4WD Slippage

djamesw · January 2, 2004

I recently got my 2002 Sierra 2500 4WD into a pretty good snow bank, and was surprized at the difficutly in getting out. I noticed that in 4 Hi, 4 Lo, or 4 Auto, the left front wheel would not even spin. (I don't know if the right one was spinning.) The left front would try to grab, spin, and then stop spinning, while the back right was spinning.

Shouldn't the fronts be locked to drive, no matter what in 4 Hi?. And I thought that the rear axle had a posi lock feature, instead of permitting just one wheel to spin.

Any comments would be appreciated.

Chris97K1500 · January 2, 2004

Your front isn't locked at all, if you get stuck, only one of your front tires will spin, the one with the least amount of traction. As far as the rear, if you don't have the G80 Code in the options list in your glovebox, you've got an open rear end, which means that the tire with the least amount of traction will spin all day long and the other will sit there doing nothing. G80 rear end was just an option, not standard. Unless you have a locker, or it's an AWD vehicle, 4x4 means only 1 front and 1 rear tire spins when you get stuck! Chris

99-2door · January 2, 2004

Chris is absolutely right. A lot of people get suprised and dissapointed when they first get into a situation like that, but the locking rear is optional.

JayMan · January 2, 2004

With the AutoTrac at least the thing is smart enough to transfer most of the power to the axle with the most traction.

Last week I tried turning around on a logging road, there was already about 1.5 ft of snow on the road. Kind of hard to tell where the road ends and the ditch begins, but I felt the rear end drop.

I pushed the AUTO 4WD button, waited a few seconds, and gently pressed on the pedal. According to my passenger, who was getting ready to push, the rear wheels spun briefly than quit, and the front end appeared to do all the work.

I know I was lucky that time, but with the AutoTrac and the G80 locker, getting stuck is rare. As mentioned, if you don't have the G80 RPO listed in the glovebox, you have an open rear end.

I like the G80 as it does NOT engage at speeds over 20 MPH. I used to have a 2WD one ton truck with a Detroit Locker. Driving uphill on snow/ice was a nightmare, as the rear end always wanted to slide out. That thing put me sideways at 40 MPH once. Never again!

djamesw · January 3, 2004

Well, it sounds like it's working like it should. This is a great place for answers, and I appreciate your responses.

Thankyou.

RyanZ71 · January 3, 2004

how much can one expect to pay for a locker and the installation of one?

iron_786 · January 3, 2004

curious as to why the g80 isnt an option for the front diff? would come in handy if your really in deep stuff

JayMan · January 3, 2004

how much can one expect to pay for a locker and the installation of one?

Probably the easiest way to go is with the Powertrax NoSlip. I already have a PowerTrax LockRight in my 1984 Ford F-150 with 8.8 rear, and thought I could upgrade my 2000 GMC. However, if the GM comes with the G80 locker, you can't easily put in a PowerTrax product.

If you're curious, check out PowerTrax at:

http://www.powertrax.com

You should be able to put it in yourself, plan on 2-4 hours of your time. A qualified shop will probably take 2 hours. Other options are Auburn Gear at:

http://www.auburngear.com

and you could always get a GM dealer to dealer install a G80, though that could be $$$.

Figure on about $350 in parts for the PowerTrax NoSlip and whatever labor charges are.

Remember the G80 disengages above 20 MPH. If you put in a full time locker, going up an icy hill in winter could put you sideways.

JayMan · January 3, 2004

curious as to why the g80 isnt an option for the front diff? would come in handy if your really in deep stuff

It has to do with how the front differential works. When you press the 2WD button, you really don't disconnect the entire front diff. This is going to be a long post, so sorry ahead of time.

The front driveshaft stops rotating, and the electric actuator moves a pawl in the differential to slide a splined collar away from the ring. So the front ring/pinion are motionless.

However, the front halfshafts with their CV joints are still turning. I think folks are surprised by this, especially how quickly the front gear oil turns black. The front case bearings are still turning whenever the truck is moving. So it's important to keep the front differential at the right fluid level, and in cold climates to use a synthetic 75W-90 GL-5 gear oil.

The fact that the halfshafts are still turning while the ring/pinion and front driveshaft are NOT would really confuse or bugger up a locking differential. You could even break parts.

The Classic GM trucks, and my 1984 Ford F-150 4x4, have manual hubs, so when you twist them to "Free," which moves a splined collar on a splined shaft inside the hub, only the wheels turn. The front axle shafts and the front axle driveshaft remain motionless.

I don't know offhand of any conversion kit for the +1999 trucks, short of a swap to a Solid Axle. Anybody can help me here??

I put a Detroit Locker in my 1984 F-150 front axle. This was expensive, since one of Ford's "better ideas" was to use an independent Dana 44 front axle with the case in two halves. No simple sheet metal cover here. You have to split the case and use a special tool, a spreader, to get out the old differential out to put the locker in, very $$$ and time-consumming.

If I put the front hubs in "Lock" with the transfer in 2WD, and turn a sharp corner at slow speeds, I feel a pronounced slip-grab motion from the front wheels. You're only supposed to use "Lock" and 4WD on slippery surfaces with this setup.

The Jeep Grand Cherokee with "QuadraDrive" uses full time 4WD with gerotor differential "locks" (Clutch plates forced together by gear oil pressure and a bias sensor) in the front and rear axles. There is a "clunk" if parking on dry pavement and that's normal. In theory, you can have 3 wheels in the air and the wheel on dry ground will still move the Jeep.

A friend of mine with a 2003 Jeep Grand Cherokee Overland proved this to me last summer. He jacked up three wheels, put it in Drive, and drove off the jackstands. I was impressed. He gets 14 MPG highway, not so impressive.

bigdogs · January 4, 2004

I know that front end bounce and jerk JayMan. I had an 80 Blazer that I put in a 14bolt 10.5" rear with a locker and a Dana 60 with a Power Lok in the front and when that was all locked you could sure feel it.

It is too bad they don't have a good "posi" or locker for the front on newer trucks.

JayMan · January 4, 2004

I know that front end bounce and jerk JayMan. I had an 80 Blazer that I put in a 14bolt 10.5" rear with a locker and a Dana 60 with a Power Lok in the front and when that was all locked you could sure feel it.

It is too bad they don't have a good "posi" or locker for the front on newer trucks.

Well, again, I think it has to do with the way the front axle is engaged and disengaged. With that sliding splined collar, I really don't see how you could make any sort of LS or locker work. You would need an "old fashioned" manual hublock with 2 speed transfer case, like on my 1984 Ford F-150.

I suppose GM could copy the Jeep Quadra-Drive system, if they could somehow get around the patents. Then again, Dodge could very easily have copied the Quadra-Drive to their Ram trucks, and they haven't. Probably too much expense, poor reliability, etc. Let's not forget the dismal fuel economy.

For true offroading I can always borrow a buddies old Jeep: lockers front and rear. I went hunting with him in that heap a couple of years ago and it took the Bone Bender a month to fix my back.

bigdogs · January 5, 2004

True, my Blazer had the manual hubs and a gear drive NP205 transfer case. It is too bad they don't still use those as they are bomb proof.

JayMan · January 5, 2004

True, my Blazer had the manual hubs and a gear drive NP205 transfer case. It is too bad they don't still use those as they are bomb proof.

You got it. I guess they want us to have good ride quality and better fuel economy. The vast majority of 4WD owners never even venture off a gravel road.