4WD and AWD systems explained

bend

Having read most of the posts on this topic, could someone help me out on a very related topic. Had a nail in one tire on my 2004 Legacy automatic. 11,000 miles.

Tire shop said if they would have to replace all four if they couldn't plug it.

Luckily, they plugged it.

Were they blowing smoke up....???

russla

I don't know your particular system, because I don't know if you have a auto or manual transmission, However, if you have three open differentials, one tyre that is slightly new than the others can be accomodated. without any significant long term issue.

however, if you have an auto locking center diff, then it can be more of a problem to have tires of different diameters on the front vs the rear.

With that said, I also don't know how worn your other three tires are, so there is a hint of truth to their recommendation, but whether it's true or not for you is dependant on your tire wear and the type of center diff you have (or locking 4wd system) actually on your car.

Regards

stever

It's true, but it depends on how different the circumference of the new tire is compared to the older ones. Subaru has specs on that; some shops will shave the new tire to make it match.

Try the Subaru Crew: Care & Maintenance or one of the other discussions in the Subaru Crew for details.

Steve, Host

ateixeira

11,000 miles of wear would be borderline. You'd have to measure the circumference of the old vs. new tires. I think they allow 1/4" variation, you might be within that tolerance.

You could have bought one new tire and shaved it to match the others, or even just found one good used tire.

But if the old 3 are well worn, yeah, I'd get 4 new ones.

-juice

adventure

mike,

I noticed some of your older posts - no offense - much of it is simply wrong. Especially when you wrote: "It is a common misconception that 4-wheel drive hi/low locks all 4 wheels. In actuality it only locks 1 wheel per axle when in 4-hi/4-low on *most* vehicles." it made my toe nails curl up.

In part time all 4 wheels get an equal amount of torque (25%) as long as traction is equal. And even when traction changes each wheel on an axle get the same amount of torque. The drive wheel theory is an old husband tale.

Cheers
Harald

russla

Hi Harald,
you are correct, but most folks just don't get the dynamics of an open differential,wrt torque distribution, so some people who do get it, try to simplify the concept for those that don't.

An open diff guarantees that one wheel will spin, if that wheel loses traction. As you point out correctly, both sides are getting the same amount of torque. The one side not spinning, is getting the same amount of torque as the side that's spinning, it demonstrates just how very little torque it takes to spin a wheel with no traction.

While the wheel spinning may not be "locked", it is easy for an outside observer to see that only one side is spinning when one gets in a slippery situation.

So a 4wd vehicle, with open diffs, can get stuck when two wheels lose traction. (and then the driver ponders that they thought they had 4wd)

They don't always remember that when there is some traction, a 4wd rig only needs half the traction of a 2wd to move forward.

ateixeira

4WD is basically 2 axle drive, unless the axles are managed.

-juice

deluxe247

I became interested in 4WD about 2 months ago after being unable to climb the moderately-steep
and wet/snowy dirt driveway in my new mountain property. My FWD lost traction at the first soft
spot near the bottom . No problem in summer when it's dry.

After becoming increasingly frustrated at the maze of AWD/4WD/VTC/LSD, etc. options available,
and apparent lack of concise literature, I found this website and thread. I've worked thru all
885 postings over about 3 weeks, and it has been helpful. Thanks to all. Mostly I realize I'm
not the only one confused!

It would still be helpful to see a single summary of available 4WD options and vehicles, with
maybe an effort to rate them according to "effective gripping" capability. Has anyone seen such a list? I know it's very complex and the vehicles keep changing, but it would really help folks like me to decide what kind of 4WD we need.

Any recommendations?

ateixeira

That's gonna be very difficult, there are so many different systems out there that it's hard to categorize.

Perhaps we can simplify by looking at how many axles are driven and how many of those axles are managed, either with traction control (T/C) or with some type of locking or limited-slip differential.

In essence we can calculate the minimum number of drive wheels that would get at least some power. So for instance:

1 wheel: FWD or RWD with open diffy and no T/C

2 wheels: FWD or RWD with LSD or T/C; AWD or 4WD with open diffy and no T/C

3 wheels: AWD or 4WD with LSD on one axle

4 wheels: AWD or 4WD with LSD on both axles or T/C

In your case you probably had just 1 single wheels spinning, FWD with open diffy and no traction control. I'm not sure that even T/C would have helped you, since all the weight was on the rear axle.

