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Old 29-03-2017
G.man  G.man is offline
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Default Part time or full time 4x4?

Hello,

This 4x4 question has popped up in my mind prior to purchasing a wrangler JK. Was nkt sure where else to post except here since I plan on getting the JK.

PreviousIy I was looking at getting an 80 series landcruiser... they come with full time 4x4 and a low gear which automatically locks the center differential (or something like that anyway)...

Part time 4x4 (I aasume the JK 4 doors are part time) are real wheel drive vehicles without a center differential.

I was just wondering what is the actual benefit/disadvantage of one over the other and how it works...

Eg: On the roads/highways the full time will be like an awd vehicle. The part time will be like a rear wheel drive vehicle. Since 4x4s are not race cars, the extra handling is kind of irrelevant as it isnt designed to go hard into corners like that anyway.

Now you go off the solid road onto hard dirt road... corrigated/sandy... what changes now?

Does rear wheel get put into 4x4 while the full time doesnt need to, do they both need to anyway and ao the difference is only on the street, once off the street they are identical.... rock crawling?

Just some easy to understand scenario would be appreciated.
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Old 29-03-2017
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On the JK you are correct it is a part time 4x4. When you change from 2 to 4 it locks the front and rear diffs together in the transfer case. A part time 4x4 has a method to slip in the transfer case that may be clutches or a fluid drive (like a torque converter on am automatic gearbox).

Because there is no slip in the part time 4x4 mode it needs the wheels to be able to slip, especially when cornering and the wheels try to spin at different speeds. So on sand or dirt part time 4x4 is fine.

A part time 4x4 in 4wd on a hard road surface will either try to slip the tyres on the road tearing off tread rapidly, or worse will load up the drive train damaging parts like universal joints, transfer case or drive shafts.

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Old 29-03-2017
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I've personally found no real need for the complication of full time 4x4 systems. One of the things I wanted when I bought a 4WD again was a simple conventional lever selected (not electronics and solenoids) part time 4x4 system.

Ask around about the long term reliability of 80 series front differentials...there are lots of stories of them failing.....and there is a kit available to convert the 80 Series full time system to part time.
I seem to recall the base model 80 series is part time from the factory.
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Old 29-03-2017
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I had one of the first full time 4wd cars here. (As far as I know. The only other 4wd cars were the Subarus, and they were FWD/4WD.) At that time, in the late '80s, it was the Toyota Corolla wagon!

Engine drives center diff, this drives front & rear diffs & they drive the wheels. You have an electric center diff lock. Current versions of cars with AWD may or may not have front & rear limited slip or diff locks.

4WD, on the gripping hand, is engine drives through transfer case to rear diff & then wheels. When you co to 4WD, the transfer case also drives the front diff directly. This is the same as AWD with center diff locked. Again, you may or may not have front & rear LSD or diff locks.

Front & rear LSD or diff locks are only really usefull if you are in very loose terrain or are on a diagonal pivot. (One front & the opposite rear wheel off the ground.)

The JK Sport comes with "Electronic Brake Lock Differential", which is a fancy way of saying it uses the brakes for traction control via the ABS if one wheel start spinning significantly faster then the others. The JK Rubicon has, I believe, electronic front & rear diff locks, as well as EBLD.

The AWD is good for onroad & slightly slippery conditions, dirt roads, wet weather, snow etc, as the power is split 4 ways, not 2, so less chance of losing traction.
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Old 29-03-2017
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Quote:
Originally Posted by LeighP View Post
I've personally found no real need for the complication of full time 4x4 systems. One of the things I wanted when I bought a 4WD again was a simple conventional lever selected (not electronics and solenoids) part time 4x4 system.

Ask around about the long term reliability of 80 series front differentials...there are lots of stories of them failing.....and there is a kit available to convert the 80 Series full time system to part time.
I seem to recall the base model 80 series is part time from the factory.
I'm the same, I felt no need for full time 4wd, its a complicated system and creates unnecessary wear on the tyres. Having mainly owned Falcons my adult life, I love my rear wheel drive and having the Jeep the same was a good thing.

Being able to shift into 4wd while doing a decent speed passing most others stopped on the side of the track locking hubs is a good feeling as well.
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Old 29-03-2017
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The XJ has both part-time and full-time, so you can pick what you like. Even in a 4WD full time is great on the road, my old XJ was a weapon in the wet at the traffic lights and my current daily driver (FWD most of the time but has predictive AWD so will put it in AWD when the wipers are on and you stomp on it rather than waiting for wheel spin etc) grips like no 2WD can in the rain out of corners etc.

In saying that I don't find I need it in the JK but it would certainly make a difference in the wet on the road.

If the 4WD you chose was full time but with no locking center diff it would struggle offroad compared to a JK, if it had a button to lock the center diff it would be no different to the JK offroad (other than the other areas it might fall down in such as traction control and flex)

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Old 29-03-2017
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So let me understand if I got this correct...

