Red Line MT-90 75W-90 Manual Transmission & Transaxle Lubricant - 1 Gallon, GL-4 Safe for Brass Synchros

Red Line MT-90 75W-90 GL-4 is a manual transmission and transaxle lubricant engineered for smooth shifting, long synchro life, and protection of gear surfaces in GL-1/GL-3/GL-4 applications.

This one-gallon manual transmission lubricant from Red Line replaces reactive sulfurs found in many hypoid oils to protect brass and bronze synchros while delivering consistent viscosity across temperature ranges. Designed for road and track use, MT-90 balances wear protection with the precise friction characteristics needed for fast, notchy-free engagement. The formula works well where special synchromesh fluids are called for and supports several motor oil equivalencies for service convenience.

How does this oil improve shifting performance?

MT-90 provides a controlled coefficient of friction so synchronizers engage predictably and quietly, minimizing notchy or abrupt shifts. It is formulated to maintain that behavior from cold starts through operating temperature, which helps clutch and shift feel remain consistent.

• Optimized friction for rapid synchronizer match-up
• Stable viscosity for reliable shifts in varied temperatures
• Reduces gear and synchro wear for longer component life

Will MT-90 harm brass or bronze synchros?

No — MT-90 is safe for copper-containing synchronizer materials because it avoids the reactive sulfur chemistries common to GL-5 hypoid oils that can corrode brass and bronze. That makes it appropriate for many older and specialty transmissions specifying GL-1, GL-3, or GL-4 service levels.

• No reactive sulfurs that attack non-ferrous metals
• Recommended where special synchromesh fluids are requested
• Compatible with transmissions requiring GL-4 performance

What viscosities and applications does MT-90 cover?

MT-90 is a 75W-90 gear oil suitable for a broad range of manual transmissions and transaxles. It also serves as an acceptable choice in systems that call for certain SAE motor oil viscosities when used per manufacturer guidance, offering flexibility during maintenance.

• Primary viscosity: 75W-90 for gear protection
• Works in some systems where 80W, SAE 40, 10W-40, or 15W-40 guidance is present
• Use where GL-1, GL-3, or GL-4 specifications are required

Why choose Red Line's MT-90 over other gear oils?

Red Line has produced performance lubricants since 1979 with a focus on engineered protection and drivetrain feel. MT-90 is formulated to deliver longer synchronizer life and dependable gear protection without sacrificing precise shift quality, making it a strong choice for both performance and daily-driven vehicles.

• Heritage brand with performance-oriented formulations
• Targets both wear protection and shift feel simultaneously
• Commonly chosen for classic cars, performance builds, and specialty transmissions

Who is this for: MT-90 75W-90 GL-4 from Red Line suits technicians, enthusiasts, and fleet owners who need a transmission fluid that protects gears and synchronizers while ensuring smooth, predictable shifts. It’s particularly useful for vehicles and gearboxes that specify GL-1/GL-3/GL-4 service or require synchromesh-friendly fluids, including many older European and performance-oriented manual transmissions. Choose the one-gallon container for workshop convenience, frequent service intervals, or multiple-vehicle maintenance.