What changes going from 2wd to 4wd auto

[Ryan2828]

I got a gear noise in my front differential that i’ve been fighting with the dealership about. They say its the tires but i drive the truck everyday i know what the tires sound like. When i hear the noise i can put the truck in 4wd auto and it goes away. Take it out of 4wd and it doesn’t return. Thats not tire noise. Its temperature dependent, above 60 degrees doesn’t do it ever.  Its in the teens now and the only way to get it to go away is switching to 4wd auto. Truck is 2017 silverado with 5.3. 10,000 miles on it. Going to another dealership and trying to have all the info i can get before i go.

[ShamrockShooter]

I got a gear noise in my front differential that i’ve been fighting with the dealership about. They say its the tires but i drive the truck everyday i know what the tires sound like. When i hear the noise i can put the truck in 4wd auto and it goes away. Take it out of 4wd and it doesn’t return. Thats not tire noise. Its temperature dependent, above 60 degrees doesn’t do it ever.  Its in the teens now and the only way to get it to go away is switching to 4wd auto. Truck is 2017 silverado with 5.3. 10,000 miles on it. Going to another dealership and trying to have all the info i can get before i go.

My 2016 just had a service 4wd message and they had to replace some sort of transfer case position sensor selonoid or something like that. When mine is in auto 4wd it makes a faint noise, nothing bad sounding though. If I put it in 4 hi and crank the wheel all the way on dry pavement it clunks a little at low speeds.

Did you ask to drive another 2017 on the lot to see if it made the same noise?

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[cbrsilv15]

Is it a really high pitched noise?

[ShamrockShooter]

There was also a TSB for a faint high pitched electrical noise coming from the Transfer Case Control Unit when in 4wd under the dash above your brake pedal. I had that fixed on mine too

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[BigBadSierra]

The tone on my front end changes the second 4 auto is engaged. I had a 2014 and a 2016 both were the same.

 

I know when it's on just by sound. 

 

When I put Goodyear DURATRAC's on the 2014 the front tires did get louder when the clutches engaged for the auto mode.

 

It's more of a growl than anything so if you have louder or grinding then it's something else.

 

 

[Ryan2828]

I would understand the differential being louder in 4wd auto. This is a whine/humming on drivers side in 2wd and putting in in 4wd auto makes it go away. Its  opposite of what of what you think should happen  

[aseibel]

44 minutes ago, ShamrockShooter said:

If I put it in 4 hi and crank the wheel all the way on dry pavement it clunks a little at low speeds.

Don't do that. You are just wearing everything out. 4wd is only for low traction situations, no need to ever use 4wd on dry pavement.

 

4auto engages the front differential. so there are more components spinning, being driven by the front wheels. thats why you hear it.

[ShamrockShooter]

Don't do that. You are just wearing everything out. 4wd is only for low traction situations, no need to ever use 4wd on dry pavement.
 
4auto engages the front differential. so there are more components spinning, being driven by the front wheels. thats why you hear it.

True but sometimes you need to turn on 4wd on dry pavement right before you turn off the road into mud. With my duratrac tires i hardly ever need 4wd anyway

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[isiddall]

22 minutes ago, ShamrockShooter said:

True but sometimes you need to turn on 4wd on dry pavement right before you turn off the road into mud. 
 

no you don't

[nluchau]

This morning due to icy roads I put my truck into 4Auto from 2Hi and the thing I notice is upon acceleration more of a groan sound but if I back off its not too bad.  Once back in 2Hi its normal again.  I do on the fly switching, don't matter the speed Im going.  

[truckguy82]

42 minutes ago, aseibel said:

Don't do that. You are just wearing everything out. 4wd is only for low traction situations, no need to ever use 4wd on dry pavement.

 

4auto engages the front differential. so there are more components spinning, being driven by the front wheels. thats why you hear it.

It does nothing to the front differential, it engages the transfer case, which could also be called a center differential in our application

 

Everything is still spinning in 2wd

[truckguy82]

1 hour ago, Ryan2828 said:

I got a gear noise in my front differential that i’ve been fighting with the dealership about. They say its the tires but i drive the truck everyday i know what the tires sound like. When i hear the noise i can put the truck in 4wd auto and it goes away. Take it out of 4wd and it doesn’t return. Thats not tire noise. Its temperature dependent, above 60 degrees doesn’t do it ever.  Its in the teens now and the only way to get it to go away is switching to 4wd auto. Truck is 2017 silverado with 5.3. 10,000 miles on it. Going to another dealership and trying to have all the info i can get before i go.

I would check your transfer case oil, maybe change it. Same as trans fluid.

 

The transfer case is really the only thing that makes any sort of change when switching from 2wd to 4auto

 

Maybe the factory put differential gear oil in your transfer case, which could potentially explain the temperature dependent issue? Just throwing something out.

[Sierra706]

I have that noise. Regard it as normal at this point


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[truckguy82]

19 minutes ago, Bushleaguechew said:

I have that noise. Regard it as normal at this point


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you have a noise in 2wd that stops when you switch it to 4auto?

['17 Sierra]

Back to the original question of what happens when you activate 4 Auto: In 2WD, your front drive shaft is not turning. The front axles are always turning though as there is no locking/unlocking hubs. Once you engage 4 Auto, the front driveshaft begins turning and the transfer case is then synchronized with the rest of the driveline, however the TC is not engaged unless tire slippage is detected and then the clutch system in the TC begins to engage the front end.