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Old 01-21-2011, 09:29 AM   #1
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Puttting it in 4Hi or 4Lo, what's really happening?

I've got a 2000 totally stock TJ Sport 4.0L 3spd auto. I've read through past threads, and I see that Part time means use it for "part time only". but what am I really getting when I pull the handle? Are all the wheels in full lock 4 wheel drive? Or is it something else? and what's the advantage to installing aftermarket lockers?

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Old 01-21-2011, 09:39 AM   #2
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Pulling the lever into 4wd means power goes to both axels. If you have open diffs, which many of us do, your only getting power to one of the two wheels on each axel.

2wd = 1 wheel powered
4wd = 2 wheel powered

lockers and limited slips will allow power to go to both wheels in the axel that has them installed

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Old 01-21-2011, 09:44 AM   #3
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There is no part time 4wd in a jeep. In 2hi you are a two wheel drive vehicle. When you pull to 4hi you are now in 4wd and it gives traction on front and rear. When you go to 4lo you engage different gears in the Tcase but it does not effect the axles. On a stock jeep there is never a time that all four wheels are locked together. The Tcase can never lock all wheels together either no matter what is modified. To get both wheels on an axle to lock requires a locker or semi locker like a posi or limited slip.
Most stock jeeps have open differentials on both ends but there was an optional limited slip in the rear on some models.
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Old 01-21-2011, 09:45 AM   #4
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X2 on peepers. Guess I was typing when his came in.
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Old 01-21-2011, 09:47 AM   #5
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Lockers will 'lock' each axle together, so the same amount of power goes to EACH wheel on that axle-no 'slip' that you get with a differential. It also can ONLY Be used on rough terrain, snow, mud, dirt...because if you try to use locked axle on TAR, you can snap an axle shaft easily when turning because the wheels are trying to turn at the same speed and one can't do it...
As Peepers says, 2 wd- 1 wheel (rear axle) turning. 4wd drive (part time) 1 wheel on each axle turning but still can get slippage. 4 wheel drive with LOCKERS you can lock rear axle, or rear and front axle at the same time (for factory installed lockers, like the Rubicons have) if you install your own aftermarket lockers, you can run 'just' front axle or 'just' rear axle when you want. But still cannot (or should not!) run them on tar or solid surface and turn!
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Old 01-21-2011, 09:53 AM   #6
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Originally Posted by Peepers View Post
Pulling the lever into 4wd means power goes to both axels. If you have open diffs, which many of us do, your only getting power to one of the two wheels on each axel.

2wd = 1 wheel powered
4wd = 2 wheel powered
That's a common but untrue misunderstanding of how axles work. Whether the axle has a limited slip differential or is open, the differential always... always always... splits the power 50:50 to each side. No matter what, even the tire on the ground that is not spinning is getting exactly the same amount of power that the spinning tire that is up in the air or on the ground that is spinning is getting.

So no matter what, each side is getting the same amount of power so in 4x4, all four wheels are being powered equally. No matter what it looks or feels like.

Here's a FAQ article on 4x4 and torque that I wrote years ago that may help... 4x4 & Torque answers

And to better understand lockers and limited slip differentials, here's one for that subject... What? Why do I need a locker? I thought I had 4WD!
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Old 01-21-2011, 10:05 AM   #7
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Perfectly said jerry... there is a great video on youtube that explains exactly how an open diff works... helped me a lot... not sure if that was one of ur links jerry but its def. an eye opener
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Old 01-21-2011, 10:07 AM   #8
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Here it is... a lil time consuming but really good.
http://m.youtube.com/#/watch?desktop...hruinbWc&gl=US
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Old 01-21-2011, 10:28 AM   #9
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There is no part time 4wd in a jeep. In 2hi you are a two wheel drive vehicle. When you pull to 4hi you are now in 4wd and it gives traction on front and rear. When you go to 4lo you engage different gears in the Tcase but it does not effect the axles. On a stock jeep there is never a time that all four wheels are locked together. The Tcase can never lock all wheels together either no matter what is modified. To get both wheels on an axle to lock requires a locker or semi locker like a posi or limited slip.
Most stock jeeps have open differentials on both ends but there was an optional limited slip in the rear on some models.
The 'Part Time' is the type of 4WD system the Jeep has. Full time 4WD means just that - its never, EVER turned off. These usually have a center differential that allows the power sent front to back to vary (to allow the axles to spin at different speeds while turning). The Wrangler does not. When the transfer case is in 4WD power is sent equally, 50:50 to both axles (and this is why it shouldn't be used on dry pavement). When the transfer case is in 2WD, its obviously not in 4WD...hence part-time.
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Old 01-21-2011, 11:04 AM   #10
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Dang, that was a lotta' reading. But it was exactly what I needed, thanks. So, when I install probably a Truetrac LSD in the front, and possibly an Ox Locker in the rear. Will "the handle" still be used or will the Lockers have their own dedicated actuating system, that nullifies the use of "the handle"?
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Old 01-21-2011, 11:16 AM   #11
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The LSD in the front will not recieve power until you pull the handle to 4wd. the rear obviously always gets power but your diff. will be open till you pull the handle on the ox locker... then both sides of the rear axle will be locked together
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Old 01-22-2011, 06:23 AM   #12
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Cool, thanks for describing that to me. Would it be worth it to put a Detroit Truetrac in both front and rear? or better to have a full locker in the rear?
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Old 01-22-2011, 06:45 AM   #13
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Quote:
Originally Posted by Jerry Bransford
That's a common but untrue misunderstanding of how axles work. Whether the axle has a limited slip differential or is open, the differential always... always always... splits the power 50:50 to each side. No matter what, even the tire on the ground that is not spinning is getting exactly the same amount of power that the spinning tire that is up in the air or on the ground that is spinning is getting.