Anything that sent power to the rear axle would be better climbing a steep hill, even RWD with traction control might manage.

For your case I would suggest at least AWD, preferably AWD with Traction Control or at least a rear Limited-slip differential.

-juice

deluxe247

Thanks, Juice, that's a great summary. An improvement might be listing some vehicles that fit in each category. Sometimes it's hard to figure it out from sales literature, and salespeople often know less than that.

I agree with your assessment of my situation, I was leaning toward a Subaru with rear LSD.

ateixeira

Sounds like you'd prefer a car, vs. a truck? Is that right?

Audi and Subaru come to mind immediately, of course. I think now all Audis use traction control, so any of those. For Subaru, you get a rear LSD in all but the base models, basically.

Which cars did you have in mind?

MB and BMW and Infiniti have AWD systems that are full-time and send power to the rear axle at all times, so those are other options.

Volvo/Ford uses a Haldex, which is FWD until there is slip, then AWD engages. It would get you up, but it might slip a little first.

Most others are also FWD with auto-AWD engagement, not permanent. I prefer the permanent systems.

Truth is I bet any one would make it up with good tires.

-juice

deluxe247

I've considered trucks for better 4WD ability, but we need the interior cargo capacity of a wagon/SUV to carry pets long distance. I initially considered a Jeep, 4Runner or Trooper. But since the vehicle would be used on-road most of the time, we'd also prefer to have decent gas mileage. That all leads us to something like the Subi Forrester.

From previous discussions in this thread, I've come to prefer proactive systems rather than reactive. Do I understand correctly that auto-AWD is reactive?

I'm a bit hesitant about traction control which uses ABS, since it seems that could lock the wheels when you might want them to move off-road.

Your comment about good tires has been a constant theme in this thread, along with reducing tire pressure, and is much appreciated. I take it that one must carry a compressor to re-pressure the tires. How do they work, and where's a good place to get one?

ateixeira

The Subaru systems are full time. auto-AWD is actually proactive, i.e. it shifts power to the rear axle at startup, before slippage occurs.

I'd recommend a Forester XS, LL Bean, or XT. The Forester X lacks the rear LSD that you'd want for that type of hill climb.

No traction control so it's ideal for you.

I got a portable compressor that came with my floor jack. It takes a long time to fill a tire, but it works, and it has an adapator for the cigarette lighter. Piece of cake.

-juice

gratefuldad

Does anyone have a handle on the 2005 Pathfinder's 4wd system. I noticed that they offer a full time 4wd system on the LE and only a part time system the SE and below. Apparently they use the ABS as a form of limited slip on both versions, not uncommon. From what I can tell, and Nissan certainly isn't shedding a great deal of light on the subject, there is no center differential on the SE. If that is the case, I am thinking 4WD high is not really an option, well at least not at anything over twenty miles an hour or so. I also can't figure out if the center differential locks in 4wd lo on the LE, if not, there are some real tradeoffs involved in deciding on which system to choose. If anyone is up to speed this stuff, I would appreciate it. Thanks Charlie

paisan

Charlie,
I had a Trooper with 2wd, AWD, and 4-Lo for years. Just picked up an 04 Armada that uses the same system as the LE Pathfinder.

Essentially you have 4 modes:

2wd: Transfer case is locked to 100% RWD
All-mode: AWD, the Transfer case constantly redistributes the power front to rear based on traction, weight shift, etc and can vary it from 0/100 up to 50/50 It'll normally when moving do a 10/90 split.
4-Hi: Transfer case is locked in 50/50 split F/R and should not be used on dry pavement
2-Lo: Transfer case is locked in 50/50 split F/R with low-gearing for extra torque, also should not be used on dry pavement.

Hope this helps, I'd definitely go for the LE with the 4 different settings including AWD.

The ABLS- Antilock Brake Limited Slip essentially creates an LSD in the front and rear axles on these trucks. It will brake a slipping wheel and send power to the opposite side. Since most mechanical LSDs wear out in 70k miles, I'd rather just keep throwing brake pads on instead of rebuilding the LSD units, at least in a non-performance car the ABLS will be more than adequet.

