GM Truck Club
THE PREMIER CHEVY TRUCK & SUV FORUM
Founded in 2004 ~ We're the #1 Chevy Truck & SUV Forum.
Silverado & Sierra | Tahoe & Yukon | Suburban & Yukon XL | SUV & CROSSOVER
Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 24

Thread: 4WD or AWD?

  1. #11

    Default

    Same but different, I know I sound confusing.
    All 4 wheels are turning all the time, but the front wheels are only getting 35% of the power and the rear are getting 65%.
    This Transfercase is designed to allow for more slippage in the front wheels and it can even handle different speeds from front to rear.
    Not sure of your experience with a normal 4wd, if you've ever popped one in 4wd, hi or low, on dry pavement or soil with good traction you immediatly feel the steering wheel shuffling, hear popping and groaning from the running gear, and steering feels weird when turning, this case is designed to allow tire slippage so you dont get those signs all you get is traction.
    It automatically adjusts tire speed to what is needed to keep in pace with whats happening with the other tires, if the right front needs to slip a little and the left front needs to go gaster the T case speeds up the left front tire (basically the clutchs inside allow less slipage and more power to get through) and the right front freewheels through the front diff (which is designed slightly different than a standard 4wd front diff).
    I wont say its a superior system over a standard 4wd but for the driver that doesnt know when to switch to 4wd and really does need it for added traction this system is a great compromise, it allows the driver to run in 4wd (technically) and not worry about differing traction, where in a standard 4wd you wont keep the front diff and T case alive long if you keep running on pavement.
    A standard 4wd's strong suit is it puts more power to the front wheels to pull equally while the rear is pushing.
    If you've ever watched rally car drivers powering through corners or mud boggers running a hole AWD helps them steer through low traction situations by pulling when it gets any small amount of grip but also spinning and steering the wheels through spots that they would normally stop turning and just push through. This makes a big difference in what direction the vehicle continues to go, if its pushing snd slipping it'll continue to go in the direction momentum is taking it, if its actually being steered it'll take a different direction.
    For your purposes this may be a good choice of a vehicle because it's no worries of whether to lock in or not, it's basically an automatic T case.
    The only time you'd ever need low is when you actually get stuck or have very little traction, at these times the power bias changes closer to 50/50 (not sure what the exact bias is in low) and the gearing for front and rear get real low. You'd never want to attempt much over 20-25 mph in low and probably want to switch back to high when traction gets better.

  2. #12

    Default

    Thanks. That's what I was looking for. I know my dad had a Hyundai Sante Fe with AWD and hated it....said it was worse that FWD...I assumed that a Tahoe would be quite a bit different, but just wanted to make sure. I'm sure all vehicles with AWD handle differently. Thanks again!

  3. #13
    Sr. Apprentice
    Join Date
    Nov 2008
    Location
    Endicott, NY
    Posts
    65

    Default

    I currently own an AWD 2003 Tahoe that I bought brand new in Dec. 2012. There are a couple of things different than a standard 4 wheel drive vehicle that was delivered that year. First, a limited slip differential was not available; Two, Traction Control (front and rear) is standard and used to limit wheel spin due to the lack of a posi; Three, Stability control was also standard on the vehicle.

    Here is a description of the transfer case used in the vehicle. Sorry, but the pictures didn't copy.
    Transfer Case Description and Operation
    The Borg Warner (BW) model 4482 NR4 transfer case is a two-speed, full time 4WD, transfer case. The transfer case has an external planetary type differential, which has two different sets of pinion gears. The planetary differential provides a 40/60 torque split front/rear full time. This means the front and rear propeller shafts are constantly being driven for maximum traction in all conditions.

    While in the 4HI mode, the transfer case external type planetary differential functions the same as a typical rear axle differential. The transfer case differential pinion gears function as the spider gears, and the sun gears function as the side gears.

    The following actions occur because of the planetary differential:

    • If the vehicle is on a hoist, and in the 4HI mode, the front propeller shaft can be rotated by hand.

    • The vehicle cannot be driven in the 4HI mode if one propeller shaft is removed.

