Question about 4-wheel drive...is it REALLY 4x4?

[d0n_3d]

OK when it comes to 4x4 stuff I am completely dumb...I have several questions pertaining to my 88 ford ranger 4x4

1. Say you lock the two front hubs but still drive in 2wd...are you causing harm doing this? I like to do this sometimes when I know the road conditions will be sloppy and I will shift to 4x4 on the fly

2. Can you drive at highway speeds with 4x4 engaged without causing harm? I have only done this a couple times and I never had problems going 55 mph in 4 wheel drive, I've heard you can damage your drivetrain by doing this all the time

3. What does 4x4 really mean? Say you have a RWD car or truck with a NONposi rear, is it really a 4x1 since only one wheel is putting power to the pavement? And it's a 4x2 if it's a POSI since both wheels are putting down power? What about if a truck is 4 wheel drive and say you have BOTH differentials NON posi...when in 4x4 essentially you are still only 4x2 because only two wheels are putting power to the pavement (one up front and one in the back) and its TRULY a 4x4 if you have two POSI units (all 4 wheels putting down power)

confused yet??? ok good now let's differentiate between 4x4 and AWD!!!

4. What is the difference between AWD and 4-wheel drive? I always thought that AWD has each wheel independently putting down power and it's computer controlled with no differentials...

ok someone clarify all this please

 

[SilverSleeper]

Okay, I can help with the AWD part.

AWD most certainly does have differentials.
It is driving all 4 wheels all the time. There is no way to shut it off. My Astro has a transfer case, but only one constant range. It also has front and rear diffs.
Typically, 4x4s have a transfer case that has high and low range. The low range is basically a set of gears that multiply the torque for off-road or trail use.
4x4 locks the front and rear driveshafts together. So it will cause damage if you turn. Since the front wheels will travel in a different arc than the rears when turning, they need to slip a little bit, or you will wear out the drivetrain. The AWD can work all the time, because the center diff (transfer case) is a fluid coupling, similar to a torque converter. It is setup to allow a certain amount of torque slippage, then transfers more torque when wheel slip is detected. Some modern systems are computer controlled, and use the ABS to keep everything straight.

Just because you dont have posi, doesnt mean you are only driving one wheel of a diff. If you put both wheels on equal traction, each will drive the vehicle with equal torque. The posi only comes into play when one tire looses traction.

Do a search at how stuff works.com on 4 wheel drive and/or AWD. Really good reading there if you really want to learn. Its where i went when I wanted to know how my AWD Astro worked.
four-wheel-drive
-HTH

 

[GN One Day...]

Originally posted by d0n_3d
OK when it comes to 4x4 stuff I am completely dumb...I have several questions pertaining to my 88 ford ranger 4x4

1. Say you lock the two front hubs but still drive in 2wd...are you causing harm doing this? I like to do this sometimes when I know the road conditions will be sloppy and I will shift to 4x4 on the fly

2. Can you drive at highway speeds with 4x4 engaged without causing harm? I have only done this a couple times and I never had problems going 55 mph in 4 wheel drive, I've heard you can damage your drivetrain by doing this all the time

3. What does 4x4 really mean? Say you have a RWD car or truck with a NONposi rear, is it really a 4x1 since only one wheel is putting power to the pavement? And it's a 4x2 if it's a POSI since both wheels are putting down power? What about if a truck is 4 wheel drive and say you have BOTH differentials NON posi...when in 4x4 essentially you are still only 4x2 because only two wheels are putting power to the pavement (one up front and one in the back) and its TRULY a 4x4 if you have two POSI units (all 4 wheels putting down power)

confused yet??? ok good now let's differentiate between 4x4 and AWD!!!

4. What is the difference between AWD and 4-wheel drive? I always thought that AWD has each wheel independently putting down power and it's computer controlled with no differentials...

ok someone clarify all this please

1: With hubs locked, but driving in 2WD, you aren't really hurting anything. You may put a little more wear up front, but on many new 4WD's, the hubs are always locked (like on my Amigo), which is how you are able to push button shift into 4WD. It engages at the front diff instead. Not recommended, may reduce your MPG by about 1.

