH. I have several flat areas around here at 35 MPH that the TCC could be locked up in. This is where a lower stall would help, but, I just lock the TC Clutch in instead with a better tune.

I disagree with lower stall ideas even for economy. Just lock the TCC clutch in and "stall" becomes irrelevant. (Of course you need a better clutch than OEM to do this.) The 6.5 isn't a long stroke engine so keeping it's RPM lugging at light throttle just smokes and burns more fuel than higher RPM with a little boost to clear the smoke. Get the heavy Suburban moving with the high speed light duty diesel and then wham the TCC clutch on. Working the engine harder with a low stall is just that - working the engine harder. Light enough throttle - just lock the converter - something GM had an issue doing below 45 MPH due to weak converter clutches, engine running well with emissions, and NVH. Gas engine min TCC lock MPH (45) carried over to diesels regardless of rear end rations. (DUH!! GM, Really?)

So fixing GM's 'don't lock the TCC below 45 MPH' in the tune is a better idea than a low stall converter. It will require a better converter clutch that can hold the engine's peak torque.

It's a real trip to do this with a high stall converter as locking it in at 35 MPH drops the engine RPM by up to 1000 RPM.

 

[FellowTraveler]

WarWagon what your thoughts on the 4L80e 6 speed with 2.98 1st gear and 2.24 2nd gear with these gears do you still feel low stall converter is not a good idea, or?

 

[WarWagon]

WarWagon what your thoughts on the 4L80e 6 speed with 2.98 1st gear and 2.24 2nd gear with these gears do you still feel low stall converter is not a good idea, or?

Transmission rebuilds cost a flat $1100. Yank Converter any way you want it is $1100. So is the cost for a 6 speed similar?

At a stoplight the converter matters until you are moving fast enough to be at peak torque engine RPM - gearing changes this.

With my setup (ATT) allowing the engine to flash up to 2K from a dig allows the turbo to immediately provide boost and clear the smoke. It's also producing more power and can light the rear wheels up - loaded with a trailer. When I need economy say at less than 50% throttle I lock the TC Clutch in - something the factory converter won't handle. So this is new thinking. Have the ECM lock the TCC in early for economy and unlock when you need power. Say at the 35 MPH example above.

With the setup I can't use lower gearing as the high stall provides enough torque to break the rear wheels loose in 1st now. I could go with 3.73's over the 4.10's for higher *cough cough* CA freeway speeds where I get passed while out of engine RPM.

A lower stall converter is closer to TCC clutch being locked up and keep the engine at low power. It makes the engine work harder even when you are trying to be easy on it. You got to get the thing moving and again most other times the TCC is locked up.

Grades at higher power where you need the TCC unlocked is the wildcard. More gears with a locked TCC would be better MPG as less heat exits the converter. Yet the ECM will lock the TCC after things get hot so this is a small window.

Where is the peak torque with your turbo setup? This matters more then anything else. A video or two sent to Yank with your goals (MPG) will also give you better advice than me. I suggest that the HX40II and ATT both do better with higher than stock stall speeds. The factory setup is for light duty unloaded as their isn't any power in the upper RPM, the trans shifts you there and the OEM turbo chokes. Light duty the TCC doesn't lock at low enough MPH

The ECM program designed to protect the weak factory TCC clutch is why a low stall converter on it's own would get better MPG's. I counter with a high stall converter giving me all the power the engine has, NOW, and locking the clutch early when I want to eek the MPG's out of it. Seriously running around for miles on a flat road at 35 MPH with the TCC unlocked is annoying and the reason I started looking for ways to have the ECM lock the TCC in. The Switch took some wear doing this and won't unlock if the TCC is slipping making ECM programming the better choice.

So low speed low power use at 25MPH and the like is where a low stall converter has an advantage. At 25 MPH patch is somewhere between 1600-2000 RPM not exactly subtle in a quiet area... Harley's come to mind.

Again our antique engine is a different beast than the new (HP War) diesels that have a lot more power, torque, and different turbo's. So advice to other diesels is generally lower stall, but, doesn't carry over to our engine.

Personally I HATE tight converters trying to push through the brakes during cold high idle etc. This is somewhat independent of stall speed.

 

[FellowTraveler]

Transmission rebuilds cost a flat $1100. Yank Converter any way you want it is $1100. So is the cost for a 6 speed similar?

At a stoplight the converter matters until you are moving fast enough to be at peak torque engine RPM - gearing changes this.

With my setup (ATT) allowing the engine to flash up to 2K from a dig allows the turbo to immediately provide boost and clear the smoke. It's also producing more power and can light the rear wheels up - loaded with a trailer. When I need economy say at less than 50% throttle I lock the TC Clutch in - something the factory converter won't handle. So this is new thinking. Have the ECM lock the TCC in early for economy and unlock when you need power. Say at the 35 MPH example above.

With the setup I can't use lower gearing as the high stall provides enough torque to break the rear wheels loose in 1st now. I could go with 3.73's over the 4.10's for higher *cough cough* CA freeway speeds where I get passed while out of engine RPM.