-mike

gratefuldad

Mike,

thanks for replying. I am a little fuzzy on the AWD system. It sounds like there is a center differential. Is that the controlling factor in where the power goes? Or is there a computer making that decision? As for not needing a limited slip diff I agree. I drove an Toyota FJ landcruiser back in college in Colorado, and I never encountered the need for a lsd. Well maybe once, I pulled off the hwy in snow storm to lock the hubs and found myself in 14 inches of snow, looked like about 2 inches, when I amde the call. Anyway, after locking it up, there was no traction. Luckily I had a frisbee to dig some trenches, no gloves though. From the sound of things I think the SE is something like the FJ, no center diff, except with electronically locking hubs, and not good for pavement. Charlie

paisan

On the LE when in 4-hi or 2-low mode it will be just like the FJ in terms of how the 4wd system works. When it's in AWD mode, there is an electronically controlled center diffy that will distribute power F/R based on input from wheel spin sensors, weight shift sensors, as well as the ecu memory of when wheelspin typically will occur, over time it "learns" where to put the power. For these big trucks the AWD mode is key for onroad stability. I wouldn't consider an SUV w/o some kind of auto-4wd or AWD unless I was a die-hard offroader (which I have done a lot of).

-mike

PS: the hubs are auto-locking essentially, there is no locking of the hubs necessary on all modern 4wd systems.

gratefuldad

Mike,
I think you are the first person I have heard make the statement about the importance of AWD in a large vehicle. I know that with the Sequoia, at least, there is nothing wrong with driving it in AWD all the time, but I have never heard anyone really express that this is a good idea. (I believe the Landcruiser only operates in AWD, ie, no 2wd option) I was hoping you might expound on the benefits of driving in AWD all the time. How does it effect handling, any effect on understeer/oversteer, obviously its a good idea on dirt or snow, but what other kind of situations does it make a difference etc. Thanks. Charlie

paisan

Well, for one thing, using the AWD, if you drive agressively will yield a far better handling characteristics. For instance if you are cruising through a turn and hit some sand on the pavement leftover from a rainstorm that put it on the road or winter salt buildup etc, you already have some power to each axle so rather than REACT to a slippage or skid which is what skid controls or traction controls will do, you simply don't get into the situation in the first place. On a larger vehicle you are just simply dealing with greater weights and therefore it's even maginfied how well the AWD can help you out. Often times, I'll run in 2wd when it's sunny, warm and I'm just crusing on the highway. However if I'm in traffic or in the city, i'll usually leave it in AWD so that in the event I need to make an emergency manuver i will have the benefit of all available traction controls to help me avoid a collision.

Also I tow a 5000-6000lb trailer often, and in those sitations I usually run in AWD as well, for the same reasons that you want to have every advantage if you get cut off on the highway by someone who isn't paying attention etc.

There will be tons of people who will come on here and argue that you waste gas, that it's not needed, etc. To that I'll say, yes, we don't NEED it, however, we don't need power windows, airconditioning, power locks, antilock brakes, power steering, power brakes, disc brakes, automatic transmissions, etc.

I have found the Armada to really handle exceptionally well with the 4-wheel indy suspension as well. If I didn't need the towing capacity of the Armada I'd actually be in a Pathfinder LE right now, think they look better too.

-mike

denali856

First of all, thanks in general for all your thoughtful, knowledgeable responses on this board. I've been reading it for a couple years or so now and it has been a great resource for learning about vehicle drive systems. I've been wanting to say that for a long time now.

I also just wanted to agree with your assessment of the degree to which AWD systems really help the handling of vehicles, ESPECIALLY large, heavy vehicles like SUVs. I think people tend to overlook this and think of AWD systems' effect on handling only of performance cars, e.g, Audi Quattros or Subarus, and to think of 4WD/AWD systems on large vehicles as being only for offroading or bad weather.