2: DO NOT drive in 4WD in your Bronco or anything that does not have a center diff like in a car. It will bind up and eventually do damage since there is no slip. 4WD in that type of vehicle is ONLY for offroad when the surface itself will allow for that slippage.

3: Unless you have lockers (not just LSD) you aren't really FOUR WHEEL DRIVE. Most likely, the front is open diff, which reduces you to THREE wheel drive. If you you have a locker in the rear, or LSD. Unless you have an Auburn or clutchless LSD, you will only have power to both wheels as long as there isn't a lot of slip. In my Amigo, I have a Dana 44 with a TracLok LSD, as in Jeeps. When 4 wheeling, you're rarely on a flat surface when you need traction. If I was a little tilted, and the "light" side was in some loose dirt, it would spin and unlock the LSD, so all the power to move was on the spinning wheel with no traction. After I put in a locker, that didn't happen anymore, power was always distributed since the rear stayed locked up. SO, if you have an open diff up front, and an open diff in the rear, you are essentially TWO wheel drive for any conditions that could warrant throwing it in 4. BTW, if you have LSD in the rear and your situation puts that one tire slipping so much that it unlocks, you can sometimes pull the emergency brake enough to put friction back on the spinning wheel and keep the LSD locked up for your next attempt, if you don't go too fast. It doesn't work nearly as well as a locker, but can sometimes give you the extra traction you need for an obstacle.

4: AWD has a center diff that allows slippage for paved surface driving. It will normally mean that it distribuites power and the front end gets 80-90% of the power until there's slippage and then it is equalized. Like on the WRX STi has a control for distributing the power, but most don't. 4WD is usually actually PART TIME 4WD. For use only when the driving surface (offroad) allows for the necessary slippage to avoid damage. You should not use this on the road except maybe in consistent ice. Snow supposedly does not provide the necessary slippage to make this safe on the vehicle.

 

[Mark E.]

1) It is ok to have the hubs locked and not engage the transfer case.

2) I would not drive with 4x4 engaged when there is a lot of traction. Only as required. Even tire wear can cause gearing changes and stress the transfer case.

3) 4x4 with open diffs is only 2 wheel drive. I consider posi diffs in 4x4's as open. When you lift a wheel off the ground, no clutch posi is going to help. This is where lockers come in. To have true 4x4, you need lockers front and rear. But a locker in the front makes steering a bitch, so there are drawbacks.

4) Don't know anything about AWD!

 

[straycat990]

it's okay to lock the front hubs in and drive. The only harm will be gas milage. I always lock mine in and drive around before I go off roading. It gets everything cover in oil again.

I would not reccomend driving on dry pavement in 4 wheel drive. That is rather hard on the equipment. In snow, ice, or any slick condition it is fine to do so. I would limit my speed though.

4x4 ..means the truck/car has 4 wheels and all 4 are drive wheels. 4x2 means 4 wheels with only 2 drive wheels

Most 4x4's have single traction diffs. Its a safety issue ... Posi front diffs can be dangerous .. spin ..lose control, posi doesn't disengage in a corner ...no turn.

 

[SilverSleeper]

Re: Re: Question about 4-wheel drive...is it REALLY 4x4?

Originally posted by GN One Day...
It will normally mean that it distribuites power and the front end gets 80-90% of the power until there's slippage and then it is equalized.

Thats not entirely true...

It depends on vehicle configuration, actually. And the ratios arent usually that high.
Those that are usually front drivers, have most of the torque up front, while those that are usually rear-drivers have the torque bias for the rear. (i.e. Astro vans are rear-wheel drive based, so the torque split for it actually is about 35% front/65% rear. Conversely, the Caravan AWD vans are about 70% front/30% rear since they are setup as a front drive vehicle.)

Some AWD systems have all lim/slip diffs. They make use of ABS to lock the spinning wheel(s) so that the torque is transferred to the wheel with traction.
Go check the site I posted a link to. It is long, but a good read if you are interested in the subject.

