Rainier AWD tech resource? [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: Rainier AWD tech resource?


JD and Beastlet
02-15-2008, 04:15 PM
Gentle People,

We're consider an '04 Buick Rainier with AWD. I haven't had much luck learning about the specifics of the AWD system and was hoping someone had come across a reference.

Thanks,

John.

ScarabEpic22
02-15-2008, 04:23 PM
There are a couple thread regarding the Bravy/Rainier AWD system, but here's the lowdown: its basically putting a TB/Voy into A4WD mode all the time. This is why they dont get as great of gas mileage, I get at least 1-1.5mpg better at 55-60 in 2HI vs A4WD (but usually its going up a pass where Id much rather be safe than sorry). There are some hardware changes, for example the front diff is not disengagable, it is always connected and a few other small things.

2001FZ1
02-15-2008, 09:05 PM
I have only had mine for a few months but we really like it. The Rainier rides much smoother than a TB or Envoy ~ it rides like a Buick should. They are also quieter on the highway.

The local mechanic told me to keep on top of the maintenance and the AWD system should be problem free for a long time ~ Change the fluids in both differential, transfer case and transmission every 40-50k miles.

The only thing I don't like about the AWD is that the front wheels take a second to engage when the rear are slipping in the snow. its kinda herky jerky if you know what I mean.

Bottom Line:
Buick is tied for #1 in reliability so they are hard to beat!
http://www.eagleherald.com/baut0810.asp

RayVoy
02-15-2008, 09:20 PM
John, to be honest, the Buick and olds trucks don't have a true AWD transfer case.
A "real" AWD system uses a continually engaged transfer case with the ability to adjust (read vary) the power being sent to the front differential. When the rear wheels are under a low traction situation, only required power is sent to the front. In other words, power sent to the front can vary from 0% through to 50%.
The Buick/Olds trucks have a 4x4 transfer case with some of the parts removed. These cases have an internal clutch pac and when the front wheels need power, the clutches operate. These cases can not vary the power, only provide 0 power (no slip) or full power (which is 50% because the other 50% goes to rear wheels).
Hope this helps

JD and Beastlet
02-16-2008, 09:58 AM
It's important for me to be as informed as possible in order to make the right decision. So...

I'm putting pieces of the puzzle together, but the pieces have come from all over. I'm going to summarize what I think I know, and I'll ask for you to let me know if I'm on the right track.

RWD (TB / Envoy)
The transmssion sends all torque to the rear via the transfer case. There's an open differential at the rear that cannot be locked, so if one rear wheel loses traction, the other won't get any traction either.

4HI (TB / Envoy)
The transmission splits torque 50/50 between the front and rear, and the front wheel hubs are locked automatically. Although the differentials are open the transfer case is locked, so the front and rear pairs of wheels are always travelling at constant speed relative to each other. This is why 4x4 shouldn't be used on dry pavement - it causes the front tires to scrub during turns. If front and rear tires on one side lose traction, the corresponding front and rear wheels on the other side won't get any traction either.

4LO (TB / Envoy)
Just like 4HI, but a reduction gear in the transfer case raises the torque while lowering the speed.

A4WD (TB / Envoy)
Like 4HI except it engages and disengages automatically rather than with the flip of a switch. When the transfer case detects slippage in the rear wheels it engages the front wheels (a) via clutches in the transfer case and (b) by automatically locking the front hubs. Same limitations with loss of traction on one side of the vehicle.

I suspect it would cause the tires to scrub if it stayed engaged on a turn in dry pavement, but I also suspect the system would sense a return of traction to the rear wheels and automatically disengage the clutches and hubs.

Neutral (TB / Envoy)
The transfer case can be put in neutral.

- - - - -

AWD (Rainier / Bravada)
Very much like A4WD, but with two important differences. It's the only mode for the transfer case and cannot therefore be disengaged, and the auto-locking rear differential engages when the driving rear wheel slips, providing torque to the other rear wheel.


There we have it. Fire away!

:crazy:

ScarabEpic22
02-16-2008, 08:41 PM
G80 is available on all GMT360s (think the Rainier and 9-7X have it std though) and is the locking rear, so for me in 2HI and the left wheel slips the rear diff locks (no locking front diffs for anyone) and I pull out of it.

4HI is a 50/50 split of power

4LO is 50/50 but with the the lowest ratio (I think its 2.7:1).

A4WD the front diff is engaged with 5% power sent to it, when the rear slips TQ is transferred via clutch packs just enough to give the rear end traction again then the clutches disengage and go back to just 5% sent forward. While the TQ is being xferred there is a delay because the clutches have to engage. No one has locking front hubs.

2HI is 100% to rear wheels

RayVoy
02-16-2008, 09:05 PM
It's important for me to be as informed as possible in order to make the right decision. So...

I'm putting pieces of the puzzle together, but the pieces have come from all over. I'm going to summarize what I think I know, and I'll ask for you to let me know if I'm on the right track.

RWD (TB / Envoy)
The transmssion sends all torque to the rear via the transfer case. There's an open differential at the rear that cannot be locked, so if one rear wheel loses traction, the other won't get any traction either.

4HI (TB / Envoy)
The transmission splits torque 50/50 between the front and rear, and the front wheel hubs are locked automatically. Although the differentials are open the transfer case is locked, so the front and rear pairs of wheels are always travelling at constant speed relative to each other. This is why 4x4 shouldn't be used on dry pavement - it causes the front tires to scrub during turns. If front and rear tires on one side lose traction, the corresponding front and rear wheels on the other side won't get any traction either.

4LO (TB / Envoy)
Just like 4HI, but a reduction gear in the transfer case raises the torque while lowering the speed.

A4WD (TB / Envoy)
Like 4HI except it engages and disengages automatically rather than with the flip of a switch. When the transfer case detects slippage in the rear wheels it engages the front wheels (a) via clutches in the transfer case and (b) by automatically locking the front hubs. Same limitations with loss of traction on one side of the vehicle.

I suspect it would cause the tires to scrub if it stayed engaged on a turn in dry pavement, but I also suspect the system would sense a return of traction to the rear wheels and automatically disengage the clutches and hubs.

Neutral (TB / Envoy)
The transfer case can be put in neutral.

- - - - -

AWD (Rainier / Bravada)
Very much like A4WD, but with two important differences. It's the only mode for the transfer case and cannot therefore be disengaged, and the auto-locking rear differential engages when the driving rear wheel slips, providing torque to the other rear wheel.


There we have it. Fire away!

:crazy:Looks like u've done a lot of reading, the truck (whichever u decide) will be in good hands :yes: