Why switch from AWD to 4WD?

[ericautopart]

I was driving in well over 15" of snow last night and this truck is an absolute TANK. I am so impressed with it. I've had a plethora of SUV's over the years and this is by far the best. I got to the office this morning and they didn't plow the lot and the explorer was unstoppable. Ok, I'm done.

 

[my pos mounty]

The only reason to chane to 4WD from the AWD system would be for off-road capabilities only. Just for that 4-LO. If your truck is going ot be a road truck, you can't beat the AWD.

A few years back, when we got a sunday night storm that dropped 16 inches of snow, I showed up at the office/warehouse right on time. Someone in the office had "forgotten" to pay the plow company for the last few storms, so they "forgot" to plow out the gated parking lot where all of the company trucks are parked. (8 Isuzu cabovers with 16 ft. boxes, 1 Ford with a 20 ft. box, 4 Chevy "express" one ton vans) Some of the other guys were convinced they could get the trucks out, all they accomplished was packing the snow down even more around them. When the "higher-ups" arrived, they wanted all of us to grab shovels and shovel out an entire parking lot!! (LMFAO@the sight of that) I asked one of the guys there that had an F-350 4X4...all jacked up, 36 inch tires, the computer controller, huge exhaust, DIESEL. He looks at me and says "No way, I aint touching them with my truck." I called him a few unflattering names in a joking manner, asked for his pull strap and told him to watch what a Ford product could do. I hooked the strap to my trailer hitch on my Mountaineer, had the drivers connect the other end to their trucks and I dragged each one out, one after the other. I was very surprised as was everyone else what my "little" truck did. All the other supers (waiting for their trucks) were quite thankful, as we all were able to drive off to our jobsites, leaving the snow cleanup to the "office jockies" that "forgot" to make the payment.
Sorry for the long story, couldn't resist

 

[BBQ Bandit]

Yup, the AWD proved itself golden this winter....

2 snowstorms in 10 days = nearly 40" in central Pennsylvania.

 

[ExploringNC]

They get away from the AWD so it won't go in and out of 4wheel automatically. They don't like the feel of it slamming into 4wheel if the tires start to spin and also for the kid at heart that like to do burn outs or donuts.

 

[my pos mounty]

You are confusing the "auto 4WD" with the AWD system There isn't any "slamming" in and out of 4 wheel as the AWD system is constantly on. The transfercase is very different from the auto 4WD system. The auto 4WD system transfercase will "slam" in and out of 4wd once the speed sensors detect wheel spin, engaging the electric clutch. However the AWD transfercase has a viscous coupling (no electric clutch) on the input shaft with a chain around the outside of it that drives the front output shaft. There is no monitoring of wheel spin anywhere as it is run by fluid pressure and is always there. Always on, not monitored, not shifted, not controlled by the computer. Very basic system.

 

[ericautopart]

Right, no slamming. The AWD is just amazing for street use. I've had an xterra, blazer, bronco, wrangler, etc. The manual 4x4's were great for wheeling but a pain for the snow. Shifting back and forth, locking hubs, etc. The explorer just does it's thing..no thinking required.

 

[gavin]

another reason for the swap from AWD to 4WD is also the savings in fuel milage, and extra power to the ground. With selectable 4WD, you're not losing any of that power when in 2WD.
Plus with all the power going to the rear wheels, gas milage will increase, instead of losing power and MPG to the front axle.

 

[SmoothJimmy]

but Gavin, the total mass of the vehicle hasn't changed whether in 2WD or AWD. You'd still have to push that unpowered front end down the road if in 2WD. So I doubt much difference in mileage between the two setups. It does 'feel' lighter though, but that's more due to the oversteer of an unpowered front.

One area where it would make a difference is wear and tear on the frontend. If it's powered, it places torque on components.

However, I just pulled apart and measured components in my Dana 35 IFS and they were like new at 155k. Have not done any towing tho.

The parts that do seem to suffer are in the 4404 transfer case. I will be replacing the chain soon, as it has stretched and makes noise when climbing, turning and coasting. But should have done that a while back anyways since Borg Warner recommends a chain replace at 60k.

 

[gavin]

but Gavin, the total mass of the vehicle hasn't changed whether in 2WD or AWD. You'd still have to push that unpowered front end down the road if in 2WD. So I doubt much difference in mileage between the two setups. It does 'feel' lighter though, but that's more due to the oversteer of an unpowered front.

One area where it would make a difference is wear and tear on the frontend. If it's powered, it places torque on components.

However, I just pulled apart and measured components in my Dana 35 IFS and they were like new at 155k. Have not done any towing tho.

The parts that do seem to suffer are in the 4404 transfer case. I will be replacing the chain soon, as it has stretched and makes noise when climbing, turning and coasting. But should have done that a while back anyways since Borg Warner recommends a chain replace at 60k.

the mass hasn't changed, but you're power also is no longer split between pushing and pulling the vehicle. You have all the power going to one spot, instead of it being split up.

