The transmission is a major factor to consider when converting to modern drivetrain components. In particular, you must determine fitment in the transmission tunnel and shifter location. Modern transmissions, with their additional gears and capabilities, are considerably larger than their older counterparts, and there are many horror stories of chopped transmission tunnels to make the driveline fit.
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The position of the engine is a big factor in determining the location and compatibility of the transmission. If an engine uses tall engine mounts, is pressed rearward, or is offset to clear components it will greatly affect the relationship of the transmission tunnel and the transmission. The bigger transmissions with extra gears do not want to fit in the early transmission tunnels.
The use of off-the-shelf components will limit your options for positioning the driveline to those designated by the vendor. With builds that start from scratch, the engine and transmission can be set for an optimum height and clearance in the tunnel.
Most street rod builders start with the chassis sitting on the correct wheels and tires, with the rear axle and front suspension set at the correct ride height. From there, the placement of the engine and transmission can be moved to clear the tunnel, as well as other components such as steering, suspension components, and ground clearance. Carbureted engines generally have a 3-degree drop at the back when installed. Looking at the carburetor flange on an old intake, the carburetor plate is machined so the carburetor is horizontal when the engine is sitting at 3 degrees. As a result, the engine is at the proper position for the ideal U-joint angles to the driveshaft. The U-joint should not operate in a straight line because the harmonics through the shaft may cause premature failure. The engine and rear-axle pinion angle need a couple of degrees offset to allow the joints to operate properly.
Many builders have claimed that the transmission tunnel on an early 1965–1970 Mustang requires modification to install big transmissions such as the T-56 6-speed. It may be possible, however, to fit the big transmissions by setting the proper ride height, pinion angle, and engine position.
On many Ford installations, the engine is offset to the passenger’s side by about 2 inches. This is to allow for clearance on the driver’s side for steering and other components. This may cause clearance issues on a chassis where the engine is designed to run down the middle. Four-wheel-drive adapters can also cause clearance issues.
There is some good news. Because the modular engine bellhousing hasn’t changed (with two very early exceptions; see Chapter 2), a full range of manuals and automatics are available for the conversion. Everything from modern 6-speeds to conversions to vintage 4-speeds and non-overdrive automatics are available. Yes, it is possible to mount a Ford Toploader behind a Coyote or even a race-prepped C4 small-block automatic.
Factory Manual Transmissions
Factory manual transmissions used behind the modular engine all have internal shift rails, as opposed to the external rods used on transmissions such as the Ford Toploader. Starting in 2005, the shifter used in Mustangs was a semi-external setup, eliminating the longer shifter rail. This can cause some difficulties with some conversions, as most aftermarket shifters are designed for the Mustang chassis.
In 1999 Ford started using a Vehicle Speed Sensor (VSS), sometimes referred to as the Output Speed Sensor (OSS) in place of a mechanical speedometer cable and gear to measure the speed of the vehicle. The speed sensor information is sent to the PCM and then is sent to the gauge cluster and the speed control servo.
On some Tremec 6-speeds, an electronic reverse lockout was used to prevent shifting into reverse, depending on the shift pattern. The reverse lockout is controlled by the PCM, and if the computer senses that the car is in motion, it locks out the ability to place the transmission in reverse. The MT-82 reverted back to a mechanical reverse lockout system.
Most pre-2011 transmissions have the same length input shaft. The MT-82 has a different length shaft, but the bellhousing arrangement makes them interchangeable.
Aftermarket Manual Transmissions
Yes, it is possible to install a Ford Toploader behind a modular engine, and if you have no need for the overdrive or are doing a nostalgic build it might be the right choice. The newest transmissions from Tremec can handle enormous amounts of power and torque, are comparable in weight (aluminum versus cast-iron housings), and have overdrive capabilities. The much narrower Toploader may fit in certain tunnels without major modifications, but also has external shifter linkage that can cause an obstruction. It can be done, but you need to weigh all the factors before deciding. If you decide to install a classic transmission with your build, you need to determine your application and performance target. Also note that this same bellhousing is also used to install Muncie- and Richmond-style racing transmissions, so if your racing class calls for one of these transmissions, it can happen. If you have decided on a Toploader, you need to refer to the bellhousing section to see how to mate the transmission to the modern engine. One of the advantages to using an aftermarket transmission is the multiple mounting locations for the shifter, allowing the transmission to be adapted to the chassis.
Factory Automatic Transmissions
All automatic transmissions on modular engines are overdrive, and most are electronically controlled. Through the years, Ford has improved the shifting and torque converters to improve mileage and performance. As with the manual transmissions, Ford began using an electronic pickup rather than a speedometer cable in 1999.
