6l80 Tc Lockup

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Anyone have the specs on Torque Converter lockup on the 6L80/90? When towing, for example, if you manually select 4th, does the TC lockup? The TC locks in 3rd and 4th on the 4L60, but I would like to know more about the 6-spds, since (of course) this affects heat generation when pulling a load.

[RyanbabZ71]

check the gmpowertrain.com website

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check the gmpowertrain.com website

 

I looked there first, but no luck. Any links?

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I have not been very successful in finding info on the 6L80/90 TC lockup function. What I have gathered so far is that the TC *can* be locked from 2nd through 6th, but nothing about how GM actually does it. I'm particularly interested in towing applications. I would think that they would lock the converter in 6th/5th/4th for certain, and probably 3rd when tow/haul is engaged? Anyone on here towing and have paid attention to how it behaves? I'm pretty sure 2nd never locks on the 4-spds, or at least not when pulling a load.

[2005LT]

Robert, although there is no way for me to confirm this but even without having tow/haul on, I can feel the torque converter locking up in most of the gears as you mentioned (4th to 6th for sure). It may even lock in 3rd but I admit I haven't paid close enough attention. Lock-up seems to vary under different throttle conditions and around shifts. It's definitely not a simple process like it used to be.

 

I notice this most on the 3-4 (I think) upshift while applying constant throttle to accelerate with RPM around 1700-1800. This occurs around 35 mph. Right after the shift into 4th while still accelerating, I can feel the truck starting to pull stronger and the engine lugging down with the RPM either remaining constant or dropping slightly. This occurs over a couple of seconds so it is quite a smooth transition and I assume this the be the converter locking up. After this point, the RPM no longer varies with throttle position/engine load which is a sure sign to me that the converter is locked. Typically, I am used to the TC lock up feeling like a "shift" but not in this truck. It's smoother and harder to notice.

 

Personally, this operation makes this truck hard to drive since it shifts very early under most conditions (ie: it's in 6th gear at a constant 35 mph with the RPM hovering around 1000) and keeps the TC locked. What kind of throttle response do you get at 1000 RPM with the converter locked?.......NONE. It's hard to keep constant speed in this scenario since about an inch of throttle pedal travel yields almost no response. You could be slightly speeding up or slowing down....it's quite tough to estimate. Then when I need to speed up, usually I get frustrated and mash the throttle (cause that's what it takes to get it to downshift under this condition) to get some response. It just lugs badly with the RPM so low when trying to accelerate...even lightly. Man, I need a Black Bear tune.

 

All I've described is with T/H turned off. Once it's on this all changes. Granted I haven't used T/H much but the lock-up is definitely more pronounced and obvious from at least 3rd gear or perhaps 2nd onward. Someone else can probably describe it better.

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Peter: That info is very helpful. It sounds like it may be better to use manual mode in 5th (6th locked out) around town? Does that help much with daily driving? With all the posts regarding the 6L80/90 and how much better some think they are (or should be) at towing, it had me thinking that it may be worth considering sooner than I normally would. When thinking on it and even test driving a couple (simulating towing), I couldn't tell much difference. The big difference seemed to be that the 4-spd used the TC more. Cruising in 4th, the TC unlocks for most grades when not towing (I never see 3rd on the interstate). When towing w/ 7k lbs, I run in 3rd and the TC unlocks for moderate grades if needed, increasing 300 rpm or so, then dropping to 2nd if the hill starts getting too steep. I haven't (and can't) tow the same load w/ a 6-spd, so I'm wondering how the TC performs on the 6L80 (i.e., does it act as an "in between gear"... or does it more-or-less try to lock into the 6 gears, with little TC work being done?

[MS3DALE]

This doesn't really answer your question,but its good informantion....

 

 

Subject: Shift Stabilization and Tow/Haul Mode Feature for Hydra-Matic® 6L80/6L90 Automatic Transmissions

 

 

Models: 2007-2009 Cadillac Escalade, Escalade ESV, Escalade EXT

 

2007-2009 Chevrolet Avalanche, Silverado, Suburban, Tahoe

 

2007-2009 GMC Sierra, Sierra Denali, Yukon, Yukon Denali, Yukon XL Denali

 

2008-2009 HUMMER H2

 

with 6L80 (MYC) or 6L90 (MYD) Automatic Transmission

 

 

Bulletin Content:

This bulletin contains information regarding Shift Stabilization and Tow/Haul mode. These features affect transmission shift patterns and the customer's perception of shift feel. Customers may notice a change in shift patterns between previously owned vehicles without shift stabilization and current vehicles with shift stabilization.

 

Shift Stabilization:

Applies to all above listed models.

 

PURPOSE

• Some customers may comment that upshifts are delayed or not available when in fact the transmission is operating normally with a feature known as "shift stabilization." This may contribute to "cannot duplicate/no trouble found." It is important that the customer be educated about this feature if this occurs.

