4L80E & 2nd Gear TCC Lock

[3500_6.5]

Second gear will not be affected by locking the converter up. It has no more stress put on it with the converter locked up than it would with it unlocked. The issue would be the stress put on the tcc and whether or not it would cause it to burn up. You will not gain any power from locking it up in second gear, the only benefit would be a brief relief from the heat build up. That would be the only reason I would see doing it.

After reading your explanation, the idea makes more sense than what I originally thought you were wanting the lock up for.

I didn't say torque multiplication was the reason for every vehicle class switching to autos, I said that everyone is doing it bc they are all around better than a standard transmission.

And I still stand by my statement that you will be losing power by swapping to a manual. Autos put down more power and is more beneficial for towing. The whole dyno numbers thing and 20% loss is a misconception and completely generalized. A 100 hp engine running through a 4l80 would then somehow only lose 20hp while a 1000hp engine would lose 200hp. The power it takes to transfer it to the ground doesn't go up as you make more hp, it should take the same amount of power regardless. And dyno numbers are a whole other can of worms to get into.

The only reason I would agree to go with a manual is if you were doing all of your towing in the mountains and you were constantly overheating the auto. I don't think a 4l80 could handle that kind of stress for very long whereas your manual wouldn't have the overheating issue. But if this scenario is an occasional one, I think doing away with the internal trans cooler and replacing the factory exterior cooler with a larger aftermarket one would do more for you to keep heat down than looking to lock the converter in 2nd. I think the lock up in second, if tranny temps are already climbing out of control, will be way too little too late. Doing both may be a good idea, but I think the better cooling ability would help a lot more.

But, to each their own. I know most people have a preference regardless of what is said. Especially from some random guy on some random Internet forum. Just want to put my two cents out there for whatever it is worth.


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[3500_6.5]

I should correct myself here; autos put down more torque than a standard. Which will absolutely help you in the scenario you are describing.


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[FellowTraveler]

I tried the bypassing the radiator trans cooler the result was higher transmission temps especially around town, stop and go traffic and rapid acceleration is when the converter fluid can easily reach 300+ deg. f so it needs the drop in temperature by going through the cooler side of radiator and then a aux cooler or two to cool it even more.

 

[3500_6.5]

I delete my radiator cooler on everything. Always stays cooler. I ran it with an aftermarket cooler on my 1 ton for a while. Worked fine most of the time, but during the hottest months here I saw temps close to 200 degrees pulling trailers. With that bypassed and an aftermarket cooler only, I have never seen above 185. Unloaded temps are consistently in the 140-150 range during the summer and lower during the cold months


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[JayTheCPA]

I should correct myself here; autos put down more torque than a standard. Which will absolutely help you in the scenario you are describing.

Possibly.

From what I understand, torque multiplication is not constant and goes down as RPM's on the front and rear side of the converter go up. Biggest benefit is when speed on the back side is 0. Given torque multiplication is dependent on total RPM's, am sensing that there is a point where it is better to just lock the converter on long pulls rather than make extra heat (along with viscosity decrease) just to try and squeeze a couple extra ponies. And that gets me thinking . . . perhaps a transmission shop has software that can run a calculation and graph the torque multiplication curve to help with making a more informed approach of where to lock and unlock the TCC as opposed to my picking a RPM

Currently, our ECM shifts based on speed and have watched the RPM's drop to 2K (and lower) without it commanding a downshift (while pulling hard). This is outside of my comfort zone as I know there are multiple items making extra heat at this RPM / power band and the cooling capability is dropping. Fixing this calls for either spending more money on a stand-alone controller or on a tune. Seeing as I am not keen on adding more complexity to the system (ie: stand-alone controller), am going to approach it from the ECM side. While looking to correct the shift patterns, am going to go after total transmission behavior and the reason why I am asking the question about the tranny's capabilities

In the bigger picture, for what I am after, the conditions to trigger the TCC lock in 2'nd are actually rare.

Aside, freely admit that I know just enough to be dangerous which is why I value inputs. Keep them coming!