Ford overdrive transmissions allow turning off the overdrive circuit in the transmission. Most systems use a normally open on-off switch to disengage the overdrive circuit. When running an older AOD, there is no provision for the TV cable used in the older transmission to adjust the pressure. When using a drive-by-wire engine setup, it is better to use a computer-controlled pressure system.
Aftermarket Automatic Transmissions
The aftermarket has vast experience with some of the older automatic overdrives used behind the modular engine. The AOD and 4R70W 4-speed automatics have been very popular with not only the early modular engine drag racers, but really found a base following with the last of the pushrod Mustang racers. Companies such as Lentech and TCI have developed the 4R70W to handle drag racing amounts of horsepower, and its smaller size over the 5- and 6-speed automatics make it a good choice when tunnel space is at a premium. It is also possible to run a C4 non-overdrive automatic, as the components have been developed by Performance Automatic. While losing the advantages of the overdrive for a street car, it is a compact unit that, built correctly, will last forever.
Transmission Crossmembers and Designs
The transmission mount hasn’t changed much over the years. In fact, the original rubber bushing from the 1960s Mustangs and other Ford cars still bolts to many of the modern transmissions. The crossmember has changed considerably, depending on model and year of the vehicle. For the more popular conversions there are off-the-shelf solutions for the crossmember. Dave Stribling Restorations sells a universal crossmember that adjusts up to 6 inches in three axis for installation into 1967–1970 Mustangs. Ron Morris Performance manufactures a crossmember that takes advantage of the inner frame rail extensions and is fully adjustable for T-56 installations in the early cars. Stifflers makes a bolt-in crossmember for conversions into Fox-body platforms, and Schrader Performance has a crossmember to mount the 6R80 transmission in earlier vehicles.
Except for the very first transmissions, the PCM controls all automatics and the circuit used is called the TCU (Transmission Control Unit). If the engine computer cannot control the transmission, or the engine doesn’t use a computer at all (carburetor), several transmission controllers are available to operate the transmission.
If there is a mismatch of speedometer output devices (mechanical speedometer and a digital VSS, or the inverse), converters are available to make the parts work together.
Manual transmissions are all shifted internally and automatics are all cable-operated. The semi-external shifters on the 2005-and-newer Mustang make conversion difficult, but many shifters are available for all the modern transmissions.
Flywheels, Clutches and Pilot Bearings
All modular engines use a zero-balance flywheel or flexplate from the factory as well as 164-tooth ring gears. Depending on the assembly plant, the flywheel has either a 6-bolt (Windsor) or 8-bolt (Romeo) bolt pattern. Ford factory clutches came in either 10.5 inch or 11 inch, depending on the application.
Since the Y-block days, or Stone Age in manufacturing time, Ford has used a .67-inch pilot shaft on the Ford transmissions (with the exception of some early 6- and 4-cylinder applications). Ford originally used an oillight bronze bushing, then went to a needle bearing system, and the new heavy-duty bearings are once again a bushing (aids with some minor imperfections with corroded input shafts that might damage roller bearings).
Bellhousing and Adapters
Because all modular engines have the same bellhousing bolt pattern (except for the very first AOD and front-wheel-drive models, see Chapter 3), the supply of bellhousings available to mount just about any transmission available is surprisingly nice. The biggest and most popular conversion is for a T-56 6-speed. QuickTime makes a bellhousing (PN RM-8080) that works with the factory fork or with a hydraulic throw-out bearing and fits all modular engine platforms. Next would be for the Tremec TKO transmissions, for their durability and ability to take abuse. QuickTime sells bellhousings with and without a clutch fork provision. Although the 4R70W is plentiful for the modular engine, a conversion kit is available from Performance Automatics, LenTech, and QuickTime.
Ford has used both cable and hydraulics to operate the throw-out bearing on the late-model manual transmissions. Some of the later-model transmissions do not have provisions for a clutch fork. In fact, Ford dropped the clutch fork in 2005 and went to a hydraulic throw-out bearing in the Mustang. A cable-style clutch was installed in the SN-95 Mustangs and a large eccentric mounted under the dash that can conflict with other c o m p o n e n t s in a conversion. Modern Driveline has solutions for both hydraulic and cable actuation of the clutch. Converting to a hydraulic throw-out bearing eliminates under-dash clutter and line-of-sight issues with cable and additional slaves cylinders. A throw-out bearing such as Modern Drivelines part MD-900-2506 for the T-56 is fully self-adjusting and with line extensions can get around header clearance issues without affecting performance. Consider eliminating all the mechanical clutch release designs and look at installing a hydraulic throw-out bearing used since 2005.