    • Operating the vehicle on the hoist, in the 4HI mode, can damage the differential pinion gears, by over-spinning.

    • Operating the vehicle with one propeller shaft removed, in the 4HI mode, causes over-spinning of the differential pinion gears.

    The BW 4482 design of the planetary differential allows use with the Vehicle Stability Enhancement System (VSES) vehicles. The VSES takes use of the planetary differential, by applying braking to a tire that has less traction and dividing the engine torque to the other axle. A high/low planetary carrier assembly provides the high and low ranges, which is a 4-pinion gear, sun gear, and annulus gear arrangement, giving a 2.64 low range reduction ratio.

    The BW 4482 case halves are high-pressure die-cast magnesium. Ball bearings support the input shaft, the front output shaft, and the rear output shaft. A needle roller bearing is located inside of the input shaft gear to support the front of the mainshaft. The rear of the mainshaft is supported by a bronze bearing inside the rear output shaft. The transfer case requires DEXRON®III ATF Fluid GM P/N 12378470 (Canadian P/N 10952622), which is red in color. An oil pump pumps the fluid through the mainshaft oil gallery to the gears and bearings.

    Transfer Case Shift Control Switch

    The BW 4482 transfer case features a 3-button shift control switch located on the instrument panel. When the vehicle has the ignition key in the RUN position, the transfer case shift control module starts monitoring the transfer case shift control switch to determine if the driver desires a new mode/range position. At a single press of the transfer case shift control switch, the lamp of the new desired position will begin flashing to inform the driver that the transfer case shift control module has received the request for a new mode/range position. The lamp will continue to flash until all shifting criteria have been met and the new mode/range position has been reached, or has been engaged. Once the new mode/range position is fully active, the switch indicator lamp for the new position will remain ON constantly. In addition, the switch includes a VSES request button which sends a voltage signal to the transfer case shift control module. The transfer case shift control module in turn sends a request via the class 2 data bus to the ABS control module which controls the VSES system.

    During normal driving situations, the transfer case operates in the 4HI mode. When the 4HI mode is selected, the transfer case shift control module sends 12 volts to an electrical motor, which is the transfer case encoder motor. This motor rotates the transfer case shift detent lever shaft which moves the shift forks and range sleeve to obtain different modes/ranges.

    The BW 4482 transfer case has the added feature of also providing the driver with 2 selectable mode/range positions and a VSES request button:
    • 4HI - Full Time 4 Wheel Drive
    • 4LO - 4 Wheel Drive Low Locked
    • VSES - Vehicle Stability Enhancement System

    The transfer case will not allow a shift into or out of 4LO unless the following criteria has been met:
    • The engine is running.
    • The automatic transmission is in Neutral.
    • The vehicle speed is below 5 km/h (3 mph).

    This transfer case also has a Neutral position. A shift to the Neutral position allows the vehicle to be towed without the transmission output shaft rotating. Refer to the Owners Manual for instructions for proper towing of the vehicle.

    Neutral position may be obtained only if the following criteria have been met:
    • The ignition switch is ON.
    • The automatic transmission is in Neutral.
    • The vehicle speed is below 5 km/h (3 mph).
    • The transfer case is in the 4HI mode.

    Once these conditions have been met, press and hold both the VSES and 4LO Lock buttons for 10 seconds. When the system completes the shift to neutral, the red neutral indicator will illuminate.

    4HI Mode Power Flow

    When the BW 4482 is in 4HI mode, the engine power flows from the transmission to the input shaft (1). The input shaft (1) is connected to the mainshaft (3) by the high/low range sleeve (2). The high/low range sleeve (2) outer teeth are engaged with the input shaft (1) high-speed teeth. The range collar is slip splined to the mainshaft (3). The mainshaft (3) delivers the power flow to the planetary differential (6), which splits the torque 40 percent through the front differential pinion gears (5) to the front sun gear (10). The torque to the front axle then goes through the drive sprocket (4), via the chain (11) to the front output shaft (12) and to the front axle. The differential planetary splits the torque 60 percent to differential rear pinion gears (9) and rear sun gear (7). The rear sun gear is connected to the rear output shaft (8) and the torque flows to the rear axle.

