Inside Dorsey Diesel’s Stage 4 4R100

Tuning, turbo, and injection system technology has come a long way for the 7.3L Power Stroke in recent years. The amount of horsepower that can be gleaned from Navistar’s dinosaur V8 is constantly on the rise, and at the present time it’s not uncommon for a 7.3L-powered Ford to be making 600 to 650 hp at the wheels. However, pushing the 7.3L platform to new heights has had its downside: a lot of dead E4OD and 4R100 transmissions. In many cases, the parts used in the built transmissions of yesteryear no longer suffice in today’s highpower environments. The sub-500hp 7.3L days are over.


The long list of improvements began with the Low/Reverse drum. In factory form, the reverse hub can actually flex and blow out under high horsepower and stress. To ensure that doesn’t happen, Dorsey CNC machines this reinforcement ring and TIG welds it to the bottom of the reverse hub.


After tearing down the ailing 4R100 in Jake Enos’s ’02 F-350, Chuck Dorsey cleaned up the case and resurfaced it via hand stone. Once the transmission case was checked for trueness, it was coated in Dorsey Diesel blue, tilted vertically on Dorsey’s transmission stand, and the Stage 4 build commenced.


Throughout the Dorsey Diesel Stage 4 build, Raybestos GPZ clutches are employed. The GPZ clutch line has become a popular choice for 4R100 builders due to its added holding capacity, higher heat resistance, and smoother engagement over competing products. On top of that, the friction material found on the GPZ outperforms the OE clutches by as much as 20 percent.


Dorsey’s preference is to build each sub-assembly first (i.e., Low/Reverse, Direct, Forward) and then install them. Here, the Direct assembly has been pieced together, complete with new bushings installed. It receives seven GPZ clutches versus the five that are found in a stock 4R100 (and sometimes four, depending on the truck). After assembling Direct, Dorsey moved on to the Forward drum: a 4140 heat-treated and stress-relieved steel piece sourced from TCS. Six GPZ clutches would be installed in the Forward drum (compared to four clutches stock).


A billet intermediate shaft upgrades one of many weak links in the 4R100. The unit used in Dorsey’s Stage 4 transmission is made from 300M billet steel and comes from TCS. Transmissions built to handle moderate horsepower (450 to 600 hp) are often equipped with a cryogenically treated stock intermediate—but the cryo’d unit that was removed from Enos’s 4R100 showed noticeable signs of wear on the engagement teeth.


To add considerable strength to the sun gear shell, a hardened version (left) replaces the OEM stamped steel unit. When the splines break off in the factory sun shell, shrapnel and debris are sent through the direct planetary, which wreaks all kinds of havoc on the gear train.


For added durability in the direct drum assembly, a heavy-duty, 45-element sprag is installed. The 45-element sprag is a direct replacement and a considerable improvement over the stock 34-element piece.


The first component to be lowered into the transmission case was the Low/Reverse hub assembly. For increased holding capacity, eight GPZ clutches are present in the Low/Reverse assembly of a Dorsey Diesel Stage 4 4R100 compared to six on a factory transmission (and just four on some cab-and-chassis models).


After the Direct, Forward, and sun shell assembly were lowered into place, the Direct band (which is only applied in Manual, second gear) was soaked in ATF and installed. Then four GPZ intermediate clutches were set in place (shown), whereas a stock 4R100 makes use of three.


Once the center support had been machined on both sides (to keep it from rocking back and forth and to accommodate snap rings), Dorsey validated its straightness with a caliper. Tightening up tolerances by way of precise machining of the center support is vital to keeping everything in a straight, centered line within the transmission.


You won’t find a gasket like this in the factory 4R100. It’s a center support gasket that Dorsey adds to his transmissions to ensure no cross leaks occur between the center support and the bearing housing.


In addition to receiving a new bearing in the center support bearing housing, new sealing rings were also installed on the outside. Notice that the sealing rings are installed in a staggered position, reminiscent of piston rings. After the center support was in place within the transmission case, the center support bolts were tightened but not yet torqued to spec.


It’s common for a 4R100 to lose overdrive when the intermediate/overdrive cylinder snap ring works itself loose. To eliminate this possibility in his transmissions, Dorsey installs a spiral snap ring. Then the intermediate/overdrive cylinder is fitted with fresh gaskets and installed on top of the intermediate return (diaphragm) spring in the transmission.


Throughout the assembly of the gear train, Dorsey simulates (and validates) clutch engagement using 150 psi worth of compressed air. Normal operating pressure within the transmission will check in at roughly 300 psi.


The next item of business called for the installation of the overdrive clutches. With five GPZ clutches being utilized in overdrive versus just two or three (depending on the truck model) being used in a factory 4R100, vastly improved holding capacity is present in the overdrive assembly of Dorsey’s Stage 4 transmission. As for the overdrive planetary, a 4-pinion, 4140 HTSR billet steel unit was used.


It’s common for the snap ring located within the coast clutch assembly to work its way loose in the stock 4R100, which causes loss of all engine braking capability. To keep the snap ring in place at all times, Dorsey machines the coast clutch drum to accept the thicker, wider, and stiffer snap ring shown on the right.


