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Old 07-01-2012, 11:30 PM   #1
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I have a quick question: I was towing my 2012 31SB with my 2008 Chev K2500 suburban, 6.0, 3:73 rear, in reverse up my driveway, about 12% grade in normal reverse, and the truck stopped about half way. The engine kept running, but would not move in reverse in anyway. I drifted back down the driveway, shifted into 4L, and had no problems with the extra torque.
My question is, does anyone know if GM built an actuator into the transfer case, controller or transmission that disengages torque if pressure/temp gets to high. I had 236 on the transmission for about 30 seconds. One other question, this truck came with the towing package, including the external trans cooler and engine cooler, but I'm still running hot, 205 on trans, 245 on engine when towing flat. I'm really dissapointed in the power from this truck to begin with, and any idea's to cool it down, increase HP would be greatly appreciated.

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Old 07-02-2012, 12:53 AM   #2
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The transmission has a limp mode. Will not shift into upper gears until the transmission cooles down. Had it happen on a motor home with the chevy 454 engine. As far as reverse it may do the same.

Did the reverse gear work after it cooled down? May want to "google" it for info.

Don't think the engine and tranny should be running that hot - may be time to flush the coolant and check the coolers to ensure the fins are not blocked with dirt and bugs.
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Old 07-02-2012, 01:17 AM   #3
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I tow with same engine and axle ratio and tow in 3rd all the time. Elimanates all the shifting and the tranny runs cooler. As far as backing that load up 12% , good thing you have 4lo. The AT will slip no matter what the temp when it is overloaded. I'm pulling a Kingston 30sb about 10,000 mi a year. The TV is an 2002 no problems. I change the tranny fluild around every 30,000 mi. I am using a K&N air intake and Edlebrock shorty headers. Seem to help with the tork a litttle. We have pulled 8% grades in Col. and go where every we want to go with this rig. Maybe just not as fast as the diesels.
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Old 07-02-2012, 02:03 AM   #4
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One of the big problems with the new body style GM's is the amount of Torque Management GM programs into the control modules. Do a Google search on Torque Management. I am going to have a custom tune made for my truck from Justin at Black Bear Performance and that will eliminate the gutless performance on the 07 and up GM's.
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Old 07-02-2012, 03:37 AM   #5
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High load with very little air flow over the transmission cooler is a real problem. In the days before so much computer control, it was ez to boil fluid out the filler tube. You did the right thing using 4L for several reasons. Next time minimize the time spent backing up or stop part way and shift back into neutral for a few min.
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Old 07-03-2012, 03:55 AM   #6
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If I ever reverse up hill I always use 4L. Never have thought about it. Just what I've always done. Thanks for the info.
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Old 07-03-2012, 10:00 AM   #7
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Had a GM rep respond to me on these issues, and per GM, my 08 K2500, 6.0, 3:73 has an Allison transmission, and I should be towing in M5 (Manual, 5th gear). As far as loss of torque backing up, and overheating transmission and/or Engine, the trucks computer will reduce horsepower and/or torque when it senses either. It will continue to reduce them until either the engine/tranmission cool down, or the pressure reduces. This is why I can't back my trailer up my driveway in normal reverse. I had to take the trailer for a 108 mile ride today to get a bunch of warranty items fixed, and putting the truck in M5 definetly made a difference. Transmission never got over 212 (maybe 5 minutes getting over the Delaware Memorial Bride, and the engine never got hotter then 235. I am going to shop for a performance chip/programmer, and go ahead and put on some extra coolers. Otherwise, stock is not bad.
Thanks for all of the info either way.

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Old 07-04-2012, 10:52 PM   #8
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Our drive is at an incline also and I always use 4Low when backing it up. Also always change tranny fluid and filter every 30,000 or 3 years.

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Old 07-05-2012, 03:21 AM   #9
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I agree with the changing. I am only at 40% on my oil, but I have a long trip scheduled soon so I'm having the oil, the cooling system, and the transmission system all serviced. Next year when I prepare for full-time I will have new tires put on the TV, probably LT's and I will also have the brake system totalled reworked...cannot be too safe as you have all said.


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Old 07-05-2012, 04:06 AM   #10
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Something to consider - 4L is a super low gear in the transfer case, which translates into less speed and more applied torque when in low-traction/low-speed situations. This is likely why it makes a difference, coupled with added traction being in 4WD. The lower gear probably compensates for computer's down-tuning.
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