Overview
The T-45 first appeared with the 1996 Mustang as a stronger 5-speed manual transmission to mate with the new Modular 4.6 V-8 engine.  It was used until around February of 2001 when mid-production 2001 Mustangs began receiving the TR3650.  

The T-45 was a BorgWarner design that was exclusive to the Mustang.  Tremec (Transmission Technologies Corporation - aka TTC) acquired BorgWarner's Light-Duty Transmission Division  around 1997. While the T-45 remained virtually unchanged, T-45 units produced by TTC bear the Tremec name as do all OEM replacement parts.

The T-45 has a single-rail shifting mechanism that is somewhat similar to the T-5 and was carried forward to the T-56.  The T-45 was the first Mustang manual transmission to have a fully synchronized reverse gear.  Some versions of the T-5 had a "Reverse Brake" feature that employed an extra synchro ring, but reverse gear was NOT fully synchronized in the T-5.

There were only three versions of the T-45 produced, and they were tagged as follows:

1381-001 - 1996-1998 Mustang GT
1381-002 - 1996-1998 Mustang COBRA
1381-011 / TNET1386 / TSET1386 - 1999-2001 Mustang GT & COBRA

1996-1998 vs 1999-2001
The T-45 can be divided into two designs. The early units were for 1996-1998 V-8 Mustangs, and the later units were for the 1999-2001 models.  Within the 1996-1998 years, the transmissions were identical between the GT and the COBRA models except for two items.  First, the COBRA T-45 employed a 7-tooth internal speedometer gear where the GT had an 8-tooth internal speedometer gear.   Second, the transmission cross-member mount for the COBRA models was located further to the rear resulting in different tail housing castings between the two models.

For 1999, Tremec invoked several changes, attempting to make the T-45 more reliable.  This included stronger shift forks for all gears, a sturdier throwout bearing sleeve on the front housing, and carbon-fiber synchro rings for gears 3, 4, 5, and reverse.  Carbon-fiber rings for first and second gears were made available later as replacement parts, but did not appear in the production units.  These rings for first, second, third and fourth gears are identical to those used in the T-56.

One additional change for 1999 was the inclusion of an all-electronic "OSS" speedometer sending unit.  1994-1998 Mustangs used an electronic signal to drive the speedometer, but these signals were generated by a "VSS" speedometer sending unit that was driven by a pair of gears.  Calibration for a VSS speedometer system was accomplished by selecting the correct gears to drive the sending unit.  For 1999, the OSS unit had no gears and was calibrated by settings in the "Tune" of the Engine Computer.  It also appears that the last productuin 2001 Mustang T-45's were tagged TNET1386 and TSET1386 with no discernable differences from the 1381-011 units.

Shifter Assembly
The T-45 uses the same shifter base as the T-5 and enjoys a broad selection of after market shifter choices that can improve the indexing of third gear on a quick shift.  

Gear Sets
There is only one set of production gear ratios for the T-45. The ratios are all 3.37, 1.99, 1.33, 1.00, and 0.67.  The ratio for reverse gear is 3.22.

 

Updates to the T-45
Numerous Service Bulletins have been issued for the early T-45's. I won't attempt to cover these in detail.  While no longer available, Ford installed "updates" to a number of 1996-1998 units for owners who complained of shifting problems with reverse gear while their cars were still under warranty.  These fixes focused on the Fifth/Reverse gear forks which were jamming and breaking.  Three stronger versions of the fork were produced as replacement parts, and the best-fitting part was selected as part of the service bulletin in an attempt to correct the issues.  Unfortunately, the forks still would jam and break.

Beginning in 1999, the stronger reverse forks, as well as stronger forks for gears 1-4, were incorporated into the production T-45's.  However, these improved 3-4 forks were made too thin, added extra play in the the shift plate, and continued to be notorious for breaking.

One additional weakness in the shift forks that was addressed by Tremec with the 1999 models is that the selector "Shift Plates" were made stronger (and are identified with a "T" stamped in the plate).  Unfortunately, these improved plates were still not strong enough and continue to break.  The Pro-Force Billet Shift Plates address this issue. 

Fluids
The current official Fluid for a T-45 is Ford's Mercon-V which is a quality synthetic blend. The Mobil-1 meets the Mercon-V specification, but is also fully synthetic. It is a general consensus that certain synthetic fluids have detergents in them that can damage the linings of the non-carbon-fiber synchro rings used in the T-45 and should be avoided.  Gear oil and motor oil are not recommended and will damage the early style synchro rings used in a T-45.

Inherent Strength
The T-45 is a rather strong transmission, but its weak spot in a high-torque application is the 10-spline input shaft. These stock shafts tend to twist or shear off when launching a 500 HP car at the drag strip. To remedy this, builders have been modifying original input shafts by grafting a new 26-spline shank onto the gear. This puts the T-45 at a higher torque rating.  Pro-Force now offers new 26-spline input shafts for the T-45.

Customizations to the T-45
Numerous custom parts are available for the T-45 to resolve the inherent issues that were never resolved by the manufacturer.  

 - Billet shift forks and plates are available for the 1-2 and 3-4 synchros that are much          stronger to avoid breakage and firm up shifting.

 - The pesky issues with reverse and fifth gears are eliminated with the use of Billet Keys

   in the 5-R Synchro hub as well as a custom redesign of the reverse hub and fork

   resulting in a "single-disconnect" design rather than an off-balanced double fork design.   - For the 96-98 models, the input/release bearing sleeve is now available as a custom

   one-piece billet design to eliminate breakage.  

T-45 to TR3650 INTERCHANGE INFORMATION:
Note: The TR3650 uses a different Shifter base than the T-45.
 - A 1996-1998 T-45 can be replaced with either a 1999-2001 T-45 or with

   a 2001-2004 TR3650 by using an electronic calibration device to convert

   the speedometer signal.
 - A modified cross member is needed to install a TR3650 in a 96-98 Mustang.
 - A 1999-2001 T-45 can be replaced directly with a 2001-2004 TR3650.
 - The reverse light switch from the T-45 is retained when converting to a

   TR3650.

This article was last updated on 12/13/2025