New in Colorado

[hilljb]

I'm originally from Flint, MI. My father and grandfather both worked for GM. I've owned and driven many GM vehicles, but this is my first Trailblazer.

I have a diff question later in this post for those that want to skip my intro and get right to the meat.

I found a 2003 LS with the 4.2 LL8 with 65K miles recently, owned by a single (old) person and in kept in mint shape. It's pretty much perfect for my daily driver and I'm going to lift it and do some mods to help me get to the trailheads I want to reach here in Colorado. I'm a photographer, and this vehicle will eventually help get me down some roads that my last rig had no chance at managing.

I've always done all the work on my vehicles. (I grew up the son and grandson of GM employees...) I've already done some small tinkering on the Trailblazer: cleaning the throttle body, tightening the intake manifold to fix some rough cold idle issues, replacing the rear calipers as they were wearing unevenly and the brake fluid needed to be changed anyway.

One thing that has surprised me about my Trailblazer is the get-up-and-go. That LL8 kicks out some power ... until I take it up to 12,000 feet in elevation, where it's a total dog. I plan on tinkering with that at some point. (I've driven a lot of vehicles in the mountains here, and my Trailblazer has more loss of power than anything I've driven above 12K. Up to about 10,500ft or so, it's reasonable.)


Now my question:

I don't have the G80 differential option, which I knew at buy time (the deal was too good and meant that adding a mech locker later would still save my wallet in the end). So, my understanding is that I have open diffs front and back. But, when I use 4H or 4L, I could swear that both front and rear diffs are completely (not slip-locked, not mech-locked) locked. Here's what happens in both 4L and 4H when you put the vehicle in gear and turn the wheel as far as possible:
1) On pavement: Move about 5 feet and bind-up happens, stopping the vehicle. I have to hit the gas and break wheels loose to move. It's relatively violent and the front diff moans if I do this on pavement.
2) On our dusty trails: Both front and rear axles independently pop a wheel loose before bind-up happens. So, if I crank the wheel and do a slow circle in a dirt lot, my wheels just go "pop pop pop-pop pop...".
When I transfer out of 4L/4H, this bind-up is entire absent.

What do you make of this? It _feels_ like the diffs are entirely locked... but that isn't an option on this vehicle, from what I've read anyway.

Cheers,
Jason

[TBYODA]

Welcome, naw that's crow hopping,

To quote Roadie from recent post on our sister site http://www.gmtnation.com.

The_Roadie" Crowhopping is an old offroaders term for the driveline binding you get in 4WD mode when the front and back driveshafts are tied together by too much torque in the transfer case. When you try to turn under those conditions, the front diff is trying to turn with a different radius than the rear, because the center of the turn is in line with the rear axle and farther away from the front. This is the 4 wheel equivalent of trying to turn an axle without a differential in the middle. The stress builds up and up and if you're on dry pavement, it may stop you from moving at all. On sand or snow, the stress will eventually break a tire loose with a hop/skid/bump/shudder.

People liken this to the way a crow "walks" by hopping both feet at a time.

Done too much, you can break a CV joint or transfer case internals.

Vehicles with true AWD modes usually have a viscous clutch transfer case that can't lock up fore/aft and don't have these issues. It was only this platform that cheaped out and used a dumbed-down NP126 transfer case as a fakey-fake AWD mode which was really the A4WD NP226 transfer case without a low range. The SS uses a non-electronic Torsen transfer case (actually works like a limited slip differential) with instant and smooth torque transfer.

I drew this up 8 years ago to explain why:

[Diacom]

1) On pavement: Move about 5 feet and bind-up happens, stopping the vehicle. I have to hit the gas and break wheels loose to move. It's relatively violent and the front diff moans if I do this on pavement.
2) On our dusty trails: Both front and rear axles independently pop a wheel loose before bind-up happens. So, if I crank the wheel and do a slow circle in a dirt lot, my wheels just go "pop pop pop-pop pop...".
When I transfer out of 4L/4H, this bind-up is entire absent.

Jason,
It is not recommended to use 4L/4H on dry pavement, the bind up is parts being stressed which will lead to breakage. Dirt roads may still have some of the noise you describe, but I would guess it's more likely the CV's making the pop noise than the wheels themselves. Use caution when depressing the accelerator pedal and having the wheel turned at full lock at the same time, this will also cause some of the afore mentioned stress than can lead to breakage if your foot gets too heavy. In most situations, if you can avoid a sharp turn it will be easier on the components and help them last longer. I do understand that this is not always possible, and knowing how your vehicle will react when in these situations is very usefull. I just caution against doing it on a regular basis.

Anyway, welcome to the Site.

[Cable810]

Welcome!!

[hilljb]

TBYoda: That makes perfect sense now. In driving a complete circle, the front wheels (by each wheel's individual turning radius) travel a combined circumference of about 2740 inches while the rear combine to only 2324 inches. Hence, the front wheels can travel a distance of up to 18% more than the rear. That's makes total sense after someone has pointed it out.

Thanks!

[TBYODA]

TBYoda: That makes perfect sense now. In driving a complete circle, the front wheels (by each wheel's individual turning radius) travel a combined circumference of about 2740 inches while the rear combine to only 2324 inches. Hence, the front wheels can travel a distance of up to 18% more than the rear. That's makes total sense after someone has pointed it out.

Thanks!

Please don't credit me but Roadie I was just passing along his great explanation.