2001 Corvette Z06 by Hib Halverson
Downstream of the Engine
Corvette engines usually bring changes to the rest of the powertrain and
that had me talking to Bill Zabritski, GMís Design Release Engineer
for manual transmissions and rear axles in performance cars. Iíve
known Bill since he worked on the ZF S6-40 development in the mid-í80s
for C4 and heís a passionate believer in the Corvette.
told me, to accommodate LS6ís increased torque, clutch pressure was
increased but pedal effort was held at a comfortable level. All C5
driveshafts are now 6061 aluminum and .315-in. larger in diameter.
Driveshaft couplings for Z06 and other stick-shift cars are upgraded
from last year.
Z06es have the Tremec six-speed manual transmission. According to
Zabritski, for í01, forward gears in all C5 manuals get sintered
carbon synchro rings as a durability improvement. Zabritski also said
Z06 uses a specific "M12" version of this transmission having
higher ratios in the first three gears (2.97/2.07/1.43 vs 2.66/1.78/1.30)
which makes the M12 a wider-ratio trans than the MN6 used in
Coupes and Convertibles. With the LS6ís flat
torque curve, Zabritski and the Corvette engineers found the
Zed-ought-six was quicker with higher ratios in the first three gears.
One problem is C5ís limited transmission and rear
axle cooling. This is a function of the carís front air dam and smooth
undercar aerodynamics. M12s get a temperature sensor that turns on a
"trans overtemp" light when trans oil gets above 325į F. At
that point, as Chevroletís press kit says, "...thermal loads
become excessive..." and "...the transmission could be damaged
if not allowed to cool down." This sensor has been standard on C5
manuals sold in Europe since 1997.
The overtemp light reminds us General Motors is still
a big company where executives sometimes make compromises. GM is aware
of the high transmission and rear axle temperatures sustained by C5s
used in motorsports applications, yet, on the Z06, which by Chief
Engineer Dave Hillís own admission, is marketed to the "extreme
performance enthusiast"; we get a temperature warning light. What
the M12 needs is either a lubricant better suited to high temperatures,
such as a synthetic like Red Line or, better yet, a transmission cooler.
Apparently, neither are very attractive for factory use, presumably,
because of cost, however, an aftermarket transmission cooler, developed
for C5 racing applications, is listed in the 2000 GM Performance Parts
The rear axle assembly used in the Z06 is generally
the same unit (3.42:1 ratio with limited slip differential) manufactured
by Getrag and used by all C5 manuals since 1997. It has one difference:
a shotpeened ring and pinion. Bill Zabritski told me this adds an extra
margin of reliability to a powertrain having increased torque output.
Zed-ought-six does Weight