When I was shopping for an SUV a few years back I drove a GMC Yukon and thought it was OK, but when I drove a Denali I immediately noticed a major improvement in handling. It felt so much more secure even on dry pavement. I remember taking it around an onramp and accelerating to merge into traffic, and noticing how much better it was able to hold speed coming around the curve and accelerate into the flow of traffic without the feeling of oversteer/'looseness' I felt on the Yukon when I'd tried a similar maneuver. It was that feeling, as much as the bigger more powerful engine in the Denali, which made my choice as much as anything.

gratefuldad

Mike,

I will add my thanks as well. Hate to keep you tied up, but I am curious about your preference for Nissan over Toyota, if there is one, I am on the fence over a Pathfinder/4Runner as my next car. I imagine that I would be pretty happy in either, but I still have to make a decision.

On another point, one thing I simply cannot understand is how few people actually opt for 4wd in any SUV. I don't know if it is the dealers/manufacturers driving the decision or whether it is people's preferences. I know that here in New Orleans, no more than three or four out of every twenty-five 4Runners or Pathfinders on the lot are actually 4wd. Even less when it comes to Sequoia's and Armada's. I know that simply by checking dealers inventories. I have even seen it where there is only say one 4wd Sequoia' out of 250 in the state of Louisiana. Its mind boggling to me that people will get into a truck based SUV without 4wd. It find it especially ironic since many of the unibody SUV's come with AWD standard. It should be the other way around. Maybe its a regional thing, but even so, they don't call Lousiana the sportsman's paradise for nothing. If I was pulling my boat out of the water on a slick boat ramp I would want AWD. Ditto getting my trailer with ATV's over the Levy. You should see how bad people tear up farm roads in 2wd when it gets a little slick. I will say that when you get out of the City you don't see alot of imports.

I must say that the descrepancy makes actually buying a 4WD SUV a difficult proposition. I looked at the local dealers inventories yesterday, and out of fifty Pathfinders, there was one LE with 4wd. The rest were all SE Off Roads. Here's something really funny, I saw a bunch of SE Off Roads with 2wd. Talk about being a poser. Anyway, just had to vent. Charlie

paisan

Denali: Yup no one realizes how important AWD is even on big trucks because it works almost transparent and most people take it for granted. The only downside I found for me personally on the denali was the AWD didn't have a low range. Not a major issue for most folks buying them but I needed the low range in addition to the AWD.

Charlie: Well for me, I find the Toyotas to be a bit too much on the bland side as far as styling. For my own purpose, the Sequoia doesn't have enough towing capacity so that knocked that out of the box. Also the toyotas here in the NE command nearly MSRP whereas the Nissans are near Invoice pricing with great financing deals. As for Pathy v. 4-runner. The Pathy wins in my mind due to the independent rear suspension, the 4-runner still has a live solid rear axle which will yield worst on-road handling, and ride. I have also heard (though I don't have specific test knowledge yet til I tow with the Armada) that the indy rear will be more stable for towing. I also think that the lack of 4wd in your part of the world is due to the warm weather there. Here in the NE you would have a hard time finding a 2wd SUV and resale on them is nil.

-mike

tngal

For no apparent reason, my Hi and Low 4WD dash lights now blink off and on 7 times about every 5 minutes. I have tested the 4WD and it SEEMS to be working, as well as electronically tested all the switches and fuses etc., but the lights have quit coming on when I switch it into Low and High gear. My Ford dealer, whom I trust about as far as I can throw him, says (without checking it) that it will be well over a $2500 charge to change out the transfer case of the 4WD, although my normal mechanic has hooked it up to a computer and is receiving no messages that anything is wrong. My question is A) has anyone else experienced this and I read something on this site about the transfer case fluid being low and causing some sensors to malfunction, which is what my mechanic believes it is. Any advise on what steps to take next or if I can check this fluid and see if I can get it topped it off? C) Any other solutions/possibilities that anyone is aware of? Many thanks from a single Mom who would like to be educated in this matter so she doesn't get ripped off (again). Appreciate it!

phil56

Is anyone familiar with the Equinox AWD and the 4WD Trailblazer (Autotrac)? If so, could someone help explain the difference between the two vehicles (in regards to the 4WD versus AWD systems)? Which system would be considered better? The way I understand it (based on reading many of the posts in this thread) is:

Trailblazer 4WD (Autotrac):

2WD - fuel efficiency (i.e. use if the weather is nice, you're on a nice road, and your looking for a gas station)

4WD Auto - use all the time unless really bad weather, off-roading, or towing. Explanation of how this helps with wet conditions? Difference between this mode and AWD? Rollover risk compared to 2WD?

