GM Truck Club Forum banner

21 - 37 of 37 Posts

·
Registered
Joined
·
419 Posts
That's on an 03 Tahoe? Had no idea any such thing existed and I thought I knew these trucks. I thought there were only two t-cases. Escalade and Denali with full time AWD, and the Auto AWD/2Hi/4Hi/4Lo. Learn something new every year!

Edit: my Expedition has full time 4wd with low range, but I never knew GM did this since the old full-time 4x4 on the square bodies. Thought that style went away with the 400s.
 

·
Registered
Joined
·
1,317 Posts
I haven't had the chance to really try out my AWD ESV in the snow yet since I have only had it since August, but I'm watching the snow fall outside the window of my office right now with the prediction of 5" by the time I go home so I'll get to really give it a workout. I can tell you it will absolutely not spin any wheel on gravel. And the comment about the lousy MPG is a load of BS too. I'm getting 20+ on a nice long highway trip. I average 16.5 with my mixed city/highway/mountain pass driving. When I tow my 4K lb trailer I am right at 14, and that's throughout the western U.S. mountains. I thought I would miss low range but I don't. If I need low range I'll use the old work truck.
 

·
Registered
Joined
·
655 Posts
When AWD started a few decades ago when manufactures started to add them the passenger cars, I always understood what the video shows. Some cars it might be the front wheels that are primary and when the primary starts to slip, the other axle gets power. Since only one axle is powered most of the time it saves on gas and it's a no brainer for most customers. Get four wheel traction and not have to think about it.
 

·
Registered
Joined
·
110 Posts
That's on an 03 Tahoe? Had no idea any such thing existed and I thought I knew these trucks. I thought there were only two t-cases. Escalade and Denali with full time AWD, and the Auto AWD/2Hi/4Hi/4Lo. Learn something new every year!

Edit: my Expedition has full time 4wd with low range, but I never knew GM did this since the old full-time 4x4 on the square bodies. Thought that style went away with the 400s.
I had a 99 Tahoe with the selectable Full Time 4WD which I usually left in 2WD mode even when driving in slippery stuff since with a limited slip diff there wasn't any need to engage 4WD.

The AWD option is different. You can't turn it off. AWD is on all the time just like it was on my Olds Bravada. The difference between the Bravada and the 03 Tahoe is the Bravada had a limited slip diff which meant you could keep going as long as one back wheel had traction. The 03 Tahoe has Stability Control and I am pretty sure they didn't know how to implement Stability Control for an AWD vehicle that had a limited slip diff at the time. Now they do.

AWD isn't a panacea. It has all of the worst characteristics of both front and rear wheel drive vehicles. When towing a heavy load around a curve while going up a hill I have had the transmission downshift and as soon as that happened the sudden torque surge to the front wheels caused them to understeer and the Tahoe moved from the right lane to the left lane. Same thing happens to FWD vehicles. Going around a curve on a slippery road it is easy to induce a 4 wheel drift as both the front will understeer and the rear will oversteer. That doesn't happen if the drive wheels are only front or rear. Stability control is very useful then as it applies a single brake or combinations of braking to keep the vehicle going the way I turn the steering wheel.

It doesn't save on gas as the front drive train is always rotating. In the old 4WD systems you could disconnect the hubs and the front drive train would stop rotating thus saving the drag on the vehicle.

Bill
 

·
Registered
Joined
·
135 Posts
Some years ago when I was searching for my truck, I had two options: Chevy or Escalade. I chose Chevy Tahoe 2004 because of its 4WD drive combined with AWD. I use AWD only on an icy road, no deep snow or mud. And I use 4WD or even 4WD Low in deep snow (especially when I tow somebody, which happens several times during the winter) or in mud. I definitely don’t use AWD in such conditions, because it’s weak. If you don’t have offroad conditions I would choose Escalade for more comfort. If you need a truck - Chevy is the choice.
 

