[kjg48359]

The following is a little information in hopes that it might increase understanding of how the AWD function in the vehicles work. This is not intended to be used for problem diagnosis or repair, but mainly as an interest in some high level system components and functioning. Replacement or maintenance on this system should only be performed by qualified personnel and in some cases may need reprogramming which can only occur with dealer specific diagnostic equipment.

Summary
The center mechanism is referred to as a "Power Transfer Unit", and it connects engine output to the rear axle. From there, the rear differential contains a computer controlled clutch mechanism. The last part of the system is a traction control system which will help to route power to a wheel that has traction if slippage occurs.

Details

Front mechanism:

The power transfer unit (PTU) is positioned in the right side of the vehicle and bolted to the transmission via an adapter plate. The primary function of the PTU is to receive power from the transmission and transfer it using helical and hypoid gear sets through the propeller shaft to the rear differential.

Rear Mechanisms:

The rear differential clutch control modules function is to control the electronic open differential. The rear differential control module calculates torque command internally according to the driving situation to achieve vehicle dynamics and traction. The electronic differential system contains the following main components:

• The rear differential clutch control module
• The rear differential clutch motor
• The rear differential multi-disc wet clutches

When the torque signal is received, the rear differential control module actuates the following components:

• The rear differential clutch motor

Controlling Mechanisms:

All of this is all controlled through inputs such as wheel speed sensors, transmission and engine information and even steering wheel angles through multiple control models:

From the owner's manual the following is found on page 203:

The AWD system delivers power to all four wheels and the system adjusts as needed to improve traction.

For a preview of the system in action, the following uTube video does a fairly good representation:

This is quite technical but should help us feel comfortable that this is a system that appears to be on par with most systems on the market.

 

[ZR2LIFE]

Good information however the Trailblazer doesn't use a system like this. Our AWD system is very basic and doesn't have clutches in the differentials. In AWD you only get power to 1 front wheel and 1 rear wheel due to the open front and rear differentials.

 

[kjg48359]

the Trailblazer doesn't use a system like this.

This is in fact the actual TB system, not a general reference. The clutches in the rear are how the system prevents the torque windup that one finds with traditional part-time conventional 4WD systems. Otherwise it would not be a daily derivable system.

If one is interested in reading more about drive systems in general, Patrick Rich posted a fairly good article on Jolopnik at How All-Wheel Drive Works: A Ridiculously Detailed Technical Explainer. For a general drivable system, there must be way to handle the speed differences between the front and rear axles in a vehicle on traction surface, and he has this explained and referenced in another video on his article for "AWD Scrub" or what he calles "crow hop." The PTU in the Trailblazer does not handle this function.

 

[ZR2LIFE]

You are posting general AWD information that isn't from the new Trailblazer. We don't have clutches in the differentials, they're open. Every review out there is quick to point out how basic our AWD system is and how easily you can get stuck since it has open differentials. To combat wheel spin TC applies brake pressure to the spinning wheels in order to gain traction with the other wheels.

 

[ZR2LIFE]

I think you might be confusing the Trailblazer with the Blazer. The 2021 Blazer RS does have an AWD system that's similar to the information you posted.

From GM Authority regarding the AWD system available on the 2021 Blazer RS.

"While the “regular” F48 All-Wheel Drive system enhances traction considerably over the standard FWD setup, the G99 Advanced Twin-Clutch All-Wheel Drive System takes it a step further, independently controlling torque at each rear wheel, and thus providing even greater control and less braking intervention. The G99 Advanced Twin-Clutch All-Wheel Drive System is equipped with an automatic locking rear differential, and will accurately apply torque between the left and right rear wheels, as needed".

 

[brownactive]

In that video why are the lights flickering so oddly? I still get a little pained that these have AWD badges slapped on them when they indeed are not.

 

[ZR2LIFE]

I wish we had the upgraded system that's available on the Blazer or Traverse. In that setup you will have at least 3 wheel drive while in AWD and it can control front/rear power bias plus control right and left power output on the rear axle. The only thing missing at that point would be clutch driven front differential, then you'd have true AWD/4WD.

