Differential Mounts

Do you feel a clunk from the rear when you release the clutch, or does the differential twist under hard acceleration? Differential bushings hold the differential in place in the rear axle, and here we have gathered polyurethane and Delrin kits for you who want more direct power transfer on the street or track.

What do differential bushings do?

The differential is typically mounted in the rear end via bushings that must hold it in position while also damping vibrations. Worn or soft rubber bushings can allow more movement during acceleration and gear changes, which can be felt as knocks or unsettled behaviour at the rear. If the car runs higher power, stiffer bushings can reduce movement. If the problem lies in the subframe itself, it is also worth looking at subframe bushings.

How to choose material and version

The choice is a trade-off between stiffness, noise and comfort, and depends on how the car is used:

• Polyurethane – e.g. BMR Street Version – is stiffer than rubber but typically still dampens a fair amount of vibration.
• Delrin – e.g. BMR Race Version – is very hard and can transmit more noise into the cabin.
• Combination kits with polyurethane and Delrin blend the two characteristics.

Whiteline is available, for example, in a Motorsports Version for the Nissan 350Z/370Z, and SuperPro offers kits for the mount on the Subaru Legacy LSi. Energy Suspension is also represented in the category.

Installation and maintenance

Check that the kit fits your exact model and year, as brackets and dimensions vary. Replacement often requires the differential to be supported, and old bushings can be hard to press out. Polyurethane can squeak without proper lubrication, so follow the manufacturer's instructions. Stiffer differential bushings can make other worn mounts more noticeable, so it may make sense to also check the transmission mounts and engine mounts.

Frequently asked questions

Will the car be noisier with stiff differential bushings?

It can be. Hard materials such as Delrin typically transmit more vibration and noise from the differential into the cabin than polyurethane. How noticeable it is depends on the car, the differential and the other mounts.

Can the car pass inspection with polyurethane or Delrin bushings in the differential?

That depends on the product and the car. Check the specific part number and which documentation is included, and feel free to clarify with the inspection centre before installation if you are unsure about the rules for your car.

How do I know if the differential bushings are worn?

Typical signs can be clunks during gear changes and load changes, vibrations under acceleration or visible cracks in the rubber. Similar symptoms can also come from driveshafts or propshaft joints, so the car should be inspected before you replace parts.