Redline Oil MT-90 75W-90 GL-4 Manual Transmission Fluid — 1 Quart, Synchro-Safe Smooth Shifting

Red Line MT-90 75W-90 GL-4 is a high-performance manual transmission and transaxle lubricant engineered to protect gears and synchronizers while delivering smooth, sure shifts.

This 1-quart Red Line formulation is designed for manual gearboxes and transaxles that specify GL-4 service and 75W-90 viscosity. It provides a balance of wear protection, friction control for synchronizers, and thermal stability for a wide variety of passenger cars, sport compacts, and light trucks. Because it avoids the aggressive sulfur additives found in many GL-5 fluids, MT-90 is safe for bronze and brass synchros while still giving robust gear protection.

How does MT-90 improve shifting performance?

MT-90 has a tuned friction characteristic that reduces notchy or grinding shifts and helps synchronizers match speeds quickly. The lubricant remains stable when cold, so shifts feel consistent from startup through operating temperature.

• Optimized coefficient of friction for smooth synchro engagement
• Stable low-temperature fluidity for predictable cold shifts
• Consistent shift feel under repeated use

Will this oil protect my gears and synchronizers?

Yes — MT-90 combines wear-reducing additives with a GL-4 formulation that is compatible with yellow metals used in synchronizers. It reduces wear on gear teeth and extends synchronizer life compared with oils that lack proper friction modifiers or use reactive sulfur compounds.

• GL-4-rated additives for gear surface protection
• No reactive sulfurs that harm brass or bronze synchros
• Formulation focused on longer component life

Which vehicles and service specifications are appropriate for this oil?

MT-90 is intended for manual transmissions and transaxles specifying GL-1, GL-3, or GL-4 service and a 75W-90 viscosity. It also works where OEMs call for special synchromesh fluids or when compatibility with brass synchros is required.

• Suitable for many passenger cars, sport compacts, and light trucks
• Compatible with GL-1, GL-3, and GL-4 service requirements
• Can replace many special synchromesh fluids in OEM specifications

How should I choose between MT-90 and other gear oils?

Choose MT-90 when the gearbox specification calls for GL-4 service or when synchro compatibility with yellow metals is important. Avoid GL-5-only oils in these applications because they commonly contain sulfur compounds that can damage brass and bronze components.

• Pick MT-90 for GL-4 or synchromesh-specified gearboxes
• Prefer it where brass/bronze synchros are present
• Consult the vehicle manual when in doubt about viscosity and spec

Who is this for? Red Line MT-90 75W-90 is aimed at drivers, technicians, and restoration enthusiasts who need reliable manual transmission protection without sacrificing smooth shifting. It is well suited for performance-minded owners, classic car restorations where brass/bronze synchros must be preserved, and any service bay replacing or topping off gear oil in GL-4 applications. Use it when your owner's manual or transaxle plate specifies GL-4 or a 75W viscosity, or when better synchronizer life and consistent shift quality are priorities.