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Old 05-26-2016, 11:15 AM   #29
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Originally Posted by franklyfrank View Post
The big deal is that while descending, with all for wheels engaged in full time four wheel high, all four TV tires are aiding in holding the TV back without having to hit the brakes as often. It is simply safer. I use it whenever I am on up or down mountainous and curve terrain otherwise it is in 2 wheel at all times.
Ok, I double checked myself by contacting our Brand Quality Manager for PUs. He verifies all I have said and also, like me, believes this is a non-issue. It is virtually impossible (on clean dry pavement) for an automatic transmission of any vintage to create more than a "chip" before GAS engine RPMs catch up to gearing/tire speeds. And then only if the operator drops too many gears relative to road speed. On modern transmissions (electronic) the trans has self protect logic the prevents dropping too many gears by operator error. I can't recall when that started, but it was MANY years ago.

In addition, there are other systems which will mediate on slippery surfaces (rain, oil/water mix, or God forbid..snow/ice). Although it is not in the owner manual nor service manual, there is logic in the traction control system to also account for the "reverse kind of slip" we are talking about here. Also Stability control and trailer sway control logics will mediate as well.

Modern GM diesels have these algorithms as well, plus the exhaust brake is tied into the remedial action as well.

We could talk about really old tech vehicles and manual transmission, and diesels with sticks, but that should be another thread.

Bottom line, with the OPs title line vehicle, as well as many other manufacturers vehicles, this is a non-issue and WILL cause accelerated wear/failure of transfer cases, especially if adopted as a practice.

All that said, if you are on a slippery or gravel/dirt surface, your advice is appropriate.
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Old 05-26-2016, 11:19 AM   #30
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Originally Posted by wbrisett View Post
To be clear on my vehicle, I do not have 4WD, but 2WD. I did have AWD, but that was on my Subaru Outback and that couldn't tow my last trailer, or the Airstream.
You're fine. Don't worry about it. Your truck has many, or all, of the remedial action safeguards I mentioned. Especially if it has the ITBC. (I am assuming you're well averse to proper mountain driving techniques....if not ask someone)
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Old 05-26-2016, 11:42 AM   #31
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FF,
Excellent point as forgot to mention having the 4x4 and available AWD setting. Never used it except for test on a ski trip/mostly cleared road.

Anyone else out there using the AWD setting while towing and would it be good mechanical practice all the time or just anticipated downhills ? Also Shifting to it while freeway speeds or only stopped ?
It's not an AWD setting...It's "auto". See above post.
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Old 05-26-2016, 07:16 PM   #32
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Why not use the brakes? Brakes, by design, are a wear item and reletivly inexpensive to replace compared to a transmission.
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Old 05-27-2016, 03:49 AM   #33
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Why not use the brakes? Brakes, by design, are a wear item and reletivly inexpensive to replace compared to a transmission.
The idea is to not burn up your brakes, instead you allow the vehicle to help you so you're not riding the brake. As several have pointed out, the grade braking feature is designed to help you without damaging the transmission. I have seen it engage a couple of times on my older (and lighter) Aframe camper, but not on steep declines, and really didn't feel the affect of it, so I had no idea how well it worked. That was the point of my discussion here.

Can you just ride the brakes? Yes... and this may be the only option depending on the vehicle. But it actually can be harder on the brakes and rotors since they can get extremely hot if you end up riding them. It's not the brake pads you worry about so much in this situation, but the rotors. Damage those and you're going to wish you hadn't.

Going through the mountains of New Mexico and Colorado will give me quite a bit of experience with the grade braking on this trip. I'll post my first hand experience in a couple of weeks when I return from the trip.

Thanks to all for the information provided.
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Old 05-27-2016, 09:23 AM   #34
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Why not use the brakes? Brakes, by design, are a wear item and reletivly inexpensive to replace compared to a transmission.

To use your brakes as a primary to slow your descent will over heat them and could make them useless.
This entire argument is pointless in my opinion. To argue against common sense, which unfortunately seems to be very common on these treads is down right stupid. Engaging all four point traction in conjunction with the engine brake to aid in safely descending on steep grades is what professional drivers do.
To suggest that the manufacturer builds a truck with this capability and than not to use it because it wears on the truck is asinine. If one doesn't have the basic understanding of the concept of using the locked 4 wheel drive option as needed and not when it isn't shouldn't be on the road pulling a trailer.
I was very specific in my initial post that I use it mostly descending and occasionally as needed, never suggested as a full time driving mode. I didn't think it was needed assuming we are all intelligent competent individuals.
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Old 05-27-2016, 09:46 AM   #35
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Originally Posted by dznf0g View Post
It's not an AWD setting...It's "auto". See above post.

Yes, you are correct as it is AUTO (was going from memory).

Perhaps AUTO would be a better compromise between 2 wheel vs 4 wheel drive on such downhills ?
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Old 05-27-2016, 11:50 AM   #36
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My vehicle has 4 drive options. 2H, AWD, 4H, 4L. The owners manual (Ford) is very clear, only 2H and AWD on pavement. 4H and 4L non pavement only othwise damage may occur. Engine braking is accomplished by shifting down thus causing the engine to be forced to rev higher which is reletively harmless. Putting into 4H or 4L on pavement will also help to slow down because the transmission is binding internally, probably overheating, and trying to destroy itself. For these reasons I don't buy the argument favoring 4H downhill on dry pavement.

