Michael Czap
December 31, 2013

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.

1. After purchasing the transmission, we disassembled it, inspected the components, took stock in what it needed, and placed everything neatly in a storage container until the replacement parts arrived.
2. For the novice transmission rebuilders out there, rebuild DVD’s can be purchased from vendors such as Hanlon Motorsports, and will guide you step-by-step through the entire process.
3. This simple synchronizer, or more accurately, “blocker ring” kit also includes a small assortment of other parts and can be purchased for around $100. This kit came included with the transmission, as the previous owner thought that was all that was needed. Not so much. There are aftermarket carbon-fiber-lined synchronizer kits that can be substituted. They tout faster shifts at higher rpm than the original components.
4. Severe-engagement tooth wear was evident on the 1-2 and 3-4 sliders. The 1-2 slider assembly is a big-ticket item at almost $300 by itself. Here you can see the difference between the old warn down sliders and the new $130 3-4 sliders. The old teeth aren’t merely rounded off, but heavily chipped as evident by the jagged edges.
5. Clean the mating surfaces gently with razor blades, scrapers and Scotchbrite pads. Power tools can quickly gouge the aluminum and are not recommended. These transmissions have precision-machined surfaces and have much tighter build tolerances than you might think. It doesn’t take much to cause case or cover misalignment.
6. The countershaft drops right in without the need for any special tools.
7. Don’t lose or damage this bearing. It’s made in Germany and costs $150 to replace.
8. The Reverse gears and Fifth-Reverse shift arm are installed next.
9. Don’t fear these needle bearings. Once you use some grease to install them, things quickly start shaping up. Tremec transmissions have very robust bearings and rarely ever need replacing.
10. Sticky with grease, the bearings are now installed onto the Fifth gear clutch cone.
11. Here we have the Tremec 3550 (upper) and TKO (lower) mainshafts. The 3550 shafts can break where they neck down toward the yoke splines, or even twist the splines themselves. Bringing a driveshaft yoke to test for twisted splines is a good idea when evaluating a used 3550/TKO 500 for purchase. The early TKO mainshaft can be retrofitted into a 3550 by simply machining the tailshaft housing to utilize the larger C-6–style tailshaft bushing. These mainshafts also store perfectly in old camshaft boxes.
12. Here’s a closer look at the differences of the 3550 versus the early TKO mainshaft, with a penny used for reference.
13. The mainshaft build starts here with it clamped in a padded vise.
14. Before you start reassembling the gears, make sure you clean up the burnished and polished surfaces left by the old brass blocker rings, as shown on this Second gear. This will ensure a fresh surface so the new rings can bed in quickly and more evenly.
15. Here is the mainshaft ready to install.
16. Here, we are installing the assembled mainshaft into the case, with the addition of the Fourth gear clutch cone. Yes, it does fit, eventually.