From Four to Five: Why Upgrade Your Mustang Transmission?

Decades ago, Ford made the jump from four-speed manual transmissions to five-speeds. Newer Cobras even feature six-speeds, so it’s natural that those who own earlier Mustangs with four-speed manuals now feel a little gear envy. Many people love the feel of having a manual transmission, but if you’re still using a four-speed, you’re missing out on a lot of performance and economy potential. Adding a transmission with additional gears places your gears closer together for better acceleration and gives you more gears to choose from for easier cruising. But which transmission is right for your Mustang? You need one that’s strong, smooth and capable of bolting to your engine, and it’s not easy to find all three attributes in the same gearbox.

Meet Keisler Automotive Engineering

If you’re considering swapping a five-speed manual into your early Mustang, you need to consider calling Keisler Automotive Engineering (865/609-8187). Located in Rockford, Tennessee, this company is an expert at adapting new manual transmissions to older cars. Although most of the company’s previous experience has been in GM and Mopar circles, Keisler is expanding into the Mustang market in a big way. In fact, when Gateway Classic Mustang heard what Keisler had available, Gateway knew it wanted one of these transmission conversion kits for its Eleanor clone that we featured in our June ’06 issue. The car was equipped with a four-speed T10 manual, and considering everything else that Gateway had built into this car, the transmission was sorely lacking.

The Keisler PerfectFit Kit and Tremec TKO-600

Keisler responded with a PerfectFit upgrade kit and a Tremec TKO-600 five-speed manual transmission. The TKO-600 is an incredibly stout piece. Unlike factory five-speeds, this one is made for performance and can handle 650 hp right out of the box. But Keisler doesn’t leave the transmissions alone. Keisler modifies them with a shifter location designed for your specific vehicle and includes a high-performance, short-throw shifter. The shift tower and tail shaft are designed to keep cutting of the floor to a minimum, and a T10-style bolt pattern means the transmission will bolt right up to your engine. But the PerfectFit kit includes much more, including a new crossmember, mount, driveshaft, speedo cable, pilot bearing, hardware and even a six-month warranty.

Additional Components for a Seamless Swap

Keisler also supplied Gateway with a clutch kit that included a new SPEC clutch disc, pressure plate and flywheel. Keisler included a new shift boot, arm and knob, too, as well as a hydraulic clutch kit with a clutch cylinder, reservoir and line. Additional parts, such as pedal assemblies, are available if your Mustang is an automatic and you want to make the swap.

Installation with Gateway Classic Mustang

We were present at Gateway Classic Mustang as Keisler and the GCM crew teamed up on the installation. Although they had a lot of manpower and expertise, you and a few friends should be able to perform the same installation in about a weekend. There are a few special tools involved, so when you call Keisler to ask what it recommends for your car, find out what you’ll need to install the kit as well. But with that said, follow along with GCM and Keisler to see how you can get more performance, fuel economy and fun out of your Mustang by upgrading to a Keisler five-speed transmission.