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How to Rebuild a TREMEC T-5 Transmission

Modern Driveline has the goods to get your TREMEC T-5 back in action

Jim Smart Mar 20, 2019
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TREMEC’s T-5 five-speed transmission has been in continuous production for more than 35 years. Originally designed and manufactured by BorgWarner and first offered in the early 1980s, the venerable T-5 has been a mainstay for longer than a lot of us have been around. The fully synchronized T-5 five-speed transmission is a countershaft-style helical gear unit. In the late 1990s, BorgWarner sold its manual transmission division to TREMEC, which is still building new T-5 transmissions to this day and are available from Modern Driveline along with all of the parts necessary to service them.

At the beginning of the 1983 model year, GM introduced the T-5 five-speed in the Camaro and Firebird to help improve fuel economy and add some snappy performance. Other automakers quickly caught on to what the T-5 did for fuel economy and performance, which means you will find many variations of the T-5 box. There have been more than 260 variations of the T-5 produced over its production life.

There are two basic types of T-5 transmissions: the original Non World Class (NWC) T-5 and the World Class (WC) T-5, introduced in 1985. Bruce Couture of Modern Driveline tells Chevy High Performance the World Class name had little to do with strength and durability, but instead the T-5’s introduction into the world market in the mid-1980s as a performance transmission. The World Class T-5 was engineered to take greater amounts of power and deliver improved shift quality via revised synchronizers and bearings, which makes the World Class T-5 easy to identify.

“All the mainshaft gears, First through Third, ride on a solid output shaft with deep oil grooves to provide good lubrication,” Bruce comments. “The lower countershaft gears spin on straight cylindrical bearings with a thrust washer in front to provide support when under load. All the synchronizer rings are made of solid bronze, which are of different size than those found in a World Class T-5.”

“No longer were First, Second, and Third gears spinning on a solid output shaft. Needle bearings were installed with each gear ratio to reduce internal friction. The lower counter gears saw tapered bearings to replace the bronze thrust washer,” Bruce adds. “All mainshaft synchronizers were fiber lined steel rings to improve ring friction surface area while overdrive (Fifth gear) remained bronze. Installing steel synchronizer rings with linings improved two things. These rings don’t stretch and break and the added friction slowing the gear faster allowing for higher shift points.”

Where the World Class T-5 story becomes more involved is the aftermarket, which came in the early 1990s. Bruce tells us the aftermarket offers performance enthusiasts heavy-duty gearsets for the T-5, with some companies claiming 600 lb-ft of torque capacity. “Our experience at Modern Driveline has been different with these gearsets. What makes these gearsets different is the steel alloy and gear shape. Changing to a harder alloy will provide more strength; however, the problem is making sure the gear has some ‘give’ to it. Too hard and gears break. Other ways of increasing torque levels is to take some of the helic out of the gear and make the gear thicker yet making it more cog like. While this will make the gear stronger, it also makes it much noisier. Many of these aftermarket gearsets are very expensive and require aftermarket main cases and mainshaft to get the specified torque ratings these companies claim. By the time the aftermarket gear and supporting parts are purchased, one should consider other options for the same money.”

Bruce stresses World Class T-5 transmissions use ATF (Dextron III) oil, not heavy gear lube. All Non World Class T-5 transmissions use 50-weight gear oil. The original Ford/BorgWarner lubrication recommendation back in 1984 was Dextron II, but because it is no longer available, Modern Driveline and TREMEC recommend the 50-weight gear oil. “When we rebuild transmissions, we can tell when the oil has been changed often because the parts are much cleaner with less overall wear and tear,” Bruce comments. Bruce suggests a magnetic oil drain plug in your T-5 to capture metal fragments that come from use. This, coupled with regular lube changes, will yield a longer transmission life. CHP

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This is the World Class T-5 five-speed transmission as most of us know it. Before you is a mid-1990s BorgWarner main case and extension housing, which hasn’t changed much since the World Class was introduced in 1985. Unless you’re performing a restoration, the World Class T-5 is the best choice.

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Modern Driveline has this World Class T-5 disassembled for this article. The T-5 is a simple overdrive manual transmission that’s easy to service. Paul Coffey, chief customer service engineer at Modern Driveline, has a very methodical approach to each T-5 he builds. He examines every part closely to ensure it’s going to operate properly when it arrives on the customer’s doorstep.

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This is the World Class T-5 rebuild kit available from Modern Driveline, which includes nearly everything you’re going to need to rebuild one, with the exception being any broken hard parts you would need to replace.

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The T-5 is a top-shifting, single rail transmission where the shifter forks are built into the top cover.

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The shifter forks need to be inspected for wear patterns like this.

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The shifter forks have these tabs or bushings that should be replaced during a rebuild. They heat up and wear out over time and use.

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The shifter forks install into the top cover like this where they are connected to the shift rail.

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Here’s a close-up of a T-5 output shaft with minute surface scoring. This shaft could be reused, but not by Modern Driveline. Galling like this only serves to create more problems even when you install new bearings. Old problems become the same problem in a new build.

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Here is the difference between old synchronizers and new ones. Look at the wear and scoring in the old synchronizers (top). Synchronizer and blocking rings must be replaced.

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The T-5’s countershaft works hand in hand with gears on the mainshaft assembly (output and input shafts) to affect gear ratio. As with other transmission components, the countershaft must be inspected closely for damage and abnormal wear. Even minor scoring will cause noise and performance issues. If you look at bearing mating surfaces of this World Class T-5 countershaft, there are virtually no wear issues. The gear teeth appear free of damage and abnormal wear.

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The countershaft is installed in the T-5’s main case as shown via a hydraulic press.

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The countershaft and idler gear are installed in the main case as shown. The reverse idler gear slides in and out to deliver reverse gear. These are the first parts installed during assembly. The reverse idler gear slides right to engage the counter gear.

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Modern Driveline stresses the need for a close examination of the gear teeth and synchronizers for damage and excessive wear. Look at these items with a magnifying glass for even the smallest imperfection, which can cause shift problems and noise. The reverse slider has minute gear tooth damage, which could be easily overlooked during a rebuild.

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The countershaft, reverse idler, and shift mechanism have been installed, making it busier inside. Yet to go in is the T-5’s output shaft.

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The T-5’s output shaft is checked for runout. Excessive runout makes it a throwaway.

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A close-up look at the output shaft shows evidence of excessive wear. Sometimes surfaces can be polished. Most of the time it’s a good idea to replace the shaft.

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020 Tremec T5 Rebuild 20/26

As parts are assembled onto the output shaft they are checked for resistance and binding. Any binding is unacceptable.

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The output shaft assembly is complete and ready for installation in the main case.

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The blocking ring and Torrington bearing are fitted into the synchronizer on the output shaft. Once this shaft is fitted into the transmission case, the input shaft will be fitted and seated.

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The output shaft assembly is installed as shown into the main case and fitted to the countershaft (also known as the cluster shaft or cluster gear).

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The Fifth gear (overdrive) fork, which is housed in the extension housing, is installed and seated on the synchronizer and fifth gear drive assembly.

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The input shaft splines into the output shaft. These needle bearings support rotation. They should be packed with assembly lube to keep the roller bearings in place during installation.

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Paul Coffey of Modern Driveline wraps up another World Class T-5 build—one of the many types of TREMEC manual transmissions they service.

Photography by Jim Smart

Sources

Tremec
Plymouth, MI 48170
800-401-9866
www.tremec.com
Modern Driveline
Caldwell, ID 83607
208-453-9800
http://www.moderndriveline.com

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