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Old 04-01-2018, 02:43 PM   #1
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Default 4wd vs 2wd with locking differential

There have been a lot of discussions here lately of the desire/requirement of having 4wd in a class B for certain traveling styles. Undoubtedly, some folks need more traction and clearance than others to get where they want to go, and others prefer the smoother, quieter, usually better driving quality of a B setup for mostly paved roads and never go to the tough places.

My basic question is if 4wd really does better than a 2wd with a locking rear axle in the type of "semi off road" driving we are talking about. I think if you think about the pure physics of it, the locking rear axle would be better, as both the 4wd and 2wd drive with locking rear axle have only two driven wheels (unless you have the less common 4wd and a locking rear axle which will win hands down), so the only real difference is which wheels they are. If weight on the wheels is the primary benefit for traction, the two in the rear would be considerably better because of the high rear weight in a B. If wheel position is the primary benefit, then the 4wd would likely be best. Example would be if one end of the van got caught in a slippery gully. Of course all of this would be based on both having adequate road clearance and aggressive tires.

I have had both types in daily drivers, but the experience is with snow, not rough roads, so really doesn't apply, I think. I found the getting going traction to be similar in the cars, but the locked rear axle squirrely in very slippery conditions with snow and ice.

Some of the Chevies have locking rear axles in them, can't say about other brands. I would also think the locking versions would be better than the limited slip style, though. Locking differentials can be put in to many different brands. The manually controlled ones are very nice.

If the final results in the real world were similar, a locking rear axle would likely be less expensive, less weight, less complicated, better fuel efficiency, maybe more reliable than all the 4wd hardware.

Has anyone had any forest service, logging road, type experience with both kinds of systems for comparison?

I will say that I would be speaking only of single rear wheel vans as I don't think anything will duals is going to well suited to the kind of roads we are talking about, and wouldn't be a valid comparison.
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Old 04-01-2018, 10:18 PM   #2
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I have taken the 210 Popular down some rocky roads & passes with the open rear end and the limited slip Dana 70 that I installed- huge difference in traction. With the open rear end it struggled up loose & steep sections while that disappeared with the limited slip as the power got put to both wheels.

Where I see the need for 4WD is in snowy, sandy and muddy terrain. While the L/S rear end will get you through most conditions it will be limited because of the weight of the 210. I saw some deep sandy roads while in Utah last week (Coral Pink Sand Dunes) and there was no way I would attempt going there without 4WD/AWD.

With 4WD capability I'd feel better about taking the 210 into places that I know are going to be challenging for a 2WD vehicle. I've been in Moab, Utah when it was dry and then it rains and turns the soil to clingy clay-cement that even stops motorcycles from off road travel. Having 4WD will help in these trying situations and allow for altenative travel routings and destinations.
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Old 04-02-2018, 12:08 AM   #3
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I guess that gets back to my original wonderment. Why is having one front and one rear wheel being driven (4wd) compared to having two rear wheel driven (locking rear axle)? Of course if you have 4 channel traction control that puts a brake onto individual wheels to prevent spinning, you can get better, but not with the traditional mechanical systems unless you have 4wd plus a locking rear axle, then you get 3 driven wheels.
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Old 04-02-2018, 01:11 AM   #4
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Quote:
Originally Posted by Hondo View Post
...With 4WD capability I'd feel better about taking the 210 into places that I know are going to be challenging for a 2WD vehicle...
I once took a group of friends up a very rough dirt road in the Mojave Desert using a four-wheel drive GMC Jimmy. On the way to our site, one of my friends quipped from the back seat, "Do you know the difference between a two-wheel drive vehicle and a four-wheel drive vehicle?

"With a two-wheel drive vehicle, you only get TWO wheels stuck in the sand."

You can probably guess what happened next.

Moral: ALWAYS file a flight plan... and it helps to know someone who has a CJ equipped with an electric winch.
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Old 04-02-2018, 03:56 AM   #5
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Quote:
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I guess that gets back to my original wonderment. Why is having one front and one rear wheel being driven (4wd) compared to having two rear wheel driven (locking rear axle)? Of course if you have 4 channel traction control that puts a brake onto individual wheels to prevent spinning, you can get better, but not with the traditional mechanical systems unless you have 4wd plus a locking rear axle, then you get 3 driven wheels.
I don't think that it works that way with 2 limited slip differentials.

The way I understand it, both F&R limited slip axles (soon to be installed IFS L/S front & current Dana 70 L/S rear in my case) all four wheels will engage if the opposite wheel begins to slip on each axle. In a slippery enough situation traction will shift back & forth between each wheel pair.

Will they all be engaged simultaneously?

Not unless you have true lockers.

It's night & day difference between 2WD & 4WD in my Avalanche in snow and mud, it's all working together and the vehicle is pulled through with confidence. Even with the traction control turned off it's much better in snow in 4WD.
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Old 04-02-2018, 11:56 AM   #6
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I don't think that it works that way with 2 limited slip differentials.