4WD Hi - use in bad weather, light off-roading, or light towing. Rollover risk? Why 4WD Auto instead of 4WD Hi all the time?

4WD Lo - use in really bad weather, when towing (heavy), or when serious off-roading. I understand in this mode, you don't want to be going fast or making quick turns.

Equinox:

AWD - ??? What's the difference between this and 4WD Auto and 4WD Hi? Is this the full time AWD explained in the early posts or the permanent AWD? What is "better?"

Background on my potential use of the vehicle: I live in the city of Chicago and have to deal with severe snow occassionally, and just snowy or wet conditions often. I also would use the vehicle to road trip and tailgate (while following my Iowa Hawkeyes...parking in grass or muddy areas depending on weather). I also would use the vehicle when camping, skiing, golfing, etc. I don't forsee myself driving through moutain terrain or anything. I just basically need an all-purpose vehicle that is comfortable, fun to drive, and can haul my stuff (and friends) around. I also try to buy American as my dad is a union electrician and my girlfriend's (from Detroit burbs) family and friends all work for American auto manufacturers or dealers. Any suggestions or insight on the above cars or others that may work for me? Thanks.

Go easy on me...I'm a first time poster!

Phil

:confuse:

paisan

A few things...

On the Trailblazer you would have:

2wd: Normal dry road, saves gas
Auto-4wd: 100% RWD til you start spinning a wheel, then it puts power to the front axle at 50/50 split. For use on paved roads, dry, wet, snowy
4-Hi: For use only off-road or in snow conditions where the road is covered in snow, and for offroading
4-Lo:Pulling a boat out of a boat ramp, or getting unstuck in really deep snow, or offroading, you can't use this on dry pavement.

The trailblazer has basically a pickuptruck frame with a body on it. It is essentially a RWD based chassis where the engine runs front to back and you have a solid rear axle. This truck is relatively heavy compared to the Equinox.

The Equinox is FWD based with a Transversally mounted motor. The AWD system on this runs at 100% FWD until wheel spin, then it puts power to the rear. There is no Low Range or 4-Hi mode. It gets way better milage than the TB and is unibody in construction.

For your purposes, the Equinox would be better IMHO. It'll get you through snow, slush, etc, and in and out of wet fields. For the winter I'd suggest snow tires on it.

-mike

phil56

Mike,

Thanks for the response. So just to clarify. Using the Trailblazer in 4WD Auto mode is nearly the same as driving an AWD Equinox. The difference being that the Trailblazer in 4WD Auto would drive in RWD until one or both of the rear tires began slipping at which time some torque would shift to the front wheels as well until the car regained traction...and the Equinox would drive in FWD until one or both of the front tires began slipping at which time some torque would shift to the rear wheels as well until the car regained traction.

Is the torque transfer 50/50 when slippage occurs in both (or neither) the Trailblazer and Equinox?

Is there any difference in the way the SUVs would react if, for example, the right side of your car went off the road (i.e. right side wheels on grass/dirt and left side wheels on pavement)?

Thanks again for the clarification.

Basically, my girlfriend is going to be leasing an SUV (which I will end up paying for and driving quite often). She gets the GM family discount, which I guess is pretty substantial. We like both the Trailblazer and the Equinox (she is probably partial to the Equinox...I'm partial to the Trailblazer). Her uncle (who tests powertrains for GM) suggested doing a 2 or 3 year lease by the end of this month (due to a bunch of deals going on) and recommended the Trailblazer because you get more car for your money (i.e. I guess the Equinox is really "hot" right now and it would end up costing nearly the same for the 2 vehicles due to the lack of discounts for the Equinox).

A year ago, I had mentioned to my dad that the Equinox (which was just coming out) looked like a pretty good, affordable SUV. He had told me that if I'm going to get an SUV, get a 4WD not an AWD...that I might as well get a car instead of an SUV if I planned on getting AWD. He told me, and I don't remember exactly, something regarding if two wheels went off road while the other two were on (similar to the situation I described above), a 4WD could save you while you'd be screwed with an AWD. Maybe I misunderstood him...maybe he doesn't fully understand the difference between 4WD and AWD...maybe he's right...that's why I'm here!