 

[WarWagon]

I would have to look up the power flow through the 4L80E for "power" and "compression braking". I forget if it is manual 3rd or second that requires the weak overrun clutch pack for "compression braking". This weak clutch pack will slip with the TCC locked and compression braking. The power flow when accelerating is different. The only way you know this clutch pack has burnt out is the engine will drop to idle while going down the freeway in manual (2nd or) 3rd. I put 30k on a trans with this clutch pack burnt up as it went forward with all gears just fine.

I get the best trans cooling with radiator and then aux cooler. I had mine backwards for years going aux cooler 1st then radiator. AC would blow the relief and trans ran at 220 all the time resulting in reduced life. Regardless with improved cooling trans temps are simply not an issue for me pulling grades. Again 220 degrees was 50K life due to TC Clutch failure. Note: I found higher trans temps with just the aux cooler and sucky AC performance. (I hate the radiator cooler leak risk.) Plumbed correctly I see 180 tops for trans temp. Unless I blow a trailer tire then it goes up... For the record the radiator cooler from the cold side does NOT heat the trans up. Possible it can heat the engine up say after a brake stall on a cold engine... Not that I do that to defrost the windows now and then.

Do not shift with the TCC locked as it risks breaking the input shaft.

Lock on lift: (You lift off the throttle and the GM tune will unlock the TC Clutch.)
Some tuners will let you keep the TCC locked when you lift.
One word: "Don't!"
On downhill grades: "Why is my engine surging?" Because the weak overrun is stick-slip-stick while burning up.
MT harshness when off-on throttle.
Risk to input shaft.

 

[FellowTraveler]

I would have to look up the power flow through the 4L80E for "power" and "compression braking". I forget if it is manual 3rd or second that requires the weak overrun clutch pack for "compression braking". This weak clutch pack will slip with the TCC locked and compression braking. The power flow when accelerating is different. The only way you know this clutch pack has burnt out is the engine will drop to idle while going down the freeway in manual (2nd or) 3rd. I put 30k on a trans with this clutch pack burnt up as it went forward with all gears just fine.

I get the best trans cooling with radiator and then aux cooler. I had mine backwards for years going aux cooler 1st then radiator. AC would blow the relief and trans ran at 220 all the time resulting in reduced life. Regardless with improved cooling trans temps are simply not an issue for me pulling grades. Again 220 degrees was 50K life due to TC Clutch failure. Note: I found higher trans temps with just the aux cooler and sucky AC performance. (I hate the radiator cooler leak risk.) Plumbed correctly I see 180 tops for trans temp. Unless I blow a trailer tire then it goes up... For the record the radiator cooler from the cold side does NOT heat the trans up. Possible it can heat the engine up say after a brake stall on a cold engine... Not that I do that to defrost the windows now and then.

Do not shift with the TCC locked as it risks breaking the input shaft.

Lock on lift: (You lift off the throttle and the GM tune will unlock the TC Clutch.)
Some tuners will let you keep the TCC locked when you lift.
One word: "Don't!"
On downhill grades: "Why is my engine surging?" Because the weak overrun is stick-slip-stick while burning up.
MT harshness when off-on throttle.
Risk to input shaft.

Since I run EVANS the interior heater starts to come up in about two minutes in mid 30 deg f weather I suspect because the coolant pulls more heat than its EGW counterpart but I'm not an expert on this one.

Only 4L80e I've seen advertised with engine braking is PA_T 6 speed 4L80e but it has a $7k tag...all the ills of the 4L80e can be fixed to extreme tq/hp levels...for GM applications the stock transmissions worked well for intended use however as always mods change that reliability so the aftermarket brings the fix @ a cost..

As the OEM code goes perhaps the 2nd gear lockup option is there for light duty applications 'only guessing here' or the 4L85e with its stronger components.

After so digging after reading a string herein on engine braking I found the closest electro-magnetic drive-train brake that should work the GMT400 HD and HD 3/4 & 1 ton applications but it would be total custom setup as the only application it is direct bolt in is for the medium FORD cab chassis..