·
Registered
Joined
·
1 Posts
For the record, I have had over 70 GM vehicles, mostly Gen 1 and 2 Blazers with a variety of axle, transmission and transfer case set ups, but currently have a 2008 Denali 6.2L AWD with Limited Slip in the rear, a 2001 Silverado 3500 dually with electronic shift 4WD and a 1975 4WD K5 Blazer with a 90 Suburban drive train (700r4/208TC).

The Denali is a wonderful vehicle, very capable, sticks to and powers through the curves likes its on rails thanks to the AWD. But it would and does poorly in any serious off road situation for a variety of reasons including the fact that there is no low range and the transfer case and axles are designed to provide both traction and slippage on paved roads, not off road. It does not wear out tires any faster than any other vehicle and averages 14mpg with the 6spd auto, a trade off for improved traction and stability on wet and slick roads.
 

·
Registered
Joined
·
329 Posts
I remember going from a 93 with 4wd controlled by floor lever to the 96 push button 4wd. I thought that was a pretty awesome step up. But there were days when I would have to debate on using 2H or 4H because of mixed road conditions. Now I own an 02 with auto 4wd, as well as 2h, 4h, 4l, and appreciate the option of auto 4wd for mixed conditions. But I would not give up my 4H or 4L for auto 4wd, especially for really bad snow or towing.
 

·
Registered
Joined
·
419 Posts
Janet, don't use the Auto 4wd! The clutch pack used for that mode is underdesigned and will overheat and burn up. It was a shitty, shitty design by GM.

As for that floor lever in the 400 trucks, it wasn't connected to the transfer case like older trucks. It was still electrically operated just like the pushbuttons but GM thought macho truck guys needed a lever. My 92 Bronco was pushbutton.
 

·
Registered
Joined
·
329 Posts
I don't know anything about the autotrac t-case design and faults, but I definitely don't want to do anything to hurt my new truck! I stopped by my local GM dealer last week to talk to head mechanic about new (to me) features on my truck and normal operating temps/pressure level for monitoring gauges. We talked about the auto 4wd and the mechanic never mentioned concerns about using it. He believed the autotrac is a great feature for our area, and can be activated when driving on freeway (up to 75mph), but to not leave it in auto 4wd, because it eats gas. He also warned to never engage it if tires are already slipping, as that can create a problem. But if there is a risk of a major component failure by simply engaging auto 4wd, then I can avoid using it.

Figures about the floor lever. What a PITA design.
 

·
Registered
Joined
·
12,469 Posts
@blackburb , I'm respectfully replying to a former post, in that I see 2 errors in that post.
I want to state up front that I am not at transfer case expert.
However, it is my knowledge that the 400 trucks used a NP261 transfer case when optioned with a manual shift t-case.
The NP261 does not use an electric shift mechanism, to the best of my knowledge it is shifted by linkage between the shift lever and the shift fork.

And, the trucks with the push buttons that have an electric shift mech, and an AWD selection.

For all intents and purposes, these trucks use the same transfer case as the AWD drive trucks.

The clutch pack is the same clutch pack in both transfer cases.

The clutch pack engages in the same manner in both transfer cases.

I don't believe one will burn up any faster that the other.
 

·
Registered
Joined
·
2,443 Posts
You’re spot on, Ray. The lever engages a switch inside the transfer case that operates the thermal actuator in the front differential. Said actuator engages the shifting fork in the diff to lock in the front axles.

The t-case shifting happens via the lever.
 

·
Registered
Joined
·
419 Posts
You’re spot on, Ray. The lever engages a switch inside the transfer case that operates the thermal actuator in the front differential. Said actuator engages the shifting fork in the diff to lock in the front axles.

The t-case shifting happens via the lever.
Correct, a SWITCH and an ACTUATOR. The lever doesn't move stuff like the old days. It's electrical, and that thermal actuator in the front diff was so slow to engage that guys who were used to instant engagement from a mechanical linkage about blew a gasket leading to the aftermarket selling a new actuator that worked more quickly. It's my understanding the case is always in 4x4 in that the front prop shaft is always turning.