Ford installed a two-piece driveshaft in many applications, such as Super Duty trucks and full-size vans prior to 2005, but in 2005, it began installing two-piece driveshafts in Mustangs for resonance compliance. These two-piece driveshafts allow for high-RPM stability and eliminate resonance that can destroy the driveshaft. This style of driveshaft has a central bearing and uses CV joints instead of a U-joint on the rear-axle side. At the rear-axle end, a damper is installed to absorb axle vibration and attenuation. Most modular engine conversions use a one-piece driveshaft due to cost, and your late-model engine doesn’t require the two-piece unit.
Primary materials for the driveshaft are steel, aluminum, and carbon fiber. Steel DOM driveshafts are the most common and the lowest cost. Aluminum driveshafts are now used in most factory installations due to their light weight and reduction in recipricating weight. Carbon fiber is the lightweight king and is very strong, but is the most expensive to build. Companies such as the Driveshaft Shop and Dynotech Engineering can help you design the right shaft for your project. Most local shops can build you a nice driveshaft with off-the-shelf parts for most projects, but as you get into higher horsepower and exotic materials, it is better to seek out companies that have real experience making these shafts. Building a shaft out of carbon fiber is completely different from welding up DOM, and I have seen a lot of shaft failures because of inexperience. Seek out a reliable builder for the more exotic shafts.
Swap Spotlight: Coyote Swap into a Fox-Body Mustang
The Fox-body Mustangs of 1979– 1993 are only second in swap popularity to the first-generation Mustangs. Indeed, there are so many Fox conversions now that the specific parts available to do this conversion outweigh those for the first-generation cars.
We didn’t need to look far to find a quality conversion. Skyler Hardy of Avon, Indiana, is the proud owner of this 1992 Wild Strawberry Mustang LX. This car began life as a 5.0 5-speed. A nice ride for sure, but Skyler just wasn’t satisfied with the performance from the original pushrod 5.0, so he opted for a 5.0 with dual overhead camshafts, in the form of a 2013 sealed crate engine.
After pulling the pushrod engine, Skyler got to work cleaning up the engine compartment for a much cleaner install. Scott Rod panels were used to smooth out the interior, and all the wiring would be hidden on the back side of the aprons as much as possible. A UPR Fox-body tubular K-member was used that was already adorned with modular engine mounts, and the UPR coil-overs were used with 10-way Strange adjustable shocks and struts. Maximum Motorsports caster camber plates were installed along with a Steeda bumpsteer kit and a Flaming River manual rack-and-pinion steering system. The rear suspension has all Team Z parts with relocated upper control arms and dual adjustable lower arms.
A Tremec 3550 5-speed with an 11-inch clutch and stock Ford adjustable clutch cable were used. Scram Speed made the throttle-by-wire pedal adapter, Stifflers made the transmission crossmember, and the whole conversion is a bolt-in affair. An aluminum driveshaft came straight from Ford Performance and ties to the 8.8 rear axle with 3.73 gearing.
The sealed crate engine didn’t need too much tweaking, but the computer was reprogrammed with a Coyote tune via Palm Beach Dyno. The Ford Control Pack computer system is mounted behind the front engine apron out of sight. American Racing Headers makes a Coyote-specific full-length conversion header, and JLT provided the cold air intake. The return system already installed in the Fox body was upgraded with an Aeromotive fuel pressure regulator attached to the stock lines. The cooling system was a generic Fox-body radiator that Skyler just had “laying around.” They had to cut off the outlet and relocate it, but it works just fine.
Skyler reports that fitting the engine was a straightforward job, and the most difficult part of the swap was routing and securing the wiring and cables. There was a small clearance issue with the number-2 header tube, so a set of spacer plates was made to raise the engine enough to clear the header tube. A set of custom heater crossover tubes was fabricated to complete the flow of coolant through the engine, and the mass air meter connections were lengthened to fit.
The 1992 Mustang LX is finished in its original Wild Strawberry paint. Mickey Thompson 26 x 6–inch radials were installed in front while 26 x 10–inch drag radials are mounted in the rear on 17 x 4.5– and 15 x 10–inch SVE drag rims. The clean lines on the outside give only a small hint to what has occurred under the hood.
Take a look at Skyler’s award-winning ride and get a feel for how a Coyote engine would look in your Fox-body platform. You can see why the Fox body crowd has been re-energized.
Written by Dave Stribling and Posted with Permission of CarTechBooks