Granted MPG gains may not be much, but I'm sure there is a noticeable improvement in the amount of power felt with being bogged down with the AWD.

that said, I love the AWD. Works great up here in Alaska, and I'm not sure I'd want to get rid of it.

 

[SmoothJimmy]

I appreciate what you are saying but any loss in "total power" to the wheels would have to go somewhere and the only place it could go is thermal energy...heat. I doubt any of the components of an AWD frontend get very warm compared to a 4WD in 2WD mode. I may be wrong on that though.

Clearly, the perceived peppiness is noticeable. While I had my front driveshaft off recently for replacement, the Ex felt livelier. I even thought I might go with 2WD for awhile since it was far less wear/tear on the 4404 chain and oh so quiet. HOWEVER, after looking at the design of the 4404 and it's viscous coupler, I realized that it was being placed under significant stress with no front shaft connected. In fact, it is subjected to the shear load of the entire engine in that configuration and would heat up, hump and stay that way. But that's a different thread

 

[gavin]

I appreciate what you are saying but any loss in "total power" to the wheels would have to go somewhere and the only place it could go is thermal energy...heat. I doubt any of the components of an AWD frontend get very warm compared to a 4WD in 2WD mode. I may be wrong on that though.

think about it... 4WD vehicles always have lower rated MPGs than 2WD vehicles

in a vehicle with selectable 4WD, you will get lower MPGs when driving in 4WD compared to staying in 2WD. Same concept, really The fact that the power split is variable doesn't change it too much, except that the loss won't be as high as a set power split.
Since the ratio is, roughly, 35/65 (I believe this is what the Ford Service Manual stated...), you're losing roughly 35% power to the front. Since there is less power at the front than the rear, the vehicle is still being pushed, the front end is really only along for the ride and to waste energy (HP, fuel).

Of course, the fact that there are no manual hubs means there will always be the drag from the front diff wasting some energy, it's not nearly as much as the wasted output from the t-case.

Clearly, the perceived peppiness is noticeable. While I had my front driveshaft off recently for replacement, the Ex felt livelier. I even thought I might go with 2WD for awhile since it was far less wear/tear on the 4404 chain and oh so quiet. HOWEVER, after looking at the design of the 4404 and it's viscous coupler, I realized that it was being placed under significant stress with no front shaft connected. In fact, it is subjected to the shear load of the entire engine in that configuration and would heat up, hump and stay that way. But that's a different thread

and with the front driveshaft out, you're still losing power through the t-case, except that in this case it's not going anywhere except to a free spinning front output shaft :

I'm always up for a debate and constructive criticism

 

[SmoothJimmy]

I also enjoy debating the issues and keeping it polite.
While I agree that 2WD vehicles are rated higher MPG than 4WD vehicles, that's not what we were debating...it's 4WD vehicles in 2WD MODE vs AWD vehicles... still have that pesky front drivetrain to push/pull around town in both of them. 2WD rigs weigh less and have less mechanical resistance.

As for real world mileage, I would suggest that conditions requiring 4WD are significantly different from those of 2WD...kinda like city vs highway MPG calculations.

The concept of "losing power to the front" suggests that this power goes into thin air. Rather, it's not lost power, but work being done by the front-end to "help" the rear. Sure , parts wear faster, including front tires doing the pulling. I got 75k out of my last Revo's though.

I will be tearing down my 4404 soon and I very much enjoyed your rebuild writeup and will be using it as a reference. One question: how much rotational play did you have in the front shaft side of the transfer case pre-rebuild and how much after the rebuild? And, did you use a Borg Warner Hy-Vo chain or a chinese one?

 

[Kriegen]

I eventually want to do the switch when my mountie is no longer my DD and I can turn it into a primarily recreational vehicle.

 

[gavin]

I also enjoy debating the issues and keeping it polite.
While I agree that 2WD vehicles are rated higher MPG than 4WD vehicles, that's not what we were debating...it's 4WD vehicles in 2WD MODE vs AWD vehicles... still have that pesky front drivetrain to push/pull around town in both of them. 2WD rigs weigh less and have less mechanical resistance.

As for real world mileage, I would suggest that conditions requiring 4WD are significantly different from those of 2WD...kinda like city vs highway MPG calculations.

The concept of "losing power to the front" suggests that this power goes into thin air. Rather, it's not lost power, but work being done by the front-end to "help" the rear. Sure , parts wear faster, including front tires doing the pulling. I got 75k out of my last Revo's though.

