Super LOUD bang in 4wheel drive

[Billflangjr]

Could be the front axle hub engagement (splines) letting go, or not engaging correctly. I've had similar noises in the past. Bad seals , vacuum leak, bad vacuum, needing cleaning/grease,...They do pop .

ml3z3c247d - Ford Actuator | Levittown Ford Parts https://share.google/b72oJ6Itcqzd7n0lc

Could be that !

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[Gros Ventre]

There is one spot I have to use 4wd and it involves a tight turn. Not too get into a lengthy explanation, but is is at the bottom of a hill with roots and pine straw. To turn around and get back up from the water is a PITA without 4wd. That is the only place I’ve heard the loud snap noise.

So be gentle in speed making the turn. Better to do it in 4H than 4L.

 

[Jerome10]

This seems pretty straightforward to me.

You cannot use 4H or 4L on non slippery surfaces and then start turning with them. You’ll bind up the driveline and it breaks things.

Pretty sure the owners manual makes this very clear. I believe it also says not to tow in 4H.

Very slippery snowy roads or off-road dirt ok. Dry pavement is no-way never do it.

4A is fine (Ford can you please offer 4A in lower trims??)

I think you can also screw up the locking diff by engaging the locker and making turns on dry pavement as well.

 

[F-150_Fan]

Not sure but the 2021 f-150 may still use axle end actuators to lock the hubs into and out of 4wd. My 2013 had vacuum IWE's and I think they switched to electric and then did away with them altogether in the newer model years.
If you have IWE's on your front axle ends it may be that one of them is not engaging or disengaging as it should. On my 2013, one of mine would not activate correctly every once in a while and it would make a bang that sounded like the diff exploded or something, but it was just the torque load on the axle end. I replaced those with new IWE's and the issue was resolved.
You may want to ask the tech to test the IWE's if your truck has them.

From Google:
Yes, 2021 F-150 4WD models use actuators
, but they switched from the older vacuum-operated Integrated Wheel Ends (IWEs) to new electric IWEs (EIWEs) for most trims, while trucks with the Auto 4WD (4A) feature have the front axles always engaged, relying solely on the transfer case for disconnection. These actuators (like part # ML3Z3C247H) lock the front axles to the wheels when 4WD is engaged, allowing for smooth transitions, a key change from the previous vacuum system

 

[DHBPhoto]

Sounds like driveline windup more than anything. It can happen on surfaces other than pavement just not super common.

Are you shifting to 4WD while stopped? Yes I know technically you "can" it's easier on the transfer case if you're rolling even 1mph.

Most of the time yes while rolling, but it doesn’t matter. I can go from 2H to 4L on dirt and just the right flex will make it happen.

 

[DHBPhoto]

So if understand correctly, your were in 4hi when pulling back on to concrete (dry concrete?) and turning right? If so it's possible you messed up a CV and it's going to eventually leave the chat whichever on it is. A bad CV will do what you describe of no noises going straight, but makes noise when turning. And if it's dry pavement your driving on, you should never be in 4wd.

That noise is your drive line being tortured to a horrible death on by using 4WD on dry pavement

Thanks guys. Dry pavement in 4H is really not that bad on your truck, so long as you're not turning tight. 4H is designed for all kinds of variable conditions — otherwise, how would you ever be able to drive down winter roads? One minute it's icy, the next it's dry. The next it's patchy.

I also get the popping in 4L while wheeling. If it's flat, we're good. If it's flexed out, it'll pop. It never happens when the wheels are straight.

 

[Micho523]

Get a magnet mount for a go pro and start watching the CV axles and front drive shaft when doing this. You may get lucky.

Is your truck lifted? A lift plus high steering angle may have put the CV joints in a bind condition.

For all those complaining about 4H on pavement... for the 4A trucks, the front hubs are permanently engaged. CV axles, front diff, front drive shaft all spin all the time.

 

[F-150_Fan]

Get a magnet mount for a go pro and start watching the CV axles and front drive shaft when doing this. You may get lucky.

Is your truck lifted? A lift plus high steering angle may have put the CV joints in a bind condition.

For all those complaining about 4H on pavement... for the 4A trucks, the front hubs are permanently engaged. CV axles, front diff, front drive shaft all spin all the time.

Only on the recent model years ... I think the 2021 in question may have the electric IWE's, but I am not certain when Ford stopped including them, ... if present then can disengage the front axles at the hubs -

 

[DHBPhoto]

Could be the front axle hub engagement (splines) letting go, or not engaging correctly. I've had similar noises in the past. Bad seals , vacuum leak, bad vacuum, needing cleaning/grease,...They do pop .

ml3z3c247d - Ford Actuator | Levittown Ford Parts https://share.google/b72oJ6Itcqzd7n0lc

The dealership is going to give the vacuum a go next time they have it in the shop.

 

[DHBPhoto]

Not sure but the 2021 f-150 may still use axle end actuators to lock the hubs into and out of 4wd. My 2013 had vacuum IWE's and I think they switched to electric and then did away with them altogether in the newer model years.
If you have IWE's on your front axle ends it may be that one of them is not engaging or disengaging as it should. On my 2013, one of mine would not activate correctly every once in a while and it would make a bang that sounded like the diff exploded or something, but it was just the torque load on the axle end. I replaced those with new IWE's and the issue was resolved.
You may want to ask the tech to test the IWE's if your truck has them.

From Google:
Yes, 2021 F-150 4WD models use actuators
, but they switched from the older vacuum-operated Integrated Wheel Ends (IWEs) to new electric IWEs (EIWEs) for most trims, while trucks with the Auto 4WD (4A) feature have the front axles always engaged, relying solely on the transfer case for disconnection. These actuators (like part # ML3Z3C247H) lock the front axles to the wheels when 4WD is engaged, allowing for smooth transitions, a key change from the previous vacuum system

Yessir, that's what we're testing next. My gut says this. Had my wife drive the truck and bang sounds like it's coming directly under the driver's feet.

 

[DHBPhoto]

Get a magnet mount for a go pro and start watching the CV axles and front drive shaft when doing this. You may get lucky.

Is your truck lifted? A lift plus high steering angle may have put the CV joints in a bind condition.

For all those complaining about 4H on pavement... for the 4A trucks, the front hubs are permanently engaged. CV axles, front diff, front drive shaft all spin all the time.

Since 20k had a level. I have 90k now. Could certainly be the front drive shaft. I does sound like it's coming from there, but it really only does it when the wheels are pointed to the left.

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