The way I understand it, both F&R limited slip axles (soon to be installed IFS L/S front & current Dana 70 L/S rear in my case) all four wheels will engage if the opposite wheel begins to slip on each axle. In a slippery enough situation traction will shift back & forth between each wheel pair.

Will they all be engaged simultaneously?

Not unless you have true lockers.

It's night & day difference between 2WD & 4WD in my Avalanche in snow and mud, it's all working together and the vehicle is pulled through with confidence. Even with the traction control turned off it's much better in snow in 4WD.
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Limited slips normally just put a clutch between the two wheels so some power is transferred to the non slipping wheel so not as positive as a locker for sure and if the traction difference is big enough. Limited slips are also normally engaged all the time, which can make them very hazardous on icy conditions at speed because the entire end of vehicle will lose traction at the same time and you can swap ends quickly.

I have been told many, many, many, times to never put a limited slip in the front of a 4wd or fwd for the exact reasons stated above about losing traction on one end of the vehicle. If it happens in the front you lose your steering also. In the front only a manual locking axle would be used to prevent hazard on the non off road stuff.

But again, all this is comparing vehicles that aren't the original question, as this is all about lockers or L/S which wasn't part of it.

Comparing the 2wd to 4wd in your Avalanche is also not looking at the setups described on the original question because it doesn't compare a 4wd with two open diffs, which is likely what the Avalanche has, to a 2wd with a rear locker. That is the comparison where both vehicles would have only two wheels actually driven at any given time, and what is of interest as to which would be better in the original question. The Avalanche is also not heavier in the rear like our vans are, so would benefit much more from having a front wheel wheel driven, where the van might benefit more from the second rear wheel being driven.
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Old 04-02-2018, 03:26 PM   #7
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Something to consider is speed vs controlabilty.

If a vehicle has a limited slip rear end or an open rear end and driving conditions are dicey then speed will have to reduced to maintain controlability. At slower speeds the limited slip will be a positive attribute when driving, allowing the driver to maintain control when it gets slippery and putting power to the wheel that needs it most.

An open rearend can't compare because the single wheel drive will always spin the one side only and traction will constantly be compromised in slippery conditions.

A locker will indeed drive both wheels at the same time and put power to both wheels. Driveablity becomes a factor though and that's why you don't see them released from the factory as much as they used to. I would imagine that a full time or E-locker on the rear axle (2wd vehicle) would have to managed carefully so that it didn't dig 2 ruts in slippery conditions. An auto locker is a neat option though I'd rather have a L/S in slippery conditions.

My 2007 Avalanche has a limited slip rear end and the IFS also drives both front wheels. In snow/sand it's a beast and all 4 wheels drive it through, not one front & one rear. The drive power is going to each of the wheels as traction decreases on each wheel, limited slip action constantly providing traction at all 4 corners.

Where the new vehicles excel is the traction control. The Avalanche has that as well and with the 4WD system set to Auto it will provide traction safely at all speeds.
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Old 04-02-2018, 03:43 PM   #8
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a good explanation-

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Old 04-02-2018, 03:53 PM   #9
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I think your question does not take into account the applications that the vehicle would be expected to perform.

In my case, I do not want to intentionnaly use my van in snow. I'm fed up of snow (I live in Montreal). I want to take my van to warmer weather and mostly to hard to reach camp spots and beaches. Also, please note that the objective was originally to travel the pan-American highway but we are currently considering shipping the Van to Europe in 2019 instead with side trips to Morocco.

That's why I decided to go with a Detroit Locker on mine.

The main reason is that there isn't a simple 4x4 conversion kit for the '96-'03 Chevys therefore I expected the cost to be too expensive. Also, I wanted to keep the van's mechanical systems somewhat stock (which I didn't achieve that well in the end... ).

But the locker is part of a "system". Which means I'm combining it with more ground clearance and recovery gear.

So I'm bringing along MaxTrax in case I get stuck. I also have a winch on the front bumper in case I get really, really stuck. And finally, a Hi-Lift jack (that can be used like a hand-winch) to pull myself out of trouble.

I don't plan on doing any real "off-roading" so 4x4 seems excessive to me.
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Old 04-02-2018, 03:54 PM   #10
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There is something missing in information here, I think. Everything I can find for Avalanches and Chevy pickups concerning Autotrak say it is only an automatic locking center differential that when in auto mode connects the front and rear drive axles to put power to the front axle. It also has manual modes that do the same thing. Nothing I found says it does anything about sending power from one side of the axle itself to the other side, front or rear. Some, not all, Avalanches also look to have come with the G80 option for the rear (only) axle, which puts an auto locking differential in the rear. It is the identical system that is used in the 70s axle in the Express van. There is nothing I found that said there is any type of power transfer side to side on the front axle, so you would be able to spin one wheel in the front without the other one turning. (open differential).

So what your Avalanche would have would be what I described as the one step up from the original question. It would be 4wd drive so both ends are driven. The rear would be able to drive both wheels because it is a locker (not a limited slip). The front would be an open differential, so could be driving only one wheel if it is on slippery surface with the the other wheel not getting any drive. This would give you 3 driven wheels on slippery surfaces, not 4.
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