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Transmission mounts secure the gearbox to the chassis and control how much the drivetrain moves under load. Factory mounts prioritize comfort, but that compliance allows flex during hard acceleration and aggressive shifting. Upgraded mounts use stiffer bushing materials to keep the drivetrain located and improve shift feel.
On turbocharged Subaru platforms like the WRX and STI, transmission mount upgrades are common alongside engine mounts for WRX and STI and clutch kit upgrades as part of a complete drivetrain refresh.
What to Consider When Upgrading Transmission Mounts
Transmission mount upgrades range from street-friendly poly bushings to full billet replacements designed for track and high-horsepower applications. The right choice depends on how the car is driven and how much torque the drivetrain is managing.
Street builds typically benefit from a 75A durometer bushing, which offers improved rigidity over stock without introducing excessive vibration into the cabin. More aggressive track or competition setups may use harder materials for maximum rigidity.
IAG Performance engineers their transmission mounts specifically for Subaru WRX and STI applications, offering billet construction designed to handle the torque output of built engine setups.
Frequently Asked Questions
What does a transmission mount do on a WRX or STI?
The transmission mount secures the gearbox to the chassis and controls how much the drivetrain moves under acceleration and shifting. On a stock WRX or STI, the factory mount is tuned for comfort, which allows some flex under load. An upgraded mount reduces that movement, improving shift feel and drivetrain response, particularly on higher torque builds.
When should you upgrade the transmission mount on a WRX or STI?
A transmission mount upgrade is worth considering any time the drivetrain is being reinforced for higher power output. Common triggers include turbo upgrades, engine builds, clutch upgrades, or any build where drivetrain slop becomes noticeable during hard acceleration. Many Subaru owners upgrade the transmission mount and engine mounts at the same time for consistent results across the drivetrain.
Will a stiffer transmission mount increase cabin vibration?
It depends on the bushing hardness. A 75A durometer bushing offers noticeably better rigidity than stock while remaining manageable for street use. Harder materials used in full competition mounts will transfer more NVH into the cabin. For a daily driven WRX or STI, a street-oriented poly or billet mount at an appropriate durometer is the right balance.
Do transmission mounts need to be replaced with engine mounts?
They do not need to be replaced together, but upgrading both at the same time is common practice on WRX and STI builds. Engine mounts and transmission mounts work as a system. Stiffening one without the other can leave the remaining stock mount as the weak point in drivetrain stability.
Related Drivetrain Upgrades
- Engine Mounts for WRX and STI commonly upgraded alongside transmission mounts for complete drivetrain stability.
- Clutch Kits upgraded clutch engagement affects how torque is transferred through the drivetrain.
- Flywheels flywheel choice influences drivetrain response and how the mount experiences load.
- WRX Engine Build and Power Goals Guide plan the full build path including drivetrain supporting upgrades.
- Built Transmissions for WRX and STI covers when and why drivetrain reinforcement becomes necessary.
- Supporting Mods for Big Turbo WRX Builds includes transmission mounts as part of the full supporting mod list.
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