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Old 12-08-2011, 02:46 PM   #41 (permalink)
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The transfer case is what needs to have differential capabilities if one is going to use 4WD on non slippery surfaces.

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Old 12-08-2011, 02:58 PM   #42 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
If there is no front hub disconnection equipment the vehicle is AWD and it never has 2WD mode.
Not true. There are lots of vehicles with permanently engaged hubs and selectable 4WD. No modern consumer truck sold in America has manual hubs. Do you think they're all AWD?

I looked up the specs for the 1994 F-150 and it was available without manual hubs. I guarantee they didn't use an AWD tcase, but most likely the same part time 4WD one you have.

On a vehicle like my Jeep without manual hubs, if you shift the tcase lever to 2WD mode, it disconnects the front driveshaft from the transmission. But the front wheels are still attached to the axles, the differential, and the driveshaft, so all those parts get turned by the road moving past the car.

Last edited by winkosmosis; 12-08-2011 at 03:09 PM..
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Old 12-08-2011, 03:12 PM   #43 (permalink)
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The 4WDs w/o manual hubs have either dashboard controlled hubs or automatic hubs. But, they have locking/unlocking hubs. IF they don't they are AWD, and there is no 2WD with AWD.

The '94s were available with dashboard controlled hubs or manual. I chose manual because I was told they were more robust than the electric ones.

A system such as you describe on your Jeep... is new to me.

http://en.wikipedia.org/wiki/Jeep_fo..._drive_systems

Looks like Jeep used a plethora of different systems. What do you have?
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Old 12-08-2011, 03:31 PM   #44 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
The transfer case is what needs to have differential capabilities if one is going to use 4WD on non slippery surfaces.
What? Why? When you go around a corner, your tires turn at different speeds which is where the diffs come in. What would make a transfer case need to act as a diff?

Quote:
Originally Posted by winkosmosis View Post
Not true. There are lots of vehicles with permanently engaged hubs and selectable 4WD. No modern consumer truck sold in America has manual hubs. Do you think they're all AWD?

I looked up the specs for the 1994 F-150 and it was available without manual hubs. I guarantee they didn't use an AWD tcase, but most likely the same part time 4WD one you have.

On a vehicle like my Jeep without manual hubs, if you shift the tcase lever to 2WD mode, it disconnects the front driveshaft from the transmission. But the front wheels are still attached to the axles, the differential, and the driveshaft, so all those parts get turned by the road moving past the car.
Like stated above, if you dont have a manual locking hub, chances are they are then automatic locking hubs which means only the wheels are turning when in 2wd.

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Old 12-08-2011, 03:33 PM   #45 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
The 4WDs w/o manual hubs have either dashboard controlled hubs or automatic hubs. But, they have locking/unlocking hubs. IF they don't they are AWD, and there is no 2WD with AWD.

The '94s were available with dashboard controlled hubs or manual. I chose manual because I was told they were more robust than the electric ones.

A system such as you describe on your Jeep... is new to me.

Jeep four wheel drive systems - Wikipedia, the free encyclopedia

Looks like Jeep used a plethora of different systems. What do you have?
I just read that some trucks have automatic hubs now... That's interesting, never heard of those. I guess they decided the gas savings of disconnecting the axle from the wheels is worth the complexity.

I have the NP231 transfer case. It has 2WD, 4WD part time, 4WD low range, and neutral modes. Wranglers also use this tcase. The other option that the Cherokee had at the time was the NP242 which also has a full time mode, with differential action. Jeep guys don't like it because it's slightly weaker, and they think full time is useless... Because they ignorant and don't realize the full time mode is useful for hard trails, wet roads, ice, etc.


Anyway it's not uncommon to have permanently locked hubs with part time 4WD. That's why lifted independent front suspension vehicles usually have problems with CV joints, because even in 2WD mode the front halfshafts are spinning.
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Old 12-08-2011, 04:02 PM   #46 (permalink)
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I have a 1998 Chevy S-10 with dash push buttons for 2WD, 4WD-HI, 4WD-LOW (selecting while only in neutral).

It sucks compared to the manual locking hubs on my now dead 1990 Geo Tracker. I'm talking drive and feel wise, I love that I don't have to get out of the truck now. The S-10 spends much less time in 4WD than the old Tracker did because of the convenience factor.

The Tracker's were awesome in 4WD and dangerous without it. Reportedly they can give a Jeep a run for the money off-road, but I never tested that claim myself.
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Old 12-08-2011, 05:46 PM   #47 (permalink)
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Quote:
Originally Posted by 66sprint6 View Post
What? Why? When you go around a corner, your tires turn at different speeds which is where the diffs come in. What would make a transfer case need to act as a diff?
Because the circle traveled by the front tires will be of a larger diameter than that of the rear wheels, just like the circle traveled by the outer wheels is larger than that of the inner wheels.
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Old 12-08-2011, 06:00 PM   #48 (permalink)
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Because the circle traveled by the front tires will be of a larger diameter than that of the rear wheels, just like the circle traveled by the outer wheels is larger than that of the inner wheels.
I can see that, but what does that effect on the street? Only thing I try to do is take turns a little wider, especially in parking lots when I have to be in 4wd with the hubs locked in my F150 cause it likes to get jumpy. I wouldnt suggest driving with it on ALL the time in the dry, but its designed to be used when needed without major issue other than normal wear and tear and lowered efficiency. I was out at a boat ramp about 20 miles out of town on a small highway when it started snowin. I hit the first underpass and slid thanks to ice build up. After doin it again on the next bridge I hopped out, locked the hubs, put it in 4 high and went 50 the whole way home. A majority of the time I was on dry ground, but when I passed under a bridge, over a bridge and hit the backroads leading to my house I was SO happy to have it engaged. I guess you just gotta stay away from doin 4wd donuts LOL

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Old 12-08-2011, 07:42 PM   #49 (permalink)
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Ardent said it right; vehicles need differential action between front and rear axles on high-traction surfaces because of the different turning circle distances. "Jumping" is very high stress on your entire drivetrain as it tries to cope with the lack of tire slip while it is locked up!
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Old 12-08-2011, 11:39 PM   #50 (permalink)
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Quote:
Originally Posted by 66sprint6 View Post
I can see that, but what does that effect on the street? Only thing I try to do is take turns a little wider, especially in parking lots when I have to be in 4wd with the hubs locked in my F150 cause it likes to get jumpy. I wouldnt suggest driving with it on ALL the time in the dry, but its designed to be used when needed without major issue other than normal wear and tear and lowered efficiency. I was out at a boat ramp about 20 miles out of town on a small highway when it started snowin. I hit the first underpass and slid thanks to ice build up. After doin it again on the next bridge I hopped out, locked the hubs, put it in 4 high and went 50 the whole way home. A majority of the time I was on dry ground, but when I passed under a bridge, over a bridge and hit the backroads leading to my house I was SO happy to have it engaged. I guess you just gotta stay away from doin 4wd donuts LOL

Matt
It's not designed for that. If you read your manual, you'll see that it's meant for loose surfaces only.

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