Uh oh, is my four wheel drive system toast?

sgiangregorio · December 20, 2004

I've noticed that the last few times I've used my four wheel drive system, that it just doesn't seem to have the "grab" that it used to. It seems far worse in Auto 4WD than in 4 High. This is on my 2002 Tahoe Z71. If in one of these settings, and again, it's worse in Auto, I'll spin out the rear end very easily. The weird thing is that it sometimes it will work fine, like it did grab. But the majority if cases it "feels" broke.

In the local coffee shop parking lot, I rolled down the window so I could watch the front wheels while sitting in snow. I then punched the gas and the front just rolled forward, but the rear did all the pushing and then it started spnning out. "NOT GOOD!" was my first though, as I had a Chevy Blazer that had a shaft score some bearing that caused fluid to leak out and burn something up. Final result: $2200.

Typically, it feels like the truck "leaps" upward and onward when everything is fine. It doesn't feel like that at all right now.

I'm really hoping it's something as simple as a frozen switch, accuator, or something. Any ideas?

Thanks.

P.S. If this is a similar and as expensive repair as my old Blazer, this will be 2 for 2 with my Chevy Trucks that have had something like this, and I won't be a happy GM customer.

asilverblazer · December 20, 2004

Switch? Seems pretty common.

chuckp · December 21, 2004

accuator

I've noticed that the last few times I've used my four wheel drive system, that it just doesn't seem to have the "grab" that it used to. It seems far worse in Auto 4WD than in 4 High. This is on my 2002 Tahoe Z71. If in one of these settings, and again, it's worse in Auto, I'll spin out the rear end very easily. The weird thing is that it sometimes it will work fine, like it did grab. But the majority if cases it "feels" broke.

In the local coffee shop parking lot, I rolled down the window so I could watch the front wheels while sitting in snow. I then punched the gas and the front just rolled forward, but the rear did all the pushing and then it started spnning out. "NOT GOOD!" was my first though, as I had a Chevy Blazer that had a shaft score some bearing that caused fluid to leak out and burn something up. Final result: $2200.

Typically, it feels like the truck "leaps" upward and onward when everything is fine. It doesn't feel like that at all right now.

I'm really hoping it's something as simple as a frozen switch, accuator, or something. Any ideas?

Thanks.

P.S. If this is a similar and as expensive repair as my old Blazer, this will be 2 for 2 with my Chevy Trucks that have had something like this, and I won't be a happy GM customer.

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Yukon04 · December 21, 2004

You should be able to here the electronic solenoid engage when you "activate" the switch. Park near a wall in a semi-quiet area and try listening for the "clunk" when you press the switch. It should sound kinda like a electric motor with an engaging clunk. Wortha try....

sgiangregorio · December 21, 2004

I hope it's something like that...it seemed fine last night on the way home, but useless this morning. I do hear a "Click" in the dash when I change settings, but I'm not sure about under the truck, I haven't listened. Although, I do know that clunk sound you mention, and I don't think I'm hearing it.

Yukon04 · December 21, 2004

I ran into the same issue on an S-10 with electronic 4X4. Not sure if the fullsize trucks operate the same. However, the solenoid is vacuum operated on that system. The hose feeding the solenoid became partially disconnected and displayed an intermittent operation. After some time, the system finally stopped working after the hose completely fell off. Check it out...

chris_kucia · December 21, 2004

I've noticed that the last few times I've used my four wheel drive system, that it just doesn't seem to have the "grab" that it used to. It seems far worse in Auto 4WD than in 4 High. This is on my 2002 Tahoe Z71. If in one of these settings, and again, it's worse in Auto, I'll spin out the rear end very easily. The weird thing is that it sometimes it will work fine, like it did grab. But the majority if cases it "feels" broke.

In the local coffee shop parking lot, I rolled down the window so I could watch the front wheels while sitting in snow. I then punched the gas and the front just rolled forward, but the rear did all the pushing and then it started spnning out. "NOT GOOD!" was my first though, as I had a Chevy Blazer that had a shaft score some bearing that caused fluid to leak out and burn something up. Final result: $2200.

Typically, it feels like the truck "leaps" upward and onward when everything is fine. It doesn't feel like that at all right now.

I'm really hoping it's something as simple as a frozen switch, accuator, or something. Any ideas?

Thanks.

P.S. If this is a similar and as expensive repair as my old Blazer, this will be 2 for 2 with my Chevy Trucks that have had something like this, and I won't be a happy GM customer.

<{POST_SNAPBACK}>

Hmm.

I tend to agree that the actuator is probably the culprit. However, I was under the (perhaps mistaken) impression that the mechanisms for full-time 4wd and auto 4wd were different. If I understand correctly, "Auto" engages a differential that only transfers torque to the front wheels when slippage between the front and rear axles is detected. Full-time hi or lo "locks" the front and rear differentials together.

On mine, the engagement "clunk" for full-time 4wd is a lot louder than that for auto, which is probably why I thought they were different mechanisms.

I could be wrong.

I think the actuator is motorized rather than vacuum. On mine it will engage without the engine running - I always put it in FT 4wd Low when I'm working under it as extra insurance to prevent rolling, especially when jacking up the rear end.

J-rod · December 21, 2004

However, I was under the (perhaps mistaken) impression that the mechanisms for full-time 4wd and auto 4wd were different.

Yeah, see JayMan's post here.

On mine it will engage without the engine running ...

Hehe, yeah I've tried that on mine too.

sgiangregorio · December 22, 2004

Well, I listening closely when hitting the button the dash. All I can hear is the click in the dash when I press the button, and something that sounds like a plunger switch under the truck. But no Clunk sound...

sgiangregorio · December 24, 2004

Whew! Only $85 to fix it, and it shows as all labor. They were able to confirm the problem. They said there is a washer on the acctuator that was bent. It wasn't allowing the "plunger" to fully seat when engages, only sometimes, thereby not engaging the 4WD system in all cases. They replaced the washer, and now I have that hard growl back when in 4x4!! Thank goodness, I was envisioning a $2000 repair like my old Blazer.

sgiangregorio · December 25, 2004

Uhmm...not so sure that was it. Tonight, I kicked it into 4 High, and nothing. Did it again later, and it worked. I've have to watch it for a few days, but that may have not been the problem.

And, since they worked on it, I've noticed a front end drivetrain "howl" sound. Similar to what it sounds like when you're on 4WD, even though I'm only in 2WD. Any ideas on that one? I think I may be imagining things, as they didn't touch that part of the truck as far as I know...