Hot Rod Overdrive Conversion - Five-Speed Fever!

Fuel economy and gas mileage are two terms that are impossible for hot rodders to ignore these days. With the current trends in the price of oil, those of us driving gas-guzzling or otherwise unfriendly fuel consumers are going to get hit the hardest. There are numerous ways to increase the fuel efficiency of your hot rod-from updating that old Quadrajet to a modern EFI system to changing the gears in your rearend-but one of the easiest and perhaps cheapest ways to go is to install an overdrive transmission. For those of you running a Muncie or similar manual trans behind a small-block Chevy, dropping in an overdrive manual trans such as a T5 or a Tremec TKO can't get any easier. And while a brand-new overdrive five- or six-speed gearbox may not be the cheapest way to reduce engine speed and gain fuel efficiency, there are junkyards full of a great alternative-the T5.

Originally manufactured by BorgWarner Automotive, the T5 transmission first appeared in the early '80s. These early T5s are classified as non-world class (NWC) and are rated for slightly less power than their later world class (WC) counterparts, which appeared by the end of the decade in the Mustang, Camaro, Firebird, and even some Jeep lines. The only American-made transmission to span more than 20 years, there is now a good supply of T5 transmissions, both WC and NWC, in salvage yards across the country. Given their relative abundance, they have become a very popular option within the hot rod crowd when it comes to an economic overdrive manual trans. With five fully synchronized forward gears, an overdrive, an internal shift-rail mechanism, and the ability to handle more than 300 lb-ft of torque, the T5 is also one of the most versatile manual transmissions available. Over the past 10 years or so, supported by a strong aftermarket industry supplying adapters to a vast number of vintage engines, the T5 has continued to increase in popularity. Add to that the compact size and light weight of the T5, and you have a transmission that seems almost tailored for use in a hot rod.

One of the problems with the later WC T5s, however, is shifter placement. While the Muncie, T10, and even the early Ford '39-style boxes placed the shifter relatively close to the bellhousing, the WC T5 places the shifter way back on the tailshaft, which is too far back for most hot rods and early trucks. This often causes interference with stock bench seats, among other things. The S-10 truck T5, however, has the shifter in a more appropriate location-about 10 inches closer to the bellhousing. While not as strong as the WC trans, the NWC S-10 transmission would be fine in a mild hot rod or truck with, say, a Flathead. But, you can have your cake and eat it too with the T5 trans. There are a few different variations of the original design because the T5 transmission has been produced in such large quantities and in such a wide variety of models, and, luckily for us, the parts needed to relocate the shifter position are interchangeable. This is great news, but unfortunately requires either finding the correct two transmissions or a good WC trans and the few parts it takes to make the conversion possible.

Recently, I became the proud owner of a '52 Ford F-1 pickup project I shouldn't have and began putting the drivetrain together for it. An old Chrysler Hemi engine from a previous project, along with a Camaro T5 transmission, was bolted together and slid between the framerails. Taking a few rough measurements, it quickly became clear that the shifter location on the Camaro trans was going to be located too far rearward for the truck cab. A call to Julian Nieto at 4C's Transmission in Whittier, California, located an S-10 tailshaft with the forward-mounted shifter location, along with the necessary shifter shaft. This swap will not only move the shifter forward about 10 inches, but will also center and level the transmission mount. Julian also installed a new rear seal in the tailshaft to ensure the final assembly would be leak-free.

With parts in hand, I headed back to my shop, where in a single evening I had the tailshafts swapped out, the internals of the transmission inspected, and the entire assembly back between the framerails of the F-1 in preparation for the crossmember and motor mounts to be installed. When the time comes for the trans to be installed permanently, it will be filled with Synthetic ATF and 12 ounces of Lucas Oil, but for now the shifter falls just under the dash and clears the stock seat assembly, enabling the use of a stock-looking early Ford shifter, all with the performance and reliability of a modern-day overdrive transmission.

Inspecting the Internals
Since the case cover is removed to install the shorter S-10 shifter shaft, it's as good a time as any to inspect the transmission internals. Visually inspect all parts except O-rings and oil seals, which should be replaced with new parts. Draining the oil out of the trans is of course necessary to thoroughly inspect the internals of the transmission and also makes the mess slightly more manageable. Be sure to inspect the trans oil for metal shavings or other indications of unnecessary contact or wear, and also inspect the internals and case as well. Check the gear tooth contact patterns and compare with the diagram shown. Parts with contact patterns shown in the accept column are good to go. Those in the reject column will wind up being wall art. The gear and spline teeth also need to be inspected for chipping and compared to the diagram shown. Small burrs, nicks, or chips that fall under the repair column can be blend-repaired using a high-speed, handheld grinding tool. The repair should be blended into the surrounding area, removing as little material as possible, and leaving a smooth contour, devoid of any sharp edges. The gear teeth also need to be inspected for contact patterns and replaced as needed. The spline teeth will not show such wear, but may show signs of step wear, which warrants replacement. Inspect the clutch teeth as well for rounding. Face rounding will cause the clutch to jump out of gear. Clutch teeth with rounding on the end are usable, but will result in hard shifting. Burrs, nicks, or chips can be repaired in the same manner as gear teeth.