 

[Buick From Hell]

All I can add pertains to NOT driving with 4WD engaged on "traction" surfaces:

Not all, but many 4WD vehicles have different front & rear gear ratio's!

 

[soonergn]

I have to disagree with the different gear ratio in each axle statement. Why would you want the axles spinning at different speeds? If you had traction at both ends the t-case would be instant grenade! All 4 wheels have to turn at the same speed inorder to keep things from binding up in a part time 4wd system. Full time 4wd and all wheel drive systems have a different t-case design to handle turning and slight variations in tire heigth due to uneven tire wear and tire production variances that would eventually cause binding in a part time system where both axles are locked together. Even in all wheel drive systems they recommend that you try to keep tire wear as even as possible to minimize t-case internal wear. If the axles had different gear ratios then one axle would have to have a shorter or taller diameter tire to make up for it.

 

[GN One Day...]

I agree on the gears. It's gotta be the same front and rear, that's what makes gear swaps in odd vehicles like my Amigo hard. Dana 44 rear you can get anything you want, but an Isuzu 9 bolt up front is not so easy. IIRC, and I haven't done this, they say that even for offroad only you don't want more than a 3% variation front to rear when all you can do is as close a match as possible. It would be different if you are running different size tires front/rear, as long as you get the final ratio's to match, but that sounds like a major pain and probably not useful.

Those with front lockers will often install manual hubs, if not already equipped (like most everything these days). That way you can make driving more tolerable by leaving one hub up front unlocked to aid in turning.

 

[Buick From Hell]

Found this webpage: http://www.pirate4x4.com/tech/bible/
and found the following, which you can verify:

"GM REAR ENDS, 3/4 ton":
1973-1980 - Corporate 14 bolt full-floating. 3.73, 4.10, 4.56 ratios available.

"GM FRONT ENDS, 3/4 ton":
Available ratios = 2.73, 3.07, 3.42, 3.54, 3.73, 4.09, 4.55

ergo:
4.10's in back with 4.09's in front...
4.56's in back with 4.55's in front...

not a LOT different, but they're different!

My old '76 V6-Buick powered Luv had 4:10's in back, and 4:11's in front. I believe my old '84 Bronco had different front & rear ratio's too...not sure why they do it??

 

[1badTTA]

The only reason for the slightly different ratios is the tooth count. 4.11:1 will use 9 teeth on the pinion and 37 on the ring, 4.10 uses 41 on the ring and 10 on the pinion. It really is just a matter of using different differential models with existing parts that are proven to be reliable, and not done for any advantage.

As far as locking diffs, the best setup all depends on how and what you are using 4wd for.

Both open or posi rear, stock and rarely used off road, mostly muddy roads and snow.

Posi front and Locker (preffered) or posi rear, best all around combination for good off and on road capabilities.

Lockers front and rear, best off road with drawbacks for onroad driving.


Also, an ARB air locker helps alot for onroad driving as it is controlled by the driver and can be unlocked when not needed unlike a detroit or lokrite(sp?) which is automatic.

The only drawback to locking the hubs (with an open front diff) is that it will make the internals turn which will cause minor wear (on the oppisite side of the gears) and reduce gas mileage. It also shouldn't be done when driving at freeway speeds as front driveshafts generally aren't balanced as well as rears (especially on older vehicles, don't ask me how I know ). The advantage is that you are able to put it into 4wd without getting out of the vehicle and the hubs are already locked (most require moving X feet to actually engage) so once you get stuck you can reach down and get it into 4wd without having to get the front wheels to turn first.

 

[Pronto]

My wife's Subaru Legacy GT wag has a limited slip rear diff. Last weekend I had to go pick up my son at a friends. There was about 12"of snow by then. When I got back the plow had just left a 3' high mound in the driveway. I swung wide and bopped through it and then pulled straight in. I was impressed, so was my son. I doesn't even have real snow tires on it.