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Discussion Starter #1
Gents,
We've had this '15 JKUR for about 4 months now and haven't had all that much time for playing off road with a couple small exceptions. We've been Jeepers for oh, going on about 30 + years now with places like Moab UT, Ouray-Silverton CO, AZ, CA and a couple other states with off road availability under out belts, numerous times. So, we've got plenty of Jeeping experience, in all kinds of conditions.

Well, this new JK of ours has what many of yours has and it's called "Hill Descent Control". Not really knowing anything about it and or when and how it's used, I cruised on over to you-tube and did a little digging around. I found a couple of videos there pertaining to it's operation.

Well, it seems it's basically a system by which the brakes are applied, automatically, when descending a hill, and the Jeep is in 4WD and specifically in 4L. Based on what I saw and was moderately explained in the videos, it's just a basic way of holding speed, without YOU actually applying the brakes 'cause it does it for you.

Well, this is our 3rd Rubicon folks. Our others were an '03 and an '04. We've got lots of miles going DOWN STEEP HILLS, using 4L and, keeping the trans in either 2nd or 1st, depending on just how slow I want to go. But, if I use 1st gear for the descent, I can get out and make lunch along side those Jeeps while they're ultra-slow rolling. Oh, by the way, both those TJ Rubicons and the present JK Rubi are all automatics. The '03 was running 4:10s with 33s, the '04 was running 4:56s with 35s and this present one is sporting 3:73s with 315s. And even this present one with 3:73s, has tons of slow crawl down hill without using any brakes with all the control in the world.

So, hence, what's the main difference between using the "Hill Descent Control" over using just 1st or 2nd gear while descending a hill that needs that kind of control??
Scott
 

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Disclaimer: I am still a newbie Jeeper (...but maybe HDC is more useful for a newbie? :shrug: )

First trip out and part of the second, I totally forgot about HDC. I found that I was often riding the brakes on steep downhills. I sometimes felt like the Jeep was picking up speed going downhill even in 4L 1st gear. I'm not sure if I was just being overly worried not knowing what to expect, or if it actually was picking up speed. Once I finally remembered about the HDC button and decided to try it out. It certainly made me less worried about going downhill too fast, although I suppose it's just the Jeep riding the brakes instead of me doing it. By the way, I was in 1st gear (maybe 2nd, don't remember now) when I used HDC. I've read that it maintains a different speed depending on if you're in 1st, 2nd, or D.

Oh yea, and I guess you have gearing on your side too with the Rubicons. I have a Sport with 3.21 axle ratio. So maybe HDC is more useful for some than others.
 

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I have a 2012 2 door COD MW3 JKR with auto transmission, 4:10 gears and 35x12.50x17 Nitto Trail Grapplers that I bought used in 2014. I have had many 4x4s over the years including several Jeeps and my method was always to put the Jeep in 4x4 low and first gear and use the engine and transmission to control my speed down steep slopes. I had never even tried the Hill descent until recently but it did really impress me and I can see that there are certain instances where it is very useful. I can definitely see where this would be useful to those with 3:21 gears.

I was on a trial ride with some other Jeeps on Black Friday and the Hill descent assist came in very handy. About a half hour in and far from the parking lot or any roads, the fuel pump went out in one of the Jeeps in our group. We still had a few hills to climb but that was no problem any of the Jeeps in the group could hook up with tow straps for those. Since his engine was not running he did not have power steering or power brakes and was concerned about having sufficient control while coasting down the slope. However before we started going down I got behind him and hooked up. I was able use the Hill Descent Assist to carefully hold back his Jeep, my Jeep (and at times the tow jeep). Everyone in our entire group was very impressed with this feature and in this case it really helped get a fellow Jeeper out of the woods safely.
 

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From the manual:

Hill Descent Control (HDC) – If Equipped

HDC is only intended for low speed off-road driving. HDC maintains vehicle speed while descending hills in off-road driving conditions by applying the brakes when necessary.

The symbol indicates the status of the Hill Descent Control (HDC) feature. The lamp will be on solid when HDC is armed. HDC can only be armed when the transfer case is in the “4WD LOW” position and the vehicle speed is less then 30 mph (48 km/h). If these conditions are not met while attempting to use the HDC feature, the HDC indicator light will flash on/off.

