What is "Lock Torque Converter"

[jblack5430]

I own a 2005 Silverado 2500HD, LS/EC, 4x4, 8.1L Vortex, Short Bed and I pull a travel trailer weighing at 9700 pounds. I use Tow/Haul Mode with Over-Drive engaged. If I choose to disengage Over-Drive, is that what is meant when one "locks the torque converter" to that the Allison transmission does not use 6 gear? Also, the truck uses regular gasoline. I do not know what Locking the torque converter means. Thank you.

[GM-Tech]

This explains it better than I could...

 

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Tow/Haul Mode

 

Tow/Haul mode significantly changes the transmission shift pattern to reduce shift cycling and to deliver better performance, control, and cooling when towing or hauling heavy loads. For instance:

 

• Upshift points are raised at light to mid throttle position to use more of the available engine power for acceleration. Downshift points are raised to enhance engine braking to help slow the vehicle.

 

• During deceleration, the torque converter clutch (TCC) remains applied at closed throttle at lower speeds to significantly improve the effect of engine braking.

 

• During acceleration, the TCC is applied in 2nd range and remains applied in 3rd, 4th, and 5th. This improves the drivetrain efficiency and significantly lowers transmission sump temperature when towing heavy loads. In Normal mode, the TCC generally applies only in higher ranges and is dependent on throttle position.

 

• Tow/haul is designed to be most effective when the vehicle and trailer combined weight is at least 75 percent of the gross combined weight rating (GCWR) of the vehicle.

 

• 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. This situation will cause a firm shift. 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. Tow/haul is recommended only when pulling a heavy trailer or a large or heavy load.

[skidooridr]

I own a 2005 Silverado 2500HD, LS/EC, 4x4, 8.1L Vortex, Short Bed and I pull a travel trailer weighing at 9700 pounds. I use Tow/Haul Mode with Over-Drive engaged.  If I choose to disengage Over-Drive, is that what is meant when one "locks the torque converter" to that the Allison transmission does not use 6 gear?  Also, the truck uses regular gasoline.  I do not know what Locking the torque converter means.  Thank you.

 

<{POST_SNAPBACK}>

 

 

 

jblack,

 

YOur Allison is a 5 speed transmission.The main reason for "lock-up" [l/u] was increased fuel economy.THere are other benefits as well,like reduced heat,etc.. but that's for later.Picture the torqu converter [ t/c ]as two fans facing each other.You turn one on [starting to take off in your truck] and slowly it forces the other facing it to start turning.[ truck starting to move ]the shifts have nothing to do with the converter for simplicity's sake here] as you're driving,and upshifting the opposite "fan" is catching up with the driving fan[the "pump" in the converter] At some point-both fans are spinning at the same speed and you have a 1-1 ratio- and a "piston" applies and "wham" clamps to the "cover" of the converter [cover as in the flywheel side]- just as a side note... new converters these days "pulse" the "lock up" coming on so it's not felt as much] anyway "lock up" is felt when the

two halves[fans] of the converter come together and the "torque converter clutch" is applied[ which sometimes can be mistaken as another "shift".-The converter stays locked up instead of the one fan constantly trying to drive the other at the speed it is going [speeding up & slowing down ] this is much more efficient than than the latter.Once the vehicle slows down to a certain speed [or you apply the brake] the "piston" unlocks from the cover-and you are no longer in "lock up".

Normally l/u comes on around 40-50mph[depending on the vehicle] hope this helps

[LarryN]

Sorry that I can't help with this but the site is requiring new members to post 5 replies (#2) before they can start a thread.

 

Make it a great day!

[resq-comm]

in the same thinking, i pull a pop-up camper (about 2000# including all the crap in it and in the back of the truck) i have a 98 GMC 2500 7.4L automatic. what is the best recommendation for towing? i have heard to "keep it out of OD, end of story" and i have heard that while that is good for local/city driving, if i am on the expressway, once i reach 55 and above and keep it there i can put it back into OD to allow my RPMs to come down and be easier on my engine. with this said, my same concer applies to my wifes 02 Toyota Highlander 4cyl. that pulls the camper fine, but again, what transmission setting do i use? neither vehicle have a tow/haul switch or option

 

 

thanks,

 

Adam

[Green_Monster]

That 454 you have in your truck should tow that camper in D without a problem. Your tranny is not electronically controlled (I think) so everything is run by your synchros. This means that the same computer that controls my tranny when I throw it in tow/haul just isn't there on yours. So your shift pattern is all based on your tranny speed, vehicle speed, and throttle position. Tow/haul is just a computer telling your tranny to perform more efficiently. You have a lot of torque on hand with all that displacement, so you shouldn't have a problem unless you are going up a VERY steep hill.

 

As for the Highlander, I would keep it in 3 if you can. That 4 banger is working overtime to tow that trailer. Keep the highlander in it's powerband and keep it in 3.

 

This is all based on my experiences and what I have have read and learned in tha past. If I am mistaken, please correct me.