A lower stall converter is closer to TCC clutch being locked up and keep the engine at low power. It makes the engine work harder even when you are trying to be easy on it. You got to get the thing moving and again most other times the TCC is locked up.

Grades at higher power where you need the TCC unlocked is the wildcard. More gears with a locked TCC would be better MPG as less heat exits the converter. Yet the ECM will lock the TCC after things get hot so this is a small window.

Where is the peak torque with your turbo setup? This matters more then anything else. A video or two sent to Yank with your goals (MPG) will also give you better advice than me. I suggest that the HX40II and ATT both do better with higher than stock stall speeds. The factory setup is for light duty unloaded as their isn't any power in the upper RPM, the trans shifts you there and the OEM turbo chokes. Light duty the TCC doesn't lock at low enough MPH

The ECM program designed to protect the weak factory TCC clutch is why a low stall converter on it's own would get better MPG's. I counter with a high stall converter giving me all the power the engine has, NOW, and locking the clutch early when I want to eek the MPG's out of it. Seriously running around for miles on a flat road at 35 MPH with the TCC unlocked is annoying and the reason I started looking for ways to have the ECM lock the TCC in. The Switch took some wear doing this and won't unlock if the TCC is slipping making ECM programming the better choice.

So low speed low power use at 25MPH and the like is where a low stall converter has an advantage. At 25 MPH patch is somewhere between 1600-2000 RPM not exactly subtle in a quiet area... Harley's come to mind.

Again our antique engine is a different beast than the new (HP War) diesels that have a lot more power, torque, and different turbo's. So advice to other diesels is generally lower stall, but, doesn't carry over to our engine.

Personally I HATE tight converters trying to push through the brakes during cold high idle etc. This is somewhat independent of stall speed.

Thanks, I have more insight now.

 

[JayTheCPA]

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?

Transmission rebuilds cost a flat $1100. Yank Converter any way you want it is $1100. So is the cost for a 6 speed similar?

Nope . . .
Am seeing the price range for just the '6 speed 4L80E' tranny is $5,300 - $7K, add in things like the TCC, shift controller, and re-gearing to 3.42's and the drivetrain just cost more than the truck. But it is only money, right?

The factory ECM will lock the TCC in 3rd gear at WOT at a specific temperature to keep temps from running away.

From what I can tell, Yes and No.
In looking at the tables that I am aware of, it does this for 4th at 44 mph, 3'rd at 35 mph, and 2'nd at 25 mph. The TCC lock speeds are flat for all the same for power levels (and not just WOT). Only variable I do not know is the TFT set point and had read that it is either 240F or 270F. From what I can tell, the speeds are changeable, but do not know whether the TFT Hot is a variable or hard coded.

 

[tanman_2006]

I have a thought on the more gears idea, I know it is said to vibrate but would a gearvendor work with the highstall converter?

 

[NVW]

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.

 

[JayTheCPA]

Correct.

Am not looking to use any manual TCC locking devices. Just the ECM and the code within.

So far, the only 'manual' control of the RPM is by shift lever and the ECM still controls the TCC.

 

[FellowTraveler]

As you already know the 4L80e can be built way beyond what you want to do however the tag is high $7k++ when compared to say an ALLISON the ALLISON is the better choice if you can do it on the cheap.

I've heard mixed reviews about manual lockup of TQ converter in newer 4L80's re-doing the temp signal will work for lockup but again if stock the converter clutch can't handle it for long.

When I went with the HD2 TransGo reprogram it was a big change for the better my shifts are firm also I run my trans temps colder than most which is a consideration when towing & AMSOIL synthetic trans fluid is a must IMHO. There are problems with parts failure when running high pressure I suggest all the SONNEX update parts but I seem to remember FERM saying they are a waste so again mixed reviews.

Another consideration that WarWagon points out is peak tq rpm it makes me wonder if running too high of a stall speed will cause other issues when converter is locked in 2nd.

Towing performance being the concern then the 4L80e 6 speed w/lower 1st gear and a stand alone controller which has better control features than the GM version.

IMHO, a low buck 5/6 speed conversion w/o lower 1st gear is a consideration because of better gear ratios for what you have in mind and perhaps a billet triple clutch or lower buck bigger single clutch assembly will suffice.

In the end it all revolves around how much you intend to spend?

 

[JayTheCPA]

. . . the ALLISON is the better choice if you can do it on the cheap.

Not sure I agree. From a overall perspective of tow capability, Yes, the Allison is better than a stock 4L80E. But mated to a 6.5, would expect the Allison's parasitic load make the truck climb hills even slower. If I really wanted to stick with a slushbox, would look into a ZF 8HP conversion rather than a built 4L80E or Allison as it weighs less.

I've heard mixed reviews about manual lockup of TQ converter in newer 4L80's re-doing the temp signal will work for lockup but again if stock the converter clutch can't handle it for long.

This has me confused. Seeing as the 4L80E is designed to run in 4'th all-day-long with the TCC locked (and presumably 3'rd) whether empty or towing, how does this affect its ability to handle staying locked for the long term?

