Shifting Six With Confidence

LS1s can be built to make tons of horsepower and torque, and usually the clutch or the rear fails first once the power is put to them. So many install a 12-bolt rear and upgrade the clutch, but what about the transmission? Sure the wonderful Tremec T-56 six-speed transmission is a strong unit that can handle quite a bit more torque than Tremec rates it for, but any unit can be improved. So what do you do to ensure proper shifting and long life with 750-800 hp and as much as 600-700 lbs.-ft. of torque on tap? We went to the source find out and, in this case, it was Michael Weinberg and Brian Johnston and their company Rockland Standard Gear, Inc.

Rockland specializes in manual transmissions and can build just about anything to withstand the rigors of racing. Weinberg is a race car driver and has competed since the 1950s at such hallowed tracks as Lime Rock and Le Mans. Through racing experience and diligent research, the company has improved the six-speed transmission's durability and performance in all of its applications including the F-body, the Mustang, the C5 Corvette and the Viper.

For this story we will concentrate, of course, on an F-body trans. As stated, the T-56 is already a very rugged box. Neither gears nor any other major parts will need to be updated for racing. In fact, the improvements are mostly for the shift components and they are pretty straightforward, as you will see.

While the parts in and of themselves are not too exotic and the required measurements aren't too difficult, you will, however, have to completely tear down the trans to install the upgraded pieces. Mike suggests that you do not attempt this at home since specialized tools are needed to do the job correctly and the price for a few of them is prohibitive unless you plan to rebuild six-speeds for a living. Though I rarely advise readers to keep their hands clean, here, you are probably better off.

To that end, this will not be a nut and bolt swap as the procedures could and have filled a book. Many pages are dedicated to the T-56 in the GM transmission repair manual. We will instead take you on a tour to aid in identifying the trans and its outward components. Then we will highlight a few of the great technical features of the T-56, point out areas in which to look for trouble and perform the upgrades. So follow along with the photographs and refer to the exploded views often to see how everything works together.

Photography by the author
Diagrams courtesy of GM
Charts courtesy of Transmission Technologies Corporation