Your vehicle and trailer brakes ought not to overheat to the point of damage or fade unless you allow the rig go too fast.
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Old 05-28-2016, 09:57 AM   #37
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My vehicle has 4 drive options. 2H, AWD, 4H, 4L. The owners manual (Ford) is very clear, only 2H and AWD on pavement. 4H and 4L non pavement only othwise damage may occur. Engine braking is accomplished by shifting down thus causing the engine to be forced to rev higher which is reletively harmless. Putting into 4H or 4L on pavement will also help to slow down because the transmission is binding internally, probably overheating, and trying to destroy itself. For these reasons I don't buy the argument favoring 4H downhill on dry pavement.

Your vehicle and trailer brakes ought not to overheat to the point of damage or fade unless you allow the rig go too fast.
Buy it or not it is obvious you don't have any experience with utilizing your vehicles capabilities and options to your advantage. And the only reason I am responding is that you are misleading people into believing that using the 4 wheel option is not advisable and that a half ton 4 wheel drive pick up is a fragile piece of equipment. That is pure poppycock.
I use it every time conditions require it. I have yet to to experience transmission over heating or any other adverse effects. Have you ever plowed snow with your pick up ? Obviously not. The stress a truck is placed under pushing heavy snow and ramming snow banks to push up the pile is far more stressful than descending at 30 or 40 MPH 30 minutes at the time.
I used a Tahoe to plow our facilities over 10 seasons. I literally beat the crap out of it plowing. It was also my daily driver and used for many trips to Florida ended up putting 230 K miles on it. Never had any Transmission or Drive train failure. So please stop projecting your anxieties on everyone else.
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Old 06-13-2016, 05:05 AM   #38
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Originally Posted by dznf0g View Post
You're fine. Don't worry about it. Your truck has many, or all, of the remedial action safeguards I mentioned. Especially if it has the ITBC. (I am assuming you're well averse to proper mountain driving techniques....if not ask someone)
Back from Yellowstone. Headed out to the black hills as well. Our steepest descent was a 8% grade. The good news is you're right, had nothing to worry about. :-) The truck and grade braking handled things like a champ.

So, bottom line, the GM grade braking system gets high marks in my book and works very, very well.
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Old 06-13-2016, 05:08 AM   #39
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Although not the rockies, I was in Smokies last week, and found the same with my 30'er in tow. You certainly use the brakes a bit more than a diesel, but not a lot. And certainly not enough to even warm the brakes much.
As I recall, 6% was common and most I saw.
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Old 06-13-2016, 06:03 AM   #40
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Originally Posted by wbrisett View Post
Back from Yellowstone. Headed out to the black hills as well. Our steepest descent was a 8% grade. The good news is you're right, had nothing to worry about. :-) The truck and grade braking handled things like a champ.

So, bottom line, the GM grade braking system gets high marks in my book and works very, very well.
Great. Thanks for the update. We are pulling our 25' out of the FL flatlands for the first time starting next weekend, and while I can do things like make sure it's level and that the WD hitch is setup right, I don't have an easy way to test grade braking. So it's good to know that it worked well for you.
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Old 06-15-2016, 11:15 PM   #41
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I have a 2015 Sierra 1500 SLT with the 6.2 liter engine and 8-speed box. Also the max trailer tow package. There are 2 modes to the hill descent control. The more aggressive mode is invoked when you use cruise control; the transmission will start downshifting when you exceed the set speed by 5 mph and will continue to downshift if the vehicle keeps accelerating spinning the engine up to about 4200 rpm. The second mode is less aggressive and kicks in based on some combination of factors that I can't figure out. The nice thing is that when cruise control downshifting happens, applying the service brakes does not trigger an upshift. You can use manual control as well, without fear of over revving. The shift command will be refused if it would cause an overrun.
Regarding the use of "auto" on your 4wd setting, I don't see why that would provide any benefit. In fact, if you're in a low-traction situation (rain, snow), you should be careful about using a lot of engine braking. Use the service brakes instead and slow down a lot. Remember that most newer US-branded trucks with integrated trailer brake controllers include ABS and D.SC. Functions.
I've descended up to 10% grades without incident, using the service brakes as needed and never got them hot enough to smell. That's pulling an FC27.
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Old 06-16-2016, 12:07 AM   #42
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Why not use the brakes? Brakes, by design, are a wear item and reletivly inexpensive to replace compared to a transmission.
You know the Runaway Truck turn outs over on 80? and there are several of them? And a few on 50 coming down Spooner. Ever see the trucks setting in that gravel? Or see a truck turned over and 80 is closed because he didn't have a Runaway turn out? Comes from inexperienced drivers riding the brakes. Best not descend at a speed where the rig pushes the engine revolutions up, that the compression doesn't hold back the rig.
First sign you have trouble is a warped rotor. Then fading. Maybe you'll see smoke.
Don't light up the forest with a fire from your brakes, not cool. They burn up the hills around Kyburz regularly with brake fires, and cigarettes.
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