4X4 low wheels turn independently?

[Jozuah]

K today i was backing my truck up over a curb, i do this often to get trash and haul it to the dumpster from my house. the "curb" is about 3 inches tall and a square edge to flat grass on the top. like i said i have done this for 2 months every 4 days. well this morning the grass was all soft and wet, after i got the rear wheels up on the grass they started to spin, the front wheels were on dry pavment mind you, and the truck was in 4x4 LOW and i actually got stuck in the grass, shifted into drive and the rear just spun, and the fronts were not spinning . the truck WAS in 4X4 because i could spin all four tires on gravel, my wife verified this. after that post by photospro about the clutchpack involved with our trucks i need to know if my TB is hurt and needs to be seen by its doctor soon....


OK heres the question.
i thought 4X4 was just that, the axles were connected mechanically and they were not allowed to turn independent ( i understand that the front axle is limited slip and the rear is a GT80)

[TrailBlazer LS]

Our front diff. is a open unit{not limited slip}. So the front wheels will not always spin together when in 4WD. With the G80 the rears will spin together when one wheel looses it's bite all the time with vehical speed at or less then 20mph. Hope this helps.

Mark.

[the roadie]

The front is not limited slip, and can't be modified to add one. But that's mostly independent of your problem, which is that the transfer case isn't a front-to-back full locker. If BOTH rear tires spin, I've been stuck on dusty hills also. Torque leaks out of both rear tires and you go nowhere.

The G80 needs a relative difference in wheel speed between the two rear tires to activate, and is meant to save your bacon when ONE rear tire has traction and the other doesn't. In cases where I've been stuck with both rears spinning, that's time to stack rocks under one or the other to make sure I get one of them traction.

If we had a full locking transfer case instead of one with clutch plates, all the torque would have gone to the front wheels in your case and you would have pulled out. Well, as long as BOTH front tires had traction because if even one of your front tires spun, the lack of limited slip or front locker would have let the spinning front wheel strand you.

I'd normally suspect your transfer case encoder motor just didn't command full clutch engagement for some reason, but if you said you could spin all 4 on gravel later, then it's not totally dead. Had you re-engaged it with the switch before you tested it on gravel?

As you can see in my Elliot Mine hillclimb video, at times I have two tires with reduced traction. One front is very high, and the opposite rear is on the ground but with very little traction in dust. So the diagonally opposite tires are spinning, but then the G80 locker kicks in, locking the two rears together. But because the transfer case is pretty well engaged (not locked) with its clutches, the front tire in the air STOPS spinning as a reflection that the torque is being transferred to the locked-up rear axle. And I continue to go up the hill. I looked at the video Teebes took of me a long time before understanding what was happening.

http://www.youtube.com/watch?v=24SwmSN0-bI

It's unfortunate, but we just don't have full mechanical connection front to back through this design transfer case. Or side to side in the front differential. So torque can leak out in unexpected ways.

One tactic that could have saved your bacon was left-foot braking, but it's not at all a natural thing to do when you've got spinning tires. If you have both rears spinning, just touch the brakes with your left foot. Brakes act as a torque valve and reduce the amount of torque leaking out onto the grass uselessly. Then the amount of torque available to the front tires goes up, and it might have been enough to pull you off the curb. Let's hope it stays soft (or you can hose it down soon) and try this again and report back!

[Jozuah]

Originally Posted by the roadie

The front is not limited slip, and can't be modified to add one. But that's mostly independent of your problem, which is that the transfer case isn't a front-to-back full locker. If BOTH rear tires spin, I've been stuck on dusty hills also. Torque leaks out of both rear tires and you go nowhere.

The G80 needs a relative difference in wheel speed between the two rear tires to activate, and is meant to save your bacon when ONE rear tire has traction and the other doesn't. In cases where I've been stuck with both rears spinning, that's time to stack rocks under one or the other to make sure I get one of them traction.

If we had a full locking transfer case instead of one with clutch plates, all the torque would have gone to the front wheels in your case and you would have pulled out. Well, as long as BOTH front tires had traction because if even one of your front tires spun, the lack of limited slip or front locker would have let the spinning front wheel strand you.

I'd normally suspect your transfer case encoder motor just didn't command full clutch engagement for some reason, but if you said you could spin all 4 on gravel later, then it's not totally dead. Had you re-engaged it with the switch before you tested it on gravel?