I will be tearing down my 4404 soon and I very much enjoyed your rebuild writeup and will be using it as a reference. One question: how much rotational play did you have in the front shaft side of the transfer case pre-rebuild and how much after the rebuild? And, did you use a Borg Warner Hy-Vo chain or a chinese one?

my old Bronco2... once winter hit, it got put into 4WD and stayed there throughout winter. Milage dropped ~120 or so miles per tank compared to summer. Granted, part of that was due to letting it warm up, but certainly not that much. It went from ~320 miles/tank to ~200 miles/tank. That's a roughly 6MPG difference.

And by losing power, obviously I don't mean it vanishes into thin air. But the measly power to the ground at the front-end doesn't considerably help move the truck. 35 + 65 = 100, but not necessarily in terms of percentage.
Take a couple equal vehicles... rear one tied to something, and one in front tied to the rear vehicle. If the front vehicle is only pulling with 35% and the rear pulling with 65% of their available power, will they be able to pull said object as easily and as quickly as a single vehicle pulling same object with 100% power? Probably not

as for my t-case rebuild; I ended up not replacing the chain. I had purchased a Hy-Vo, but managed to get the wrong one. As I have stated in that thread, there are 2 different chains with same # links, same width, and same # pitches. Not discernable difference.
Except that the replacement I had was actually 1 link narrower than the one that was in the case. But it was still good and tight, so I didn't worry about it. As for rotational play, honestly can't say. There was some before and after. I know in my thread I said it felt like there was less play after the rebuild, but it could have been the placebo-effect.

 

[ericautopart]

Oh boy, what have I started? :bsnicker:

 

[eXcali]

I like the AWD just fine. Another point people have not hit on is this: The stock 4x4's are 4.0 V6... the AWD is 5.0 V8.... There's your difference in MPG. But if we are blindly comparing apples to oranges: My 80 Bronco gets about 9 mpg in 2wd, but my AWD Explorer gets about 16!

Ericautopart, I've left the front hubs locked in on my Bronco this winter. When it's icy or snow I'll just shift it into 4x4. The AWD is very capable on the Explorer so I let my wife drive it in bad weather and I get the fun0 5.8 Bronco to play in.

 

[SmoothJimmy]

and you're comparing summer driving with winter driving in Alaska? Granted, a summer in Alaska often is worst weather than winters here in California. Having spent several summers visiting family in Cordova I can testify to that. Nothing like exchanging 80 degree days for 33 and blowing 50 out on the Copper River flats. Brrr. But that Copper River King sure is tasty!

But, if your Bronco was in 4WD all winter long, mustn't a good bit of that time been spent driving on snow covered roads with lots of extra friction to overcome? Nevermind the wheelspin for giggles bit. Don't deny it!

I remember the HV-051 vs HV-070 issue you had. I guess I'll have to crack the case to find out which one I have.

 

[gavin]

I like the AWD just fine. Another point people have not hit on is this: The stock 4x4's are 4.0 V6... the AWD is 5.0 V8.... There's your difference in MPG. But if we are blindly comparing apples to oranges: My 80 Bronco gets about 9 mpg in 2wd, but my AWD Explorer gets about 16!

incorrect the same vehicle, when given a choice between selectable 4WD and AWD, the selectable 4WD will get better MPG when operating in 2WD. We're not comparing the V6 with the V8 I know better than to do that! :

and you're comparing summer driving with winter driving in Alaska? Granted, a summer in Alaska often is worst weather than winters here in California. Having spent several summers visiting family in Cordova I can testify to that. Nothing like exchanging 80 degree days for 33 and blowing 50 out on the Copper River flats. Brrr. But that Copper River King sure is tasty!

But, if your Bronco was in 4WD all winter long, mustn't a good bit of that time been spent driving on snow covered roads with lots of extra friction to overcome? Nevermind the wheelspin for giggles bit. Don't deny it!

I remember the HV-051 vs HV-070 issue you had. I guess I'll have to crack the case to find out which one I have.

actually, the highway was relatively dry and clean a lot of the time. Yes yes, you shouldn't use 4WD on dry pavement... well it lasted a couple winters like that without an issue. It died for other reasons, not related to the t-case

I also filled up the tank multiple times a week; driving to class and whatnot was a ~60 mile round-trip.

I know temperatures variations can affect MPG, but 6MPG is a lot I'd say atleast 3 of those MPG lost were due to 4WD.

And actually, the summer temperatures in south-central (Anchorage) don't vary that much.

 

[SmoothJimmy]

I don't know anything about the Broncos. Did the entire front drivetrain rotate when the Bronco was in 2WD or did it have locking hubs? If I were to switch to a 4406, I'd still be turning the front train, just not powering it, right?

 

[gavin]

I don't know anything about the Broncos. Did the entire front drivetrain rotate when the Bronco was in 2WD or did it have locking hubs? If I were to switch to a 4406, I'd still be turning the front train, just not powering it, right?

all the older 4WDs used to have selectable hubs, so essentially nothing in the front diff was turning.

And yes, the front end parts would still be rotating, just not receiving any power.