The Tremec T56 Six-Speed:
Revolution and Evolution
Contributing Editor
Tremec, also known as Transmission
Technology Corp., is a major producer of manual-transmission
and drivetrain components. Tremec operates a world-class plant
that is producing transmission products for many of the
world’s major auto and truck manufacturers.
Tremec has taken the T56 to new levels of
production and development, and this unit is now the six-speed
of choice for many of the popular sports and performance
vehicles on the road today. As such, this unit offers
opportunities for repairs in your shop and for performance
upgrades that you can offer your customers to add to your
profits.
The T56 was used first in GM’s F-body
Camaro and Firebird models behind the LT1 engine and later
coupled to the LS1 and LS6 engines.
GM later had Tremec develop the T56 for use
in the C5 generation of Corvettes. This unit was mounted behind
the driver and mated directly to the differential to give the
’Vette better balance and weight distribution. It is the
transmission used in the new generation of C6 Corvettes.
The General also used the T56 in the new
Cadillac CTS-V performance model, which uses a Corvette Z06
engine and drivetrain, and in the new Pontiac GTO. Chrysler
uses the T56 behind its Dodge Viper V-10 and in the new sport
pickup truck that uses the same engine. Ford uses the T56 in
the Cobra R Mustangs and the later-model Mustangs, and Aston
Martin uses a version of the T56 equipped with an extension
housing that contains a number of shift solenoids to enable
“paddle-shift” capability from the steering wheel.
This transmission is available in several
ratios:
2.97 1st, 2.07 2nd, 1.43 3rd, 1-1 4th, 0.80
5th, and 0.62 6th, 3.28 reverse
2.66 1st, 1.78 2nd, 1.30 3rd, 1-1 4th, 0.74
5th, and 0.50 6th, 2.90 reverse
Equipped with an aluminum case, extension
housing and bellhousing, the T56 uses advanced synchronizer
technology and a single-rail shift system. The synchronizers
are double-lined rings using steel inner and outer cones on 1st
and 2nd gears. The linings on the synchro rings were paper
clutch material on early production units, and Tremec has
upgraded that to carbon-fiber linings. The shift forks are
aluminum for 1-2 and 3-4, and reverse is synchronized for
smoother
engagement. This unit is specified to use
synthetic ATF for lubricant.
There are two solenoids on the
transmission. The reverse-lockout solenoid is by the shift
tower. The shift pattern locates reverse to the right of the
5th-gear slot on the shifter. Reverse has a 45-lb. spring load
on the gate to keep the driver from catching reverse when
making a shift to 5th. During a shift to reverse, the solenoid
will activate, overcoming the spring tension and allowing
reverse to be reached with fingertip effort.
The other solenoid, on the transmission
main case, is the “skip-shift” feature. This is an
attempt to meet stricter environmental and pollution
regulations. Automatic transmissions shift at open-throttle
position; manual gearboxes always shift at closed throttle.
Since closed-throttle positions generate more pollution, the
skip-shift solenoid was added to try to control throttle
opening and shift position. If you drive the vehicle at normal
rates of acceleration or beyond, the skip-shift solenoid will
not function. At very light throttle, the computer will
activate the solenoid in 1st gear, forcing
the driver to shift from 1st to 4th, which
shuts down the fuel in the engine-management system to prevent
an over-rich condition. The only people who will see the
skip-shift activate have to be driving like the proverbial
“old lady.”
On the C5 generation of Corvettes, Tremec
developed triple-ring synchronizer technology. This consists of
an inner lined steel cone that rides on the cone of the speed
gear, a double-lined synchro ring and an outer steel cone. This
effectively triples the friction capacity of the synchronizer
and makes for very smooth shifts at high engine speeds. This
was necessary in the C5 and C6 Corvettes because of the high
driveline inertia generated by connecting the differential
directly to the transmission. Without the conventional
driveshaft and mounts to absorb some of the torque,
synchronizer capacity had to be raised to overcome the
driveline inertia prevalent during downshifts.
New for the C6 Corvettes is an internal oil
pump that is driven by the front of the countershaft. A
positive-displacement pump provides pressurized feed to a
transmission cooler and then back to the unit, similar to
cooling for automatic transmissions.
The T56 is an excellent transmission for
the performance cars it was designed for, but it is easily
adaptable for a variety of other performance uses. With two
overdrive gears it provides excellent fuel economy, which at
current gas prices is a big plus. Also, this unit is adaptable
to a wide variety of cars for which it was never intended. The
double overdrive gives the hot-rodder with a radically cammed
engine the ability to cruise without the valves climbing out
onto the hood. There are any number of kit cars, hot rods and
older muscle cars that the T56 can be used in to replace the
four-speeds and T5s that they were built with.
The T56 is capable of handling up to 550
lb.-ft. of torque as it comes from the factory. We have
modified many of these units to handle up to 800-900 lb.-ft. of
torque.
The performance aftermarket in this country
generates $67 billion a year. As you fight your daily battle
for
repair business in your market, it might be
wise to study this market and see where you can find yourself
some extra sales. Tremec has designed two aftermarket units
that will replace T5s and four-speed Saginaws, Muncies and T10s
with a minimum of engineering work. If you have a customer with
a late-model Mustang with a 3650 trans, the T56 can be a direct
replacement offering a six-speed and better performance. You
can up your customer’s performance and fuel economy at
the same time,
all the while dealing with people who are
eager to spend money on their toys.
The GM T56 units are designed with
27-spline output shafts that match the 700-R4 and 4L60-E. We
routinely retrofit a
30-spline Viper output shaft into the F-body cars for weekend warriors who want to be able to drag-race their street cars. The Viper shaft is a much beefier unit capable of much greater torque and abuse than the stock shaft.
30-spline Viper output shaft into the F-body cars for weekend warriors who want to be able to drag-race their street cars. The Viper shaft is a much beefier unit capable of much greater torque and abuse than the stock shaft.
For the C5 Corvettes there is available a
300 moly output shaft that is capable of withstanding abuse and
racing and is a must for Corvettes that have had their
horsepower increased with turbos, superchargers or nitrous. You
can furnish ratio changes, upgraded steel 3-4 forks,
billet-steel solid synchro keys and even a gear set capable of
handling 1,000 horsepower engines. Performance sells, and you
can get a piece of this action without a huge investment.
Adding niche markets to your customers will generate more of
the business you want to have. 
©2005 Transmission Digest