    4LO Lock Mode Power Flow

    When shifting the transfer case to the 4LO Lock mode, it commands the encoder motor (12) to turn the shift detent lever shaft (13), to rotate the shift detent lever cam (16). There are two cam profiles on the shift detent lever cam (16) functioning at the same time. The range profile on the shift detent lever cam (16) moves the high/range shift fork (18) and the high/low range sleeve (4) rearward to the 4LO range position.

    The mode profile on the shift detent lever cam (16) moves the mode shift fork (17) rearward along with the mode shift collar (6).

    The high/low range sleeve (4) outer teeth disengage from the input shaft (1) high-speed teeth. The high/low range sleeve (4) outer teeth then engage in the high/low planetary carrier teeth (19). The power flow is now from planetary teeth on the input shaft (1) to the planetary gears (2) in the carrier. Rotating the planetary gears, which are engaged in the annulus gear (3), rotates the planetary carrier. The planetary carrier delivers the power to the high/low range sleeve (4). The high/low range sleeve (4) then drives the mainshaft (5), providing a 2.64:1 reduction to the speed of the mainshaft (5).

    The mode shift collar (6) locks the mainshaft (5) to the drive sprocket (7). Torque is sent by the chain (14) to the front output shaft (15) and to the front axle.

    The rear propeller shaft power flow is delivered by the case of the planetary carrier (8) being splined to the mainshaft (5). The power flows from the planetary carrier case to the rear pinion gears (11), to the rear sun gear (9), and to the rear output shaft (10).

    The torque distribution in this mode is now determined by vehicle dynamic conditions and weight distribution. The planetary differential (8) is not operating, and both the front and rear propeller shafts are being driven at equal RPMs, therefore giving a 4 low lock mode. This mode should only be used for extra traction during off road use. Using this mode on dry pavement will cause tire scuffing.

    Neutral Mode Power Flow
    Shifting to the neutral position, the high/low range sleeve is centered between the input shaft and the high/low planetary carrier. The high/low range sleeve is not engaged with either the input shaft or the high/low planetary carrier teeth. The planetary differential is in the 4HI mode.

    Transfer Case Electrical Components
    View the list of major electrical components that make up the full time four wheel drive transfer case (FT4WD) system below.

    Service 4WD Indicator
    The SERVICE 4WD indicator is an integral part of the cluster and cannot be serviced separately. This indicator is used to inform the driver of the vehicle of malfunctions within the FT4WD transfer case system. The SERVICE 4WD indicator is controlled by the transfer case shift control module via a Class 2 message.


    Bill

  4. #14
    Sr. Apprentice
    Join Date
    Nov 2008
    Location
    Endicott, NY
    Posts
    65

    Default

    Here is a GM Bulletin on the differences of the types of wheel drive systems:
    #01-04-18-001F: Driveline Characteristics for All-Wheel Drive (AWD) and Four-Wheel Drive (4WD) Systems - (Feb 4, 2008)
    Subject: Driveline Characteristics For All-Wheel Drive (AWD) and Four-Wheel Drive (4WD) Systems
    Models: 2008 and Prior GM Passenger Cars and Light Duty Trucks
    2008 and Prior HUMMER H2, H3
    2002-2008 Saturn VUE
    2005-2008 Saab 9-7X
    with Four-Wheel Drive (4WD) or All-Wheel Drive (AWD)
    DEFINITIONS
    AWD vs. 4WD
    The very basic difference between AWD and 4WD is the intended usage of the systems.

    AWD is usually intended for on-road use in inclement weather conditions, while operating smoothly on dry pavement by allowing for a difference in speed between the front and rear axles while turning. These systems are not selectable and do not have low range gearing for the transfer case. These systems can be found in cars or trucks.

    4WD is primarily found in trucks and can be broken down into Part-Time, Full-Time, and Automatic Transfer Cases. These selectable systems have modes intended for on-road use and other modes intended for off-road or low traction situation usage. All current GM 4WD systems have a low range available in the transfer case.