Ray, I have two long time (25 years for one, over 40 for the other) certified mechanics who are personal friends and both drive 800 series Chevy 4x4s that said explicitly NOT to use the Auto 4wd function on them because they will roast the clutches sooner rather than later. I'm not a total expert, but I don't believe it's the same clutch pack as the AWD cases. I could be wrong on that, but I will go with what these well respected mechanics told me.
 

·
Registered
Joined
·
419 Posts
Janet, no offense, but I would never take advice from the dealer. They always have ulterior motives ($)
 

·
Registered
Joined
·
329 Posts
No offense taken. I was merely information gathering from a variety of sources to gain general knowledge.

My understanding of chevy t-cases is limited. My first burb's t-case blew up before I began wrenching. I remember it was a $2,000+ job to rebuild case and install new actuator. Knock on wood the 4wd systems on my other chevys have never failed. My only first-hand working knowledge is on the most basic of systems ever made -- the 92 wrangler. We installed a t-case into our jeep after the original one grenaded, and can clearly visualize the outside lever to engage t-case. That system was simple, but I never want to tackle that job on my chevy trucks, if I can avoid it!

As for using auto 4wd, I will certainly look into concerns about the autotrac feature before using regularly.
 

·
Registered
Joined
·
162 Posts
@blackburb , I'm respectfully replying to a former post, in that I see 2 errors in that post.
I want to state up front that I am not at transfer case expert.
However, it is my knowledge that the 400 trucks used a NP261 transfer case when optioned with a manual shift t-case.
The NP261 does not use an electric shift mechanism, to the best of my knowledge it is shifted by linkage between the shift lever and the shift fork.

And, the trucks with the push buttons that have an electric shift mech, and an AWD selection.

For all intents and purposes, these trucks use the same transfer case as the AWD drive trucks.

The clutch pack is the same clutch pack in both transfer cases.

The clutch pack engages in the same manner in both transfer cases.

I don't believe one will burn up any faster that the other.
Pretty close. NP261SHD was available with the ZF6 manual transmission in the HDs. But all the research I did when I was looking for my truck said that was the only way to get one, and it’s not a true manual t-case. Engaged by vacuum. Manual T-case in the sense that you pull a lever with shift linkage stopped with the NP208 solid axles with locking hubs. Allison auto trans trucks got the NP263SHD (push button autotrac). Not sure about the 8.1 burbs and avalanches but I would assume it’s the same.

Janet I wouldn’t use the auto function for the simple fact that we have big blocks. If you hit a patch of black ice and it kicks in while your rear wheels are spinning up in the 2-3k RPM range, that NP263 is gonna grenade, or your front driveshaft is gonna look like a barbershop pole. Just make the call for 4wd while idling and stick with it.
 

·
Registered
Joined
·
1,317 Posts
I have had several opportunities over the past week, and several snow storms, to exercise the AWD on my Escalade. To include 3 1/2 hours of 45mph in steady snowfall, and pulling an old hood full of kids around town. I drove through so much heave wet snow it looked like I had custom ground effects the full length of my Escalade that were riding about 1/2 inch off the road. Not even enough space for one finger between the tire and the snow packed in the wheel well. This morning it was a mix between ice and 3 inches of slush covering the road. This thing handles like a 6000 lb dog sled! I attribute a good portion of that to the tires. They are fairly new and clean themselves out very well. I'm not even sure what they are, they were on it when I got it. I can't tell you the difference between the auto 4x4 on the AutoTrak T-case and this AWD T-case, but I can attest to the ability of this T-case. I grew up in northeast Wisconsin, use to be a courier/delivery driver all over the northern Midwest. I have driven tens of thousands of miles in winter conditions in everything from a crappy little Ford Escort station wagon, to a 4X4 diesel truck pulling a 30' box trailer. This AWD Escalade is the most comfortable, relaxing, stable vehicle I have driven on winter roads. It's definitely a keeper! I believe I may have settled on the second permanent vehicle for my driveway!
 
21 - 37 of 37 Posts
Top