4H / 4A / 2H

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zak99b5

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If it's like my 2010 Suburban system, 4WH locks the transfer case. Need to be on slippery surfaces, or the drivetrain will jerk and bind. On 4WAuto, a clutch in the transfer case allows the fronts to engage/disengage as needed, so there's no binding. So it's fine to use in all road conditions. But I use 2WH to use the clutch in the transfer case as little as possible and save a little gas.
 

LokiWolf

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If it's like my 2010 Suburban system, 4WH locks the transfer case. Need to be on slippery surfaces, or the drivetrain will jerk and bind. On 4WAuto, a clutch in the transfer case allows the fronts to engage/disengage as needed, so there's no binding. So it's fine to use in all road conditions. But I use 2WH to use the clutch in the transfer case as little as possible and save a little gas.
These transfer cases do not lock. They are TOD, and use clutches. The only locking transfer cases I know of in the F150/Expedition line currently are in the Raptor, or the Tremor with 402A package.
 
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Meeker

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This! Much better explanation than I did in the other thread.

40MPH is the lowest I have seen the front go to zero in 4A, very light throttle.

It actually never really engages or disengages the front drive shaft, because the Center Diff in these is not on off, it is TOD(Torque on Demand), and clutch based. It can go from Zero to 50% and any in between at the demand of the computer.
I can add some nuance to this, after trying this out on my commute home yesterday...

In drive mode "Normal" and 4A selected, it behaves as you say, below a certain speed it drives the rear wheels only.

But in drive mode "grass/?/snow", which enables 4A, the front wheels are driven at all speeds. They appear to get a bit less than 50% but definitely not zero...

Not sure how Sport behaves.
 

LokiWolf

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I can add some nuance to this, after trying this out on my commute home yesterday...

In drive mode "Normal" and 4A selected, it behaves as you say, below a certain speed it drives the rear wheels only.

But in drive mode "grass/?/snow", which enables 4A, the front wheels are driven at all speeds. They appear to get a bit less than 50% but definitely not zero...

Not sure how Sport behaves.
Yeah, "Snow" is basically 4H, pretty much 50/50.

Sport is the same as normal, but because of throttle mapping being WAY more aggressive, it is harder at the lower speeds to reach the light throttle thresh hold for it to lower the clutch pressure down that low for the front axle. It also favors the rear in Sport.
 

Meeker

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Yeah, "Snow" is basically 4H, pretty much 50/50.

Sport is the same as normal, but because of throttle mapping being WAY more aggressive, it is harder at the lower speeds to reach the light throttle thresh hold for it to lower the clutch pressure down that low for the front axle. It also favors the rear in Sport.
Sheesh, I mis-spoke above! I meant the following:

"In drive mode "Normal" and 4A selected, it behaves as you say, above a certain speed it drives the rear wheels only."

I was trying to highlight that drive mode affects whether you have 4A at highway speeds (you said above 40 mph - I didn't test the exact threshold, trying to keep my eyes on traffic :) ).

Your point about the low speed behaviour is still valid I believe...
 

LokiWolf

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Sheesh, I mis-spoke above! I meant the following:

"In drive mode "Normal" and 4A selected, it behaves as you say, above a certain speed it drives the rear wheels only."

I was trying to highlight that drive mode affects whether you have 4A at highway speeds (you said above 40 mph - I didn't test the exact threshold, trying to keep my eyes on traffic :) ).

Your point about the low speed behaviour is still valid I believe...
I figured. Yeah, same.
 
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wannabeMtb

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I can add some nuance to this, after trying this out on my commute home yesterday...

In drive mode "Normal" and 4A selected, it behaves as you say, below a certain speed it drives the rear wheels only.

But in drive mode "grass/?/snow", which enables 4A, the front wheels are driven at all speeds. They appear to get a bit less than 50% but definitely not zero...

Not sure how Sport behaves.

Can I ask how you inferred the number 50% ? Is there some indicator or digital display that tells that ? I may have missed tha
 
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wannabeMtb

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So all awd or 4wh will bind and have noise especially on surfaces that aren’t slippery. I wouldn’t run it in anything other than 2wh when on clear pavement. Even wet pavement ideally 2wh only.

Having said that my stock OEM tires even with 15,000 on them were horrendous even on wet bay area highways. I couldn’t stand them anymore and got BFG Trail Terrains which are a hybrid A/T 3peak rated tire for SUVs. The difference was massive totally different vehicle. Even the Tahoe trips on the typical packed icy trash secondary roads which demanded snow mode 4hi just to get around with lots of sliding. The new tires I could go everywhere in South Lake in 2wh with virtually zero sliding. Massive difference can’t even compare the two tires.

I only run 4whl modes when traction is an issue for 2wh. So Tahoe trips snow mode goes on at the chain control check and off the moment roads are generally clear. These 4whl systems use clutches to drive power to tires with traction and using them when road surfaces are not an issue just creates heat and excess wear on the system.

Most definitely treat the stock tires as complete trash especially for Tahoe conditions. Even in 4whl the stock tires severely hampered the expedition vs new 3peak tires we’re better in 2wh than the OEM’s were in 4whl..
My neighbor just got a Expedition and I warned him about the stock tires. He’s a car guy made a week long trip family snow trip. He got back and told me yep tires are terrible and on the list to replace. He said even snowy roads he struggled to get the Expedition to move a few time. Same issue I had in Tahoe with my old stock tires. The same places my old tires were just not able to get it done in 4whl my new tires could easily do in 2whl. Tires are a huge deal even with 4x4 systems.

Good info. Yeah, Tahoe side roads are the most tricky. Those roads are not cleared / salted well. The main roads (non highway) are somewhat better; but still tricky. I was there just this past weekend when there was a snow storm. Even after several hours of snow, the South Lake Tahoe blvd was not cleared / salted well. I was scared driving next to toyota camry's zipping along at 45 miles an hour - i am sure they were 2WD

My tires also just have 3k miles on them ; with the vehicle being brand new and bought just a few months back. I am hesitant to buy new tires just cause in my mind it feels like wasting money; altho money is not an issue. But your description of "massively totally different vehicle" is making me think.

I only run 4whl modes when traction is an issue for 2wh. So Tahoe trips snow mode goes on at the chain control check and off the moment roads are generally clear. These 4whl systems use clutches to drive power to tires with traction and using them when road surfaces are not an issue just creates heat and excess wear on the system.

Do you do any change in setting while driving in rain in bay area ?
 

LokiWolf

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Can I ask how you inferred the number 50% ? Is there some indicator or digital display that tells that ? I may have missed tha
No number, but half up the scale could be inferred to be 50%. Not sure I would make that assumption. But if all 4 wheels are at the same level in the graph, then I would assume 50/50.
 

m3olsen

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Can I ask how you inferred the number 50% ? Is there some indicator or digital display that tells that ? I may have missed tha

No number, but half up the scale could be inferred to be 50%. Not sure I would make that assumption. But if all 4 wheels are at the same level in the graph, then I would assume 50/50.
@wannabeMtb , we're referencing the Power Distribution display. See posts 13 and 16, amongst others.
 

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