4A or 2H? Which is the best?

[Boostedblues]

Some people have had issues. https://www.bronco6g.com/forum/thre...ers-fault-for-using-4a-on-dry-pavement.50838/

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[Aonarch]

I'm not locking the front diff, just the center diff/transfer case. I'm pretty sure that 4A is "unlocked" or slip for on road driving and 4H locks the transfer case so front and rear prop shafts can spin at the same speed. I wouldn't want to snap an axle with the front diff locked haha!

I'll try it for a while and see what happens. Thanks!

That is what I was describing to a point.

 

[Aonarch]

Some people have had issues. https://www.bronco6g.com/forum/thre...ers-fault-for-using-4a-on-dry-pavement.50838/

Now I want to lookup the owners manual to see what the verbage is with 4A.

 

[Michael.J]

4A is ok to drive around in but like anything it will cause additional wear. Any slip from a stop will engage 4H momentarly. And steering will briefly feel different thank 2H. MPG may slip a little but that is mostly determined by driving style.

 

[ejones91]

Now I want to lookup the owners manual to see what the verbage is with 4A.

FOUR-WHEEL DRIVE AUTO

Four-wheel drive auto provides electronically controlled four-wheel drive power to both the front and rear wheels, as required, for increased traction in varying on-road conditions. The four-wheel drive auto tuning varies based on selected Drive Mode. See Selecting a Four-Wheel Drive Mode (page 205).

Note: Four-wheel drive auto can turn on or off automatically based on Drive Mode selection. See Selecting a Four-Wheel Drive Mode (page 205).

 

[brkdncr]

I'm an automotive engineer (I never designed any drive train), but my understanding is that 2H the engine only turns the back axle.

are the wheels still connected to the front axle? If so then the engine is pushing the wheels and pushing the axle.

 

[indio22]

FYI, below is some info I found on how 4A in a 2022 F150 works. I don't know if Bronco is the same, but probably there is a tcase clutch as well, with sensors deciding when to lock/unlock:

Ford Workshop Manual
(TCCM = Transfer Case Control Module):
_____________________________________

307-07A Four-Wheel Drive Systems
2022 F-150
Description and Operation Procedure
revision date: 03/24/2022

Four-Wheel Drive Systems - Vehicles With: 2-Speed Torque On Demand Transfer Case - System Operation and Component Description
......

In 4WD AUTO (4A), the TCCM continuously monitors conditions and driver input to send torque automatically to the front driveline by controlling the transfer case clutch, providing 4WD capability. The TCCM sends a duty cycle command to the transfer case clutch coil as a torque request based on combination of preemptive and wheel slip response algorithm. Preemptive response is based on steering wheel angle, vehicle speed, throttle positions and available powertrain torque. Wheel slip response is based on monitoring the average front and rear wheel speeds.

When 4WD is no longer needed (during cruising or steady state driving) system defaults back to RWD (rear wheel drive) mode by setting the duty cycle output to 0.

TCCM increases the duty cycle to prevent or control slip under any of the following conditions:

• Slip is detected.
• Heavy acceleration (throttle position).
• Straight-ahead steering wheel angle.

TCCM decreases the duty cycle to prevent or reduce vehicle bind under any of the following conditions:

• Low speed.
• Low acceleration (throttle position).
• Tight turn steering wheel angle.

The TCCM has a thermal hardware protection strategy which monitors the amount of energy going through the clutch. This strategy has 2 levels of protections:

AUTOLOCK: If the system is in 4WD 4H [***] and TCCM detects driving conditions that require greater 4WD performance, the TCCM temporarily turns on 4WD (4H) from 4WD AUTO (4A) after detecting driving condition and informs the customer via the message center indicating 4X4 TEMPORARILY LOCKED. The 4WD system automatically returns to 4WD AUTO (4A) after the system no longer detects these driving conditions and informs the customer via the message center indicating 4X4 RESTORED.

POWERTRAIN TORQUE PROTECTION: If the system is in 4WD AUTO (4A) and TCCM detects excessive stress or high energy going through the clutch (clutch is slipping excessively while the system is commanding max clutch torque), clutch output will be turned off and message center indicates 4x4 TEMPORARILY DISABLED. When the system had the ability to cool off, 4x4 operation will be automatically restored.

NOTE: The 4x4 Temporarily Disabled message can be dismissed by the customer however it's advisable to let the TCCM clear the message itself, which indicates that the 4x4 system has resumed normal operation.

 

[JBlanco]

I'm pretty sure it's in 4A, but I'll check. My understand of how it works based on what I have read is that 4A allows slip and 4H locks the transfer case. I certainly wouldn't want to use 4H on the road!

Maybe the system doesn't even let you use it above certain speeds, but I don't know.

 

[da_jokker]

Just a chime in on something that most people get wrong.