When enabled, HDC senses the terrain and activates when the vehicle is descending a hill. HDC speed may be adjusted by the driver to suit the driving conditions. The speed corresponds to the transmission gear selected.

Gear Approximate HDC Set Speed
1st 1 mph (1.5 km/h)
2nd 2.5 mph (4 km/h)
DRIVE 7.5 mph (12 km/h)
REVERSE 1 mph (1.5 km/h)

However, the driver can override HDC operation by applying the brake to slow the vehicle down below the HDC control speed. If more speed is desired during HDC control, the accelerator pedal will increase vehicle speed in the usual manner. When either the brake or the accelerator is released, HDC will control the vehicle at the original set speed.

Enabling HDC

Shift the transfer case into 4WD LOW range. Refer to “Four-Wheel Drive Operation” in “Starting and Operating” for further information.
Press the “Hill Descent” button. The “Hill Descent Control Indicator Light” in the instrument cluster will turn on solid.
Note: If the transfer case is not in 4WD LOW range, the “Hill Descent Control Indicator Light” will flash for five seconds and HDC will not be enabled.

Disabling HDC

Press the “Hill Descent” button or shift the transfer case out of 4WD LOW range. The “Hill Descent Control Indicator” light in the instrument cluster will turn off.
 

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Gents,
We've had this '15 JKUR for about 4 months now and haven't had all that much time for playing off road with a couple small exceptions. We've been Jeepers for oh, going on about 30 + years now with places like Moab UT, Ouray-Silverton CO, AZ, CA and a couple other states with off road availability under out belts, numerous times. So, we've got plenty of Jeeping experience, in all kinds of conditions.

Well, this new JK of ours has what many of yours has and it's called "Hill Descent Control". Not really knowing anything about it and or when and how it's used, I cruised on over to you-tube and did a little digging around. I found a couple of videos there pertaining to it's operation.

Well, it seems it's basically a system by which the brakes are applied, automatically, when descending a hill, and the Jeep is in 4WD and specifically in 4L. Based on what I saw and was moderately explained in the videos, it's just a basic way of holding speed, without YOU actually applying the brakes 'cause it does it for you.

Well, this is our 3rd Rubicon folks. Our others were an '03 and an '04. We've got lots of miles going DOWN STEEP HILLS, using 4L and, keeping the trans in either 2nd or 1st, depending on just how slow I want to go. But, if I use 1st gear for the descent, I can get out and make lunch along side those Jeeps
while they're ultra-slow rolling. Oh, by the way, both those TJ Rubicons and the present JK Rubi are all automatics. The '03 was running 4:10s with 33s, the '04 was running 4:56s with 35s and this present one is sporting 3:73s with 315s. And even this present one with 3:73s, has tons of slow crawl down hill without using any brakes with all the control in the world.

So, hence, what's the main difference between using the "Hill Descent Control" over using just 1st or 2nd gear while descending a hill that needs that kind of
control??
Scott
HDC came from LandRover of the early 2000's and is still today a standard feature on LandRovers/RangeRovers.

It is a heavily overlook feature by JK/JKU owners and is most beneficial to newer Jeepers learning the ropes. When engaged it basically mimics the feel of 1st gear low range with 4:10 gears and 4:1 transfer case. It is almost to slow when used in 1st gear but one can add a little throttle if needed or shift to 2nd gear.

The HDC is GREAT if the slop or hill one is going down is slick (icy, snow covered, loss gravel or muddy) offering far superior control over just low range 1st or 2nd gear. Although not designed for it, also works well on ice covered flat surfaces at slow speed such as driveways and parking lots.

The down side to HDC is prolonged heavy use will overheat the ABS/TC system which means possible NO BRAKES. Seen this happen in LandRovers but yet to see it first hand in a JK/JKU.

I encourage even experienced Jeep owners to play around with it and experiment. Most that do find they like it especially on slick downhills.
 