So no matter what, each side is getting the same amount of power so in 4x4, all four wheels are being powered equally. No matter what it looks or feels like.
Very well said. Also, on the Rubicon I believe that either the rear, or the front and rear, can be locked.
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Old 01-22-2011, 11:45 AM   #14
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The 'Part Time' is the type of 4WD system the Jeep has. Full time 4WD means just that - its never, EVER turned off.
Not quite, the Selectrac and Quadratrac systems used in Cherokees, Grand Cherokees, and Liberty have full-time 4x4 systems that can be turned off. I had a Cherokee with a Selectrac system with a selectable full-time 4x4 system in additional to a selectable part-time 4x4 system. Full-time just means it doesn't have to be turned off if you drive on dry roads or surfaces with good traction. It can be left on full-time if desired. Only some full-time systems cannot be turned off.
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Old 01-22-2011, 12:15 PM   #15
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Not quite, the Selectrac and Quadratrac systems used in Cherokees, Grand Cherokees, and Liberty have full-time 4x4 systems that can be turned off. I had a Cherokee with a Selectrac system with a selectable full-time 4x4 system in additional to a selectable part-time 4x4 system. Full-time just means it doesn't have to be turned off if you drive on dry roads or surfaces with good traction. It can be left on full-time if desired. Only some full-time systems cannot be turned off.
I stand corrected. Every full time system I'd seen up to this point (including the Quadradrive II and Quadratrac II used on Grand Cherokees) did not offer any option to turn it off.
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Old 01-22-2011, 12:20 PM   #16
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I need to read the entire thread before posting. :/
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Old 01-22-2011, 01:53 PM   #17
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Originally Posted by Peepers View Post
Pulling the lever into 4wd means power goes to both axels. If you have open diffs, which many of us do, your only getting power to one of the two wheels on each axel.

2wd = 1 wheel powered
4wd = 2 wheel powered

lockers and limited slips will allow power to go to both wheels in the axel that has them installed
not exactly. unless theres a significant grip difference on each axle.
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Old 01-22-2011, 04:37 PM   #18
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I've read on other jeep sites that you can trick your open diff by applying the brakes while giving it gas. Long technical explanation about how it tricks the axles into distributing the torque more evenly to the 4 wheels. Never as good as a locked diff bit supposedly can help us unlocked guys get unstuck if you practice (guess this was the way it was done in the old days before all these fancy lockers).
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Old 01-22-2011, 04:56 PM   #19
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Nice.

