4wd auto vs, 4wd high

[alfcapone]

I have a no mod -99, and i've got 4wd auto and 4wd high/low, and when you read in the manual you shuldn't drive with 4wd high on dry pavement.
But the LS in the rear has no problem on dry pavement, and i don't have any lockers in front, then the front shuld work like an ordinary diff, right?
And an ordinary diff, dosn't have any problems with dry pavement, because the wheels can turn with different speeds, right?
And then if i'm in 4wd high on dry pavement, the LS can take care of the different speeds of the tyres in the back, and the ordinary diff in the front shuld be able to take care of the dfferent speeds in the front, because it's just an ordinary diff, right?
So, whats with the transfer case, why shuldnt it work do drive with 4wd high on dry pavement, i dont get it

 

[justin146]

What you have to think about is the fact that while in a turn, the front driveshaft is turning faster than the rear. This is where it will bind because 4hi locks the two together.

 

[alfcapone]

The driveshaft to the frontaxel shuldn't go any faster when your making a turn.
Only the driveshaft in the frontaxel to the right wheel (if your turning left) will go faster, and then the driveshaft to the left wheel will go slower automaticly.
The driveshaft speed to the front axel shouldn't be any different.

 

[SWLathrop]

The transfer case in an Explorer that has the "AUTO" mode has a set of clutches in it that allows slippage. Even though the front and rear axles have the same gear ratio, the front axle still tends to turn faster than the rear. So with the clutches in the T-case, this is no problem. However, when locked in "4 HI", the front and rear axles cannot "slip" thus the reason why you cannot drive on dry/hard surfaces while in "4 HI", but can in "AUTO" mode. The LS rear axle has nothing to do with the different 4 wheel drive modes. Normally, an Explorer equip'd with the "AUTO" mode will not hear any noise when switching from "AUTO" to "4 HI". This is because of the clutch pack in the T-Case. While an Explorer with "2WD" mode will have a tendacy to "CLUNK" when going into "4 HI" due to the lack of this clutch pack. 4WD is 4WD, when on dry/hard packed surfaces, stay out of 4WD because something has to give.

 

[alfcapone]

Well i won't test 4wd high on dry pavement, that was never my intention, "If you can't afford it, don't test it" like some one said..
But i still have a hard time understanding why the front end must bind, when there is no locker and an ordinary diff.
Why are there differenses in speed between the two axels

 

[Nate1]

When you make a very sharp turn with something silly like a lawnmower, you will notice the rear wheels on the lawnmower spin much slower than the front. The same is true in our explorers. It all has to do with circles and geometry, and if you want me to I can get into the gruesome details, but suffice it to say that when you turn, your front spins faster than the rear, and when everything in our cars is locked up tight, there isnt much room for speed differences. Not to mention that if you have increased tire wear on your rears and they have a smaller radius they will cause some speed differences, so any locked 4x4 mode on pavement or anything high traction is a bad idea.
-----Nate

 

[justin146]

You would probably blow a CV joint because it seems to be the weakest link in the front end.

 

[Morgan97Ltd]

i've tried to park in my moms pathfinder in 4high on dry pavement in the past. now i know better but it is not an easy task and u can just feel the car struggling to move all the wheels

 

[TPLYNCH]

Originally posted by alfcapone
The driveshaft to the frontaxel shuldn't go any faster when your making a turn.
Only the driveshaft in the frontaxel to the right wheel (if your turning left) will go faster, and then the driveshaft to the left wheel will go slower automaticly.
The driveshaft speed to the front axel shouldn't be any different.

Even though there is an open differential in the front, one wheel will always be going a certain speed in relation to the drive shaft. If both the front and rear driveshafts are turning at the exact same speed (as is the case when in 4hi of lo) then one front wheel and one rear wheel will alway be trying to turn at the same speeds. The problem is in turns, the front wheels will always be turning faster than the rear wheels, which causes the front driveshaft to try and turn faster than the rear driveshaft. Since the speed of the driveshaft is locked at the t/f case, then the only way for the wheel to "speed up" is to slip. On hard surfaces, it is harder for the tire to slip and thus the binding is greater and greater force is tranferred to the cv's and hubs etc. until the wheel is able to slip.

Hope this makes sense....

 

[Ray Lobato]

Originally posted by alfcapone

But i still have a hard time understanding why the front end must bind, when there is no locker and an ordinary diff.
Why are there differenses in speed between the two axels

You are not taking into concideration physical tolerances, and the fact that things will not ware evenly

eventhough you have the same gears, front and back, and the the same tires, front and back, there is still enough differances that the front driving wheel will not turn exactly the same as the rear driving wheel.

In 4wheel drive with open diffenentials, you are actually driving 2 wheels. One in the front and one in the back.
If you were to loose traction on one tire on the front and one tire in back, you would not be able to go anywhere. Do you understand this much?
Now back to the front and rear stuff.
front to back it not the same way, when in 4hi the transfercase is locking the both drivelines together, so they will turn at the same rate, but physically that is not possible becaues nothing is exactly the same

Because of physical differances, one set of wheels will start to turn faster than the other set. After a certian amount of time the faster wheels will start trying to over power the slower turning wheels. The drivelines and axles will start to twist. When on soft surface the built up pressure will cause the wheels to slip and the drivelines and axles will return to normal (untwisted)mode until it buildspressure back up the the whole thing happens again.
when on hard surface, it takes too much pressure to break the wheels free to relieve the stress and things start to break.
Hope this helps.

 

[alfcapone]

Ok, you all convinced me now!!
Thanx!

 

[Matte]

It´s simple for you to test the theory of this in snow or
sand. If you make a sharp turn and then look at your
tracks on the ground you will see that the rear wheels
take a shorter way in the circel than the front wheels.
Thats why the front shaft rotate faster.