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Discussion Starter #6
Thanks to all who've contributed to this query. We not only have this HDC in our Jeep but also the "Hill Start Assist" option too. We've not really tried that one out either. If I'm not mistaken, for it to work with an automatic, while holding the vehicle on a hill, in prep for take-off when the light turns green, you simply slide your foot off the brake pedal and over to the skinny one. And, at that time, the vehicle is NOT SUPPOSED TO DRIFT BACKWARDS, correct?
Scott
 

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I tried Hill Decent first time out at the OHV park. It worked well.

Unfortunately, I've forgotten about it on every trail run I've been on. So never used it in the real world.

Seems it'd be useful on long decents.
 

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Thanks to all who've contributed to this query. We not only have this HDC in our Jeep but also the "Hill Start Assist" option too. We've not really tried that one out either. If I'm not mistaken, for it to work with an automatic, while holding the vehicle on a hill, in prep for take-off when the light turns green, you simply slide your foot off the brake pedal and over to the skinny one. And, at that time, the vehicle is NOT SUPPOSED TO DRIFT BACKWARDS, correct?
Scott
Correct. Works well.
 

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One feature of Hill Descent Control being overlooked is the system's ability to apply the brakes to an individual or pair of wheels in response to a wheel sensor sensing the slip angle moving in a direction opposed to where the steering is pointed. Similar to the on street performance of the Electronic Stability Control when it senses a slide or skid, the system applies brakes to individual wheels and/or cuts throttle in order to bring the skid back in line with the yaw control/steering input.
The system was invaluable going down Black Bear Pass in the rain.....then the snow.....then the rain again. I'm a decent driver, but this one exceeded my skillset. By a bunch.
If I had the mailing address of the HDC engineering team at Chrysler, I'd mail them a thank you.


 

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Discussion Starter #10
billum,
Been on Black Bear a couple times. It's a great run. Tons of sights/views etc. And, the section at the top can develop a bit of pucker factor if one's not used to that sort of thing. All those runs in that Ouray/Silverton/Animas area are really fun and scenic.
Scott
 

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HDC is s great tool for rigs that have limited gearing, limited flex and open diff's, or any combination of the 3.
In a rubi with deep gearing, locked diffs and the sway bar disco'd... I don't know that it's better/worse/needed.
The gearing will keep the speed super slow if all the tires are on the ground, the sway bar disco'd will help keep all the tires on the ground, and, should tires be in the air, the lockers will keep them spinning at the same speed as the tires with traction... slow.
Now, in an automatic, in the days before electronically controlled transmissions, even given all the above, the trans would let the convertor slip and build speed, so HDC was a good thing even if geared/flexy/locked... not so much with todays outfits as the trans will stay super slow.

In summary...
HDC is a great tool if the vehicle is not equipped to control speed mechanically.
I know a few times I've descended nasty terrain in my rubi, sway bar links removed so fully disco'd (flex in check), 5.13's and a 4:1, (gearing in check) but having not locked the diff's, there have been moments when tires were dangling that the rig would lunge forward (thanks to gravity) as the diff's would free wheel for a moment when there was no traction to those tires. HDC would control that had I turned it on (or had I been locked)... if I even have HDC on my rig... I honestly don't know if I do or not... hmm.
 

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I've used it a handful of times. Sort of a reverse or very low speed cruise control lol. I am low enough geared I can crawl hills in 4lo/1st, without manually braking (automatic). But HDC has one thing I do not - it is entirely computer controlled. Which means it can react to control speed/slip far faster and more efficiently than I can react - all I have to do is steer. By the time I could even process in that split second that there was a need to react - the computerized brain would have already executed. Could I have made the hills without it? Sure. But I am all for using a technical assist if I have one available.
 

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billum,
Been on Black Bear a couple times. It's a great run. Tons of sights/views etc. And, the section at the top can develop a bit of pucker factor if one's not used to that sort of thing. All those runs in that Ouray/Silverton/Animas area are really fun and scenic.
Scott
Agreed, Ouray/Silverton/Telluride is a beautiful area/trails/scenery.

The pucker factor I was referring to in this case was descending Black Bear in the snow/rain. Wet tires on wet/snowy rocks and particularly off camber veins of smooth granite that ran the full width of the trail was a dumb move on my part. Wouldn't repeat regardless of how well my Jeep was set up mechanically/electronically.
 
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