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Unread 01-10-2011, 10:39 AM   #1
troy32323
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4 Wheel Drive

I am a little confused about the 4 wheel drive on my JK. As I understand it when I put it into 4 wheel drive nothing changes in the rear end (no locker). The only thing that happens is the front drive is engaged.

I always thought if you drove a 4 wheel drive vehicle on the road it would blow the differential. I just read a thread on here a few days ago that said in 4 wheel drive the front and rear are engaged but with limited slip differential.

My question is if the rear remains the same and the front differential is a limited slip like the rear then it will not hurt it to drive in 4 wheel on the pavement?

Not planning on doing this but trying to understand how it works.

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Unread 01-10-2011, 10:47 AM   #2
Croce
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Correct. you dont want to drive it on dry payment, i believe it can cause damage to the transfer case not the Diff (i'm probally wrong on that part)
You only want to use 4WD in slippery situations


I'm sure someone will chime in with a more technical anwser
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Unread 01-10-2011, 11:05 AM   #3
troy32323
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That is what I always believed. I rarely use 4 wheel in the snow as I am always worried about the occasional dry patch where the snow has blown off the road.

After reading the thread that states you will just run the front and rear with a limited slip differential I have been wondering why you cannot drive in 4 wheel on pavement.
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Unread 01-10-2011, 11:42 AM   #4
mickeymeanie
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We had about 5 inches of snow around here yesterday... not something we see very often in TX...

Anyhow, I took the opportunity to go for a spin in the JKU yesterday... BIG difference in drivability between 2WD and 4WD. I backed out of the garage already in 4WD and drove around for a bit. Stopped in front of my daughters friends house waiting on her friend I put it back in 2WD just to see what the difference would be... as soon as I eased on the gas to leave the rear tires spun and smacked the rear tire into the curb... put it back in 4WD and simply wheeld away.

Later I took it up to a large parking lot filled with several inches of fresh snow... put it in 2WD and drove around a bit... it did okay with concentrated moderation of the gas pedal... then I put it back in 4WD and it would go and do whatever I wanted without issue...

I will say, donuts in a snowy parking lot are much more fun in 2WD though... seemed nearly impossible in 4WD... :-)
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Unread 01-10-2011, 11:44 AM   #5
troy32323
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Uh.... Thanks for your story
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Unread 01-10-2011, 11:52 AM   #6
mickeymeanie
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Quote:
Originally Posted by troy32323 View Post
Uh.... Thanks for your story
Oh, sorry... I was getting to the point that I hadn't even considered it being an issue hitting an occassional dry patch while in 4WDH...

I always figured it was something you just didn't want to do consistantly on dry pavement, LSD or not...
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Unread 01-10-2011, 12:38 PM   #7
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Using 4wd on a non slip surface will stress the entire drive train
And the weakest point will or can be damaged
This is likly be the front axle u joints or the drive shaft joints!
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Unread 01-10-2011, 02:30 PM   #8
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Iv driven on the highway in 4HI on dry pavement and my T-case hasn't grenaded yet. Turning is what will stress the drivetrain. If it's snowy and there is a small dry patch up ahead, then dont sweat it being in 4HI. If you have a long streach of cleared snow though, put it in 2WD.
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Unread 01-10-2011, 02:40 PM   #9
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Sharp turns on dry pavement are a bad idea. Moderate turns are why 4hi is limited slip and not fully locked. You aren't going to hurt an axle or a tcase unless you are being an idiot in 4hi.
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Unread 01-10-2011, 03:04 PM   #10
troy32323
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I guess what I am getting at is the rear does not change when you put it in 4 wheel right? If the rear has no problem making turns all the time you drive your car why would the front when it is engaged in 4 wheel drive? It has the same differential set up right?

Am I wrong in my assumptions?
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Unread 01-10-2011, 03:11 PM   #11
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The only difference is that your front axle has a u-joint behind each wheel that allows the wheel to turn while the axle is engaged. Those joints do NOT like being turned while the steering is at full lock. If you keep your turns reasonable (say, maybe 70% of full turn or less), you shouldn't have any problems.

Yes, I know, the manual says otherwise. You have to keep in mind that a lawyer wrote that document. CYA reigns supreme.
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Unread 01-10-2011, 03:45 PM   #12
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Unread 01-10-2011, 03:47 PM   #13
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Quote:
Originally Posted by troy32323 View Post
I guess what I am getting at is the rear does not change when you put it in 4 wheel right? If the rear has no problem making turns all the time you drive your car why would the front when it is engaged in 4 wheel drive? It has the same differential set up right?

Am I wrong in my assumptions?
Your right. Nothing changes in the differential. Think of the transfer case as a differential for the driveshafts. Normally the front gets no power. In our Jeeps, we are just locking the driveshafts together exactly as you would lock axles together. Thats all the happens.
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Unread 01-10-2011, 05:03 PM   #14
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Yup, the two drive shafts are locked when in 4 wd and hence the front and rear axles are also locked in rotation, not the diffs! The problem is when turning, the front wheels travel a different distance than the rear wheels so the axles want turn at a different rate creating stress and whAt is often called wheel hop. An awd car has a differential and not a tcase that allows for this difference between the f/ r axle hence can be in awd all the time.
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Unread 01-10-2011, 09:59 PM   #15
troy32323
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Quote:
Originally Posted by RockyClymer View Post
Yup, the two drive shafts are locked when in 4 wd and hence the front and rear axles are also locked in rotation, not the diffs! The problem is when turning, the front wheels travel a different distance than the rear wheels so the axles want turn at a different rate creating stress and whAt is often called wheel hop. An awd car has a differential and not a tcase that allows for this difference between the f/ r axle hence can be in awd all the time.
This makes a lot of sense to me. The Tcase locking the drive axle together not like a differential in an AWD. Now I can understand how the larger radius of the front wheels turning will bind up with the smaller radius of the rear wheels. Now I can continue my paranoia about driving in 4H on the street.
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