How does Xterra AWD Work? - Second Generation Nissan Xterra Forums (2005+)
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post #1 of 14 (permalink) Old 01-10-2017, 01:55 PM Thread Starter
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How does Xterra AWD Work?

Hello - new member, first post.

I'm looking at some Xterras as my new truck - have read lots of great reviews. One thing I've not found is a good description of the AWD system. Could some experts help me out?

From what I have found, it seems:

- front wheels are independent; rear is an axle
- there's 2wd, 4hi an 4lo
- 2wd sends the power to the rear wheels
- you can switch into 4hi on the fly, but only below 62mph
- but once in 4hi, you can drive more than 62mph
- you can use 4hi on dry pavement without hurting the truck because the rear diff is not locked
- 4hi controls power distribution by applying the brakes, using the abs system, to wheels that spin faster (unlike some awd systems that use clutches in the difffs)
- you have to be at a stop to switch into 4lo
- max speed in 4lo is 30mph
- on the Pro-X4 models, there's a rear diff locker switch that locks the rear diff. In this mode, you definitely would not drive on dry pavement.

Is that right? Guidance will be much appreciated.

Thanks.
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post #2 of 14 (permalink) Old 01-10-2017, 02:04 PM
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Xterra's don't have an AWD Drive System - It's a Selectable 4x4 System.

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post #3 of 14 (permalink) Old 01-10-2017, 02:11 PM Thread Starter
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Quote:
Originally Posted by Old Navy View Post
Xterra's don't have an AWD Drive System - It's a Selectable 4x4 System.
Sloppy of me - nomenclature corrected. Thanks.

As for the rest?
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post #4 of 14 (permalink) Old 01-10-2017, 02:12 PM
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Originally Posted by 4wd_bob View Post
- you have to be at a stop to switch into 4lo
Not just stop, you've got to put it in N (with foot on the brake)
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post #5 of 14 (permalink) Old 01-10-2017, 02:12 PM
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If I didn't include anything, it is because you are correct.

Like Old Navy said, it is selectable 4x4. There is no center differential. When you go to 4wd, 50% of power is applied to the front, and 50% is applied to the back at all times unlike a typical AWD with no traction aids where power will normally be applied to one of the 4 wheels with the least resistance (at least in limited traction situations).

Quote:
Originally Posted by 4wd_bob View Post
Hello - new member, first post.
- front wheels are independent; rear is an axle
.
That refers to suspension, not driveline. Front is independent suspension, rear is a solid axle.

Quote:
Originally Posted by 4wd_bob View Post
- you can switch into 4hi on the fly, but only below 62mph
- but once in 4hi, you can drive more than 62mph
.
I have never tried to switch to 4hi above 62mph, but that is something you should never need to do. If you need 4wd you probably shouldn't be going 62+...
But yes, I forgot I was in 4hi once on the highway and cruised home at 65-70mph. It is not going to cut your fuel off at 62mph or anything.


Quote:
Originally Posted by 4wd_bob View Post
- you can use 4hi on dry pavement without hurting the truck because the rear diff is not locked
Not necessarily. Going straight you should be fine. However, slow speed tight turns in 4hi on pavement still have the chance to damage the drivetrain. You will notice making tight turns in a parking lot in 4hi it feels like the parking brake is applied.


Quote:
Originally Posted by 4wd_bob View Post
- 4hi controls power distribution by applying the brakes, using the abs system, to wheels that spin faster (unlike some awd systems that use clutches in the diffs)
It is called "ABLS" or "Active Brake Limited Slip". It applies brakes to the spinning tire when the other is stuck. This is NOT the same as having a locker.

Here is an example of this on my X at 0:27. You can see as driver's front tire goes in the air (and the passenger side front is stuck on the hill) it applies brake to the driver's front tire.



Quote:
Originally Posted by 4wd_bob View Post
- you have to be at a stop to switch into 4lo
- max speed in 4lo is 30mph
You have to be in neutral. You SHOULD be at a stop. It will switch if rolling in neutral sometimes but you risk damaging drivetrain again. So you should be stopped and in neutral to swap. Max speed is more/less correct. Again, if you need to go faster than 20mph or so you will find you probably shouldn't be in 4-lo.

Quote:
Originally Posted by 4wd_bob View Post
- on the Pro-X4 models, there's a rear diff locker switch that locks the rear diff. In this mode, you definitely would not drive on dry pavement.
Correct. If you are dry pavement 2wd will be fine 99% of the time. Locking rear diff is for the more extreme 4x4 situations where traction is very limited.
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Last edited by AlbatrossCafe; 01-10-2017 at 02:17 PM.
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post #6 of 14 (permalink) Old 01-10-2017, 02:18 PM
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Quote:
Originally Posted by 4wd_bob View Post
Hello - new member, first post.