 

[Canada03ZR2]

In that video why are the lights flickering so oddly? I still get a little pained that these have AWD badges slapped on them when they indeed are not.

All LEDs flicker, our eyes just cant detect it. When the flicker is close to the shutter speed of the camera this funny thing happens. If you were to go take a video of your TB with the daytime running lights on it would probably look similar.

 

[Quaid]

This is in fact the actual TB system, not a general reference.

@kjg48359
Great write-up! Thank you for this contribution to the community.

What is your source for the exact details of the 2021 Trailblazer AWD system? I haven't been able to find this level of detail (yet), and I'm sure that it will clear up any confusion if you explain where your information comes from.

 

[kjg48359]

@kjg48359
Great write-up! Thank you for this contribution to the community.

What is your source for the exact details of the 2021 Trailblazer AWD system?

You're welcome Quaid. This is from the GM service manual that the dealerships should have access to. From what I understand, it is in the process of being released to 3rd parties but I am not sure of what the time frame is. I am an employee (and a new owner, so for me, learning and enjoying the vehicle I hope should be as exciting for myself as it is for everyone else!).

 

[Milk Man2828]

Taken from GM's notice to the NTSB for the creation of the Buick Encore GX 20-NA-032 (The Trailblazer made to look nice for old folks as far as I know), presented without comment:

Differentials
The AWD system has a driver-selectable disconnect and has a single-clutch rear drive unit. The rear drive unit design allows for independent and balanced torque distribution between the front and rear wheels in an up to 50-50 split under certain driving conditions. The rear drive axle has an extended torque tube that allows a shorter 2-piece driveshaft.

 

[thecrowtv]

Taken from GM's notice to the NTSB for the creation of the Buick Encore GX 20-NA-032 (The Trailblazer made to look nice for old folks as far as I know), presented without comment:

I looked at the Encore for about 10 seconds and realized if I bought a Buick I'd age 20 years instantly

 

[Trail Blazed]

I looked at the Encore for about 10 seconds and realized if I bought a Buick I'd age 20 years instantly

😄

 

[dcbridgwater]

At least the Encore GX has the headlights in the proper place and contoured to the body instead of being too low and recessed. Who ever designed the Trailblazer headlights wasn't the brightest person in the world. I have never seen headlights like on the Trailblazer get covered with road salt to the point of almost being worthless so fast. I almost went with the Encore GX, probably would have if they offered something similar to our Active package. Well anyway after 9 months the only thing I have to complain about is the headlights, so that's not to bad I guess.

 

[ZR2LIFE]

This is intesting. I wonder why all the reviews from Car & Driver, Motor Trend, etc are quick to point out the open front and rear differentials and how easily the Trailblazer can get stuck? I know we share the AWD system with the Traverse and Blazer, but it's supposed to be the basic AWD not the upgraded system. Anybody want to pull their rear diff apart and investigate? 🤣

 

[kjg48359]

This is intesting. I wonder why all the reviews from Car & Driver, Motor Trend, etc are quick to point out the open front and rear differentials and how easily the Trailblazer can get stuck? I know we share the AWD system with the Traverse and Blazer, but it's supposed to be the basic AWD not the upgraded system. Anybody want to pull their rear diff apart and investigate? 🤣

I've only seen some service documentation, but there are clutch packs that are hydraulic and controlled by a subsystem inside the unit. For normal service there is a fill/drain plug to allow the regular differential oil to be replaced, But if the disc packs have an issue, there is a separate sub-system that once you open that there is a more complicated bleeding process for the hydraulic fluid that is controlled by the GM service equipment that operates directly on the unit.

I think probably one of the bigger limitations is really the suspension. I don't think there are many vehicles are really have suspension articulation and ability to equalize tire pressure on uneven ground. Since this based on a car, it will have those limitations as well.

 

[ZR2LIFE]

View attachment 537

Just some pics I took on my last oil change. The diagram does look the same as the pictures.

 

[Vizman56]

😄

😂