Modified Mustangs & FordsHow To Drivetrain
Tremec 3550 Five-Speed Transmission Rebuild
Slick Shifting Upgrade
While the Top Loader transmission will always hold a place in our hearts for the untold gear exchanges it has made in our classic Fords, many people are turning towards overdrive transmissions for better fuel economy and added strength. Tremec remains the go-to standard for brand new gearboxes, but if you like to have a more hands-on and/or budget-conscious approach, rebuilding a used unit might be right for you.
As a longtime Fox Mustang enthusiast, this author remembers the early ’90s 5.0 craze well. The Fox Mustang was a clean slate. The engine wasn’t that great, nor was the suspension, brakes, rear axle, chassis, or transmission for that matter. But Ford built plenty of durability into those stock components—the engine, as well as the rearend, could handle just about everything you could throw at it in that time period. It became apparent, once you added some horsepower and started running slicks or power shifting, that the T-5 transmission would start showing its weakness. It was not so much a weakness, but more to the fact that it was being asked to perform at a level beyond its intended design.
Later T-5s were the strongest, and soon the ’93-’95 Cobra T-5 “Z” internals were the hot ticket to build the highest torque rated T-5s of the time at 330 lb-ft. But the bolt-ons still kept coming and the horsepower levels kept rising. Nobody had much to offer in the way of a heavy-duty transmission that would handle the newfound levels of horsepower and torque. Some resorted to installing Top Loader four-speeds for track duty, and the more affluent racer sprung for boxes from Jerico and Liberty. There was nothing really affordable or practical for the street until the Tremec 3550 and TKO transmissions debuted.
At the time of the 3550’s release, the GM folk were all about the T-56 six-speeds in their new F-bodies. But to the Ford gang, the five-speed 3550 was a godsend. Torque ratings were very conservatively rated at 350 lb-ft for the 3550 and 375 lb-ft for the later TKO. Ford even saw fit to install the 3550 into its ’95 Cobra R behind a 351 Windsor. Times were pretty good for a while.
Tremec transmissions may seem daunting to work on, but they actually require fewer special tools to rebuild than a T-5 does. Simple handtools and a pair of expanding ring pliers are about all that is usually needed.
Back then, these transmissions retailed for around $1,200, and you still needed to buy a new bellhousing as well as perform a few modifications to the car to get it to fit. Adjusted for inflation, that price has easily doubled for the new Tremec TKO 500 and 600 series transmissions.
These transmissions have been coming up for sale more and more frequently in the recent years, but unfortunately, many have been abused and lived hard lives. Let’s face it; someone didn’t pony up the cash for an expensive transmission because he wanted to install it behind a stock 5.0 daily driver. No, more likely the owner blew up his T-5 because of the power upgrades and/or racetrack use, so an upgrade was required.