Quote:
Originally Posted by Bubba68CS View Post
The 'Part Time' is the type of 4WD system the Jeep has. Full time 4WD means just that - its never, EVER turned off. These usually have a center differential that allows the power sent front to back to vary (to allow the axles to spin at different speeds while turning). The Wrangler does not. When the transfer case is in 4WD power is sent equally, 50:50 to both axles (and this is why it shouldn't be used on dry pavement). When the transfer case is in 2WD, its obviously not in 4WD...hence part-time.
I have another Jeep that has both. When you pull the lever and the dash light says "Full Time", it means you may drive it anywhere anytime, all the time. When it says "Part Time" it means try to stay clear of dry pavement for the reasons you articulated so well. Good job Bubba68CS.
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Old 01-22-2011, 05:21 PM   #20
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I have another Jeep that has both. When you pull the lever and the dash light says "Full Time", it means you may drive it anywhere anytime, all the time. When it says "Part Time" it means try to stay clear of dry pavement for the reasons you articulated so well. Good job Bubba68CS.
ok let me get this right one more time.
the difference between a FULL time and a PART time systems is the whether the prop shafts go to the front and back locked or not. a part time system have a locking mechanism that locks front and rear prop shafts together. the reason calling it a part time system is that it CANNOT be used all the time due to when turning the front and rear prop shafts have to have different speed other wise the wheels would jump and hop.
a full time system has a mechanism that allows the front and rear shafts have different speed, usually a center differential. however this layout has a flaw. we all know that an open diff sends more power to the side that has less grip, so when front and rear tires have significant grip difference, it would make situation worse sometimes a 4WD could act like a FWD or RWD, or even one wheel drive if one tire is on ice and the rest is on pavement.
there are systems that has a locking center diff that can be switch on working like a part time system or switched off working like a full time system.
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Old 01-22-2011, 05:24 PM   #21
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I've read on other jeep sites that you can trick your open diff by applying the brakes while giving it gas. Long technical explanation about how it tricks the axles into distributing the torque more evenly to the 4 wheels. Never as good as a locked diff bit supposedly can help us unlocked guys get unstuck if you practice (guess this was the way it was done in the old days before all these fancy lockers).
some new cars have this electronic diff that is basically an open diff added individual shaft braking system, so when one wheel is spinning, the system applies brake to that wheel sending power to the one thats not spinning.
however by doing that you loosing pulling power because the brakes are wasting power and torque.
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Old 01-22-2011, 05:51 PM   #22
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a full time system has a mechanism that allows the front and rear shafts have different speed, usually a center differential. however this layout has a flaw. we all know that an open diff sends more power to the side that has less grip, so when front and rear tires have significant grip difference, .
Don't confuse a full time system center differential with an open differential. When talking about open differentials, we are referring to the axle differential.

There are a number of technologies for full time systems and traction control systems. I have a Durango with Full Time. It is a very basic system and basically the same as the Jeep Selec Trac. The front/rear torque split is fixed. There is no shifting of power.
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Old 01-22-2011, 05:57 PM   #23
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Don't confuse a full time system center differential with an open differential. When talking about open differentials, we are referring to the axle differential.

There are a number of technologies for full time systems and traction control systems. I have a Durango with Full Time. It is a very basic system and basically the same as the Jeep Selec Trac. The front/rear torque split is fixed. There is no shifting of power.
Yup, a number of technologies exist to shift power front to rear. Torsen differentials and viscous coupling are two others...with the viscous coupling being used in some of the Jeep systems.
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Old 01-22-2011, 06:22 PM   #24
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Don't confuse a full time system center differential with an open differential. When talking about open differentials, we are referring to the axle differential.

There are a number of technologies for full time systems and traction control systems. I have a Durango with Full Time. It is a very basic system and basically the same as the Jeep Selec Trac. The front/rear torque split is fixed. There is no shifting of power.
yes, I know they have vehicles that has better center diff system. they are not always open diff.
a rule of thumb is a part time system have locking mechanism that does not allow different shaft speed.
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Old 01-23-2011, 12:22 AM   #25
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old dodge power wagons were the "full time systems"
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Old 01-23-2011, 10:39 AM   #26
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old dodge power wagons were the "full time systems"
The old Dodge Powerwagons I drove in the Air Force in the late sixties all had part-time 4x4 systems. Full-time 4x4 is a relatively new thing that probably took off more in the 80's. My '89 Cherokee came with Selectrac that had a full-time 4x4 system in addition to also having a part-time 4x4 system.
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Old 01-23-2011, 01:16 PM   #27
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Also happening when you shift into 4 HI 4 LO

In 2 HI - Your transmission is turning a shaft which is spinning another shaft inside your transfer case. The power from the trans is passed through the xfer case to the rear diff. When you shift to 4HI - - it 'transfers' this power to the front diff as well as the rear diff. When in 4HI you should experience the same RPM at various speeds as you would in 2HI because there is no 'reduction' in the transfer case in 4HI. BUT when you go to 4LO...... The xfer case serves as a gear reduction unit. Hence in 4LO you have plenty of rpm and slow speed (creeper gear).

Notice that in 4LO you can take off in 2nd or 3rd gear without trouble, but that you could not even get close to 50 mph without your motor screaming.
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Old 01-23-2011, 02:56 PM   #28
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The old Dodge Powerwagons I drove in the Air Force in the late sixties all had part-time 4x4 systems. Full-time 4x4 is a relatively new thing that probably took off more in the 80's. My '89 Cherokee came with Selectrac that had a full-time 4x4 system in addition to also having a part-time 4x4 system.
i believe it was 74-76 when jeep came out with the original Quadratrac. My 77 cherokee is a full time system. It has a clutch pack for it acting like a limited slip (allowing the driveshafts to spin different speeds), then it also has "emergency drive" and is a switch you flip and it changes the transfer case into a solid lock so it sends the same power/speed to the front and rear.

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