The passenger side reveals the vent tube up top and the reverse lights switch (plug in the center).	A metal trim tag identifies the transmission. Of all the numbers on this tag, according to Mike Weinberg, the only one that matters to you if you are ordering parts for your T-56 or are looking for one of these transmissions at the swap meet or in the boneyard is "1386," denoting the T-56. The number after it ,"020," is the design level (latest for F-body)--011 or 013 would be from a Viper and 025 from a Vette.	On top of the trans near the vent tube is another identifier on a sticker. The "13-86-020" again is the trans model number 13-86 and the "020" is the design level. The "DXA is a GM code and T0143533" is unknown.
T-56s employ an integral clutch housing with an adapter ring, which increases its resistance to driveline bending under power. Here we see the hydraulic clutch actuator cylinder set-up as well. The traditional Chevy bolt pattern is used for the LS1 so anyone who wants to retrofit into a BOP application will need an adapter plate. Note the small pipe plug on the lower left of the hydraulic assembly under the strengthening rib. This is an access hole to check the auxiliary counter shaft (a.k.a. 5th speed gear counter shaft) endplay. More on that later.	Here is an exploded view of the trans case showing the 6th gear and reverse assemblies. Note that the T-56 has designed into it a constant mesh, synchronized reverse system, which provides more positive engagement, reduced noise and improved durability.	This view illustrates how the 1st and 2nd gear assemblies fit into the case.
Exploded view of adapter plate and gears:Here we see how the main shaft and the input shaft and gear assemblies attach to the front adapter plate.	Exploded view of shift shafts and clutch cover:The T-56 uses an internal single rail shift system to improve shift feel and durability over the old external shifter and rod designs that are exposed to the elements and require periodic lubrication and maintenance.	Exploded view of extension housing:These are the parts that go into the extension housing.
Exploded view of reverse lockout and shifter.	Vice president of remanufacturing for Rockland Standard Gear, George Kreppein handled the performance building of our 900-mile Tremec T-56. He began with the removal of the reverse lockout solenoid and then the hydraulic clutch actuating assembly and the clutch housing.	With the bolts removed, the extension housing is split from the case. Here we can see the shift shaft up top, the main shaft with the reverse gear in the middle and 5th and 6th gears on the auxiliary counter shaft on the bottom in the main case. In the extension housing is the reverse idler gear and bracket.
Here is just one of a few specialty tools that are used to rebuild the transmission. This one you won't find listed under J in the service manual either since it was built by Rockland Standard Gear to pull the 5th-6th speed driven gear. Note the 5th and 6th gear assemblies are finer cut than the 1st-4th. As such, they are much quieter in operation but not as strong as the 1-4 gears. In drag racing you wouldn't use the overdrive gears anyway so it's not a problem. But even road racers with engines that have enough power to pull 5th gear have not experienced problems with this finely-cut piece.	These bolts locate the linkage selector inside the trans and are referred to as the 5th-6th lever guide bolt and the interlock guide bolt. They must have been taken out prior to removing the main case.	George removes the main case from the front adapter plate to reveal the shifter rods and forks and the gear assemblies. Note the position of his left hand to hold onto the offset shift lever, which comes off with the case.
This is the 3-4 shift fork. Though it's fine for stock applications, it tends to wear over time, increasing side play where this hard steel shift interlock plate rides in the fork. The result is the trans popping out of gear.	Though tough to see here, this 900-mile transmission is already beginning to show signs of wear in the shift interlock plate slot.	Here's the cure for fork wear and the trans jumping out of gear--a much heavier and stronger steel fork from Tremec (right). You can also see in this photo that the fork rides in the 3-4 synchronizer hub and contact is made with the plastic pads found at the tip of the fork. They to need to be checked for wear as they usually go first. With such low mileage, ours had none.
Synchro rings will also be upgraded. The standard synchro ring on the left features a friction material much like that used in automatic transmission clutches. Again, fine for street use but for racing, they don't hold up nearly as well as Rockland's replacement pieces, which feature a carbon fiber lining that is much more heat resistant and has a higher coefficient of friction.	Mike Weinberg and George pointed out another area to pay attention to--the union of the counter shaft (bottom) and the auxiliary counter shaft (top). They are select fit and should not exhibit any sideplay when together. And the teeth are examined for breakage.	For preassembly, the counter shaft and the main trans case are installed onto the front adapter plate and measurements are taken for counter shaft endplay. It should be 0 endplay with 0 preload. If it's higher than 0 the shaft can move back and forth and cause hard shifting and increase parts wear. Ours was .002 so shims were needed to correct it. Here that measurement is being taken through the case.
The auxiliary counter shaft (a.k.a. 5th speed gear counter shaft) must be set to 0 endplay with 0 preload as well. Its end has been drilled and tapped at Tremec to accept a bolt, as you can see in the spare auxiliary counter shaft shown in the photo. A dial indicator then reads off of the top of the bolt to check the endplay. The access hole is where the plug was shown in the earlier front-of-the-trans-photo.	Here is the setup on the front adapter plate. The counter shaft rides on it via tapered roller bearings. Beneath the bearing race is where shims are added to achieve the 0 endplay that was measured in the previous photos.	Another great feature of the T-56 is the use of double-cone syncros. Note the added friction cone with the tabs between the synchro ring and the inner cone. It has a friction surface on both sides effectively doubling the lining area thereby increasing holding ability and adding durability. Older 4-speed transmissions don't have this feature nor do early T-5s but the later World Class T-5s do. The Vette T-56 actually has triple-cone synchros but Mike says that upgrade to triple-cone synchros is not feasible for the F-body T-56.
This is the gear select interlock plate, which slides into the shift finger to prohibit shifting into two gears at the same time. When pushed to the limit, they crack. George has highlighted with marker where he checks for those cracks prior to reassembly.	Note the transmission is reassembled from the front adapter plate back so it is very important to have a fixture that turns the transmission upright for assembly. Here we see the main shaft and counter shaft installed with gears and syncros and the shift rods and forks in place. Bearings and other wear items are replaced in each transmission when the mods are made.	The offset shift lever must be installed and held as the main case is slipped over the previously shown assembly. Then the two bolts that hold the shift interlock and rail in place are installed after the holes are aligned with the case. George warns never to use an impact gun on these bolts.
With the case in place George presses on 5th-6th speed driven gear using a pipe and a hammer. Pipe is shown, hammer is not.	Here are 5th and 6th gears on the auxiliary counter shaft in place to the right and the reverse gear on the main shaft along with assorted bearings and the reluctor for the speedo is installed on the left. Note that the T-56 uses tapered roller bearings on the shafts, as you can see on the auxiliary counter shaft, to reduce noise and improve durability.	One last mod is the installation of a silicone bronze "no walk" extension housing bushing that is longer than its babbit counterpart to negate any wobble of the shaft and improve the driveshaft yoke support. It will be installed with the lubrication hole lined up with that of the extension housing and it is staked once its tapped into place to ensure that it will stay there.
Then the extension housing is bolted on. The clutch cover will come next as will the clutch actuating assembly, and the job will be complete.

ABOUT ROCKLAND STANDARD GEAR AND ITS OWNERS
Mike Weinberg, one of two partners in Rockland Standard Gear, has been racing since 1957. He started in midgets and has been through all the chairs, drag racing, road racing, and he is currently driving a Vette in the Grand Am Cup series, the road-racing arm of NASCAR for Powell Motorsports, where his team has won four championships in the last five years. Weinberg holds seminars around the world for the transmission repair industry and provides tech support over the phone for Rockland's customers.

Brian Johnston, the second partner in the business, has developed the company's inventory computer system and he tracks the various upgrades and changes made to a bewildering array of transmission models. He ensures that Rockland is always prepared to serve its customers promptly and expertly, and provide the latest written technical information packaged with their orders.

Rockland Standard Gear started in 1981 distributing manual transmission and drivetrain parts, and remanufactured transmissions to dealers and the repair industry from a 2,000 square foot facility with Mike Weinberg and Brian Johnston as the principle owners. Over the years, the company has been involved with a lot of race teams and large firms like Gale Banks and Lingenfelter, which has provided valuable research in improving both the components and transmissions that the company sells. A free flow of information back to the manufacturers has also resulted in improved OEM designs.

Rockland tests the parts that it receives from suppliers on a regular basis to make sure that the quality is there initially and that it doesn't degrade over time. Specifications are compared to those housed in the company's computer system. An outside lab with the proper test equipment, including a profilemeter among other machines, is employed to do the testing.

Today, Rockland Standard Gear calls a 66,000 square foot facility home, has a client list exceeding 12,000 and provides parts and transmissions and most importantly technical support to all of North America, Europe, parts of Africa, the Middle East and down under in Australia.

Ignore the torque range figures in this chart as this trans is built to handle much more power now.