In addition to being modified to provide higher flow and pressure, Dorsey treats the transmission pump to several upgrades. The first improvement is a custom-machined boost valve and sleeve (right), which is what controls converter lockup. In stock form, the 4R100’s converter lockup is pulse-width modulated, which allows for controlled slippage of the converter clutch. In a Dorsey Diesel 4R100, lockup is solid (no slipping) and the lockup event occurs on fluid dump.


Another trick Dorsey employs in the pump entails the use of a heavy-duty spring on the pressure regulator. The pressure regulator is what controls the internal pressure of the transmission, and the orange spring shown here allows a peak pressure of roughly 300 psi to be achieved (compared to 210 psi stock). In addition, the spring is of a progressive rate design, which means pressure increases with engine rpm.


After testing various parts combinations on his 7.3L over the years and perpetually ramping up power along the way, the built 4R100 in Jake Enos’s ’02 F-350 was on the verge of calling it quits. As the owner of Irate Diesel Performance—a company that specializes in all areas of 7.3L performance—Enos regularly uses the truck to showcase just how fast a 7,900-pound 7.3L Super Duty can be (12.40s on fuel, 11.70s on spray). He not only wanted the truck back on the racing circuit as soon as possible, but he needed a transmission that could hold up to the rigors of competition and the stress of 800-plus horsepower.


With a new pump gear installed, the pump halves were aligned via a band clamp and all bolts were torqued to spec. We’ll note that Dorsey double-checks every fastener he torques throughout the assembly process, and that all reusable fasteners are cleaned up in a bolt tumbler.


Perhaps the most recognizable upgrade in the Dorsey Diesel Stage 4 transmission is this billet input shaft. Like the billet intermediate shaft, it too came from TCS and is made of 300M billet steel. Heattreated and precision ground, this input shaft is rated to handle 2,000 lb-ft of torque.


Once the input shaft was set inside the pump and the pump was bolted into the case, the transmission was flipped over and the previously installed center support bolts were tightened. If the center support bolts back out, you can lose Reverse and your forward gears as well as build a ton of heat in the transmission. Dorsey installed brand-new center support bolts, coated their threads with Loctite, and torqued them to spec.


In high-horsepower, competition-style environments, a transmission’s case can flex tremendously. When this happens on a 4R100, the two-piece rear case bushing is known to wear prematurely and fail. Dorsey installs this one-piece Sonnax bushing in his transmissions to prevent this from happening.


Because the composite Second-to-Third shift valve (bottom) used from the factory is known to bend, lose its anodizing, and dig into the valve body, Dorsey machines his own 2-3 shift valve out of steel (top). In addition to being vastly stronger, Dorsey’s custom 2-3 shift valve works in conjunction with a stiffer spring to ensure the 2-3 shift never hangs.


While setting up the valve body, Dorsey checked all modules for trueness using a straight edge and a 0.002-inch feeler gauge. During the preparation process that takes place before assembly, all components of the valve body are re-surfaced via hand-stone (i.e., the accumulator body, valve body, separator plate). Here, Dorsey ensures the accumulator body meets his tighter-than-factory specification for allowable tolerance.


Within the accumulator body, Dorsey increases the fl uid pressure that’s applied to the clutches by installing a 0.500-inch line pressure modulator valve and sleeve. The 0.500-inch piece is primarily reserved for competition builds such as this Stage 4 version. From left to right, the business ends of 0.500-inch, 0.427-inch, and 0.372-inch line pressure modulator valves and sleeves are shown (we’ll note that the 0.372-inch unit is found in the stock 4R100).


Leaving nothing to chance, Dorsey installs a brand-new Ford solenoid pack in every 4R100 he builds, along with a new fi lter and custom steel fi lter locking tab. For this build, Dorsey topped things off with a new standard capacity Dorman transmission pan.


After installing a 70psi spring in the 4R100’s bypass tube to keep the rear sprag and rear of the transmission cool, it was time to put the fortifi ed unit back into the truck. If the pink torque converter doesn’t look familiar to you, it should. It’s a Stallion model triple-disc converter from Precision Industries—one of the most proven torque converters in the 7.3L Power Stroke world.


To ensure the center section never gets ripped out of the fl ex plate, a billet unit was sourced from Precision Industries. Its fl ex plate meets SFI 29.3 specifi cations, comes with an unconditional lifetime warranty, and retails for less than $500.


For added insurance, a 37-row stacked plate transmission cooler from Mishimoto would be installed along with the Dorsey Diesel Stage 4 4R100. Designed for the 6.0L Power Stroke, this massive cooler should have no problem keeping ATF temps where they need to be.


After successfully installing the transmission back in the truck, Enos took his Super Duty on a fi rst test drive. Upon his return—and with the “all clear” from Dorsey—he wasted no time helping himself to a tire-melting burnout.

For the ultimate race-ready 4R100, the truck was dropped off at Dorsey Diesel in Park Hills, Missouri, for one of that company’s Stage 4 builds. Once the four-speed had been torn down, cleaned up, and its case re-surfaced, it was fitted with a host of billet and precisionmachined hard parts, upgraded clutches, steels, a high- ow pump, modified valve body, and a few trade secrets. A Precision Industries triple-disc converter and Mishimoto 37-row transmission cooler would round out the long list of improvements.