 

• The purpose of shift stabilization is to reduce shift busyness during conditions that would otherwise produce frequent upshifts and downshifts, such as trailering, operating on grades or at higher altitudes.

 

• Shift stabilization is an algorithm in a vehicle's software/calibration that determines if and when to prevent upshifts under load. Shift stabilization only affects upshifts and not downshifts.

 

ACTIVATION

• This feature is internal to the vehicle's software/calibration and requires no customer action to activate.

 

• Shift stabilization is effective in normal mode, cruise mode, and in tow/haul mode.

 

FUNCTION

• Shift stabilization calculates the required torque at the wheels in the current gear as well as the maximum torque available at the wheels in the next higher gear. If the torque in the higher gear is not sufficient, the transmission will remain in the current gear. If the torque in the higher gear is greater than or equal to the required torque, than the upshift is allowed.

 

• High throttle opening will disable shift stabilization and normal downshifts will occur.

 

• Shift stabilization occurs in the 6L80/6L90 for only 2-3, 3-4, 4-5, and 5-6 upshifts.

 

• Shift stabilization might be disengaged in the following situations:

 

• During cruise control operation when the "decrease" button is tapped or held, shift stabilization may be disengaged.

 

• If a significant "bump" in the road is encountered, shift stabilization may be disengaged.

 

Tow/Haul Mode:

Applies to all models listed above.

 

PURPOSE

• It is important to note that the customer may accidentally engage the tow/haul button and then comment about delayed or harsh shifts when not pulling a trailer or under heavy load. Normal function of tow/haul mode when used in inappropriate conditions may contribute to complaints that "cannot duplicate/no trouble found."

 

• Tow /Haul mode will optimize gear selection for operation with heavy loads (such as towing):

 

• optimize acceleration performance for launches and rolling accelerations

 

• reduce shift cycling

 

• optimize braking performance and speed control during engine braking situations

 

• improve vehicle speed control while requiring less throttle pedal activity

 

• Because tow/haul mode maintains lower gears longer and increases shift pressures, it will degrade fuel economy and generate shift feel concerns if it is used inappropriately in unloaded driving conditions.

 

ACTIVATION

• Tow/Haul is selected or de-selected via a switch on the end of the transmission shift lever for all models. A light on the instrument panel will illuminate to indicate that tow/haul has been selected.

 

• Tow/Haul must be reselected every time the vehicle is started (if desired).

 

FUNCTION

• Tow/Haul is designed to be most effective when the vehicle and trailer combined weight is at least 75% of the vehicle's Gross Combined Weight Rating (GCWR).

 

• Operation of tow/haul in a lightly loaded or non-loaded vehicle will not cause damage. However, there is no benefit to the selection of tow/haul when the vehicle is unloaded. The tow/haul switch is not a performance switch.

 

• Selection of tow/haul when unloaded may result in unpleasant engine and transmission driving characteristics and reduced fuel economy, since upshifts occur at higher engine speeds. Tow/Haul is recommend only when pulling a heavy trailer or a large or heavy load.

 

• Automatic downshifting (Normal - Powertrain Braking) to assist speed control will activate when Tow/Haul mode is active and the brake pedal is depressed (even lightly). Downshifts are commanded at higher speeds than normal resulting in engine braking that assists with speed control. After a powertrain braking situation ends, upshifts will typically be commanded when the accelerator pedal is pushed down. (a quick increase in accel pedal may be required)

 

• Starting in the 2009 model year, a similar function is available during cruise control operation (in Tow/Haul only). Automatic downshifting (Cruise - Powertrain Braking) to assist in speed control will activate when vehicle speed has increased from the set point by a certain amount. Multiple downshift may be commanded depending on the amount of deviation of vehicle speed to the set speed. As vehicle speed slows and approaches the original set speed upshifts will be commanded to return to a normal operating condition.

 

• At some speeds and on some downhill grades, the transmission may not be able to command a gear low enough to slow the vehicle to the set point without overspeeding the engine.

 

• In this case the transmission will command all available downshifts but if further engine braking is desired the driver must press the brake pedal to slow the vehicle enough so additional downshift(s) can be commanded.

 

• Pressing the brake pedal has the normal effect of cancelling cruise control operation and in this case a transition to Normal - Powertrain Braking is completed.

 

• As always, if cruise control operation was cancelled through usage of the brake pedal, it must be reinitiated by tapping either the Set or Resume Cruise switches.

 

Refer to vehicle Owner's Manual for further information regarding tow/haul mode.

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Thanks Rich! Lots of good info in that TSB.

