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Old 04-01-2018, 03:43 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, 11:18 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, 01:08 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, 02:11 AM   #4
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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, 04:56 AM   #5
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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, 12:56 PM   #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, 04:26 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, 04:43 PM   #8
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a good explanation-

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Old 04-02-2018, 04:53 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, 04:54 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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Old 04-02-2018, 04:56 PM   #11
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One option to be considered would a movable winch that can be used on the front or the rear.
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Old 04-02-2018, 05:12 PM   #12
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Quote:
Originally Posted by Mat Mobile View Post
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.
Actually, you have addressed the original question, but the conversation has drifted from that since the original post. You are doing nearly exactly what one side of the comparison was put out as, and have good reasons for doing it that way. You have the rear locker with more clearance as was the original scenario. You have added backup methods to get unstuck, which is just plain smart.

Your choice of a Detroit locker will be fine for you as you will not be on slippery surfaces at over minimal speeds. As I am sure you know, a fully locked rear drive axle can be scary wicked and near undriveable on icy stuff. The GM locker only comes on when a wheel slips and disengages at something like 20 mph so much safer on ice.

You will have two driven wheels to get you going, as would a 4wd with open diffs on each end, and the comparison of those two setups is what was asked. Of course a locked rear with 4wd so one front tire driven will be better, but that wasn't the question. There are always a lot of people that think 4wd means 4 wheels driven all the time, but that is really only true in pure offroad stuff, from what I have seen, either with lockers on both ends or welded diffs. 4wd plus a manual or auto locker in the rear is going to be about as good as it gets on road if you get slippery conditions, unless you did a manual locker in the front like an air locker and only used it if you got stuck.

I think it will be very interesting to here how well yours works in tougher terrain compared to the 4wd drive vehicles without locking rears.

Does your locker ratchet on tight turns, or is the wheelbase long enough that the tires can scuff enough to cover it?
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Old 04-02-2018, 05:15 PM   #13
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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.
The Avalanche IFS drives BOTH front wheels in slippery conditions. Power is transferred to whatever wheel isn't slipping and this would make me think it is acting like a limited slip.

The rear axle is a G80 Differential, heavy-duty locking rear, GT4 3.73 ratio. It is a true G80 Eaton autolocker, not a limited slip. Traction control will slow the slipping wheel is those conditions while allowing drive power to the wheel that isn't slipping- turning off traction control allows full auto lock when needed.

Newer Express vans offered traction control and I'd bet that it's the same axle and control.
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Old 04-02-2018, 05:23 PM   #14
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Having driven trucks and ridden motorcycles off road in excessively steep and loose, rocky conditions, I'd rather have a L/S out back than a full locker in 2WD. Fully locked traction will eventually break free and both wheels will spin. With a L/S the power will shift back and forth putting power where it is needed.

The rock crawlers like full lockers/welded spools and that works for them at those slow speeds and demanding conditions.

But for the everyday driver, traction controlled vehicles make everyone safer as the ability to lose control is diminished.
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Old 04-02-2018, 05:31 PM   #15
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If you are talking about having traction control that selectively brakes individual wheels, I mentioned that early on, and is not part of what was being compared. Those have nothing to do with the Autotrac and are separate item if they put them on different vehicles. Full traction control is a totally different animal than we are discussing, and is normally part of the stability control. Some traction control programs, especially on 2wd and fwd just reduce engine output when the ABS senses spinning tires.

The vans got stability control is about 2008, but not sure if they got traction control or not, as it would just be on the rear wheels on most of them, as 4wd was not common except on the 1500.
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Old 04-02-2018, 05:44 PM   #16
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If you are talking about having traction control that selectively brakes individual wheels, I mentioned that early on, and is not part of what was being compared. Those have nothing to do with the Autotrac and are separate item if they put them on different vehicles. Full traction control is a totally different animal than we are discussing, and is normally part of the stability control. Some traction control programs, especially on 2wd and fwd just reduce engine output when the ABS senses spinning tires.

The vans got stability control is about 2008, but not sure if they got traction control or not, as it would just be on the rear wheels on most of them, as 4wd was not common except on the 1500.
Sure, I understand- I was just posting up what the Av has as a comparison and since you questioned it.

I have been to places in the Rockies on a motorcycle that few will ever see, some very steep and loose passes/trails that tests a rider's metal and knowledge of the proper use of available traction on a fully manual vehicle.

My weapon of choice is this highly modified Kawasaki KLX 450R (Imogene Pass, Colorado)-



On a modified dirt bike / dual sport, the clutch is all you have to control the power put to that single rear wheel. The rider is Mr. Limited Slip, controlling how much power to use and when to apply/remove it.

If it was just an throttle with auto trans & no traction control the bike would be unrideable in the steep & loose terrain and I would suspect that a locked rear end in a 2WD would act the same way, and an open rear end even worse.

Adding any traction to the front wheels will increase the ability to apply that engine power to the front wheel(s). Having a limited slip rear end shift drive power to the wheel that needs it most would greatly enhance traction in these demanding situations as well as driving in snow/sand/mud.

And as you know, on ice it's always going to be dicey regardless of the configuration.
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Old 04-03-2018, 04:23 PM   #17
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Love the KLX & Imogene! How about "Black Bear"? Grt pic too.
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Old 04-03-2018, 06:11 PM   #18
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I'm following the conversation with interest. I had a Suburban with the Eaton auto locker and the one time on snow I punched it in 2wd from a stop to see what it did, I had to spin the tire uncomfortably fast to engage it. I was always happier in snow, ice, sand and gravel in awd ( or 4hi if on soft surface). My brother had a rwd work truck with manual locker, and could get out of any NC muddy construction site as well as the 4wd work trucks, with a little more fuss manually engaging and disengaging it. He thought it just depend on if one side was slick (like a rut) or if both sides of the back was slick (like backing down a boat ramp).
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Old 04-03-2018, 10:04 PM   #19
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Rode Black Bear that same day...Silverton...Black Bear Pass... Telluride for lunch... Imogene... Silverton
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Old 04-04-2018, 01:52 AM   #20
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Rode Black Bear that same day...Silverton...Black Bear Pass... Telluride for lunch... Imogene... Silverton
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