As you can see in my Elliot Mine hillclimb video, at times I have two tires with reduced traction. One front is very high, and the opposite rear is on the ground but with very little traction in dust. So the diagonally opposite tires are spinning, but then the G80 locker kicks in, locking the two rears together. But because the transfer case is pretty well engaged (not locked) with its clutches, the front tire in the air STOPS spinning as a reflection that the torque is being transferred to the locked-up rear axle. And I continue to go up the hill. I looked at the video Teebes took of me a long time before understanding what was happening.

http://www.youtube.com/watch?v=24SwmSN0-bI

It's unfortunate, but we just don't have full mechanical connection front to back through this design transfer case. Or side to side in the front differential. So torque can leak out in unexpected ways.

One tactic that could have saved your bacon was left-foot braking, but it's not at all a natural thing to do when you've got spinning tires. If you have both rears spinning, just touch the brakes with your left foot. Brakes act as a torque valve and reduce the amount of torque leaking out onto the grass uselessly. Then the amount of torque available to the front tires goes up, and it might have been enough to pull you off the curb. Let's hope it stays soft (or you can hose it down soon) and try this again and report back!

once again you have answered a question posted with the exact answer i was looking for .. ill hose it down tomorrow and try again, thanks for the fantastic post roadie and your videos make me want to,..... well lets just say they make me all happy.

josh

[guano2]

When I got my T/B at 34th soon after I went to pick up a garden tractor w/ my trailer in this guys yard w/ the 4whl light on the dash on all I could do was spin 1 rear wheel got it out after turfin the guys lawn. I didn't think it was engaged,didn"t screw with it for sometime after that eventually went to use it and switch lights were out just 2WHL.Try pulling the fuse under hood #8 ATC maybe it will relearn like mine did {just checked fuse location for you } I just cleaned T Body waiting now... Goodluck ehh I'd go with roadie on this one "spins on gravel" Think I jumped the gun although could have just been crankie going all the way in. {I just cleaned my t/ body and my brain and can"t do a thing with it.}

[the roadie]

Originally Posted by guano2

...all I could do was spin 1 rear wheel...

Do you have the G80 option? If not, you can be in 4HI or 4LO, and have just ONE rear tire on leaves, snow, or ice, and not be able to move. GM should not have even sold a 4WD vehicle without bundling an LSD or locker with the package, it's so useless.

[starchief1959]

(kind of)

Sounds like people are getting our 4wd LOW confused with 4wd LOCK. In the past, the 2 were usually one in the same system but now they are different because the use of 4wd is typically for driving down the road in snow or ice instead of being used where needed. 4wd vehicles are now everyday vehicles instead of "work" vehicles like they were used for in the past.

[lightguypro]

so my question is..it seems all confusing..but if the 4x4 drive option is there and you dont have a g80 whats the point..
if your driving up snow or dirt you can slide out of control? correct?
is it better to go off road with the traction control on so you dont have to use the left foot method?

[RayVoy]

Originally Posted by lightguypro

so my question is..it seems all confusing..but if the 4x4 drive option is there and you dont have a g80 whats the point..

The G80 will give you the equivalent of 3 wheel drive. 1 front (left or right) and both rears. Without the G80, you have only 2 wheels with traction, one of the fronts and one of the rears. Read this thread ... http://forums.trailvoy.com/showthread.php?t=22688 its got some good info.

[the roadie]

Originally Posted by lightguypro

so my question is..it seems all confusing..but if the 4x4 drive option is there and you dont have a g80 whats the point..

All good questions. If you're in a region of good traction, 4WD can divide the torque nicely so no one wheel tends to spin out. Most folks aren't riding the rutty trails like I am with one wheel in the air a lot. For my mission, G80 is absolutely essential. If I didn't have it, I would not have added other mods to the truck.

The G80 isn't as useful in mud, where you are probably spinning all four tires at full throttle anyway. If you're in a region of low traction, you need the entire traction contribution from each of the four tires, and you only get that by spinning them. I hate mud.

if your driving up snow or dirt you can slide out of control? correct?

You can always have that happen. G80 doesn't help an out of control slide. And you can't pre-lock the rear up. You have to allow the slip to start, hopefully without so much throttle that you damage the G80 when it engages with a clunk. Note this hillclimb where I did a full throttle 4 wheel spin to conquer a hill that mocked me before. Not my usual style. I'm actually a bit embarassed to have done this with so little finesse and control. But I wanted UP.

http://www.youtube.com/watch?v=7OkERcoN0FY

is it better to go off road with the traction control on so you dont have to use the left foot method?

Left foot braking is for when you've started two wheels slipping and aren't going anywhere. You should ALWAYS be in 4HI or 4LO when you're off pavement, so you avoid the time delay of A4WD engagement. It's especially necessary to be in 4LO before you need it, because if you're not in it and need to be, you might not be in a position to go into neutral and coast for a bit to get it to go in.