3.42 to 3.73 gear swap: Boost Your Car’s Power with a 3.73 Gear Swap

Are you looking to improve your vehicle’s acceleration and towing capacity? If so, you might have considered swapping your gears from a 3.42 to a 3.73 gear ratio. But what exactly does this mean, and how does it impact your vehicle’s performance? 

In this comprehensive article, we’ll dive deep into the world of gear ratios, discuss their importance in vehicle performance, and provide a step-by-step guide to performing a 3.42 to 3.73 gear swap. 

We’ll also cover some essential post-installation tips and considerations to ensure optimal performance and longevity of your new gears. So buckle up, and let’s get ready to revamp your ride!

3.42 to 3.73 gear swap

Understanding Gear Ratios

A gear ratio is a fundamental concept in mechanical engineering, particularly when working with gear systems. It describes the relationship between the input and output gears, determining the rotational speed and torque of the output gear. 

Gear ratios are essential for understanding how machines work and are crucial in applications such as automotive transmissions, bicycles, and industrial machinery.

To better understand gear ratios, let’s break it down into several components:

Gears: Gears are toothed wheels that mesh together to transmit motion and force. They come in various shapes and sizes, with the most common being spur gears, helical gears, bevel gears, and planetary gears.

Input Gear (Driver Gear): This is the gear that receives power from an external source, such as a motor or engine. The input gear initiates the motion, and its rotation is the input speed.

Output Gear (Driven Gear): This gear receives motion from the input gear, and its rotation is the output speed. Output gears are typically used to drive a specific mechanism or load.

Gear Ratio: The gear ratio is the relationship between the number of teeth on the input gear (driver) and the number of teeth on the output gear (driven). It is usually expressed as a simple fraction:

Gear Ratio = (Number of teeth on output gear) / (Number of teeth on input gear)

  • The gear ratio determines how the input speed and torque are transformed into output speed and torque:
  • If the gear ratio is greater than 1, the output speed will be lower than the input speed, but the output torque will be higher. This is called a reduction or step-down gear ratio.
  • If the gear ratio is less than 1, the output speed will be higher than the input speed, and the output torque will be lower. This is known as an overdrive or step-up gear ratio.
  • If the gear ratio is equal to 1, the output speed and torque will be the same as the input speed and torque.

How gear ratios affect vehicle performance?

Gear ratios play a critical role in vehicle performance by influencing factors such as acceleration, top speed, fuel efficiency, and drivability. 

A vehicle’s transmission system employs different gear ratios to optimize the engine’s power and torque characteristics. Here’s how gear ratios affect various aspects of vehicle performance:


Lower gear ratios (higher numerical values) provide more torque to the wheels, resulting in quicker acceleration. This is because a lower gear ratio increases the mechanical advantage, allowing the engine to apply more force to the wheels. 

However, lower gear ratios also result in reduced top speed. Generally, the first few gears in a vehicle’s transmission have lower gear ratios for better acceleration from a standstill.

Top Speed

Higher gear ratios (lower numerical values) allow for higher top speeds, as the engine can spin at lower RPMs (Revolutions Per Minute) while maintaining the same wheel speed. 

This is beneficial for cruising and maintaining high speeds with less engine stress and noise. The highest gear in a transmission typically has a higher gear ratio for this purpose.

Fuel Efficiency

Gear ratios also affect fuel efficiency. Higher gear ratios enable the engine to run at lower RPMs, which can reduce fuel consumption. Modern vehicles often feature overdrive gears or additional high gears to improve fuel efficiency during highway cruising.


The range of gear ratios in a transmission, along with the smoothness of gear transitions, affect drivability. 

A well-chosen set of gear ratios can provide a balance between acceleration, top speed, and fuel efficiency, making the vehicle more versatile and enjoyable to drive.

Towing and Climbing

Lower gear ratios can provide more torque at the wheels, which is essential for towing heavy loads or climbing steep inclines. 

Vehicles designed for heavy-duty applications, such as trucks and off-road vehicles, may have transmissions with lower overall gear ratios to maximize torque and pulling power.

Reasons for Swapping Gears from 3.42 to 3.73

Swapping gears from a 3.42 to a 3.73 gear ratio in a vehicle’s differential can have several benefits, depending on the intended use and desired performance characteristics. Here are some reasons for making the switch:

Enhanced acceleration and performance

A higher numerical gear ratio (in this case, 3.73) provides more mechanical advantage, which increases torque at the wheels. 

This results in quicker acceleration, making the vehicle feel more responsive and powerful, particularly during take-off from a standstill or when overtaking.