 

[JayTheCPA]

I would have to look up the power flow through the 4L80E for "power" and "compression braking". I forget if it is manual 3rd or second that requires the weak overrun clutch pack for "compression braking"..

From observation, am rather sure it is 2'nd, but not really an issue to me as 3'd holds back the load well enough when coming down 6% grades. Although, I might need to re-think that as I have yet to do the 9% grade that I cross every few seasons.

Only 4L80e I've seen advertised with engine braking is PA_T 6 speed 4L80e but it has a $7k tag...all the ills of the 4L80e can be fixed to extreme tq/hp levels...for GM applications the stock transmissions worked well for intended use however as always mods change that reliability so the aftermarket brings the fix @ a cost..

Which highlights my focus on getting out of the 4L80E (among other aspects) as it it is just not economical to make that dog hunt. ~$7K is the basic entry price, it also needs a stand-alone controller and possibly some other add-ons. And to properly take advantage of the gearing, the truck should get a re-gear to 3.42's. In my case, this means two differential re-gears. I'll pass . . . ;-)

After so digging after reading a string herein on engine braking I found the closest electro-magnetic drive-train brake that should work the GMT400 HD and HD 3/4 & 1 ton applications but it would be total custom setup as the only application it is direct bolt in is for the medium FORD cab chassis..

Seems that we found the same information. I am seeing shops that do installation for micro-buses, so not convinced that a solution is purely home-brew. My reasoning is that if it works in a F350, it should work in the GMT400

 

[FellowTraveler]

Another way to look at the expense "is if its a keeper the cost of getting the 6 speed 4L80e is cheap when compared to a newer truck that may be able to meet your requirements."

While the IDI 6.5 is less efficient than a DI when prices are compared for PM and parts the IDI is hands down a better deal for the $$$$. Your ahead of the game w/P400 already in your Burb............

 

[3500_6.5]

Overrun clutch is applied in manual 1st thru 3rd. Lock up should not affect it. It is used only for engine braking. Manual 2nd, applies a band that isn't applied in drive or overdrive, as does first. But the overrunning clutch is there to stop the freewheeling when the go pedal is released. The only way I believe you can burn this clutch up is from engine braking.... Like using it to slow you down going down a mountain with thousands of pounds behind you.


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[3500_6.5]

Although after rereading what warwagon said, I think we are saying the same thing. I think.

If you are wanting to lock the converter up in 2nd, under acceleration going up the hill, the overrun clutch will not be used (applied, but no power is being put through it). Going down the other side though, with the converter locked up in second, the overrun clutch will have power going through it and the stress being put on it is increased when if the converter is locked up too. But for acceleration, it should not matter.


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[3500_6.5]

Possibly.

From what I understand, torque multiplication is not constant and goes down as RPM's on the front and rear side of the converter go up. Biggest benefit is when speed on the back side is 0. Given torque multiplication is dependent on total RPM's, am sensing that there is a point where it is better to just lock the converter on long pulls rather than make extra heat (along with viscosity decrease) just to try and squeeze a couple extra ponies. And that gets me thinking . . . perhaps a transmission shop has software that can run a calculation and graph the torque multiplication curve to help with making a more informed approach of where to lock and unlock the TCC as opposed to my picking a RPM

Currently, our ECM shifts based on speed and have watched the RPM's drop to 2K (and lower) without it commanding a downshift (while pulling hard). This is outside of my comfort zone as I know there are multiple items making extra heat at this RPM / power band and the cooling capability is dropping. Fixing this calls for either spending more money on a stand-alone controller or on a tune. Seeing as I am not keen on adding more complexity to the system (ie: stand-alone controller), am going to approach it from the ECM side. While looking to correct the shift patterns, am going to go after total transmission behavior and the reason why I am asking the question about the tranny's capabilities

In the bigger picture, for what I am after, the conditions to trigger the TCC lock in 2'nd are actually rare.

Aside, freely admit that I know just enough to be dangerous which is why I value inputs. Keep them coming!