In terms of mixed reviews on manual lockup of the TCC, I am aware that using a switch type device (like one fro BD) can cause issues with the ECM going into limp mode. But again, I am not interested in any external devices to lock the TCC, just the OE shift lever and the ECM's code so that I have as native a system as possible.

Towing performance being the concern then the 4L80e 6 speed w/lower 1st gear and a stand alone controller which has better control features than the GM version.

Possibly, but am focusing on how to write a better set of code and not a better engineered transmission.

In the end it all revolves around how much you intend to spend?

Agree. And at this point I only intend to spend money on one (maybe two) more tune(s) to get this dog (the 4L80E) to hunt gears a little better on the climb. After that, will spend the money on different transmission which moves decisions on the the shift points to the lose nut behind the wheel.

Remain convinced that the OE code can handle climbing behavior better, and the only question is whether 2'nd gear is up to running with TCC locked for a bit.

 

[FellowTraveler]

Not sure I agree. From a overall perspective of tow capability, Yes, the Allison is better than a stock 4L80E. But mated to a 6.5, would expect the Allison's parasitic load make the truck climb hills even slower. If I really wanted to stick with a slushbox, would look into a ZF 8HP conversion rather than a built 4L80E or Allison as it weighs less.




This has me confused. Seeing as the 4L80E is designed to run in 4'th all-day-long with the TCC locked (and presumably 3'rd) whether empty or towing, how does this affect its ability to handle staying locked for the long term?

In terms of mixed reviews on manual lockup of the TCC, I am aware that using a switch type device (like one fro BD) can cause issues with the ECM going into limp mode. But again, I am not interested in any external devices to lock the TCC, just the OE shift lever and the ECM's code so that I have as native a system as possible.




Possibly, but am focusing on how to write a better set of code and not a better engineered transmission.




Agree. And at this point I only intend to spend money on one (maybe two) more tune(s) to get this dog (the 4L80E) to hunt gears a little better on the climb. After that, will spend the money on different transmission which moves decisions on the the shift points to the lose nut behind the wheel.

Remain convinced that the OE code can handle climbing behavior better, and the only question is whether 2'nd gear is up to running with TCC locked for a bit.

From what I've read here and there and conversations w/Bill Heath if I remember right locking the converter in lower gear at lower speeds and rpm is not a good idea, and because I at times suffer from some-timers I forget exactly what issues it causes but I remember wanting lockup longer and in lower gear too.

As for running locked in forth while cruising a stock 6.5 turbo diesel is not putting lots of tq or hp through the drive-train so the clutch can handle it as designed, its when you mod for performance etc. the stock transmission gets iffy and at higher rpm's (especially towing) (throw in some hills) all clutches and the converter clutch start to take a beating.

The OE code can be tweaked however the weak link is the stock trans/converter IMHO. Have you considered the TransGO HD2 re-programmer it also fixes some pressure related failures the 4L80/85e suffer then increase pressures through programming.

 

[JayTheCPA]

Am not looking to throw more money at a transmission that is going to get yanked. Even with knowing that the 4L80E is coming out, am planning to share my experiences with at least one tuner so that the community as a whole may benefit.

In terms of the tranny that I have, it was rebuilt during the Burb's motor transplant (only things re-usable were the case and pump). Am told by the rebuilder that all of the OE issues were 'corrected', but did not get a parts list. Also, the rebuilder knew that I would tow and I did have the extra capacity pan installed.

Had I known that the motor would take an extensive amount of time to replace, would not have rebuilt the 4L80E, would have pressed hard for a ZF6 (given that the whole powertrain was out of the truck), and settled for a NV4500 if I had no other choice. Only reason I had the tranny rebuilt was that we all thought the motor transplant would have gone a lot quicker than it actually did, and nobody had gathered all the misc parts for the conversion.

 

[FellowTraveler]

Am not looking to throw more money at a transmission that is going to get yanked. Even with knowing that the 4L80E is coming out, am planning to share my experiences with at least one tuner so that the community as a whole may benefit.

In terms of the tranny that I have, it was rebuilt during the Burb's motor transplant (only things re-usable were the case and pump). Am told by the rebuilder that all of the OE issues were 'corrected', but did not get a parts list. Also, the rebuilder knew that I would tow and I did have the extra capacity pan installed.

Had I known that the motor would take an extensive amount of time to replace, would not have rebuilt the 4L80E, would have pressed hard for a ZF6 (given that the whole powertrain was out of the truck), and settled for a NV4500 if I had no other choice. Only reason I had the tranny rebuilt was that we all thought the motor transplant would have gone a lot quicker than it actually did, and nobody had gathered all the misc parts for the conversion.

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

After warm up drive about 2 mph then tromp the throttle to the floor that rpm peak on your rpm gauge as truck starts to move will be the converter stall speed then use your EDGE to guesstimate the peak tq rpm if your peak tq rpm is around 200 rpm above your stall speed then tweaking the code will work some if the stall speed is higher than peak tq rpm your wasting power and no amount of tweaking will help IMHO.

 

[Will L.]

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.