4A is for on-road use and engages the front axle whenever you are on the throttle. Many people will state that for a kicks into 4H "when needed" And this is not the case.

When you get on the throttle It sends power to the front axle. When you let off the throttle or maintain, the front axle does not get power. When you make sharp turns, it tends to disengage the front axle as well.

 

[broncobase1]

I don't have the advanced transfer case, but it doesn't make any sense 4A would improve handling. Maybe it feels different, but is it really an improvement? If I had it, I would only use 4A in slipery conditions.

 

[da_jokker]

I still need to ForScan sport mode onto my truck. If it's only a nominal difference in MPG, it might be worth it.

4A maybe nominal, but sports mode is not.

Nothing like screaming at 3,000 RPM while you're doing just 40 mph down a city street for gas mileage!

 

[Dreamer]

FYI, below is some info I found on how 4A in a 2022 F150 works. I don't know if Bronco is the same, but probably there is a tcase clutch as well, with sensors deciding when to lock/unlock:

Ford Workshop Manual
(TCCM = Transfer Case Control Module):
_____________________________________

307-07A Four-Wheel Drive Systems
2022 F-150
Description and Operation Procedure
revision date: 03/24/2022

Four-Wheel Drive Systems - Vehicles With: 2-Speed Torque On Demand Transfer Case - System Operation and Component Description
......

In 4WD AUTO (4A), the TCCM continuously monitors conditions and driver input to send torque automatically to the front driveline by controlling the transfer case clutch, providing 4WD capability. The TCCM sends a duty cycle command to the transfer case clutch coil as a torque request based on combination of preemptive and wheel slip response algorithm. Preemptive response is based on steering wheel angle, vehicle speed, throttle positions and available powertrain torque. Wheel slip response is based on monitoring the average front and rear wheel speeds.

When 4WD is no longer needed (during cruising or steady state driving) system defaults back to RWD (rear wheel drive) mode by setting the duty cycle output to 0.

TCCM increases the duty cycle to prevent or control slip under any of the following conditions:

• Slip is detected.
• Heavy acceleration (throttle position).
• Straight-ahead steering wheel angle.

TCCM decreases the duty cycle to prevent or reduce vehicle bind under any of the following conditions:

• Low speed.
• Low acceleration (throttle position).
• Tight turn steering wheel angle.

The TCCM has a thermal hardware protection strategy which monitors the amount of energy going through the clutch. This strategy has 2 levels of protections:

AUTOLOCK: If the system is in 4WD 4H [***] and TCCM detects driving conditions that require greater 4WD performance, the TCCM temporarily turns on 4WD (4H) from 4WD AUTO (4A) after detecting driving condition and informs the customer via the message center indicating 4X4 TEMPORARILY LOCKED. The 4WD system automatically returns to 4WD AUTO (4A) after the system no longer detects these driving conditions and informs the customer via the message center indicating 4X4 RESTORED.

POWERTRAIN TORQUE PROTECTION: If the system is in 4WD AUTO (4A) and TCCM detects excessive stress or high energy going through the clutch (clutch is slipping excessively while the system is commanding max clutch torque), clutch output will be turned off and message center indicates 4x4 TEMPORARILY DISABLED. When the system had the ability to cool off, 4x4 operation will be automatically restored.

NOTE: The 4x4 Temporarily Disabled message can be dismissed by the customer however it's advisable to let the TCCM clear the message itself, which indicates that the 4x4 system has resumed normal operation.

By adjusting the display to show the off-road mode and cycling to the powertrain distribution, you can see where the power is going ( front and rear ) when accelerating. Once on the highway, or just cruising, you’ll only see power applied only to the rear tires.

So the information provided by @indio22 appears to be correct for the Ford Broncos equipped with the 4A transfer case option

 

[BigGreenPony]

I suspect that people that are blowing up the front diff are doing more than "normal driving"

 

[Aonarch]

I don't have the advanced transfer case, but it doesn't make any sense 4A would improve handling. Maybe it feels different, but is it really an improvement? If I had it, I would only use 4A in slipery conditions.

Not it will not.

4A is not All-wheel drive, where there is always power going to all 4 wheels. That can help with handling in a way, but AWD cars typically have understeer.

4A is not instantaneous enough for my liking.

4A just engages the front differential when the sensors tell it to, and that is like just putting it in 4H, but with a bit more slip allowed to prevent binding.

For the people who use 4A regularly, I highly recommend following aggressive fluid change intervals with the front diff and tcase.

 

[Noremac]

on the road, I run 2wd 97% of the time. that last 3% is usually spirited stoplight to stoplight goofing off. With how the suspension is designed, it hikes the front end up under heavy acceleration in 4a, which also is fun.

the downside is, less gas mileage, and does lose traction on the drivers front tire just enough for the truck to torque steer to the left ever so slightly from a dig

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