Bulletproof Your Dodge Transmission - Diesel World

Brown’s Diesel and Goerend Transmission Build a Race-Ready 47RH Four-Speed Automatic

It’s no secret that diesel engines can handle stupid amounts of power. But transmissions? Not so much. The 47RH four-speed in our ’95 Dodge was based on an original 727 muscle car transmission (’89 to ’91 Dodges actually had 727 three-speeds), except the 47 Series has an overdrive gear along with a lock-up converter. This gave Dodge diesels a whole new rpm range as well as lock-up for better mileage and increased power to the ground. The 47RH is a solid piece, and that reliability extends to the later 47RE and 48RE models found in ’96-’07 Dodges.

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With a factory power rating of 160 hp and 400 lb-ft of torque, the Dodge four-speeds have to be fairly strong, not for the horsepower rating, but rather the torque. This means that with tricks like increased line pressure, the torque-handling capability can be bumped even higher. Converter clutches can only handle so much power, so new triple-disc converters were developed by aftermarket suppliers. Then came billet shafts, Alto clutches, and other goodies. Some transmissions can handle 1,000 hp and 2,000 lb-ft of torque. This is the type of transmission we’d be building.

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Before the factory Dodge 47RH four-speed could be removed, everything connected to the transmission had to be disassembled. The team of Garrett Von Flue and Gustavo “Goose” Quezada started with the driveline. Remember to check those U-joints!

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The shifting linkage, wiring, and four-wheel drive shifter also had to be disconnected before the trans could go anywhere.

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Underneath the Dodge you can see the flywheel with the inspection plate removed but not the converter bolts! There’s actually an access panel further up on the bellhousing. The engine can then be turned over with a barring tool to access each bolt.

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After loosening everything up, one of Von Flue’s last steps before removal was removing the factory transmission pan and draining all its fluid.

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After loosening the transmission-to-engine bolts, everything was ready to come out! The sturdy stock pan was reinstalled and the transmission was lowered out of the truck with a transmission jack.

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Once on the bench, the 47RH could now be disassembled and inspected. The first step was to remove the valvebody.

For help with supporting our massive power goals, we turned to Brown’s Diesel in Riverdale, California, and Goerend Transmission in St. Lucas, Iowa. Although it seems unlikely, a cross-country partnership has been established for more than a decade between Goerend, who builds the valvebodies and converters, and Brown’s Diesel, who installs them. In addition to drag racing diesels, Brown’s has built transmissions for sled pulling, off-roading, and sand drags, which makes getting down the dragstrip seem simple in comparison.

Our plan for the transmission started at the back of the engine, where the flexplate (which commonly breaks at 400 to 500 hp) will be replaced with a stronger one. Next up, we will add a triple-disc torque converter, which will be stronger, feature a billet front cover, three clutch discs, and different internals to allow it to stall at around 2,500 rpm. This will make the engine quick to get up on boost, even with larger turbos. A billet (usually 300m steel) input shaft will be used, as will aftermarket intermediate and output shafts, because the truck will see hard usage. Finally, the valvebody will be reworked by Goerend, and the transmission will be assembled with tricks and extra clutches at Brown’s Diesel.

While Dodge transmissions aren’t cheap (base towing rebuilds at Brown’s start at around $5,200 installed), when it’s all finished, we’ll have a hell of a piece. Need to tow 20,000 pounds? No problem. Headed to the dragstrip? That’ll be fine, too. This transmission will be able to handle anything we can throw at it. When you’re trying to make 1,000 hp, that’s exactly what you need.

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Next, the torque converter was removed and the front input shaft and pump assembly were taken out.

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With the pump out of the way, the easiest way to remove the drums, clutches, and bands was through the front of the transmission. A number of internal snap rings hold many of these items in place, so removal was performed slowly and carefully.

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Next up was the overdrive section, which had its own assembly. It was removed and taken apart separate from the main case for ease of reassembly.