And one final question...I know this is off-topic but maybe someone could give me some insight. Lease or buy??? My family has always bought and my dad believes that when you lease and consider all the "hidden fees," you're getting ripped off because at the end of the day, you have nothing to show for it. My girlfriend's family always leases. They believe that the car depreciates faster then what your paying so you end up saving money by leasing. I think the answer lies in how long you would plan to keep your car (or maybe in what kind of car you are getting...Mercedes will depreciate slower than Saturn). If you buy and then want to get a new car in a few years, you'd probably be better off leasing. If you are the type who will buy a car and milk every last mile out of it, buying is probably the better option. Is that a fair summary or am I missing something? Thanks.

Phil

tidester

You may want to look into Lease Questions - Ask Here.

tidester, host

paisan

Onroad the AWD will be a better bet. The trailblazer might have a slight advantage in that I believe it has a rear LSD optional which would shift power from side to side on the rear axle, however since it's a RWD based version you are more likely to slip in a sitation where you drop 2 off the side than in a FWD based. Also I believe when the auto-4wd kicks in it just goes to 50/50 split immediately.

Fuel consumption on the Trailblazer will be significantly more due to weight, engine size, drivetrain loss, and areodynamics, so that is something to consider on Equinox v. TB.

As for leasing, I'd lease an American car cause in 3 years there is likely to be a problem with parts falling off (knobs, window motors, etc. etc) so you don't want to be stuck with it. As a general rule though buying is better unless you can gain a tax benefit from the lease or you don't drive that many miles with your vehicle. For me I drive way too much and would be over the lease limits quickly.

-mike

ateixeira

I believe the nox uses a Rotary Blade Coupling. FWD until slip, then the rear axle kicks in.

So you can't lock the axles together, nor do you have a low range.

So it's like 4WD-auto, except backwards, as in the axles are reversed.

-juice

phil56

Mike and Juice,

Thanks for all your help! I can't believe how tricky this AWD versus 4WD stuff can be. Thanks for clearing up my questions.

Phil

:shades:

lazzarich

I am sure this has been asked and answered hundreds of times, but what is an open differential and what is a closed differential (limited slip/positrac). I understand the basic operation of the differential/CV joint allowing different rates of speed in turns. It is always described as a redistribution of power when one or other wheel slips.

In a non limited slip diff - what happens when one wheel is on soft sand ?
In a limited slip diff - what happens when one wheel is on sand?
In a 4Runner with an X switch - what happens when one wheel is on sand?

Is it true that having a 4wd without a limited slip is far les effective than with a limited slip?

paisan

I believe the 4-runner X switch just locks the center diffy. I'll do some research and let you know for sure on that one.

Open Differential: Power is normally 50/50 split between both wheels on a given axle. Once slippage occurs, power is directed to the slipping wheel.

Locking Differential: Found on a bunch of pickups these days as an option, essentialy only for use offroad, mechanically locks both wheels on a given axle so they both get 50/50 torque split of power and will spin both wheels or neither wheel.

Mechanical LSD/Posi Rear: This setup uses clutch plates in the rear differential to move some power from a slipping wheel to a non slipping wheel when you are spinning wheels.

Electronic LSD: This setup applies the brake to a slipping wheel thus directing power to the opposite wheel. This is used on the Nissan trucks on both front and rear, Subaru VDC models, Mercedes Benz cars and trucks and others I'd imagine too.

Viscous Limited Slip Differential: This is similar to the operation of the mechanical LSD but uses a sealed fluid that when heated up from a spinning axle will force power to the opposite wheel.

Hope this helps.

-mike

rsholland

Drew, that's not full-time AWD, but rather on-demand AWD. If it were full-time, it would always be engaged to some degree.

Bob

stever

Just catching up in here Bob? That post you're replying to dates back to 2001. Not that clarification isn't always appreciated

Steve, Host

rsholland

Interesting... That post that I just responded to just showed up as a new post on my computer. Very strange...

