Change 4x4 to AWD?

nmollo · February 3, 2003

I have a 99 Sierra SLT Z-71 Step-side 4x4.

I just took a 2001 sierra C3 for a ride, the AWD is amazing!

I was wondering if there is a way to Change the tranfer case or computer to accomodate the AWD. The truck already has auto 4-wheel drive I am wondering if there is a way to trick the cars computer into thinking the truck is AWD.

Any feedback would be appreciated.

Thanks.

AirForceAngler · February 4, 2003

I think that putting it into "Autotrac" or Auto 4wd is basically the same as AWD. If you wanted, you could just leave it there, but you'll notice a slight drop in mileage which is one of the reasons they give you the option.

DuckhunterInTN · February 4, 2003

I'm thinking that the transfer cases on the 4wd and the Awd are different. The autotrac is basically "on-demand" 4-Hi, coming on when it detects slippage. The AWD actually sends (some) power to all the wheels all the time....

99silveradoz71 · February 5, 2003

I'm thinking that the transfer cases on the 4wd and the Awd are different. The autotrac is basically "on-demand" 4-Hi, coming on when it detects slippage. The AWD actually sends (some) power to all the wheels all the time....

I'd agree, AWD usually has some percentage front and a larger percentage rear most of the time.

cyrylyn · February 5, 2003

I'm thinking that the transfer cases on the 4wd and the Awd are different. The autotrac is basically "on-demand" 4-Hi, coming on when it detects slippage. The AWD actually sends (some) power to all the wheels all the time....

I'd agree, AWD usually has some percentage front and a larger percentage rear most of the time.

I disagree - Autrotrac is still going to perform mostly the same. I think 4-HI is a bad way to describe it. In 4-HI the front axle is locked, making turning difficult on pavement, however the autotrac is much smoother.

Z71GUY · February 5, 2003

C3 AWD vs Auto 4wd are not the same. As mentioned above, the C3 AWD always sends a small amount of power to the front end. Auto 4wd does not. Take a C3 out for a spin and do some slow tight turning in a dry parking lot....it turns fine. Go take a Silverado out and do the same thing with Auto engaged....the front end will hop a little bit almost as if it was in 4hi...does not hop nearly as bad because there is no power being sent like 4hi.

This is proof enough that they are completely different systems. Personally, I would NOT drive in Auto 100% of the time....the system was not designed for it. The AWD on the other hand is.

Overall, if you want a true AWD system, go buy the C3.

DuckhunterInTN · February 5, 2003

Yep, exactly. I am not saying that in auto 4wd that 4-hi is on all the time, I am saying that it kicks in whenever it detects slippage. That is why it is called "Auto" not "Full-time".

cyrylyn · February 7, 2003

C3 AWD vs Auto 4wd are not the same. As mentioned above, the C3 AWD always sends a small amount of power to the front end. Auto 4wd does not. Take a C3 out for a spin and do some slow tight turning in a dry parking lot....it turns fine. Go take a Silverado out and do the same thing with Auto engaged....the front end will hop a little bit almost as if it was in 4hi...does not hop nearly as bad because there is no power being sent like 4hi.

This is proof enough that they are completely different systems. Personally, I would NOT drive in Auto 100% of the time....the system was not designed for it. The AWD on the other hand is.

Overall, if you want a true AWD system, go buy the C3.

that's funny, because I have such large gripping tires, and they don't hop at all.

Z71GUY · February 7, 2003

You must have an odd setup then. Out of 4 Z71's that I have ridden in with Autotrac they ALL do the same thing. Also all of the GM shops I've been to has explained to me this is normal when in auto because of the front end being locked (its not a locker of any kind so its nothing like a rear end being locked). Keep in mind, this is NOT normal driving speeds, but much slower and tight turns (ie dry parking lot). Even my fathers LD2500 with Auto does the same thing...I've even read members stating that Auto feels strange on dry roads at low speeds during "tight" turns.

I've even driven a C3 and I can personally tell you that it feels much different than my truck in Auto 4wd.

TRUST ME, C3 AWD is NOT the Silverado's Auto 4wd. Go to a good GM dealer and ask a few guys in the shop that have worked on both....simple way of finding out for sure.

Z71GUY · February 7, 2003

This will put an end to this discussion.

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...from Pickuptruck.com (article about the C3):

Let's discuss the advantages of full time all wheel drive. GMC makes the claim that the Sierra C3 has the best on-road, wet or dry pavement handling performance ever engineered into a full size pickup. In theory its quite easy to agree with this statement.

Manually engaged four wheel drive trucks lack a component critical to full time all wheel drive trucks - a center differential. A differential is a set of gears that takes torque from the driveshaft and splits it evenly between the two output axles allowing them to rotate at different speeds. Without the center differential, when you engage a part time four wheel drive system, you wind up locking the front and rear axles of the truck so that they rotate at exactly the same speed. (READ THIS ---> ) In a straight line you won't notice too much of a difference between part time four wheel and full time all wheel drive but when you go to make a turn the laws of physics catch up with you. Because the distance the front wheels travel while turning is not the same distance as the non-turning rear wheels you wind up 'scrubbing' the tires on the road as they seek to even the difference in speeds between the front and rear wheels. You'll feel this as resistance in the steering wheel during a turn. This is also the reason the truck manufacturers recommend you don't engage part-time all wheel drive on dry pavement - you'll chew up your tires fast. On wet pavement the tire wear problem for part time four wheel drive trucks is significantly reduced because the slippery surface acts as a lubricant to reduce the amount of friction between tire and road as it scrubs off the difference speed.

In an all wheel drive truck, no matter how you turn the wheels or in what driving conditions, there is no scrubbing resistance because the center differential, acting with the front and rear differentials, continuously transfers torque from any slipping wheel to those with a firmer grip.

The Sierra C3's all wheel drive uses a viscous coupling to automatically lock the differentials at the first sign of traction loss. The viscous coupling is composed of a strong and lightweight magnesium housing that surrounds the

two axles with a silicone based fluid. The viscosity of the fluid varies from the consistency of karo syrup to the consistency of silly putty depending on the load it is placed under. As slippage occurs the disc plates within the differential shear this fluid so that faster rotating plates, those connected to slipping wheels, transfer power to slower rotating plates, the ones connected to wheels with better traction, which 'locks' the differential. Because of their fluidic nature viscous couplings continuously transfer

torque at all times and in a such a way that the driver never notices an adjustment in wheel traction.

For those out there who have doubts about the durability or superiority of full time all wheel drive versus part time four wheel drive consider the following. The Range Rover and Hummer H1 use permanently engaged all wheel drive systems and both vehicles are among the most capable off-roaders available, bar none. On road you need only look to the German luxury manufacturers which consider full time all wheel drive an essential safety component, such as Audi's Quattro system.

On most all wheel drive luxury cars you will normally find a 50/50 power split between front and rear power distribution but because this is a pickup truck with an unloaded bed, the default split on the C3 is set to 38/62.

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I'm still looking for our center diff on our trucks....Hmmmm....

jr.parrish · February 8, 2003

The Range Rover and Hummer H1 use permanently engaged all wheel drive systems and both vehicles are among the most capable off-roaders available, bar none.

So are the H1's not really 4X4's?

We have a 03 Denali w/ AWD and I am considering trading the truck in for a Sierra Denail, but I like going on the beach with it alot, so I was thinking I'd be better of with something else that is a 4X4? This article makes me question whether AWD would do as well as 4 wheel drive would offroad.

Any input to this?