4H / 4A / 2H

wannabeMtb · Jan 30, 2023

Noob expedition owner. Just want to make sure I am not doing anything wrong w.r.t 4WD / AWD

First question:

My 2022 expedition makes some weird sounds from the transmission when I am running on 4H at slow speeds. Is this normal ? I had just returned from a snow mountain trip to Tahoe (360 miles round tip). I had switched from 2H to 4H when I started encountering snow going uphill on the mountain. I left it at 4H even while coming back and back to regular roads (Bay Area). And now when driving slow on residential roads in bay area, the 4H is making weird sounds and there are a few jerky movements.

Second question:

Want to confirm that my following understanding is correct
4H : Use this to force vehicle to run power to all 4 wheels ALL the time
4A : Vehicle computer decides whether to power 2 wheels or 4 wheels. Vehicle computer may decide to run at 2 wheel drive when road conditions allow it.
4L : To be used only at very low speeds and to be used for say pulling the vehicle out of a ditch or when stuck on snow/sand

LokiWolf · Jan 30, 2023

2 Things:

1) Expedition does not have AWD, it has 4A. They are not the same.
2) You should NEVER run 4H/4L in anything except for low traction situations, like driving in actual snow. More below.

4WD, in our case 4H, and 4L will cause binding, because all the wheels should be going the same speed(Yes - oversimplified, because with 2 open Diffs it should be 2 - 1 front and 1 rear). In 4H, both the front and rear Driveshaft is engaged and power is going down both all the time. On dry pavement or any surface with good traction this will cause binding, clunking, chattering, and other things similar.

4A(4WD Auto), is almost like AWD, except the decision about power to the front wheels is made by the computer using the TOD(Torque on Demand) Center diff. If it senses traction loss in the rear, power is sent forward. The front driveshaft is already in play. If driving along, on Dry pavement, engaged 4A, and you should feel a difference, because the front spinning mass is now engaged, just not getting any of the drive power.

Basically when things start to get slippery use 4A, then when it gets serious use 4H. OR, you could use the modes and let the computer do what it does REALLY well. The Snow mode works well.

Only advantage to 4H in snow conditions over 4A is Engine braking. In slippery downhill situations it can be helpful.

wannabeMtb · Jan 30, 2023

LokiWolf said:
2 Things:

1) Expedition does not have AWD, it has 4A. They are not the same.
2) You should NEVER run 4H/4L in anything except for low traction situations, like driving in actual snow. More below.

4WD, in our case 4H, and 4L will cause binding, because all the wheels should be going the same speed(Yes - oversimplified, because with 2 open Diffs it should be 2 - 1 front and 1 rear). In 4H, both the front and rear Driveshaft is engaged and power is going down both all the time. On dry pavement or any surface with good traction this will cause binding, clunking, chattering, and other things similar.

4A(4WD Auto), is almost like AWD, except the decision about power to the front wheels is made by the computer using the TOD(Torque on Demand) Center diff. If it senses traction loss in the rear, power is sent forward. The front driveshaft is already in play. If driving along, on Dry pavement, engaged 4A, and you should feel a difference, because the front spinning mass is now engaged, just not getting any of the drive power.

Basically when things start to get slippery use 4A, then when it gets serious use 4H. OR, you could use the modes and let the computer do what it does REALLY well. The Snow mode works well.

Only advantage to 4H in snow conditions over 4A is Engine braking. In slippery downhill situations it can be helpful.

Thank you for the detailed reply !

So is it ok to leave it at 4A all the time in suburban driving if I am ok with any loss in fuel economy ?

zak99b5 · Jan 30, 2023

I'd be more worried about any damage to the transfer case that's making the sound.

LokiWolf · Jan 30, 2023

wannabeMtb said:
Thank you for the detailed reply !

So is it ok to leave it at 4A all the time in suburban driving if I am ok with any loss in fuel economy ?

Yes, Many do. Personally I was taught how to drive on RWD overpowered vehicles, so I prefer the handling characteristics and behavior that brings. In dry situations, my recommendation is to leave it in 2WD. Unless you are leaving the light at full throttle every time, 2WD and the ELSD will handle it just fine. Sport actually engages 4A for that exact reason, for traction under hard acceleration.

LokiWolf · Jan 30, 2023

zak99b5 said:
I'd be more worried about any damage to the transfer case that's making the sound.

Yeah, not a bad point. @wannabeMtb Does it make any weird sounds now that you have turned 4H off and on dry roads?

Rob6805 · Jan 30, 2023

I told my wife to just use the drive modes. Put it in Snow mode when it's snowing. The only thing I do not like is that the drive mode reverts back to normal on a key cycle.

LokiWolf · Jan 30, 2023

Rob6805 said:
I told my wife to just use the drive modes. Put it in Snow mode when it's snowing. The only thing I do not like is that the drive mode reverts back to normal on a key cycle.

I actually kinda like it. I come home after driving the Expedition, I had it in Sport cause I was having fun, and when the wife drives it the next day it is back to Normal...

SyndicateZ · Jan 30, 2023

I have HD tow with the 3.73 eLSD. I dont even have a 4H. I wouldnt ever use it anyways. 4A is the choice in snowy, icy roads.

wannabeMtb · Jan 30, 2023

LokiWolf said:
Yeah, not a bad point. @wannabeMtb Does it make any weird sounds now that you have turned 4H off and on dry roads?

No it doesn't thankfully

4H / 4A / 2H

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