Tremec T56 (MM6) Features & Benefits
OVERVIEW
This six-speed is known throughout the industry for its ability to withstand extreme torque loads such as those demanded by the Corvette's LS1 and LS6 engines, as well as rigors of competition driving. Nevertheless, it's an extremely flexible unit. In addition to outstanding strength, the use of six speeds offers a wide range of ratios, allowing for a tall first gear for outstanding off-the-line acceleration, as well as over-driven fifth and sixth gears for a high top speed and good fuel economy while cruising.
NEW OR CHANGED FOR 2001 MODEL YEAR
# Taller First Gear Ratio for Improved Acceleration in Corvette Z06
# Carbon Blocker Rings for Increased Durability
CUSTOMER BENEFITS
CARBON BLOCKER RINGS
Blocker rings are an intermediary part between the synchronizer sleeve and the gear cone. When the synchronizer sleeve slides over, it first pushes the blocker ring against the gear cone, and the blocker acts as a cone clutch to help speed up or slow down the gear to the desired speed prior to the synchronizer sleeve sliding over further to engage the gear. These rings now use a carbon friction lining material, which is more resilient and offers improved high-energy performance. This allows the gearbox to better withstand aggressive shifting and leads to a longer life under typical high performance circumstances.
HISTORY
The T56 was developed as a higher-torque evolution of the well-proven T5 five-speed used in the Pontiac Firebird since 1983. The T56 made its debut with the 1993 Firebird. The unit first appeared in the Corvette in 1997 as part of the introduction of the C5 with the LS1 engine.
SIX FORWARD SPEEDS
The use of six speeds allows for a reasonably close-ratio spread of gears, which gives the driver a wide range of gear choices depending on the performance demanded of situation out on the road. Meanwhile, the double-overdrive on the top two gears (both have ratios of less than 1:1) drops engine revs for comfortable cruising, while also helping to meet stringent fuel-economy standards.
DOUBLE-CONE AND TRIPLE-CONE SYNCHRONIZERS
The T56 uses double-cone and triple-cone synchronizers. Double-cone synchronizers have friction material on both sides of the synchronizer rings. The extra friction material provides higher energy capacity for shifts. Triple-cone
synchronizers provide a third surface in the synchronizer assembly lined with friction material. This third friction surface further shares in the work load of accelerating and decelerating driven gears to the desired speed. With these multiple-cone synchronizers, the T56 has a high synchronizer capacity and attains greatly reduced shift effort given the overall size of the transmission. (The alternative solution to reduce shift effort would be to use larger diameter synchronizers, which would increase the overall size and weight of the transmission.)
FIFTH AND SIXTH GEAR SYNCHRONIZERS ON THE COUNTERSHAFT
The T56 employs an innovative arrangement of components to ease shifting in all forward gears. The fifth and sixth gear synchronizer assemblies are located down on the countershaft instead of on the mainshaft with the other synchronizers. When a shift occurs, the synchronizer has to slow down or speed up the entire mass of the free-running transmission components (gears, countershaft, input shaft). Placing the fifth and sixth gear synchronizers on the countershaft reduces the reflected inertia of these parts. Therefore, with each shift, the synchronizers have less work to do, resulting in easier shifting. Placing the fifth and sixth synchronizers on the countershaft also reduces driveline rattle by taking advantage of the reduced inertia effects.
NEEDLE BEARINGS UNDER ALL SPEED GEARS
The use of needle bearings under all of the speed gears (driven gears on the mainshaft) results in reduced friction. Needle bearings are made up of a steel or plastic cage that holds many tiny cylindrical rollers or needles, which greatly reduce drag between the gear and the shaft. They also provide for much more efficient lubricant flow.
By comparison, some production car transmissions make do with a journal with an oil passage, and the gear slides on a thin film of oil. Under high-load or high-speed applications it may be difficult to maintain a proper oil film and problems may occur. The reduction in friction provided by the needle bearings results in reduced shift effort and increased high-speed performance.
OVERALL LOW SHIFT EFFORT
The double- and triple-cone synchronizers, the carbon friction material, the placement of the fifth and sixth gear synchronizers on the countershaft, and the needle bearings all contribute to reduced shift effort. In fact, on the T56, provisions for artificial "feel" have been added to give the driver more feedback through the shift lever. Extra shift detents are incorporated which can be tuned to give the desired mechanical "click" as gears are engaged.
SINGLE-RAIL SHIFT SYSTEM
The T56 uses a unique single-rail shift system, wherein all of the shift forks for all gears are located on a single rail. This is a simple solution that provides enhanced shift feel and outstanding durability.
TAPERED ROLLER BEARINGS
The T56 uses tapered roller bearings to support the mainshaft and countershaft. Tapered bearings take up any thrust loads and reduce shaft endplay (the tendency of the shaft to move back and forth longitudinally within its mounting.) Less endplay leads to improved durability while reducing noise.
POWDER METAL BLOCKER RINGS FOR HIGH QUALITY
The T56 uses powder metal blocker rings instead of machined blocker rings. Whereas machined blocker rings are formed by machining away material until a desired shape is attained, powder metal parts are formed by pouring a fine metal power into a die, which is then subjected to extreme heat and pressure to cause the powder to flow and fuse into a solid material. This process allows for more precise detail on each part and for more consistency between parts than does machining. The result is higher quality throughout the gearbox.
CONSTANT MESH, FULLY SYNCHRONIZED REVERSE
Many transmissions require the direct engagement of an additional gear between the mainshaft and the countershaft to change the direction of output rotation for reverse. The engagement of this extra gear is often harsh because of the forced meshing of gear teeth. On the T56, reverse gear is constantly in mesh, and its
engagement is controlled by synchronizer sleeves just like the forward gears. This greatly reduced noise and harshness when selecting reverse and improves durability.
INTEGRAL CLUTCH HOUSING
The T56 uses an integral clutch housing with an adapter ring to mate the transmission to different engines. This arrangement contributes to improved rigidity at the transmission/engine interface while maintaining mounting flexibility.
ALUMINUM CASE
The aluminum die-cast housing on the T56 is durable yet extremely lightweight.