Bob

stever

We added the Outback to the discussion category list so maybe that's how it wound up on your radar. It did make me feel a bit old reliving 4 year old posts. :shades:

Steve, Host

rsholland

Ah ha! I'm sure that's the answer, as I haven't seen it before on the Subaru-linked threads.

The way I have my computer set up is that any Subaru-related thread automatically shows up, so if this has been just added to that group, then that's what just happened. Thanks, as I was getting worried that I had been geezing again...

Bob

ateixeira

Think about that fact - the power takes the path of least resistance.

In an open diffy, if it finds one wheel slipping, all the power goes there and the other wheel does absolutely nothing.

With limited-slip, it allows some slippage on one slide, then gradually sends power to the other side. It can do this with traction control (most modern luxury models), a torsen differential (what Audi used to have), or a viscous/fluid-filled (Subaru).

A locking differential means both wheel will rotate at the same speed no matter what. So the wheel on sand would never slip in the first place, the other wheel would just do all the work and the one on sand would just go along for the ride, but at the same speed.

The problem with the locker is that on dry pavement it will bind, i.e. when you do a U-turn the tires will have to scrub off the difference in speeds. Draw two concentric circles, the outer wheel travels a greater distance, and the locker doesn't allow it to do that, so the tires are forced to squeel.

So each has its advantages. Open is cheap. Limited-slip is versatile. Locked is best for pure off-roading.

-juice

forddude

Have your mechanic check out the following things:

The transfer case shift motor encoder position pids during the 3 possible positions (he'll know what I'm talking about- he will need a Ford Workshop manual and an adequate diagnostic tool.

Also, make sure that when you shift into 4x4 Low, that you have the vehicle in neutral, apply the brake, then switch the system to 4x4 Low. otherwise it will not shift.

If you have anymore probs, let me know, I may be able to help.

-forddude

paisan

On the rear of the STi I believe.

-mike

lazzarich

Thanks for the informative responses. I have a 4Runner with full time 4wd and have always struggled with understanding the role the differential plays in the game. Previously owned an Isuzu Rodeo with 4wd and limited slip. Was very effective - never got stuck in some tough places in the Anza Borrego desert.

ateixeira

Good catch, STi is pretty exclusive and I didn't think of that.

4Runner probably uses traction control to manage both differentials, doesn't it?

-juice

tngal

Many thanks and I will get back with you when I speak with him. I really appreciate it, Forddude!

tburns

I have the same problem with my '98 Ford Explorer. My mechanic was unable to find a code for the problem. Although he thinks it is related to the new transmission that the dealer installed. The dealer says it is not related, but will check it out for a mere $79 per hour.
Have you found out what the problem is? I too am a single Mom and would appreciate any help.

donl1

Any thoughts...good or bad...on the Ford Five Hundred AWD. Is the Haldex a proven product? How does it rank with other AWD systems? When you are driving in heavy snow is it better to turn off the Traction Control so as not to have it intrude on the forward speed. Have had many 4X4's in the past but none for over 10 years. First experience with a AWD vehicle. :confuse:

paisan

Haven't had a chance to check it out yet or what system it has. I would think it's an electronic system putting 100% power to the front wheels until slippage then diverting some to the rear. Once I have a chance to research it a bit I'll weigh in with an opinion.

-mike

ateixeira

That's correct, they use Volvo's Haldex system, not unlike the 4Motion on the Gold and Audi TT.

It's quick-acting, but it is primarly FWD and not really full-time system. It's part-time on-demand, and engages automatically and relatively quickly.

I think for the price you are getting a pretty good system and overall value. Not very exciting, but extremely roomy.

-juice

paisan

I actually like the looks of it. Seems a bit sportier than the Tarus that it replaced. Amazingly I rarely see any Taruses anymore on the road, and to think just a few years ago they were like one of the top 5 cars sold.

-mike

ateixeira

They are all in Orlando in the rental car lots. All of them.



-juice

forddude

Yeah, the Ford version of Volvo's Haldex AWD system bullet-proof.

I've heard that these system very rarely have problems (at least on the Volvo models).

One drawback of the Ford version of the system is that there is no instrument cluster fault

light to indicate that the system has problems or is not operating correctly-- -

you won't know unless you use a scan (diagnostic) tool to communicate with the ABS

module and check for AWD system fault codes.

-fordude