4 WD engaged all the time?

srekab · July 1, 2015

I had the right front wheel jacked up today and I couldn't turn it. It was mechanically locked with the other side and or the rear. I was short on time and couldn't check into it any further at the time. The truck was supposed to be in 2 WD at the time. Shoudn't the right and left front tires spin freely of each other when not in 4 WD? I'm also having vibration issues at high speeds. I'm thinking if 4 wd isn't disengaging that might be causing my high speed vibrations

newdude · July 1, 2015

Try cycling the 4x4 between 4hi and 2hi. Do you have it in Auto 4x4 by any chance? How about brake drag? They put little to no grease on the caliper slide clips and pins.

srekab · July 1, 2015

I didn't have a lot of time to try things, tomorrow I'll do some more checking into the situation. It was however a definite gearing "clunk "in the differential when I tried to spin the wheel with the opposite on the ground.

newdude · July 1, 2015

If it happens to be in auto, the front diff is locked when in auto and 4x4 powerflow is all controlled at the transfer case. 4hi, everything is engaged, case and front axle. Could be an axle actuator or communications issue for it.

srekab · July 1, 2015

If it happens to be in auto, the front diff is locked when in auto and 4x4 powerflow is all controlled at the transfer case. 4hi, everything is engaged, case and front axle. Could be an axle actuator or communications issue for it.

When in "Auto" mode the front hubs are locked in all the time. When in 2wd mode they are unlocked. Is this correct?

newdude · July 1, 2015

When in "Auto" mode the front hubs are locked in all the time. When in 2wd mode they are unlocked. Is this correct?

Yea. The transfer case clutch set engages 4x4 when necessary based on wheel slip. Front axle is engaged.

srekab · July 1, 2015

Yea. The transfer case clutch set engages 4x4 when necessary based on wheel slip. Front axle is engaged.

Are the front axles or hubs unlocked when in 2wd mode so they spin freely of each other then?

jay15892 · July 2, 2015

The hubs don't "lock". It has an axle disconnect. Then the transfer case applies power as needed when in auto. Or all the time in 4hi.

srekab · July 2, 2015

OK, lets see if I get his right. When in Auto the front axles are "locked" with the front drive shaft ready for traction when the transfer case sends them power in a slippery condition. When in 4wd front axles and transfer case and rear axles are all linked together for traction. Now, in 2wd mode the front axles are disconnected from the transfer case and also from the other front axle. What I'm saying is that the front axle drive shaft is disconnected from the front wheel hubs so that the drive shaft does'nt turn when in 2wd.

ajdata · July 2, 2015

Is the indicator light lit on the 4x4 selector knob? I had a similar issue back in October with my truck. Turned out the dealership incorrectly applied a transfer case update. And so I was "locked" in 4x4 mode for several thousand miles. After this was corrected my vibration issues went away too.

The reason I ask about the indicator light, because I was told that my light was not lit which indicated to the tech there was a problem. Since I bought the truck this way I didn't know there was a light on the knob.

Good luck.

srekab · July 2, 2015

I've noticed the light when switching positions but i don't know for sure if it remained on in each position. I'll check that. Boy, I would be very happy if this was my vibration issue. I do know the truck had a software update installed concerning the 4wd.

ajdata · July 2, 2015

Here is a link to a post I made when GM discovered the problem. I uploaded the actual service write-up....I hope this helps and that your fix is this simple.

http://www.gm-trucks.com/forums/topic/153186-shake-or-vibration-issues/page-250?do=findComment&comment=1536891

srekab · July 2, 2015

I did some more checking today and it seems that all the 4wd engagment system is working. Thing is I have been driving the truck in "Auto" mode which keeps the front axles engaged with each other and the differential. this is probably where some of the vibration is coming from. haven't had a chance to drive it at high speeds yet. I been working a lot of hours this week and only have a little time to work with the truck. This is why you should always read the owners manuals when getting a new vehicle. But why didn't my dealer know this when they checked out the vibration?

SouthernSilveradoGuy85 · July 2, 2015

I did some more checking today and it seems that all the 4wd engagment system is working. Thing is I have been driving the truck in "Auto" mode which keeps the front axles engaged with each other and the differential. this is probably where some of the vibration is coming from. haven't had a chance to drive it at high speeds yet. I been working a lot of hours this week and only have a little time to work with the truck. This is why you should always read the owners manuals when getting a new vehicle. But why didn't my dealer know this when they checked out the vibration?

Simply having it in auto 4 won't cause a vibration. The only thing close would be the feeling of it being in 4x4 while turning where it would feel like it's harder to turn, but that would mean for it to think you need 4x4 while you have it set on auto.

As for using it. I see 0 need for keeping it in auto 4 unless it's snow/ice patches where the road isn't consistent, mostly when snow/ice is melting. Some people say they put it in auto when it rains which also doesn't make much sense because these trucks have Traction Control and Stabilitrak. If my old 86 Chevy C10 and 98 Z71 without any of those driver assist did fine in hard rain then these new truck with those systems would have no problem. To add to that, I usually always had the cheapest tires on those 2 trucks. The only time I didn't was when I put BFGoodrich All-Terrain T/As on the 98 once, other than that they always had regular street tires and the last set on the 98 was only $425 which that including the balance and mounting. So in normal condition, even hard rain, just have it in regular 2wd. Even having it in auto will drop your mpgs so there's really 0 gain. It may make you feel safer to have it in auto 4 in rain, but it doesn't really help.

srekab · July 2, 2015

When I picked the vehicle up from the dealer just a short while back it was set in auto. Like I said I neglected to read how the system was supposed to function and left it there. I am pleading ignorance in that case. I agree after reading the manual there is no need for auto unless you are in immediate need of 4wd. I will always keep it in 2wd in highway high speed conditions. As far as causing a vibration when in auto mode at highway speeds I would say it shouldn't cause a vibration but whos to say it couldn't. The truck shouldn't have vibrations at any speed in or out of 4wd under any conditions. But, it does.