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cstrunk

cstrunk

Well-Known Member
Mar 21, 2006
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Longview, TX
My 2007 GMC Sierra 1500 Vortec Max 6.0l 4x4 is having some intermittent issues. When I put it in reverse and give it anything more than low throttle, it sometimes makes a loud clunk noise and stops. Scares the crap out of you. Today it did it but maybe not quite as loud but was followed by a metallic grinding/whirring noise (fast but slowing down). I put it in neutral and it stopped. Put it back in reverse and eased out without issue. I've never had any other issues. After it happens I've always been able to put it back into reverse, I just ease on it.

My limited research indicates it could be the transfer case instead of the automatic transmission. Thoughts?
 
Gears aren't happy somewhere. Do you have an 'Auto' position for your 4WD? Sometimes that causes issues if it's trying to engage when it shouldn't be. Are you turning when backing up?
 
JM4CY said:
IDK but it sounds expensive.
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Yeah... and I just finished up with $4k of other repairs/much needed maintenance. Too scared to ask the last mechanics to look into it...

Colorado said:
Can you tell where the "clunk" sound is coming from?
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Only thing I can tell is it's under the truck in the middle to rear area. Not exactly sure.

HOTDON said:
Gears aren't happy somewhere. Do you have an 'Auto' position for your 4WD? Sometimes that causes issues if it's trying to engage when it shouldn't be. Are you turning when backing up?
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Yeah I had someone years ago tell me to just keep it in 2wd until you need 4wd, don't just leave it in Auto. I'm usually backing up straight but sometimes it happens in the turn I don't think that affects anything.
 
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Best guess would be transfer case or rear differential, maybe something like a pinion bearing. It doesn't really sound like a transmission issue, but it's possible. As HOTDON said, gears aren't happy somewhere.
 
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cstrunk said:
My 2007 GMC Sierra 1500 Vortec Max 6.0l 4x4 is having some intermittent issues. When I put it in reverse and give it anything more than low throttle, it sometimes makes a loud clunk noise and stops. Scares the crap out of you. Today it did it but maybe not quite as loud but was followed by a metallic grinding/whirring noise (fast but slowing down). I put it in neutral and it stopped. Put it back in reverse and eased out without issue. I've never had any other issues. After it happens I've always been able to put it back into reverse, I just ease on it.

My limited research indicates it could be the transfer case instead of the automatic transmission. Thoughts?
Click to expand...
I'm assuming when it's in 4WD your are talking about? If so, yes transfer case/differential and not transmission.
 
I don't think it sounds like a transfer case thing. Hopefully it's your shift linkage, but honestly I think it's going to be in your transmission.
 
cstrunk said:
My 2007 GMC Sierra 1500 Vortec Max 6.0l 4x4 is having some intermittent issues. When I put it in reverse and give it anything more than low throttle, it sometimes makes a loud clunk noise and stops. Scares the crap out of you. Today it did it but maybe not quite as loud but was followed by a metallic grinding/whirring noise (fast but slowing down). I put it in neutral and it stopped. Put it back in reverse and eased out without issue. I've never had any other issues. After it happens I've always been able to put it back into reverse, I just ease on it.

My limited research indicates it could be the transfer case instead of the automatic transmission. Thoughts?
Click to expand...
I'd take it to a mechanic.
 
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