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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29427
Experience:  GM Grand Master Technician 2007. 14 years experience.
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Cam. I have a 2007 Chev Avalanche. When I'm driving and put

Customer Question

Hey Cam. I have a 2007 Chev Avalanche. When I'm driving and put the truck into 4wd auto or 4wd hi, a dull grinding ish sound starts ...almost like it's trying to shift into 4wd but can't. Sometimes it will go away. If I stop and put the truck into 4wd hi, I can hear the requisite clunk and it seem to be okay until I try shifting out of 4wd on the fly. If I shift out of 4wd on the fly it makes the noise. If I stop and shift it from 4wd to 2wd drive it seems fine. If I put it in 4wd auto from stop, when I start driving, it makes the noise. Any ideas?
Submitted: 11 months ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 11 months ago.

Hi there, thanks for requesting me.

IT sound to start with like your tires may be different sizes or worn differently. So we need to check the ruling circumference.
In a flat parking lot make a mark at the very bottom of each tire. Then drive ahead 1 full turn of the tire until the left front is back at the very bottom. Then compare the marks. All must be with in 1 inch. More than that will cause issues in the transfer case and a noise like you have described.
Ofcourse if you have 2 new tires and 2 old or difference sizes then this test is pointless. All tires must the the same.
Your uncertainty of the noise makes me think the noise is actually the noise created when the clutch pack slips, which is a low odd growling noise that pulses on and off. Does this sound right?

Customer: replied 11 months ago.
All my tires are exactly the same. I rotate them every 7-10 000 km.
Expert:  GM Tech (Cam) replied 11 months ago.

O, do the check I suggested next and see please.

Customer: replied 11 months ago.
I'm certain of the noise ...just tough to articulate the exact sound.I can tell you exactly the conditions when it makes the noise, though:1) Switching into 4wd auto or 4wd hi on the fly
2) Switching out of 4wd auto or 4wd hi on the flyIt does not make the noise if I stop and shift into 4wd hi and then stop to switch it out.If I stop to switch it into 4wd drive auto and then continue on, it will make the noise when the 4wd engages.
Expert:  GM Tech (Cam) replied 11 months ago.

If you could pinpoint the location of the sound, where would you put it at?

Customer: replied 11 months ago.
It's quite a pervasive sound. I thought maybe the front diff but after change the actuator and spinning the tires, perhaps its transfer case. The sound deadening material on the LTZ is decent, so it's tough to pinpoint a specific place.
Expert:  GM Tech (Cam) replied 11 months ago.

Ok, is there any contamination in the fluid of any of the diff or transfer case?

Customer: replied 11 months ago.
I haven't had a chance to check either, yet. Still on duty, but I'm trying to get some better ideas for when I take another run at it tomorrow ....so I can avoid replacing stuff that doesn't need. Would you rule out encoder motor? I have one in the box I could probably return.
Expert:  GM Tech (Cam) replied 11 months ago.

My honest thought is the front axle sliding gear itself may either be in backwards or there is a problem there. This could be checked without much trouble, only removing the axle assembly on the passengers side.

Customer: replied 11 months ago.
In backwards? Interesting....
Expert:  GM Tech (Cam) replied 11 months ago.

The leading edge is chamfered to allow it to mesh. Backwards has it flat edges together and it would not engage and the sound you may be hearing is that.

Customer: replied 11 months ago.
I'm trying to find a picture on the internet. So far, I've done all my own work on the truck since I got it at 96 000km. It has over 230 000 km on it now. I haven't done anything like that to the axle area. I can't think of when anything would have been replaced backwards.
Expert:  GM Tech (Cam) replied 11 months ago.

Ok, has anyone had this apart?

Did this work properly the last time or last year?

Customer: replied 11 months ago.
I had the axles off to install a 6" Fabtech lift. I upgraded the upper control arms at the same time. I also changed the PS wheel hub. I had a pro shop do a proper alignment. It was all done in the summer months, so I can't pin point the first time the 4wd started acting up.
Expert:  GM Tech (Cam) replied 11 months ago.

OK so tires are bigger. This brings me back to the first test I mentioned, before we do anything lets try that and see the results.

Customer: replied 11 months ago.
the tires are bigger. They have about ten thousand kilometers on them. They're all the same size. The lift kit is pretty much the same as my dealership put on some of their brand new vehicles. I chayyed with the guy in the accessory department that sells them and they have had no such issues. Did not have four wheel drive issues the whole time I had my lift kit new tires. The aftermarket Pro Shop was very happy with the job I did on the lift and tires. I reprogrammed everything using the Hypertech programmer so much speedometers even correct. I am 99% sure the tires are all the same diameter still. But, with that said I will verify tomorrow.
Expert:  GM Tech (Cam) replied 11 months ago.

It’s the place to start and it costs nothing. Lets reconnect when you have that.

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