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Old 03-03-2017, 07:59 AM   #1
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Braking with a new truck.

Looking for information on my new truck. I recently purchased my first 2500 HD. Its a 2016 2500 HD Diesel with the Allison Transmission. We are towing a 2014 Laredo 330BH.

My question is regarding downshifting when towing. I was reading another thread on here regarding this topic. When the truck is in tow mode, when I depress the brake does it down shift 1 gear for every time depress like other Gm class A's chassis?

Also how about when exhaust brake is engaged?

I know I should read my manual, If I had time to read that thing, I would be single without 4 pre teen kids.

Also any other cool/useful info to know about this new purchase.

Any and all info is appreciated.
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Old 03-03-2017, 03:13 PM   #2
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I'd really suggest taking a little time to read the appropriate sections of the owner's manual. That way you get the 'straight dope.' Better to find time to read now, instead of in the waiting room of the dealer's service/repair center.

I know Ford's newer 6 speed transmissions offer the 'downshift on braking' when in Tow Mode, don't know or want to spend the time to look up about your GMC product.
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Old 03-08-2017, 01:55 AM   #3
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Welcome to the forum.
In general you'll want to engage the tow/haul mode whenever you're towing / loaded. It will adjust the Alli's shift points, up and down to accommodate your increased weight.
Also energize engine braking it will cause the down shifts to be more aggressive taking some of the load off of your braking systems. Both truck and trailer.
This works very well on long grades that can and will overheat brake systems on gasoline (lower compression) tow vehicles.
The engine braking primarily uses the engines high compression drag as reverse (BHP) brake horsepower. The higher the RPM the more BHP. It also uses the control vanes incorporated into the turbocharger to restrict this internal air flow.
Granted EB'ing will help reduce brake wear while driving the empty truck, but we find it a little to aggressive jerky when not towing / loaded. Also not desirable in limited traction conditions with a light rear-end.
Yes applying the brakes decelerating on a decent will "usually" cause a downshift, but it mainly depends on the engine RPM, speed, and other function being monitored by the ECM & TCM. Those modules will protect the engine from over revving, some more brake could be required. Remember though the max. engine braking force is at a higher RPMs. This can take a little getting used to. With some hrs. in the saddle you'll realize that the cruise control (if equipped) does a pretty darn good job of controlling that D-Max / Alli on most single digit% grade decents. We travel most of the western passes towing our nearly 20K# 5'r on cruise. GM has done a great job refining these control modules.
We tend to try and crest a hill / pass at the speed we'd find comfortable during the decent, say slightly below the speed limit. this will generally require less brake pedal applications.
Towing:
tow/haul on
engine braking on
Cruise on

Enjoy & Happy trails.
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Old 03-09-2017, 08:52 AM   #4
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I Totally agree with MtnTrek above ! One thing I might add is our setup (same as yours basically) will Not engage the exhaust brake until you get up to 45 mph once to lock up the torque convertor... Then it will brake down to about 15 mph before the torque convertor lets go and you are coasting... Something to remember on steep curvy roads... You can always still downshift (manually) the trans to help in braking... Over all,,, I Love the Duramax/Allison package !!!
Monkey
PS, you need to turn on the exhaust brake after every engine start if you want it... It does not "stay" on....
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