You are right on the torque multiplication. The closer the output torque converter speed gets to input tc speed, the less torque multiplication you get. But the heavier you are, the longer the input and output rpms stay further apart, increasing the length of time you have torque multiplication. So you would have to pay attention to the amount of rpms you are dropping when the converter locks up to see if it is worth keeping it unlocked or to lock it up.

There are a lot of other factors that play into that too. Like heat. No point in multiplying your torque if you're expending more energy in heat than you are getting extra to the ground. Also, would be the rpms and where you have power. You don't want to hold higher (or lower) rpms if it is out of your power range. But that usually only applies when you are actually accelerating or trying to maintain a speed. If you are holding wot and are losing speed at all rpms, your peak power isn't powerful enough anyway. Then you would be most concerned with what you've mentioned; getting to the top without overheating everything and causing damage. Which I couldn't imagine your lock up idea hurting in this situation as long as you're not lugging the engine. Only way to know is trying[emoji3]


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[WarWagon]

Overrun clutch is applied in manual 1st thru 3rd. Lock up should not affect it. It is used only for engine braking. Manual 2nd, applies a band that isn't applied in drive or overdrive, as does first. But the overrunning clutch is there to stop the freewheeling when the go pedal is released. The only way I believe you can burn this clutch up is from engine braking.... Like using it to slow you down going down a mountain with thousands of pounds behind you.


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Exactly. It is like 2 frictions and very small with zero room for improving it. Compression braking with the TCC unlocked doesn't appear to hurt it with a stock converter, but, with the TCC locked the vehicle's own weight w/o towing can slip it. Least it did for me on the grades around here. So Compression Braking IMO is the only complaint I have with the 4L80E because it is a legit and unfixable weak point. Brakes are cheaper and, yes, I eat them often...

Note the ballooning of the converter with reverse powerflow through it unlocked and additional flex plate age cracking risk.

Compression braking is hard on everything from the differential to the engine in varying degrees of reduced life.

 

[Will L.]

There is a calculation to do when deciding about the cost of jakebrakess on a rig. If you don't tow weight down enough grades, the added cost of engine wear isn't worth it.

Around the southern Nv, Northern Az, and Southern California, no fuel trucks use them. It is FAR less expensive to upgrade brakes and get a lot longer engine life.

I thought about it on my hummer because of the redunkulis things I do with it at geared up at 10,000 lbs. After talking to a few different people that know the 4l80e way more than me, I decided only if I ever go to a manual transmission.

I'm guessing I am still lighter than what your towing Jay, Just got me to thinking what you haul and how bad are the hills out your way.

 

[FellowTraveler]

6.5td powered K2500 Suburban 8.6k+ GVWR tow capacities listed in the GM C/K Up-fitter manual lists only two gear ratio options and their perspective towing ratings.

3.73 6k trailer & load, 750 lb. limit @ tongue weight distribution hitch required.

4.10 7.5k trailer & load, 900 lb. limit @ tongue weight distribution hitch required.

Consider 3.42 then 5k is the trailer & load limit w/500 lb. limit @ hitch tongue.

All numbers are for stock drivetrain.

Thrown in larger tire diameter those towing numbers are reduced.

While 4.56 & lower ratio gears can be installed the Suburban chassis and suspension becomes the limiting factor unless properly modified to increase its capacity.

Throw in wind and hills and that load in the big box your towing becomes more a hassle to pull.

Now for the turbocharger which is a torque multiplication device problems do rear their ugly head when going to larger turbine cm and any larger compressor. The torque output rises at higher rpm's than with stock choked turbo IMHO knowing where that torque output is on the rpm scale is most important to the tweaking of trans controller, this becomes more a problem when you don't know exactly what turbo you bolted on your 6.5td.

