Transform Your Classic Ford: Installing the Tremec TKX 5-Speed in Your 65–73 Mustang

If you’re a classic Ford enthusiast who wants modern drivability without losing that vintage Mustang feel, the Tremec TKX five-speed manual transmission is one of the best upgrades you can do. At Stang-Aholics, we specialize in TKX conversion kits built specifically for 1965-73 Mustangs and other classic Ford applications—and this blog post will walk you through why the TKX is such a great fit, what you’ll need, and how your car will feel when it’s done.

TKX 5 Speed Manual Transmission for Classic Ford Mustangs and Other Classic Fords

Why Choose the Tremec TKX for Your Classic Mustang?

Old factory 3 and 4-speed transmissions in classic Mustangs were great for their era—but for today’s driving, highway cruising, and higher-performance builds, they often fall short. The Tremec TKX changes the game.

Here are the top reasons the Tremec TKX stands out:

The Ford-specific versions are 26-spline input and are .68 overdrive (Close ratio) or .72 Overdrive (Wide Ratio), both are rated for approximately 600 lb-ft of torque in a very compact design!
Gear ratios for the FORD TKX 5 Speed are as follows:
Close-Ratio version: 1st = 2.87, 2nd = 1.89, 3rd = 1.28, 4th = 1.00, 5th (overdrive) = 0.68
Wide-Ratio Version: 1st = 3.27, 2nd = 1.98, 3rd = 1.34, 4th = 1.00, 5th (overdrive) = 0.72
Input/output splines: 26-spline input and 31-spline output.
Compact end-loaded design: It fits transmission tunnels in the classic Ford Mustangs and many other classic Fords with minimal or possibly NO modification.
Top Tier Build quality: The TKX features a three-piece aluminum housing, upgraded multi-cone synchronizers, carbon/bronze hybrid rings, built-in reverse light and cruise switches, and is rated with smooth shifting up to approximately 7,500 rpm (depending on application).
The overdrive 5th gear makes highway cruising much smoother, lowering engine RPMs and reducing fatigue.

In short: You get a modern 5-speed with strong, modern performance internals, great shift feel, and an overdrive gear—perfect for a 1965-73 Mustang so you can love your classic and get out there and drive!

What You’ll Need for the Installation

Since we at Stang-Aholics provide complete TKX conversion kits for classic Mustangs, here's a list of what’s typically required (and what our kits come with) when doing a TKX swap:

Core Components in Our Kit:

New Tremec TKX 5-speed Manual Transmission: Ford 26-spline input, Close-Ratio .68 OD version or Wide Ratio .72 OD Version
Transmission Mount/Crossmember: Transmission mount/crossmember Kit with Hardware for Install (specific for your Mustang’s year and chassis)
Matching bellhousing (Ford pattern) - Cast Aluminum or QT Heavy Duty Steel (For High Horsepower Applications)
Clutch kit and flywheel Package - We make sure the clutch disc and flywheel package is designed to perform well together and matches 26-spline input.
Additional Items Needed for Clutch Install: Pilot bearing, throw-out bearing, Cable kit w/ clutch fork, or hydraulic conversion kit
Clutch Pedal Assembly: If Your Car is currently an Automatic Transmission or you are missing your clutch Pedal, we have you covered!
Speedometer Connection: We can provide a traditional Mechanical Cable with Gear or Electronic speedo-compatible wiring for use with the TKX
Shifter Arm of your Choice: We can provide a Billet Aluminum, Black Anodized Aluminum, or Round Chrome arm with Slight Layback to the Driver and 5-Speed Shifter Ball
Driveshaft Components: We can provide a Driveshaft Slip Yoke or a completely new Drive Shaft Assembly with Slip Yoke and U-Joints (ordered later when ready to take measurements)
Correct TKX fluid: We provide the Tremec recommended Break-In Fluid (For first 500-1,00 Miles) and Final Run Fluid, Clutch Fluid If Running a hydraulic throw-out bearing

We ensure the proper shifter location: The TKX allows multiple shifter positions- We ensure the shifter is positioned to use the stock shifter hole in your tunnel with NO Modifications!
Extended Transmission Warranty: We provide a 3 Year Extended Warranty on all TKX Transmissions purchased from us, so you have peace of mind knowing we have you covered!

What It Feels Like on the Road

Once the TKX is installed, you’ll immediately feel the difference. Here’s what your Mustang will gain:

Lower RPMs at highway speeds: With the 0.68 overdrive or 0.72 gear, your car will cruise more comfortably, engine noise drops, and you get less wear on your drivetrain.
Stronger durability: The 600 lb-ft rating means the TKX can handle high-horsepower/torque builds and heavy use.
Modern Shift feel: Crisp, short-throw shifting via the shifter assembly, high-quality synchronizers, and the solid internal architecture included with every transmission!
Better versatility: Whether you’re cruising, commuting, or hitting the twisties, the TKX gives you the flexibility and performance you need.
Great fit for Mustang 1965-73 chassis: With the right kit (like ours engineered kits at Stang-Aholics), you maintain classic looks and compatibility with the stock transmission tunnel and shifter opening!

Why Stang-Aholics Is Your Best Choice for a TKX Conversion

At Stang-Aholics, we don’t just sell parts—we live Mustangs. Here’s why our TKX conversion kits stand apart:

Each kit is application-specific for your Mustang’s year (1965-73) and chassis.
We include all the critical fitment components: the correct Tremec TKX transmission with the shifter in the stock location, bellhousing, Flywheel and clutch kit, Transmission Mount/Crossmember, Cluth Pedal Assembly (if needed), Hydraulic Throw-Out Bearing or Cable Clutch Kit, driveshaft slip yoke, Electronic or Cable speedometer and adapters, Complete Fluids, Complete Hardware package, and thorough installation manual and warranty documentation.
We provide expert support—you don’t just get parts; you get the guidance from enthusiasts who’ve done these swaps.
Quality matters: We stick with Tremec’s specifications to make sure you get the right transmission, bellhousing, and clutch combination, so your build has longevity and performance!
We ship quickly and fairly—so you can get back to wrenching and driving.

Conclusion: Drive Your Classic Ford with Confidence and Modern Performance!

Upgrading your 1965-73 Mustang (or other classic Ford) with the Tremec TKX 5-speed transmission is one of the smartest moves you can make. You retain the character of your classic Ford, but gain modern performance, better drivability, and a transmission built to handle your build's Horsepower and Torque. The Tremec TKX isn’t just an upgrade — it’s a complete transformation for your Mustang and Classic Ford vehicle. With state-of-the-art internals, OEM-grade engineering, and track-tested durability, it’s the ultimate replacement for outdated 3-speeds, 4-speeds, or overworked T5s.

Ready to make the Upgrade? Browse our TKX Conversion Kits on Stang-Aholics and let’s get your Mustang ready for highway cruises, weekend drives, and all-out driving enjoyment!

Click here to view our kits: Stang-Aholics.com

Let’s get your classic driving like it was built for today—because you and your classic car deserve nothing less.