In addition
to the engines, suspensions, transmissions, and other choices, GM also
added some cool technologies to the pickups. One we fell in love with
on the SUV is the Eaton G80 rear-locking differential. Under regular dry
pavement conditions, the system works like a regular open differential,
but, as soon as wheel slip occurs, either in forward or reverse, the system
immediately kicks in.
The way Eaton
describes the system, the differential is set up with a flyweight governor
that responds to differences in wheel speeds, and disc packs that are
mounted between the side gear and the case. Whenever one wheel spins faster
than the other, the governor spins rapidly, causing the flyweight to open.
That flyweight catches on a latching bracket and the lockup process starts.
During lockup, a self-energized clutch system causes a cam plate to ramp
against a side gear. This ramping action compresses the disc packs. The
ramping continues until both axles, and therefore both wheels, are spinning
at the same speed. Now the system is at is full lock, which prevents any
further wheel slip. (Note: Axle lockup only occurs at speeds below 20
mph.) The entire process occurs instantly, and is virtually unnoticeable
by the average driver. When both wheels regain traction, unlocking occurs
and things go back to normal.
The biggest
benefit to the system is on slippery boat ramps or in serious off-roading
conditions. Although we didn’t have a chance to try it out during
our test drive, previous exposure to the G80 system with the SUVs shows
that the rear locker really does provide grip without spinning the wheels.
Another added
benefit to the Silverado/Sierra is the addition of safety features like
StabiliTrak, GM’s oversteer/understeer stability control program
with rollover mitigation technology standard on Crew Cabs and available
on Extended Cab models. Also available are roof-mounted head curtain airbags,
and GM’s industry-exclusive rear impact sensors for rear-end collision
protection.
Driving
Impressions
First, if
you currently own a Silverado or Sierra, you’ll be impressed with
the ride and handling improvements on the 2007s. Just as SUVs have stopped
feeling truck-like, so have the full-size pickups. That’s not to
say you’ll think you’re cruising down the highway in a Corvette,
but gone is the wandering steering feel, the bumps and rattles, and even
the unpleasant ride that most pickup owners had to compromise on to get
the utility features.
Whether we
were in the Work Truck or the LTZ, in either the Silverado or Sierra,
we were impressed with the amount of sound-deadening throughout the cabin.
The fit and finish all around was near perfect, and the ease of use of
all the knobs and switches were equally welcome. Our one gripe inside
was the door handle location is a bit low and awkward; if GM fixed that,
this interior (especially on the LTZ) would be award winning.
At the Proving
Grounds, we jumped in and out of a handful of different trucks, including
a GMC Sierra SLT 2WD with the 6.0-liter engine and the MHT suspension
with a 3.73 rear gear. We drove the Silverado Crew Cab LTZ Z85 loaded
with a payload of wood, and then another Sierra 4x4 unloaded. We also
did a towing exercise versus the competition. And a few weeks later we
spent some seat time in the GMC Sierra as part of a combined ride and
drive with the new Acadia.
