Before the first hot rods were regularly fitted with automatic transmissions, rodders rowed and speed-shifted their manual transmissions with great precision and enjoyment for decades. Today, for a number of reasons, installing an automatic transmission in a rod or custom is no longer the automatic decision (no pun intended) it was in the last few decades. Whether it is for added mileage, performance, or just the pure nostalgia of three pedals, rodders have been opting to use manual transmissions in great numbers lately.
The addition of a Fifth or Sixth gear and the wide selection of gear ratios in the modern manual transmissions have made this choice much more appealing. We will focus on the popular GM T5 unit found in many S-10s, Camaros, Firebirds, and Astro vans. Some swapping of parts may be required for a more friendly installation, but the pieces are readily available used or brand-new at your local parts counter.
The T5 five-speed was originally manufactured by Borg Warner Automotive in 1982 and is still being manufactured today by Tremec. The T5 is the only American-made standard transmission to span almost 20 years of production (GM's Muncie four-speed previously held that honor). Because of the large quantities of T5s produced, many parts are interchangeable, allowing one to create interesting five-speed combinations.
The commonly found S-10 and Camaro gearboxes are getting a lot of attention and interest because they all include a Fifth-gear Overdrive and use the standard GM bellhousing bolt pattern. The T5s can also be found under many late-model Ford Mustangs, as well as a few different Jeeps and other brands (each with their own mounting pattern). The Ford pattern was also used by AMC and Nissan.
Many internal parts are interchangeable, but there are two basic grades of T5s: World Class (WC) and Non World Class (NWC). WC is a later version with many upgrades for smoother operation and improved reliability.
There are several T5 applications to consider. NWC T5s were introduced in 1982 in S-10 Blazers. Those used in the GM S-10 pickups from '83-87 are good candidates, but they do require some modification to work with the earlier clutch and flywheel packages. By 1983, Ford started using them in the Mustang, GM had them in the F-body (Camaro and Firebird), and AMC had them in the Eagle and Jeep lines. AMC dropped the T5 by 1985 to make room for cheaper Peugeot and Toyota boxes. By late 1985, the first WC boxes were used by Ford and had First, Second, and Third gears riding on roller bearings instead of solid shafts. The counter gears saw an upgrade to tapered bearings. Fiber-lined rings and dual cone-designed rings replaced the bronze synchro rings to improve ring surface area. GM started using WC boxes as early as 1988 in the Camaro/Firebird line but still kept NWC boxes in S-10s and Astro vans. Most of the GM T5 installations were all World Class by the mid-'90s.
RatiosThe close-ratio T5 gearbox uses a 2.95 First gear and is the best choice if you desire a performance-oriented setup. Information from the Chevy dealer shows two ratios available from '85-90 in the S-10, though there may be others; ML2 code in the glovebox is 4.03 First and 2.37 Second; ML3 is 3.76 First and 2.18 Second.
An early box with mechanical speedo is a plus since it's very expensive to change from electronic to mechanical speedo drive. S-10 boxes can be found for $50 to $100 at swaps, but the V-8 variants with 2.95 First will run more (around $200)-but crafty hunters can always find them for much less.
Before You InstallBefore you purchase a used transmission, it's a good idea to take a peek inside, or at least before you install it. You can't just pop a cover off to inspect these; you must pull off the tailshaft housing and shifter to get the top cover off. You may as well re-shim the endplay off the main shaft while you're doing this. These transmissions use tapered roller bearings and any endplay will result in sloppy bearing clearance as in sideways play. One might also consider bearings and synchros at this time, along with changing the speedo drive gear, if necessary. Also remove the C-clip from the rear of the output shaft so there is no interference installing your new driveshaft.
Some additional simple mods will need to be done to the tranny. First ream or drill the four mounting holes to open them up from the metric size to half inch. You will notice the input shaft, the pilot part of the shaft, and the front bearing retainer are longer than the stock tranny's. Cut about a quarter-inch off the pilot to match the stock one. This still leaves the overall length of the shaft a little long, but this should not be a problem; you can drive the pilot bushing in further if it does interfere.
Selecting a TransmissionSo, which tranny is right for you? That depends. The major differences are in the ratio spacing and First and Overdrive ratios. Some users have reported that the 4.03 First gear models are too low for normal street use with smaller engines. Tire size matters too, so changing to a taller (larger-diameter) tire will offset this somewhat since most of the S-10 trucks used relatively small tires. A taller tire will result in a higher (lower numerically) effective ratio in all five forward speeds. The lower Fifth gear ratios will give you higher, quieter top gear cruising speed due to lower engine rpm.
The Camaro/Firebird F-body transmissions are another T5 option. These are desirable for the better ratio spacing, higher First gear, and ease of adapting to the early bellhousing and clutch, but the shifter location is all wrong for most early vehicles. Luckily, the more user-friendly S-10 rear shifter housing can be bolted to the beefier Camaro gearbox.