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Bump... still looking for info on towing with the 6L80 and how the TC lockup function operates. I've Googled it and found nothing

[2005LT]

I understand better now what you're trying to get at Robert and unfortunately I haven't towed enough to properly answer your question. I'm sure someone here can though, just need them to see the thread. Free bump.

 

I've considered running around town in 5th since that's certainly an option. I'd probably lose a little bit of economy since I'm sure that's why it was programmed to run at low RPM. Over time I've gotten more used to it. I'm sure the 6 speed would tow great for you. The extra number of gears to pick from really helps out. I've noticed this when driving the steep mountain passes out here. It's nice to have it downshift to 5th (or 4th on occasion) without totally revving it's guts out.

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Bump. Anyone payed attention to their TC lockup vs gearing when towing or hauling a load?

[TorkFaze]

If anything, the 6-speed trucks apply the converter more often than the 4-speed. Dunno which engine you're most interested in (there are slight differences between how the 5.3 and 6.2L are done), but in general, unless you're at pretty low RPM (not so likely when towing), you'll have the converter applied. Tow/haul uses the converter more aggressively than regular. Heat is one of the reasons...the other reason is that especially for gears 4,5,6, the gear spacing is tight enough that if you need more torque, a downshift gives you similar torque AND similar RPM to a slipping converter in the upshifted gear, so except for a few specific situations, the trans will downshift rather than unlock and make heat.

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If anything, the 6-speed trucks apply the converter more often than the 4-speed. Dunno which engine you're most interested in (there are slight differences between how the 5.3 and 6.2L are done), but in general, unless you're at pretty low RPM (not so likely when towing), you'll have the converter applied. Tow/haul uses the converter more aggressively than regular. Heat is one of the reasons...the other reason is that especially for gears 4,5,6, the gear spacing is tight enough that if you need more torque, a downshift gives you similar torque AND similar RPM to a slipping converter in the upshifted gear, so except for a few specific situations, the trans will downshift rather than unlock and make heat.

 

Thanks TFaze. That's exactly the kind of information I was looking for. I'm towing a 7k lb (loaded) camper, and with everyone onboard and connected, I'm right at GVWR on the truck, and not far south of GCWR. When towing, I pull in 3rd, which unlocks for moderate inclines, dropping to 2nd on steeper ascents. I've never lacked power in 2nd, and have thus far had throttle to spare. Looking at the numbers on the 6L80/3.42 and 5.3, I would expect that the same configuration would run in 4th most of the time, maybe use 5th on flat/gentle terrain (a little better than 4th/3.73 on the 4 spd). It will need 3rd on climbs, but I was wondering if 3rd will "unlock" and give something in-between 3rd and 2nd... to keep from revving *way* up?

[nickvrebel]

I'll be able to give you exact specifications in about a week... I have HP Tuners on order and that will give me the tables to see what conditions would have to be met for lockup.

 

I've tuned on 2000 and 2003 trucks with the 4L60e, but it's been a few years. I had to order a newer style cable from HP Tuners to hook up my new truck, but I should have access to all of the tables to see what the criteria would be.

 

That being said, any custom tuner (not talking handheld) would be capable of making it lockup at any time you want.

[TorkFaze]

... but I was wondering if 3rd will "unlock" and give something in-between 3rd and 2nd... to keep from revving *way* up?

 

 

At the higher rpm (3200 or so) that you'd have in 3rd at 55mph with a 3.42 axle, unlocking the converter would only buy you a little more rpm (slip ~300-400 rpm) and a little more torque to the wheels. That said, I'm pretty sure that there are some conditions where you can run 3rd with converter released at heavy throttle to do as you suggest. Honestly, it's been too long since I looked at the 5.3L/MYC trans shift schedules to say for sure. The good news is that the smaller slip across the converter in these cases won't make as much heat as if you were trying to pull the hill in 4th with TCC off with much larger slip.

 

The 6-speed trans trucks have a pretty good trans cooling package on them. For the record, I don't subscribe to the "anything over 170F means your trans is toast" theory that you see on the net (and have access to a bunch of data on Dex VI to support my position). That said, I have not seen any worrisome trans temps on any of my testers in towing at GCW on some pretty aggressive hills in pretty warm ambient temps. Yea, you can beat a 6-speed vehicle up and get things hot, but the trans fluid is almost always the last fluid to get to a point where I'd be uncomfortable.

 

I'm biased, but I think the 6-speed really tows nicely. Features like grade braking and cruise grade braking (both active only when in T/H and Drive range or M6) as well as the ratio steps make the towing experience really nice. It launches better with a load than previous transmissions due to the big first gear and it's not as busy as a trans with bigger ratio steps. It probably runs at a lower average RPM, too. The lower average rpm is probably better fuel econ when towing, but even if that's not measurable, the reduced engine noise at lower RPM certainly is nice!

 

Ready to buy one yet??

 

TF