Here is why a dyno isn't the answer when you have an auto trans: http://www.thetruckstop.us/forum/threads/dyno-numbers-automatic-transmission.44053/#post-497361

CKO HX series are all over the board and other aftermarket turbos for the 6.5td are too so you really don't know anything w/o map or the turbo specs so it's a cr_p shoot....knowing this is important. Any aftermarket tuner should know the turbo specs and be able to give you basic out put numbers with their tune so you know too again w/o those turbo specs it's a c_ap shoot.

With a stock or rebuilt 4L80e a torque converter w/better, larger and/or multi clutch (s) is simply a good idea.

 

[FellowTraveler]

Overrun clutch is applied in manual 1st thru 3rd. Lock up should not affect it. It is used only for engine braking. Manual 2nd, applies a band that isn't applied in drive or overdrive, as does first. But the overrunning clutch is there to stop the freewheeling when the go pedal is released. The only way I believe you can burn this clutch up is from engine braking.... Like using it to slow you down going down a mountain with thousands of pounds behind you.


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Eat them brake pads because they are cheaper...............

 

[JayTheCPA]

No point in multiplying your torque if you're expending more energy in heat than you are getting extra to the ground. Also, would be the rpms and where you have power. You don't want to hold higher (or lower) rpms if it is out of your power range. But that usually only applies when you are actually accelerating or trying to maintain a speed. If you are holding wot and are losing speed at all rpms, your peak power isn't powerful enough anyway. Then you would be most concerned with what you've mentioned; getting to the top without overheating everything and causing damage. Which I couldn't imagine your lock up idea hurting in this situation as long as you're not lugging the engine. Only way to know is trying[emoji3]

BINGO! This is exactly what I am going after

Compression braking with the TCC unlocked doesn't appear to hurt it with a stock converter, but, with the TCC locked the vehicle's own weight w/o towing can slip it. Least it did for me on the grades around here. So Compression Braking IMO is the only complaint I have with the 4L80E because it is a legit and unfixable weak point. Brakes are cheaper and, yes, I eat them often...

Note the ballooning of the converter with reverse powerflow through it unlocked and additional flex plate age cracking risk.

Compression braking is hard on everything from the differential to the engine in varying degrees of reduced life.

And that is the main reason why the 4L80E has to go. I already warped a *new* set of Raybestos rotors. Another factor that kills the 4L80E is that if my RV brakes fail, the *only* remaining stopping power left is the truck's brakes. After the truck's brakes degrade / fail from overheating, I am left with deciding whether there is an embankment available for the hard stop. No thank you.

For comparison, in my DI rig, I actually lost RV brakes (that trailer was ~6K#'s as loaded) coming down a 9% grade. Not a partial failure, but complete. All I had to do was drop the ZF into 3'rd, watch the RPM's to keep them under redline, and only had to use the brakes when entering a switchback. Aside from entering a switchback, the brakes were not necessary. Sure, I crept down at 25 - 35 mph, but I did not care. Bonus was the Wife never even knew that there was an issue.

And as a point of order, the effect is more of engine braking versus compression braking. IIRC Compression braking uses an external device (like exhaust restriction or valve modification). Sure, there are factors that affect the engine when holing back the load, but this is still using a native action to the engine versus applying external force to it.

Eat them brake pads because they are cheaper...............

Need confidence in the system as a whole, so munching brakes is not going to work as the plan. Looking into a driveline retarder is by far the better solution than wondering if the brakes will survive the next descent.

 

[3500_6.5]

Only took a couple pages of talking and explanations, but I think we're on the same page now lol


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[FellowTraveler]

OK, then how much you want for the 99 Burb?

 

[JayTheCPA]

OK, then how much you want for the 99 Burb?

Ha! The Burb is definitely the keeper, but I *am* going to correct the 4L80E Better question is how much are y'all willing to pay for the 4L80E when I yank it! After all, I need to cut the cost of a ZF conversion somehow.

Oh, and WW, of all the people on here, I am just a tad surprised that you never looked into a driveline retarder rather than fry the brakes as SOP. Yes, sure friction brakes are relatively 'cheap' in the bigger picture, but there is no price one one's life when dealing with significant grade on a regular basis. Although, this is another discussion for another thread.