A look at 4H (not 4A) operation

[R8er]

What was all that loose bolts noise.
Cool video
But that weird mechanical noise was unreal

A lot I think was the resonance from the exhaust/cat and the infamous whine from the transmission.
Another interesting thing to see is the active air dam.

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[HammaMan]

It would be nice to have someone do a video of something other than a 2021.

In XL / XLT you'd see the same behavior.
In TODs, it's always spinning in 22+
In tremor or raptor, the behavior would be the same entering 4a or 4h.

In my case, an XLT w/ TOD swapped in, the behavior in 4a/4h is the same as tremor/raptor and 21 TODs.

 

[Aonarch]

In XL / XLT you'd see the same behavior.
In TODs, it's always spinning in 22+
In tremor or raptor, the behavior would be the same entering 4a or 4h.

In my case, an XLT w/ TOD swapped in, the behavior in 4a/4h is the same as tremor/raptor and 21 TODs.

I want to swap a TOD t case into my '24 XLT, do you know if the EIWEs will be ok? Will I need to swap them out?

I was thinking of doing the Tremor knuckles and CVs at the same time.

 

[HammaMan]

Yeah, they'll be fine. Requires specific part number TCCM in order to control them.

 

[Mud]

I mounted an old GoPro under the truck because I was curious to see how the 4H axles operated. Seems there’s a bit of misunderstanding out there. Here’s my 2021 5.0. Around 9:55 I turn on 4H to watch it operate. Then 10 seconds later I turn it off. Interesting to see it not disengage right away, maybe the EIWE waits to slow down first? It seems to disengage after I make a right hand turn and get back on the throttle.

A mechanic said they disengage after 2 miles even in 2wd. Not sure why?

 

[Davexxxx]

The front axles being live, is not a new thing.

My 01 was like that.

It had what was called at the time, automatic shift on the fly. A knob on the dash electrically shifted from 2W to 4H, or 4L. All that did was engage, change, or disengage the transfer case connection to the front.

It did NOT crab, in 2H but they spun all the time.

 

[DEEPDOWN]

4A (Four-Wheel Auto): This is where the Raptor shines. It's an "on-demand" system that constantly monitors traction and automatically sends power to the front wheels as needed. This provides excellent stability and control in varying conditions like rain, snow, or light off-road trails. It's safe to use on any surface, including pavement. TOD + 4a Hi Lock

This is not a Raptor only feature. Lariat 502A/Tremor 402A and higher all have the AWD option, which functions exactly as you describe. This can even be observed in the IPC graphic. On a dry road power will be observed to be only directed to the rear axle(s). And even on loose substrate or snow once a cruising speed has been established again the truck becomes primarily rear wheel drive, but as soon as front wheel slippage occurs one can visually see power being shifted towards the front. It’s actually quite entertaining to watch.

 

[Aonarch]

Yeah, they'll be fine. Requires specific part number TCCM in order to control them.

Has anyone documented the as built changes, and can that be done with Forscan, or do you need FDRS?

 

[HammaMan]

This is not a Raptor only feature. Lariat 502A/Tremor 402A and higher all have the AWD option, which functions exactly as you describe. This can even be observed in the IPC graphic. On a dry road power will be observed to be only directed to the rear axle(s). And even on loose substrate or snow once a cruising speed has been established again the truck becomes primarily rear wheel drive, but as soon as front wheel slippage occurs one can visually see power being shifted towards the front. It’s actually quite entertaining to watch.

That's not my vernacular -- I posted in an ai summary and left inaccuracies because I found it kind of hilarious.

Has anyone documented the as built changes, and can that be done with Forscan, or do you need FDRS?

I think there's 1 or 2 as a courtesy to other modules. Between the TCCM and the button, it just works. Pretty sure there's 1 in the PCM and ABS. Searching the sheets for thing like '4wd' and 'tod' will turn up results.

 

[Aonarch]

I read another thread that says the front axle is engaged on *ESOF at startup if the temperature is below 32F for two minutes.


Ahhhhh! Eureka. This is what I've been feeling in the morning.

Edit: I meant ESOF not TOD

 

[HammaMan]

I read another thread that says the front axle is engaged on TOD at startup if the temperature is below 32F for two minutes.


Ahhhhh! Eureka. This is what I've been feeling in the morning.

22+ TOD are always live / can't disconnect.

XL/XLT/Raptor/Tremor turn them on below freezing to keep them cycling. Self-cycling 4WD components, can't argue w/ it.

TOD xfercase is a clutch system. You can search on how it works. Variables are used to determine clutch apply pressure. It's basically a wet clutch to the front wheels. Unlike ESOF, the clutch will slip before driveline damage can occur. Double edged sword if you're really hardcore off-roading, the clutch can overheat and disengage. GM only uses TOD and their so called raptor/tremor competitors are a joke when the clutch throws in the towel after overheating.

TOD is the way to go for non-serious off roading / heavy street use. Perfect in slick conditions as well as performance street applications. ESOF street performance use is ballsy, especially in a heavy truck.

Hi-lock is TOD in 4a, fully ESOF dog locked in 4h, while also dead front axle in 2WD.

 

[Aonarch]

Sor

22+ TOD are always live / can't disconnect.

XL/XLT/Raptor/Tremor turn them on below freezing to keep them cycling. Self-cycling 4WD components, can't argue w/ it.

TOD xfercase is a clutch system. You can search on how it works. Variables are used to determine clutch apply pressure. It's basically a wet clutch to the front wheels. Unlike ESOF, the clutch will slip before driveline damage can occur. Double edged sword if you're really hardcore off-roading, the clutch can overheat and disengage. GM only uses TOD and their so called raptor/tremor competitors are a joke when the clutch throws in the towel after overheating.

Hi-lock is TOD in 4a, fully ESOF dog locked in 4h, while also dead front axle in 2WD.

Sorry I meant ESOF. Was distracted while typing.

But thanks for the details! I'm new to this platform.

On cold mornings I felt like the front end was engaged, not 4H, but more like an AWD system giving off mechanical drag. The logic to engage diff to help warm it up, makes total sense now in retrospect and confirms what I was feeling.

 

[Big Dog Daddy]

@R8er Great video, thanks for sharing. I'm interested in doing some under truck and under hood videos as well. I've been looking at some magnetic and suction mounts for a gopro. What mount did you use for this video. Would you mind posting a picture and or link the the mounting system you used for your video. Thanks.

 

[R8er]

@R8er Great video, thanks for sharing. I'm interested in doing some under truck and under hood videos as well. I've been looking at some magnetic and suction mounts for a gopro. What mount did you use for this video. Would you mind posting a picture and or link the the mounting system you used for your video. Thanks.

sure. I just got some of these:
https://www.amazon.com/GoPro-Grab-B...349350df99ab33631b&qid=1740356128&sr=8-1&th=1

I also used a water proof case which connects to one of those brackets. The 3m tape on those sticks good. I cleaned off the transmission cross-member with brake clean and then stuck one of those on just left of center behind the front driveshaft.

 

[adaycj]

Yeah, they'll be fine. Requires specific part number TCCM in order to control them.

Do you have a specific TCCM part number that is known to work? I'm in the middle of this on a 24, and it isn't like the 21-23. Different TCCM plugs, reconfigured power and grounds, and the wires don't land on the same pins for 50% or so of the plugs. Not 100% I'm going to be successful.

I personally think that a high lock version would be easier, even with the driveshaft issues.

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