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47RE Transmission Rebuild: $4,000 DIY Build for a 650 HP Diesel

Published December 3, 2023 · Updated August 27, 2026

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A 1996 Ram came back from an engine build making far more power than its factory 47RE automatic could hold: the transmission started slipping on the dyno at just over 400 horsepower. Upgrading an engine and leaving the transmission alone is one of the most common and most expensive mistakes in diesel builds, so the gearbox came out and was rebuilt to take 650 horsepower and more than 1,300 lb-ft of torque.

This is a single project rather than a product comparison, and the rebuild was done the way it would be in a home garage rather than on a shop's transmission bench. The case was stripped to bare metal, each subassembly rebuilt on its own, then clearances and end play set with a feeler gauge and a dial indicator before the air checks. Billet parts replace the pieces that fail under the high line pressure of a performance valve body, and the clutch packs gain capacity: third gear goes from four clutches to six on high-energy semi-metallic GPZ lining, and the overdrive pack from five friction plates to six.

Price of a 650 HP 47RE: Built Unit vs. Home Rebuild

US dollars, lower is better. These rows are project costs, not the prices of two competing products: the first is the quote for a transmission bought already built, the second is what the parts and a do-it-yourself rebuild came to.

A 47RE bought already built to hold 650 horsepower was quoted at over $7,000. Doing the same work at home came to roughly $4,000 once the billet parts, the rebuild kit and the high-performance torque converter were paid for, so the labour bought back about $3,000. The transmission is also only half the bill, with the engine and transmission upgrades together running about $10,000.

Full results table

Rank	Product	Result
1	Rebuilt at Home from a Kit	$4000
2	Bought Already Built (Quoted)	$7000

Factory vs. Billet Driveline Parts

Weight in pounds, heaviest first. Each pair is a factory component and the upgrade that replaced it, so the heavier item in each pair is the billet part.

The billet flex plate weighs almost twice what the factory one does, 12.6 pounds against 6.81, and is built for around 2,000 horsepower where the factory piece was never designed past 500. The torque converter puts on 8.1 pounds moving to the high-performance unit. Cutting the original open showed hot spots on the lock-up friction lining and a thin, welded back cover that flexes away under load, which is exactly what the slip on the dyno had been doing to it; the replacement uses a solid billet cover and three friction discs.

Full results table

Rank	Product	Result
1	High-Performance Torque Converter	63.80
2	Factory Torque Converter	55.70
3	Billet Flex Plate	12.60
4	Factory Flex Plate	6.81

Acceleration Before and After the Build

Seconds, lower is better. Every row is the same truck, in stock form and after the engine and transmission work, rather than a comparison between products.

Stock, the Ram needed 17 seconds to reach 60 mph, and over 45 seconds with a 10,000-pound trailer behind it. After the engine work and the rebuilt transmission the same run took 7.5 seconds, and that was with the tires spinning on a loose backcountry road. The passing figure is the one that changes daily driving: 40 to 60 mph fell from almost 10 seconds to under 3.

Full results table

Rank	Product	Result
1	40-60 mph, After the Build	3
2	0-60 mph, After the Build	7.50
3	40-60 mph, Stock	10
4	0-60 mph, Stock	17
5	0-60 mph, Stock, Towing 10,000 lb	45

The Verdict

The build did what it set out to do. On the dyno the truck made 527 horsepower and over 1,200 lb-ft of torque, and the rebuilt 47RE held it, the same transmission that had been slipping at just over 400 horsepower before the work. Acceleration to 60 mph dropped from 17 seconds to 7.5, and the 40-to-60 mph passing time from almost 10 seconds to under 3. Economy held up as well: the drive out from Missouri to Utah averaged just under 15.5 mpg at a 75 mph speed limit, despite a 4.10 axle ratio that is poor for highway speeds, and the same roads on the way home returned close to 2 mpg better on the improved timing, injectors and turbo.

On money, a ready-built 650-horsepower 47RE was quoted at over $7,000 against roughly $4,000 to build one at home, and the engine and transmission upgrades together came to about $10,000. Set against a replacement vehicle, that is around $60,000 cheaper than buying new. Doing it in a home garage is realistic too: the transmission and transfer case came out in about an hour and 15 minutes without a lift, a block of wood and a hammer stood in for proper seal and bushing drivers, and a homemade compression tool handled the clutch springs.

Two things decide whether a rebuild like this lasts, and neither is muscle. The first is measurement. The front drum wants 0.025 to 0.035 inch between the snap ring and the reaction plate, the third-gear drum 0.090 inch, and input shaft end play has to fall inside the 0.034 to 0.084 inch spec, which this build hit at 0.050. Seat the input assembly wrong and the end play goes with it, which is enough to destroy the transmission inside the first 20 miles. The second is fluid. The new clutches shed a lot of material during break-in, so the filter and fluid want changing at 1,000 miles, then every 30,000 miles after that.