    CHARACTERISTICS
    Disclaimer: Even though a certain amount of noise or feel can be expected, GM may offer service procedures or components, or change vehicle design, which may reduce perceived noise levels in the interest of customer satisfaction.

    AWD
    There are two different categories of AWD systems. The first category is full-time AWD. This type of transfer case delivers torque to the front and rear axles at all times. This ratio can vary depending on the system, but is usually about a 30/70% front to rear split but also can vary depending on traction conditions, up to 100% front or rear. This type of transfer case can have a viscous coupling for low traction conditions along with a planetary gear set to allow for difference in speeds between the front and rear axle, or an open type of planetary gear set differential, which uses brake based traction control for low traction conditions. An example of a vehicle with an open differential/traction control type of transfer case is a 2003 Escalade. RPO codes for these types of transfer cases are NP3 (NVG 149, BW 4473 viscous clutch) and NR3 (BW 4476, 4481, 4485, open differential) or NR4/NR6 (BW 4493, 4494 open differential).

    The second category is an on-demand AWD. This type of AWD basically delivers torque only to a primary driving axle unless reduced traction is experienced. At that point, the system electronically or mechanically will apply torque to the other axle. Depending on the type of system, this can provide up to 100% of the torque to the axle with traction. These transfer cases use an electronically actuated clutch pack, a hydraulically actuated clutch pack, or a viscous coupling to allow for a difference in speed between the front and rear axles.

    PART-TIME 4WD
    Part time 4WD refers to vehicles equipped with a transfer case to split power between the front and rear axles of the vehicle. This traditionally is a 2-speed selectable transfer case that can be shifted into 2HI, 4HI, 4LO and usually a Neutral position. The 4WD modes of Part time systems do not allow for a difference in speed between the front and rear axles while turning. This system effectively locks the front and rear propeller shafts together. When turning, the tires must allow for the different turning radius of the front and rear axles, which is why this is intended for low traction or off-road use. These systems have low range gearing for the transfer case.

    FULL-TIME 4WD
    A second version of a 4WD transfer case is a full-time 4WD transfer case. This style of transfer case has an open center differential to allow for different speeds between the front and rear axles and operates similar to an AWD system. This transfer case can be locked to operate like a Part-Time 4WD transfer case (no difference between front and rear prop-shaft speeds) and/or uses a traction control system to assist in low traction situations. These transfer cases also have a selectable low range. An example of this type of 4WD is the H2. RPO code is NR4.

    The NR4 transfer case (available in non-luxury utilities) has no switch selection to lock into a part-time 4WD mode as described above. There are only 3 selections on the controls: Disable Stabilitrak, AWD and 4LO. The Owner's Manual describes this system as an AWD system.

    AUTOMATIC TRANSFER CASES
    The last category is a combination of 4WD and On Demand AWD. These transfer cases have a 2HI, Auto-4WD, 4HI, 4LO and Neutral position and would fall in the general 4WD category. This transfer case has the operating characteristics of both an On Demand AWD and a Part-Time 4WD system depending on the mode selected. This transfer case uses a clutch pack to allow for a difference in speed between the front and rear axles in the Auto-4WD mode. In the 4HI or 4LO modes, there is no allowance for the difference in speed between the front and rear axles.

    4WD
    While operating 4WD vehicles in the 2HI mode, they should perform similarly to an equivalent 2WD version of the vehicle. However there are still additional components on the vehicles and there may still be some slight differences in characteristics. Some Part-Time 4WD transfer cases may make a slight gear rattle type of noise when operated in 2HI at low engine speeds, similar to a manual transmission gear rattle type of noise. This can originate in the synchronizer assembly from engine harmonics. This noise will usually be reduced or eliminated while driving in a 4WD mode because the synchronizer assembly clearances will be taken up once engaged in 4WD. Operating the engine at a slightly higher rpm should reduce this noise.