The S-10 T5 has turned out to be the transmission of choice when trying to put an Overdrive manual transmission in early Fords and other hot rods and customs for many good reasons, like size and adaptability. Because the T5 has internal shift linkage that can't be altered easily, most prefer to use the S-10 T5 because the shift linkage is set far forward on the transmission in comparison to all the other models. Using the S-10-style shifter housing means the shifter will be located close to the stock location and will not come out under the seat. You will want to use an early T5 if you are using an original mechanical or cable drive speedometer, and you'll want to use a later transmission with a pulse generator if you're using electric gauges.
Bellhousings and AdaptersA wide variety of adapters are available to connect early engines to modern manual transmissions. They range from vintage units originally designed to adapt Chevrolet three- and four-speed manual transmissions, to brand-new kits made with the T5 mating in mind. For ease of following this story, the focus will be made on mounting the GM-based T5 transmission, but alternative versions of this popular gearbox were made with different mounting patterns (Jeep and late-model Ford, to name a couple) that can also be adapted using similar methods.
Certain engines, like late Flatheads and early Hemis, will require the use of both a factory bolt-on bellhousing and an aftermarket transmission adapter to complete the conversion. Some of the alternative engines, like Ford Y-blocks and Cadillacs, may use a combination of adapters, such as first a unit that would adapt the engine to an early Ford transmission (a style of adapter commonly made in the early days of rodding for Ford cars using an early Ford driveline) then bolting a second early Ford to a GM manual transmission adapter (a style of adapter available today from sources such as Speedway Motors or Wilcap) to complete the adapter process.
The selection of adapters used will require some backyard engineering in some cases when it comes to making the connection with the clutch and flywheel, so the use of a good machine shop may be necessary to assist with getting everything to hook up.
Clutches and FlywheelsOne of the trickiest parts of these conversions can be figuring out the correct clutch and flywheel package. The input splines of the T5 transmission are shorter than the earlier manual transmissions, and the splines also differ in both size and number as well. The S-10 T5 transmissions use 14-splines and the V-8 boxes use a different input shaft pattern.
When dealing with American engines, the most commonly used clutch and pressure plate combinations are 10-, 10.5-, and 11-inch clutch and pressure plates (although some applications can be smaller). The main differences in all clutch packages are the type of arms used to engage the pressure plate and the center hub (puck) used in the clutch disc to match the input shaft in the transmission. Companies like McLeod can build custom clutch packages to fit just about any combination a rodder can dream up, and they can build each one to fit the specific needs of each consumer. When ordering a clutch package, know what you want as far as a stiff or softer clutch pedal and what kind of driving you will be doing with your car, because boulevard cruisers and Top Fuelers each use very different clutch packages.
One way to think of the relationship between the pressure plate, clutch disc, and flywheel is that it uses the same principles as a disc brake setup. The throwout bearing engages the pressure plate the same way a brake caliper pushes the brake pad against the rotor, which in this case is the clutch disc and flywheel. The rotor must be totally flat and the brake pad in optimum condition for brakes to work properly, and the same is true with the clutch disc, pressure plate, and flywheel surfaces. If a clutch disc is worn or oily, or the pressure plate and flywheel surfaces are not completely flat, these parts cannot correctly transfer the power from the engine into the gearbox. Just replacing a clutch disc without at least resurfacing the pressure plate and flywheel surfaces is not recommended.
Pilot BushingsThe pilot bushing is usually made of brass or bronze and is used to locate the input shaft of the transmission into the crankshaft of the engine, thus putting the engine and transmission in the exact same plane. Custom pilot bushings are available from most transmission suppliers and good conversion kits will include this important piece. Be sure to carefully measure the inside diameter of the crank opening and the outside diameter of the input shaft to ensure that you order the correct bushing.
When driving in the pilot bushing adapters, remember there is a different depth depending on what transmission you are using. If you are using an '82-92 S-10 five-speed, drive the adapter in until it bottoms out. All other transmissions drive it in until it is flush with the rear of the flywheel-locating flange, since the '82-92 S-10 five-speed input shaft is slightly longer than the standard GM transmission.
Shifters and AccessoriesTo make shifting a fun and positive experience, many aftermarket companies, like B&M, Hurst, Lokar, and McLeod, offer a wide selection of aftermarket shifters that improve both shift characteristics and look stylish inside your rod or custom. While the stock shifters have a longer and sloppier throw, the aftermarket shifters can provide a much more positive and tighter shift pattern.
Clutch ActivationThere are two choices when activating any clutch: mechanical or hydraulic. The first choice, mechanical activation, will require a clutch pedal (currently a hot item in any hot rod) connected to a series of linkages to activate a clutch fork or shaft that will engage the throwout bearing and pressure plate.
The second choice will again start with a clutch pedal (can be floor- or firewall-mounted) that will activate a small hydraulic cylinder (through a hose connection) that will activate another cylinder on the other end that will engage the throwout bearing and pressure plate. This type of setup is particularly helpful in vehicles without the space for mechanical linkage that can become something of an involved project in many situations.
Kits and SuppliersAn average rodder can most likely figure out how to mate a later transmission to their early engine, but to save a lot of frustration from trial and error and grief that may include pulling a drivetrain package numerous times before complete success, a transmission installation package put together by one of many suppliers will most likely be a welcome sight.
A transmission installation kit takes out the guesswork of frustrating "backyard engineering" that can be both expensive and time consuming. Consult the suppliers listed below before tackling one of these conversions.