Custom Semi-Truck Transmissions
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Custom Semi-Truck Race Transmissions

Built for semi-trucks. Built to win.

Every race transmission is purpose-built for your race application, powerband, and driving style. Eaton Fuller based. CNC machined. Raced hard. Proven results.

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Use the Gear Analyzer

Semi-Truck Applications Only

Not an automotive shop.

Race Proven In The Real World

Not just bench built.

CNC Machined Gears & Shafts

Ultimate strength.

Direct Builder
Support

Talk to Jimmy.

Built to Handle Extreme Power

Built to win.

Built for Competition

Our custom race transmissions are engineered for racers who demand strength, consistency, and the right gearing to put power down and cross the finish line first. We build complete Eaton Fuller based transmissions with custom rear sections, CNC machined gears, shafts, and components designed for your exact application.

Custom Semi-Truck Race Transmission with Blue Housing on a Workshop Table
  • Eaton Fuller based platforms (13- & 18-speed)
  • Custom rear sections
  • CNC machined gears & shafts
  • Precision setup for your engine, tire, and track
  • Built for durability under extreme loads
  • Designed to work with properly set slipper clutches

Ready to Build a Winner?

Tell us about your truck and racing program and we’ll build it right.

Four Race Ratio Options

We offer four proven race ratio sets engineered for different powerbands, tracks, and driving styles. Use our Gear Analyzer to see how each ratio works with your setup.

Race Ratio #1

Custom Semi-Truck Race Transmission Gear Ratios for 10-Speed Racing Applications
  • 1st 8.67 / 6.43
  • 2nd 6.27 / 4.65
  • 3rd 4.58 / 3.40
  • 4th 3.32 / 2.46
  • 5th 2.61 / 1.93
  • 6th 2.42 / 1.80
  • 7th 1.88 / 1.40
  • 8th 1.37 / 1.00
  • 9th 1.00 / .74
  • 10th .73 / .54

Race Ratio #2

Custom Semi-Truck Race Transmission Gear Ratios for 10-Speed Racing Applications
  • 1st 7.30 / 5.41
  • 2nd 6.09 / 4.51
  • 3rd 4.52 / 3.35
  • 4th 3.32 / 2.46
  • 5th 2.47 / 1.83
  • 6th 2.20 / 1.62
  • 7th 1.83 / 1.35
  • 8th 1.36 / 1.00
  • 9th 1.00 / .74
  • 10th .74 / .55

Race Ratio #3

Coming Soon

Race Ratio #4

Coming Soon

Final ratios may vary slightly depending on your transmission model and application.

Built for These Disciplines

Red Semi-Truck for Quarter Mile Racing at Jimmy's Custom Speed Shop

Quarter Mile Racing

Launch. Shift. Win.
Green Heavy-Duty Semi-Truck Competing in Uphill Truck Racing

Uphill Racing

Power up. Conquer the hill.
Loaded Semi-Truck Pulling a Heavy Trailer During a Truck Racing Competition

Loaded Competition

Maximum load. Maximum performance.
Black Semi-Truck Competing in Sled Pulling at a Nighttime Truck Racing Event

Sled Pulling

Pure Power. Relentless Control.

Our Build Process

Consultation

We learn your setup, goals, and racing style.

Analysis

We use real data and the Gear Analyzer to dial in your ratios.

Build

CNC machined components. Precision assembly.

Test & Verify

Checked for strength, quality, and accuracy.

Delivered Ready to Win

Shipped or picked up. Track ready.

Real Results. Real Trucks.

FULL-THROTTLE LAUNCH

When the lights drop, there’s no holding back. Raw diesel power, massive smoke, and trucks charging hard down the track.

BOBTAIL LAUNCH

No trailer. No extra weight. Just raw diesel power. Watch this Dodge bobtail launch hard and lay down a serious cloud of smoke on the strip.

LATE-NIGHT WRENCHING

When the work gets tough, the crew keeps pushing. Late-night repairs, heavy equipment, and no shortcuts—just the work it takes to get back on the track.
View More Results

Frequently Asked Questions

What type of racing do you compete in?

Tell us your specific discipline, such as quarter-mile drag racing, uphill racing, loaded or bobtail competition, or sled pulling. The racing format, track surface, and distance help us select the right gearing and transmission setup.

Is the truck loaded or bobtail?
Let us know whether the truck competes loaded, bobtail, or in both configurations. Vehicle weight significantly affects launch characteristics, gear spacing, acceleration, and the amount of load placed on the transmission.
What transmission is currently installed?
Provide the transmission manufacturer, model, speed count, and any known modifications. We specialize in custom Eaton Fuller-based 13- and 18-speed race transmissions, so this information helps us evaluate compatibility and plan the correct build.
What differential ratio are you running?
Provide the truck’s exact rear differential ratio, such as 3.55:1 or 4.10:1. The differential ratio works together with the transmission ratios and tire diameter to determine acceleration, engine RPM, and vehicle speed in each gear.
What tire diameter are you using?
Tell us the actual tire diameter or loaded rolling diameter whenever possible. Tire diameter changes the truck’s effective gearing and directly affects engine RPM, launch performance, and top-end speed.
What is your engine’s operating RPM range?
Provide the RPM range where the engine produces usable power, along with its maximum safe operating RPM. We use this information to select ratios that keep the engine inside its strongest powerband after every shift.
What RPM do you currently shift at?
Tell us the RPM at which you normally shift under racing conditions. Your shift point helps us calculate the RPM drop between gears and determine whether the current transmission is keeping the engine in its optimal power range.
What clutch is installed?
Provide the clutch manufacturer, model, size, disc configuration, and whether it is a slipper clutch. The clutch setup affects launch behavior and must work correctly with the transmission, engine power, vehicle weight, and intended application.
What problem are you trying to correct?
Describe the issue as specifically as possible. Common problems include weak launches, excessive wheelspin, engine bogging, falling out of the powerband after a shift, poor top-end speed, large gaps between gears, missed shifts, or repeated component failures.
What performance result are you targeting?
Tell us what a successful build should accomplish. Your goal might be a quicker elapsed time, stronger low-end pull, maximum launch torque, improved high-RPM performance, greater durability, more consistent shifts, or better performance at a particular track. Include current and target performance numbers whenever available.

Not an Automotive Shop

We specialize in semi-truck racing and heavy-duty applications only.

Your win starts here.

Let’s build a transmission that’s built for your track, your power, and your goals.
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