    While a vehicle is traveling down the road, the tires rotate a certain number of times per mile depending on the true tire radius. If all the tires do not have the exact same true radius (due to load, tire pressure, wear, build variances...), they will turn at slightly different rates. Also, unless the vehicle is traveling in a perfectly straight line, the front and rear axles are traveling in a slightly different arc, which means the front and rear axles are traveling at slightly different average speeds.

    These systems either do not have a center differential or it has been bypassed (when used in 4HI or 4LO in Part-Time or Automatic systems, or 4HI Lock or 4LO Lock on Full-time 4WD), so the front and the rear propeller shafts will turn at the same speed, which leads to the front, and rear axles rotating at the same average speed. Using the 4WD modes (4HI, 4LO, 4HI Lock, 4LO Lock) will usually increase noise in the axles, transfer case and the rest of the driveline and is usually greater at higher speeds and will usually increase the more the vehicle is turned. As the vehicle turns, the front and rear axles follow a different arc. When this occurs, the only place to compensate for this binding is between the contact patch of the tires and the ground. This can feel like the vehicle is vibrating, crow hopping or grabbing. Even if the vehicle is driven in a straight line, there are slight differences in tire circumference that will cause some driveline binding. If a vehicle had the exact same size tires and was driven in a perfectly straight line, the fact that more parts are moving would mean that there would be more noise and possibly some feel of the system operating.

    Use of 4HI or 4LO and 4HI Lock or 4LO Lock on Full-time 4WD is intended for use on a low traction surface such as snow, ice, mud or sand. On a low traction surface, the differences in front and rear axle speeds will not have as much effect on binding because of the lower traction levels between the surface and the contact patch of the tires. On a high traction surface, the higher traction levels will create more binding and noise in the driveline.

    As a result, a small amount of noise or feel of the system operating can be expected when using 4HI or 4LO in Part-Time or Automatic systems, or 4HI Lock or 4LO Lock on Full-time 4WD. The noise and feel can vary depending on the transfer case type, GVW ratings (generally the higher the GVW the more noise it will make), vehicle build variations, gear ratios in the axles, axle type, tires, and importantly driving conditions.

    AWD
    AWD systems are intended for use in high and low traction situations without operator input. These systems will generally be quieter on high traction surfaces than a similar 4WD used in 4HI or 4LO. However, these systems will generally make more noise than a similar 2WD vehicle simply because there are more parts rotating and more gear sets interfacing. Once again, these systems may make more noise in turns, and in some situations you may be able to feel the system operating, even on high traction surfaces. Additionally, you may feel transfer case operation in on-demand AWD systems. These systems generally react to a speed difference between the front and rear axle and it may be possible to detect this by hearing a noise, or actually feeling the engagement of the system.

    Bill

  5. #15
    Master Mechanic Jimmeh's Avatar
    Join Date
    Apr 2009
    Location
    Columbia Falls, Montana, United States
    Posts
    806
    Blog Entries
    3

    Default

    Quote Originally Posted by BillD64 View Post
    I currently own an AWD 2003 Tahoe that I bought brand new in Dec. 2012.
    I read the whole thread post, and I had to think more about this than anything else in the post. Totally mind blowing!
    2005 Chevy Silverado W/T
    4X4|4.8 with some mods (has only slightly more pull than a 5.3)|Auto|4 door ex cab|Cooper Discoverer AT/3's in 285-75/17's on Helo 842's|Cooper Discover M+S 265-75/17's on Devino DV349's|Flowmaster 40 Single in Dual out with custom bent pipe from the end of the cats back|2" Procomp leveling kit|Custom made center console|Custom dyno tunes|Air Raid CAI|Air Raid Throttle Body Spacer|Apex brand topper|Kenwood Head Unit with Kenwood speakers|Painted mirrors/grille|Debadged except front emblem|Bilsteins front and rear
    Planned mods not in order
    2 inch lift|Custom front/rear bumper|hitch tire carrier|roof basket on topper, bars on cab|finish center console build|install Midland CB|Power options|Tint|Custom made raised bed in the bed of the truck|Lund LunarVisor
    Also have a 1992 Ford Ranger with a lot of stuff done to it. Currently waiting for a bit of a rebuild.


