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NP231 doubler / crawlbox

srimes

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It's an easy analogy to help understand what happens when engine braking. If you start to consider everything moving it makes everything difficult to understand. If you picture the engine braking enough to stop the Jeep entirely it's easy to see when the rear diff unlocks the wheel with traction rolls down the hill as the opposite wheel without traction spins backwards. When everything is moving down the hill with the driveshaft spinning that really simple concept becomes difficult to see.

OK, so the driveshaft is locked like the tranny is in park or gear with the engine off. There isn't enough traction so the jeep is sliding down the hill.

Say 1 tire is on ice and the other on pavement. The tire on pavement rolls down the hill while the tire on ice spins backwards. There is little resistance to going down the hill. The spinning tire on ice provides very little lateral resistance. The rolling, non-spinning tire on pavement has great traction and resistance to sliding sideways.

If the axle was locked both tires would be sliding. The tire on pavement would resist rolling down the hill (it's locked and not rotating) so there'd be less tendency to slide in the 1st place, but once it is slipping it would have less resistance to sliding sideways than with the unlock diff.

I'd have to go with unlocked in this scenario.
 

SvtLdr

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OK, so the driveshaft is locked like the tranny is in park or gear with the engine off. There isn't enough traction so the jeep is sliding down the hill.

Say 1 tire is on ice and the other on pavement. The tire on pavement rolls down the hill while the tire on ice spins backwards. There is little resistance to going down the hill. The spinning tire on ice provides very little lateral resistance. The rolling, non-spinning tire on pavement has great traction and resistance to sliding sideways.

If the axle was locked both tires would be sliding. The tire on pavement would resist rolling down the hill (it's locked and not rotating) so there'd be less tendency to slide in the 1st place, but once it is slipping it would have less resistance to sliding sideways than with the unlock diff.

I'd have to go with unlocked in this scenario.
In THIS scenario, I'd stay the hell off the hill that's half ice and half pavement! ;)
 
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JMT

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In THIS scenario, I'd stay the hell off the hill that's half ice and half pavement! ;)
I’ve done 100 yard long hill descents that were snow or ice and I’ve done them in 4:1 and 2.72 and both lockers and only front locker. I’ve always been ok, but sometimes I end up going faster than I want to stay straight. 😆 It can be discomforting.
 
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jjvw

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Imagine a Jeep sitting on a hill facing down, one rear tire has traction and the rear axle is locked. The driveshaft is fixed, now the rear axle is unlocked, what happens as the locker is disengaged?
What happens if the locker is disengaged while facing downhill (uphill or flat) is that the Jeep can steer better. And it's a rare and specific case that one would be facing downhill and accelerating to the extent of spinning a tire or two.
 
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SvtLdr

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What happens if the locker is disengaged while facing downhill (uphill or flat) is that the Jeep can steer better. And it's a rare case that one would be facing downhill and accelerating to the extent of spinning a tire or two.
I do my best to avoid tight maneuvers on steep loose inclines. Set up on a good line and stick to it, make slight corrections as needed which can be done with the rear end locked.
 

Gollywomper

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A Dana 300 flipped with 4-1 would be great for most folks. And the ability to clock it to what ever position isn’t a bad way to either. At 12” long would solve a lot of rear drive line worries as well. If someone didn’t need the doubler gear choices.
 
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srimes

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A Dana 300 flipped with 4-1 would be great for most folks. And the ability to clock it to what ever position isn’t a bad way to either. At 12” long would solve a lot of rear drive line worries as well. If someone didn’t need the doubler gear choices.

Is it OK to send it in 3rd and low with a 4:1?
 

jjvw

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I do my best to avoid tight maneuvers on steep loose inclines. Set up on a good line and stick to it, make slight corrections as needed which can be done with the rear end locked.
All I know is that when rolling, a locked rear restricts steering. There isn't a case where locking the rear improves steering.

I also know there are a wide range of scenarios where it doesn't matter what you do until certain things do start to matter and you need to actually begin operating the Jeep.
 
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pagrey

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What happens if the locker is disengaged while facing downhill (uphill or flat) is that the Jeep can steer better. And it's a rare and specific case that one would be facing downhill and accelerating to the extent of spinning a tire or two.
I thought we were talking about uneven terrain, low traction using engine braking going downhill, why are you talking about accelerating? When using the engine to slow the rig down having the rear locker engaged helps keep the back end from attempting to be the front end. This is extremely common where I wheel but if you see it different that's fine, no big deal.
 

jjvw

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I thought we were talking about uneven terrain, low traction using engine braking going downhill, why are you talking about accelerating? When using the engine to slow the rig down having the rear locker engaged helps keep the back end from attempting to be the front end. This is extremely common where I wheel but if you see it different that's fine, no big deal.
We have a trail out here called Red Cone. The highlight is a fairly long, very steep, very low traction descent with a few uneven sections down a narrow ridge. On the way down, you are almost able to stand with full weight on the brake pedal as you fall forward in your seat. It is easy to go into a slide and if you slip too far one way or the other, it's about 2000 feet to the bottom with nothing to stop you.

There are three very strong recommendations that will keep you alive on this section. Idle down the hill in a low gear to keep the speed down. Turn off both lockers to prevent unnecessary loss of traction. And if the Jeep starts to slide, give it a little bit throttle so that you can recover some traction and steer again.

Red-Cone-Pass-13.jpg

RedCone106.jpg


I've been down this about a dozen times and I have had to drive out of a slide more than a couple times. Really it isn't any different than driving a downhill on an icy road. Go slow, control the speed, and do everything you can to maintain traction. Lockers are very rarely a part of that equation.
 

pagrey

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@jjvw, it's cool, you do you. No need for the silly, "you could die" thing. Here's what ARB says on the matter:

"When a vehicle travels downhill and its weight is transferred forward, a rear Air Locker can also be of benefit. On downhill descents a vehicle with an open diff can experience a sliding effect as drive transfers from one axle to the other. A rear Air Locker will counteract this motion giving more control and a safer, slowed descent."


Opinions vary on everything, not the end of the world.
 
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Gollywomper

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There is no set method for descents. Terrain plays too large of a role. The biggest thing is if the tires are sliding you have limited/no control. When that happens you have to have the ability to “let it go” a bit to regain control.
 
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freedom_in_4low

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I'm in the open diff descent crowd. One tire may slip, but one has a pretty good chance of holding on and even if it's not controlling your descent, it's at least rolling over the terrain and keeping you pointed. With a locker, if you lose one you're gonna lose both.
 

pagrey

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it's at least rolling over the terrain
An open diff allows one wheel to stop entirely, what you talking about? In 4wd if the front wheels have good traction and the rear is unlocked the only scenario where either rear wheel is spinning the correct speed is when they are both spinning the same speed as the front, otherwise one is skidding slow and the other fast. That's how the transfer case and differentials work. Unfortunately not too many people seem to have thought this out?

Edit: I'm sure the next suggestion on this thread will be 2wd, wait for it...
 

jesseshoots

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We have a trail out here called Red Cone. The highlight is a fairly long, very steep, very low traction descent with a few uneven sections down a narrow ridge. On the way down, you are almost able to stand with full weight on the brake pedal as you fall forward in your seat. It is easy to go into a slide and if you slip too far one way or the other, it's about 2000 feet to the bottom with nothing to stop you.

There are three very strong recommendations that will keep you alive on this section. Idle down the hill in a low gear to keep the speed down. Turn off both lockers to prevent unnecessary loss of traction. And if the Jeep starts to slide, give it a little bit throttle so that you can recover some traction and steer again.

View attachment 302090
View attachment 302091

I've been down this about a dozen times and I have had to drive out of a slide more than a couple times. Really it isn't any different than driving a downhill on an icy road. Go slow, control the speed, and do everything you can to maintain traction. Lockers are very rarely a part of that equation.
This mimics the situation I was in. Engine braking with a Detroit in the rear caused the back end to lose traction and start sliding. Had I known better at the time I would have powered out of the slide, but it was my second time out in the TJ.
 
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