I'm looking at some Xterras as my new truck - have read lots of great reviews. One thing I've not found is a good description of the AWD system. Could some experts help me out?

From what I have found, it seems:

- front wheels are independent; rear is an axle
- there's 2wd, 4hi an 4lo
- 2wd sends the power to the rear wheels
- you can switch into 4hi on the fly, but only below 62mph
- but once in 4hi, you can drive more than 62mph No, do not exceed 62mph in 4x4. If you can drive that fast in the conditions you don't need 4x4
- you can use 4hi on dry pavement without hurting the truck because the rear diff is not locked No, NEVER use 4x4 on dry pavement. This is not an AWD system and therefore does not have the clutches and viscous couples required to do so. This will cause binding in the transfer case.
- 4hi controls power distribution by applying the brakes, using the abs system, to wheels that spin faster (unlike some awd systems that use clutches in the difffs)
- you have to be at a stop to switch into 4lo And in neutral
- max speed in 4lo is 30mph I would not exceed about 15mph, 4lo is for crawling along at a snails pace.
- on the Pro-X4 models, there's a rear diff locker switch that locks the rear diff. In this mode, you definitely would not drive on dry pavement.

Is that right? Guidance will be much appreciated.

Thanks.

My corrections are in Red. Mostly right, with a few major no-nos.
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post #7 of 14 (permalink) Old 01-10-2017, 02:28 PM
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Don't use 4 hi or lo on dry pavement or just wet pavement for that matter. When the X is in 4wd, the front and rear wheels are all connected together. So things will bind up when the wheels aren't straight ahead. Yeah you can drive it but the fighting due to the binding will wear the drive system out in due time. The rear open diff on nonlocking models does allow the rears to turn independently from each other but one is still connected to the fronts.
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post #8 of 14 (permalink) Old 01-10-2017, 03:41 PM Thread Starter
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Hey, thanks for all the detailed and helpful replies!

So - basically there's a traditional 'open' differential at front and back, and ABLS is essentially like a classic traction control system that puts the brakes on a spinning wheel, so one side of the diff is locked, or limited in slip, by the brakes, forcing the torque to the other side. Front or back, you can have different rotation right to left - but there's no front/back slip mechanism in the transfer case. Hence - dry road = no go. Got it. Thanks.

I'm looking for a successor to my Ford Expedition, which has full-time AWD - Ford calls it "Automatic AWD" - which is set and forget. (Has 4hi and 4 lo too). It's nice to have it - if I forget to evaluate the slipperiness of a road to decide which mode to drive in, no worries - it evaluates it all the time. Having trouble finding anything similar on a work, hauling, and of-road capable truck - but it's on every suburban family hauler for some reason.

OK, back to the search. And thanks again.

Last edited by 4wd_bob; 01-10-2017 at 03:44 PM.
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post #9 of 14 (permalink) Old 01-10-2017, 04:49 PM
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One more thing to add.

The Pro 4X models come with a factory installed electronic locking rear differential (locker) that can only be engaged when the transfer case is in 4 Low.

There is a bypass mod allowing you to engage the rear locker in 4Hi or 2WD but that's not how they come from the factory.
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post #10 of 14 (permalink) Old 01-10-2017, 06:01 PM
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Quote:
Originally Posted by 4wd_bob View Post
Hey, thanks for all the detailed and helpful replies!

So - basically there's a traditional 'open' differential at front and back, and ABLS is essentially like a classic traction control system that puts the brakes on a spinning wheel, so one side of the diff is locked, or limited in slip, by the brakes, forcing the torque to the other side. Front or back, you can have different rotation right to left - but there's no front/back slip mechanism in the transfer case. Hence - dry road = no go. Got it. Thanks.

I'm looking for a successor to my Ford Expedition, which has full-time AWD - Ford calls it "Automatic AWD" - which is set and forget. (Has 4hi and 4 lo too). It's nice to have it - if I forget to evaluate the slipperiness of a road to decide which mode to drive in, no worries - it evaluates it all the time. Having trouble finding anything similar on a work, hauling, and of-road capable truck - but it's on every suburban family hauler for some reason.

OK, back to the search. And thanks again.
I had a Jeep Grand Cherokee with a full time viscous coupling 4WD system (it also had factory limited slip diffs on both ends). It was nice in many ways. Its saved my but more than once when I unexpectedly hit a bad patch of road while likely driving way too fast.

The X is a traditional 4WD system with a selectable transfer case. Its better in many ways and not as good in others. It depends on what you want to do with it, where you drive, and how you drive. Most of the time while driving on pavement, unless your in a snow storm or similar your going to be wanting to run in rear wheel drive.

The thing I love most about the X is its stupid simple and wildly reliable, something my Jeep never was.
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