Part time 4wd like the JK is a rear wheel drive vehicle on the street.

A full time 4x4 like the aniversary/GXL 80 series Landcruiser is AWD on the street (like an SUV/Nissan skyline etc... ?)

A part time 4x4 in 4wd mode is identical to a full time 4wd in 4wd mode?

So offroad they are the same, on road they are not... ?

Can 4x4 alwyas be engaged when on hard dirt surface etc just so that it is '4x4' or is it specifically for harder stuff and even for that is not good?

EG: Touring norhtern territory a lot of roads are dirt roads but hard... would you use 4x4 mode or not good in a part time?

Just trying to understand from a practical standpoint how they differ...

Last edited by G.man; 29-03-2017 at 12:04 PM.
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Old 29-03-2017
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I have to say that I disagree with some of the comments below. I found my JKU very tail happy. Full time 4WD would have helped the handling a lot. The car I had previous to the JK & the car I have now are both AWD/full time 4WD and it was something I really missed when I had the JK.

My take on it is that:
- Part time 4WD may ultimately be stronger and simpler as it uses a transfer case instead of centre diff.
- Part time 4WD can only be used off road, but can be used on any dirt surface. I used to religiously change to 4WD whenever I was on a dirt road as it handled way better. Others don't seem to bother and run in 2WD until they "need" 4WD but I figured if you've got 4WD and it handles better in 4WD then you might as well use it. It can get to be a bit of a pain constantly changing between 2WD & 4WD as the road surfaces change though.
- For something that handles as badly as a 4WD (big, heavy, top heavy, higher profile tyres, generally softer suspension, etc) having full time 4WD will help the handling on road. Does it use more fuel and increase wear in components. No idea, but if it does it's worth it as far as I'm concerned.
- As long as you can lock the centre diff then once locked full time 4WD is effectively the same as a part time 4WD system that has 4WD engaged.
- Full time 4WD can work without driver intervention on all surfaces, high traction or low, tarmac, ice, dirt, rock,...... It is there to provide extra traction immediately as/when it's needed (oily roads, wet roads, wet manhole covers, bumpy potholed corners,......). You don't have to consciously think about engaging 4WD.

Comparing my JKU to my current 200 series, I would take full time 4WD every time given the choice. I loved the JK, but that was one area where it was lacking. In the 200, even with considerably more power I can pull away in any conditions without fear of it spinning wheels and going nowhere. My JK would spin wheels in the dry if I was a little over zealous pulling away, and in the wet I had to be very cautious. Even with the 200's extra weight I can turn corners and any reasonable speed without fear of the back end stepping out. That certainly wasn't the case in the JK.

If it were available (which it isn't) I think full time 4WD would be a fantastic addition to the JK, though I'll bet there are a good few Jeep purists out there who'd disagree. Not having it wouldn't stop me from getting another JK if I was in a situation where I could get another one, but if it had full time 4WD it would make it all the more attractive.

As an aside, I also think the JK's traction control worked far better in 4WD than it did in 2WD. It always seemed very late to cut in when it was in 2WD. Stability control would cut in quite quickly. Traction control wouldn't. Comparing to the 200, the full time 4WD system works so well that you've got to be really trying for it to even need to use traction control (on road).

I'm not saying that everyone should sell their Jeeps and buy a 200, not at all. If I didn't need a car capable of towing heavy loads I'd still have my JK but I certainly think that full time 4WD is safer, and ultimately a better system for general day to day 4WD's. For hard core off roaders perhaps part time is better, for most other people I'd rate full time 4WD every time.
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Last edited by Paul-JK; 29-03-2017 at 12:59 PM.
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Old 29-03-2017
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So essentially offroad both are the same. When 4x4 (real 4x4) is engaged thrn they are the same.

The only difference is while you are not in '4x4' mode, as one is rear wheel and the other all wheel.

Is that basically it?

Now you got 4wd Hi and Lo...

Which would you use offroad (like a dirt highway where you drive 80km or so)? What about where you drive slow like through a forest trail where the ground is dirt/rocky, so its still hard (not sand soft like) but due to rocky you drive slow over it...

Sure you can leave it in rear wheel drive... but... if you wanna use it like a 4x4... hi/lo ?

Also... i read about part time 4x4 you usually have to get out of the car to lock the hubs ao that the 4x4 function works... is that the case with the wrangler jk 4 door or what?

Can it be locked from inside on the fly so you dont have to stuff around with stopping for 4wd to work... just pull 4x4 lever in and it be in 4x4 mode?

Can you just drive with hubs locked for every day city/freeway driving?

Anything else im missing in the above elaborate thanks guys.

First 4x4 for me, so pardon ignorance.

Last edited by G.man; 29-03-2017 at 08:23 PM.
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