Improved towing and hauling capabilities

If a vehicle is used for towing or hauling heavy loads, the increased torque provided by the 3.73 gear ratio can make it easier to tow heavy trailers or carry additional weight. 

The added torque helps the vehicle maintain speed on inclines and allows for smoother starts with a heavy load.

Off-Road Performance

For off-road vehicles, a higher numerical gear ratio can improve traction and performance in challenging conditions. 

The increased torque provided by the 3.73 gear ratio can help the vehicle climb steep grades, traverse rough terrain, and power through mud or sand.

Compatibility with Larger Tires

If larger tires are installed on a vehicle, the overall gear ratio may be effectively reduced, potentially impacting acceleration and towing capacity. 

Swapping to a higher numerical gear ratio (such as 3.73) can help counteract this effect and restore the vehicle’s performance characteristics.

Possible Drawbacks For Swapping Gears from 3.42 to 3.73

However, there are also potential drawbacks to swapping gears from a 3.42 to a 3.73 ratio:

Reduced Fuel Efficiency

The higher numerical gear ratio will cause the engine to operate at higher RPMs for a given speed, which can lead to increased fuel consumption, particularly during highway cruising.

Lower Top Speed

Since the engine will reach its maximum RPM at a lower vehicle speed with the 3.73 gear ratio, the top speed may be reduced compared to the 3.42 gear ratio.

Additional Costs

Swapping gears in a vehicle’s differential can be labor-intensive and may require specialized tools and expertise. This may result in higher costs for parts and labor.

Components and Tools Needed for a 3.42 to 3.73 Gear Swap

Swapping gears from a 3.42 to a 3.73 ratio can provide improved acceleration and towing capacity. To perform a successful gear swap, you’ll need several components and tools. Here’s a breakdown of the essentials:

1. Replacement Gear Set

  • 3.73 ring and pinion gear set: This is the main component you’ll be changing. Make sure to purchase a high-quality set compatible with your specific vehicle make and model.

2. Installation Kit

  • Bearing and seal kit: Includes pinion and carrier bearings, pinion seal, and other necessary seals.
  • Shims or crush sleeve: Used to set the pinion bearing preload and adjust backlash.
  • Gear marking compound and brush: To check the gear contact pattern during the installation process.
  • Thread locker: For securing bolts and preventing them from loosening.

3. Specialty Tools

  • Torque wrench: To ensure proper torque specifications are met during installation.
  • Dial indicator with magnetic base: For measuring backlash and pinion depth.
  • Pinion depth setting tool: To establish the correct pinion depth.
  • Bearing puller and installer: For removing and installing bearings without damaging them.
  • Two-jaw puller: To remove the carrier and pinion from the housing.
  • Inch-pound torque wrench: To measure the rotational force when setting the pinion bearing preload.

4. Miscellaneous Items

  • Jack stands and hydraulic jack: For safely supporting and lifting the vehicle.
  • Drain pan, gloves, and shop rags: For handling fluids and keeping the workspace clean.
  • Gasket maker or gasket: For sealing the differential cover.
  • Gear oil and limited-slip additive (if applicable): To refill the differential after installation.

Step-by-Step Guide to Performing a 3.42 to 3.73 Gear Swap

Performing a gear swap can be a complex task, especially if you’re new to working on differentials. Here’s a step-by-step guide to help you perform a 3.42 to 3.73 gear swap. 

Keep in mind that this is a general guide and may vary depending on your specific vehicle. Always consult your vehicle’s service manual for detailed instructions and specifications.

Preparing the Vehicle and Removing Components

Start by parking the vehicle on a level surface and engaging the parking brake to ensure it doesn’t move. Place wheel chocks around the front wheels for added safety. 

Use a hydraulic jack to lift the rear of the vehicle and then support it with jack stands placed under the rear axle or frame. Remove the rear wheels to gain easier access to the differential.

Draining the Differential and Removing the Cover

Place a drain pan underneath the differential to catch the gear oil. Loosen and remove the bolts securing the differential cover. 

Carefully pry off the cover with a flathead screwdriver or similar tool, allowing the gear oil to drain into the pan.

Removing the Axle Shafts

Depending on your vehicle, you may need to remove brake components such as calipers and rotors to access the axle shaft retaining clips or bolts. 

Once accessible, remove the retaining clips or bolts, then gently slide the axle shafts out of the differential, taking care not to damage the seals. Set the axle shafts aside in a safe place.

