Differential Bushes

Diff bushes mount the differential housing to the supporting structure of the vehicle, helping control its movement while isolating some driveline vibration. Differential bushes are used at front and rear differential mounting points depending on the drivetrain layout.

The amount of movement at these mounts can influence how the driveline responds as torque loads change during acceleration, deceleration and gear changes. Differential mount bush kits can use complete replacement bushes or inserts designed to work with the existing factory bush. The appropriate design depends on the mounting arrangement and the level of control required.

What Are Diff Bushes?

Diff bushes are compliant mounting components positioned between the differential housing or its mounting assembly and the vehicle structure. They locate the differential while allowing a controlled amount of movement and helping isolate vibration from the body or chassis.

The differential transfers drive between the input from the drivetrain and the driven wheels. As torque changes, the differential housing reacts against its mounting points. The bushes at those points help manage that movement rather than creating a completely rigid connection.

Wear or excessive compliance can allow the housing to move farther than intended when drivetrain loads change.

Front and Rear Diff Mounts

The location of the differential depends on the drivetrain layout.

Rear-wheel-drive and all-wheel-drive vehicles can use rear differential mounts to locate the differential against a subframe or supporting structure. Four-wheel-drive systems can also use bushes to support and locate a front differential.

Although both perform a similar mounting function, front and rear diff bushes are application-specific. Their dimensions, mounting positions and required compliance depend on the differential and surrounding structure.

What Do Differential Bushes Do?

Differential bushes control how much the differential housing can move as torque passes through the drivetrain. Under acceleration, deceleration and gear changes, the differential reacts against its mounts as load changes direction and intensity.

Controlled compliance helps isolate vibration while maintaining the differential's position. Excessive movement can make the driveline feel less direct and can contribute to movement at the mounting points when torque is applied or released.

Controlling differential movement can also help maintain more consistent driveline geometry, including the relationship between the differential and connected driveline components.

The goal is not simply to make the mounts as rigid as possible. The appropriate level of compliance depends on the vehicle, bush design and intended use.

Types of Differential Bush Kits

Differential mount bush kits can take different approaches to controlling movement. Some replace the original mounting bush completely, while others work with the existing bush to reduce its available movement.

Rear Diff Mount Bush Kits

Rear diff bushes locate the rear differential against its mounting structure and control movement as torque is transferred to the driven wheels.

They are particularly important when drivetrain load changes rapidly. Acceleration, lifting off the throttle and gear changes can all change the direction or intensity of the forces acting through the differential mounts.

Replacing worn rear differential bushes can restore control where the original mounts have deteriorated. Performance-oriented designs may also reduce compliance beyond the original setup, but this can change the amount of vibration transmitted into the vehicle.

Front Diff Mount Bush Kits

Front differential bushes perform the same basic mounting function at the front differential of applicable four-wheel-drive systems.

The mounts need to control the differential housing as torque passes through the front driveline while accommodating the compliance required by the original mounting arrangement.

Front diff bushes should not be confused with components designed to reposition the differential. A replacement mounting bush controls movement at the existing mounting point rather than deliberately changing the differential's installed position.

Insert Bushings vs Full Replacement Kits

An insert and a full replacement bush address differential movement differently.

An insert is designed to fit into available spaces or voids in an existing factory bush. By filling those areas, the insert can reduce how far the original bush deforms under load without requiring complete removal of the factory mounting bush.

A full replacement kit removes the original bush and substitutes a new mounting component. This allows the replacement bush itself to determine the compliance and movement at that mounting point.

Because the installation method and resulting behaviour differ, an insert should not automatically be treated as equivalent to a full replacement bush.

What Are the Signs of Worn Rear Diff Bushes?

Worn rear diff bushes can allow excessive differential movement and may contribute to noises or changes in driveline behaviour as torque loads change. These symptoms can also come from other drivetrain components, so inspection is needed before attributing them to the differential mounts.

Signs worth investigating include:

• A clunk when taking off
• Knocking or movement during gear changes
• A noticeable clunk as the throttle is applied or released
• Excessive visible movement at a differential mounting point
• Cracked, separated or distorted mounting bushes
• Vibration that changes with drivetrain load
• Wheel hop under acceleration

Wheel hop in particular can involve tyres, suspension geometry, dampers and other bushes as well as differential movement.

CV joints, tailshaft components, centre bearings, engine or transmission mounts and other driveline bushes can also create similar noises or vibration. Inspection by a qualified technician is the best way to identify the source before replacing components.

Will Performance Diff Bushes Add Noise or Vibration?

Reducing compliance at a differential mounting point can increase the amount of noise, vibration and harshness transmitted through the vehicle.

The original mounts contribute to driveline isolation as well as differential location. A performance-oriented bush that allows less movement may provide a more controlled connection, but some of the vibration previously absorbed by the mounting system can instead reach the chassis and cabin.

The effect depends on the bush design, mounting position, vehicle and intended use. Some performance differential bush applications specifically carry an increased-NVH consideration, so this trade-off should be considered when choosing a setup for a road or performance vehicle.

Diff Bushes or a Diff Drop Kit?

Diff bushes and diff drop kits perform different jobs.

A diff bush controls movement where the differential is mounted. It does not deliberately lower or reposition the differential.

A diff drop kit is used on applicable lifted 4WD suspension systems to reposition the front differential, helping address driveline geometry following a ride-height increase.

If the issue is worn or excessively compliant differential mounts, replacement bushes address the mounting point. If the objective is correcting differential position after a suspension lift, that is a different modification.

How Are Diff Bushes Replaced?

Replacing diff bushes requires the differential to be safely supported before its mounting points are loosened. Depending on the design, access may require surrounding driveline or suspension components to be moved or removed.

What the Job Involves

A full bush replacement can involve:

• Safely raising and supporting the vehicle
• Supporting the differential
• Removing components that obstruct access where required
• Loosening or removing the applicable differential mounts
• Removing or pressing out the original bushes
• Inspecting the mounting points, sleeves and hardware
• Installing the new bushes in the correct position and orientation
• Reassembling the mounts and surrounding components
• Tightening fasteners according to the specified procedure

Insert-style bushings can require a different process because the original bush remains in place.

Press tools or other specialised equipment may be required for complete replacement bushes. Installation should follow the procedure specified for the vehicle and bush design.

Safety Considerations

A differential is heavy and must be securely supported before its mounts are removed. Never rely on a jack alone to support the vehicle while working underneath it.

Driveline components can also shift when mounting points are released. If the job requires substantial disassembly or the correct supporting and pressing equipment is not available, installation by a qualified technician is recommended.

Choosing Diff Bushes

Choose diff bushes according to the differential location, mounting position and required replacement type. Determine whether the application requires an insert or a complete replacement bush and consider the potential NVH trade-off where a performance-oriented design reduces mounting compliance.

Shop Differential Bushes with Whiteline

Differential bushes are part of our suspension bushes range, alongside subframe bushes for IRS cars chasing less wheel hop.

Improve control at worn or excessively compliant differential mounting points with application-specific diff bushes. Shop with the added confidence of our warranty and 60 Day Returns.