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Many tow rig owners will choose aftermarket (or “billet”) input shafts only, but because we’d be drag racing, we chose to go with billet input, intermediate, and output shafts that we acquired through Goerend Transmission. While many people dislike having all three shafts billet because of a lack of give, as long as the transmission isn’t set up with extremely hard shifts (which it shouldn’t be), everything should be OK.

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Pump gears are often checked for wear and then replaced if needed.

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The planetaries in Dodge transmissions are extremely tough, especially the later 6-pinion steel planetaries in the 48 Series transmissions. We upgraded our 5-pinion aluminum 47RH planetaries to the 48s for added strength.

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Before reassembly, all the existing transmission pieces must be measured for wear, inspected for scarring, and replaced if necessary.

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Some parts (known as “soft” parts) are wear items and can’t be reused. For performance builds, additional clutches with a more aggressive material can be installed for additional holding power.

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Not all ofthe hard part upgrades are in the valvebody. Brown’s and Goerend go with a different lever, strap, anchor, aluminum accumulator, and second-gear apply piston, as the existing parts aren’t always strong enough to handle the additional pressure of a turned-up transmission.

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Once the case was cleaned, shop owner Richard Brown started reassembly through the front of the transmission. Some parts like the drums and sun shells were reused, but everything else including the planetaries, shafts, clutches, steels, and gaskets, and O-rings were new.

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The second gear band is a crucial piece of the puzzle and must be adjusted carefully to avoid slipping or snapping. Brown has done more than a thousand Dodge transmissions, so he has it down.

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Brown assembles the overdrive section of the transmission separately from the rest of the unit. The overdrive includes new clutches and a new, stronger aftermarket output shaft.

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There actually must be some room for expansion of parts built into the transmission, so some backlash is needed in order to ensure the transmission doesn’t weld itself together. Brown measures every build with a dial indicator before it is installed, and if it isn’t within specs, it comes back apart.

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Goerend Transmission supplied the “brain” of the transmission in the form of one of its performance valvebodies. Shifts are firmed up, pressures are increased, and every valvebody is bench tested before it leaves the shop.

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We also went with a deep transmission pan from Goerend, which has added capacity, cooling ribs, and a magnetic drain plug that will trap any particles.

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The filter on our valvebody received a spacer that moved it downward in order for the pick up to be at the bottom of the deep pan.

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Goerend Transmission is famous for its triple-disc torque converters, which have been proven in 1,500-2,000 horsepower trucks. Because we were thinking about running a big single turbo, we chose a converter that stalls at roughly 2,500 to 2,700 rpm.

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Brown’s Diesel tech Quezada assisted in putting the rebuilt transmission in the same way it came out. Before everything went together though, we had to take care of the flexplate.

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Factory flexplates are known to break with as little as 500 hp, and Brown’s has the carnage to prove it. Again we went with Goerend Transmission for a flexplate. We chose the SFI-approved version because we’d be hitting the strip on a regular basis.

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Thankfully, there’s not much wiring in Dodge transmissions, and every connector was different, so all the electrical was a snap.

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Our transmission had previously been gone through, and someone had used heater hose for transmission lines when they reinstalled it. DO NOT EVER DO THIS! Our lines had already been coming apart because of the heat and were about ready to fail.

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Our modified factory lines were replaced by Brown’s with barbed fittings (these are a must have) and temperature-rated high pressure hose.

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Now it was time for the driveline to go back in; some heavy items like the transfer case are much easier to install when two people are available.

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Quezada also wired switches into the harness so that we could manually control lock-up and overdrive. This would come in handy when driving around (and racing) with a big single turbo.

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Probably one of the most important parts of the whole install is the last step: checking the fluid. Richard Brown prefers to check and recheck after the transmission has gone through all the gears and lock-up, the final reading was done with the transmission in drive at 1,000 rpm, and the fluid was topped all the way off until the full mark.

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OK, so now we had a transmission that could handle some power, but still no power! Next up, we’ll see what a set of Scheid Diesel’s injectors can do!