Taking Out the Carrier and Pinion

Before removing the bearing caps, mark their orientation with a permanent marker or similar tool so that you can reinstall them correctly. 

Next, remove the bolts securing the bearing caps and carefully take off the caps themselves. 

Utilize a two-jaw puller to extract the carrier assembly from the housing. Be cautious when doing this, as the carrier assembly can be quite heavy. Once the carrier is removed, you’ll need to take out the pinion. 

Remove the pinion nut and any washers or spacers, then extract the pinion yoke or flange with a puller or by carefully tapping it with a soft-faced hammer. Finally, remove the pinion from the housing.

Inspecting and Replacing Components

Examine the bearings, races, and seals for any signs of wear or damage. If necessary, replace them using a bearing puller and installer. 

Assemble the new 3.73 ring and pinion gear set onto the carrier and pinion, making sure to lubricate the bearings with gear oil.

Setting Up the Gears

Install the pinion in the housing, using a new crush sleeve or shims to set the pinion bearing preload. 

Reattach the pinion yoke or flange and torque the pinion nut according to your vehicle’s specifications. Use a pinion depth setting tool and dial indicator to ensure the proper pinion depth.

Reinstall the carrier assembly in the housing, using new shims or adjusters to set the backlash and carrier bearing preload. 

Ensure that the backlash and contact pattern are within specifications by using a dial indicator and gear marking compound.

Reassembling the Differential and Axles

Once the gears are properly set up, reinstall the bearing caps in their original orientation and torque the bolts according to the manufacturer’s specifications. 

Carefully slide the axle shafts back into the differential, making sure not to damage the seals. Reinstall the axle shaft retaining clips or bolts, followed by the brake components if they were removed earlier.

Clean the differential cover and housing mating surface, then apply a gasket or gasket maker. 

Reinstall the differential cover and torque the bolts to the specified value. Fill the differential with the recommended gear oil and add a limited-slip additive if required.

Finishing Up

Reinstall the rear wheels and lower the vehicle from the jack stands. Remove the wheel chocks and disengage the parking brake. 

Test-drive the vehicle to ensure the gear swap was successful and listen for any abnormal noises.

Post-Installation Tips and Considerations

After successfully completing a gear swap, there are some important post-installation tips and considerations to keep in mind:

Break-in Period

New gears require a break-in period to ensure proper wear and longevity. During the first 500 miles, avoid aggressive driving, hard accelerations, and heavy towing. 

This allows the gears to wear-in gradually and evenly. After the initial 500 miles, change the gear oil to remove any metal particles generated during the break-in process.

Monitor for Leaks and Noise

Keep an eye out for any oil leaks around the differential cover and axle seals, particularly during the first few days after the swap. 

If you notice any leaks, address them immediately to prevent damage to the new gears. 

Additionally, pay attention to any unusual noises coming from the differential, such as whining or grinding. These could indicate an issue with the installation that requires further attention.

Recheck Torque Specifications

After the first 100 miles, it’s a good idea to recheck the torque specifications for the differential cover bolts, pinion nut, and lug nuts to ensure they are still within the recommended range. This helps prevent leaks and ensures proper performance.

Reevaluate Vehicle Performance

After the break-in period, assess your vehicle’s performance, particularly in terms of acceleration, towing capacity, and fuel economy. 

The gear swap should result in improved acceleration and towing capabilities, but it may also affect fuel economy, particularly at highway speeds. Be aware of these changes and adjust your driving habits accordingly.

Consider Speedometer Calibration

Changing the gear ratio can affect the accuracy of your speedometer since the vehicle’s speed is calculated based on the original gear ratio. To correct this, you might need to recalibrate your speedometer. 

This can often be done using a handheld tuner, through a dealership, or by a professional mechanic with the appropriate tools.

Keep Records

Document the gear swap, including the date, mileage, and any replaced components. This information can be helpful for future maintenance or if you decide to sell the vehicle.


Performing a gear swap, such as upgrading from a 3.42 to a 3.73 gear ratio, can improve your vehicle’s acceleration and towing capacity. 

However, the process can be complex and requires attention to detail, proper tools, and components. Make sure to follow your vehicle’s specific service manual and guidelines for a successful gear swap.

After the installation, adhere to the break-in period recommendations, monitor for leaks and noises, recheck torque specifications, and recalibrate your speedometer if necessary. By taking these precautions, you can ensure the longevity and optimal performance of your new gears.

If you’re not experienced in working with differentials or feel uncertain about any part of the process, it’s highly recommended to seek assistance from a professional mechanic to ensure the job is done correctly and safely. Happy driving!

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