    "The only woman I'm pimping from now on is Sweet Lady Propane. And I'm tricking her out all over this town."

  6. #16

    Default

    there is usually the auto on the top of the four buttons then 2wd then 4hi an then 4lo. i havent ever seen a 2wd/4wd/awd actuator or heard of a transfer case like that either so its probably just 4hi

  7. #17
    Sr. Apprentice
    Join Date
    Nov 2008
    Location
    Endicott, NY
    Posts
    65

    Default

    Quote Originally Posted by Jimmeh View Post
    I read the whole thread post, and I had to think more about this than anything else in the post. Totally mind blowing!
    Yep, just turned over 9 years and 84.5K miles. Since I retired 6 years ago the mileage on this vehicle has dropped to about 6K a year. I use it to tow the Corvette to the track and in the winter. Have 4 Bridgestone Blizzaks that I run on it for the winter. With those it is fantastic in the snow.

    Bill

  8. #18
    Sr. Apprentice
    Join Date
    Nov 2008
    Location
    Endicott, NY
    Posts
    65

    Default

    Quote Originally Posted by pantydropper View Post
    there is usually the auto on the top of the four buttons then 2wd then 4hi an then 4lo. i havent ever seen a 2wd/4wd/awd actuator or heard of a transfer case like that either so its probably just 4hi
    Here is a picture of the drive control buttons on my Tahoe. This is the same system that was standard in the Escalade. Not a lot of Tahoes were sold with the option.



    Top button is for turning off Stabilitrak. The system normally runs in 4 Hi and you can switch it to 4 Lo if you need to go slow or have some real grunt. 4 Lo also turns off the Stabilitrak.

    Bill

  9. #19
    Master Mechanic Jimmeh's Avatar
    Join Date
    Apr 2009
    Location
    Columbia Falls, Montana, United States
    Posts
    806
    Blog Entries
    3

    Default

    Quote Originally Posted by BillD64 View Post
    Yep, just turned over 9 years and 84.5K miles. Since I retired 6 years ago the mileage on this vehicle has dropped to about 6K a year. I use it to tow the Corvette to the track and in the winter. Have 4 Bridgestone Blizzaks that I run on it for the winter. With those it is fantastic in the snow.

    Bill
    You said you bought a brand new 2003 Tahoe in December of 2012.... That is what was mind boggling, lol.
    2005 Chevy Silverado W/T
    4X4|4.8 with some mods (has only slightly more pull than a 5.3)|Auto|4 door ex cab|Cooper Discoverer AT/3's in 285-75/17's on Helo 842's|Cooper Discover M+S 265-75/17's on Devino DV349's|Flowmaster 40 Single in Dual out with custom bent pipe from the end of the cats back|2" Procomp leveling kit|Custom made center console|Custom dyno tunes|Air Raid CAI|Air Raid Throttle Body Spacer|Apex brand topper|Kenwood Head Unit with Kenwood speakers|Painted mirrors/grille|Debadged except front emblem|Bilsteins front and rear
    Planned mods not in order
    2 inch lift|Custom front/rear bumper|hitch tire carrier|roof basket on topper, bars on cab|finish center console build|install Midland CB|Power options|Tint|Custom made raised bed in the bed of the truck|Lund LunarVisor
    Also have a 1992 Ford Ranger with a lot of stuff done to it. Currently waiting for a bit of a rebuild.


    "The only woman I'm pimping from now on is Sweet Lady Propane. And I'm tricking her out all over this town."

  10. #20
    Sr. Apprentice
    Join Date
    Nov 2008
    Location
    Endicott, NY
    Posts
    65

    Default

    Quote Originally Posted by Jimmeh View Post
    You said you bought a brand new 2003 Tahoe in December of 2012.... That is what was mind boggling, lol.
    Didn't even notice. I guess that would be mind blowing. Something from Star Trek, exceed Warp 9 go into the future and then come back. I meant Dec.2002.

    Bill

Page 2 of 3 FirstFirst 123 LastLast

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •