GL-4 Gear Oils

We strongly recommend using a GL-4 spec transmission oil in the Mitsubishi manual transmissions. This oil offers good protection for the gears and bearings against wear out.  Do not use any oil that has a GL-5 rating in the transmission, for these oils will not give the best shift quality because the GL-5 rating might end up being too slippery for the synchronizers to be effective for high rpm shifts.

There are several GL-4 gear oils on the market for you to choose from. Redline MTL is excellent for those who autocross because its lower viscosity will improve shift quality in a cold transmission. Daily drivers & weekend warriors should use Redline MT-90. I highly recommended this gear oil for road racing type service as it has proven itself a worthy oil for those who want to shift fast, yet are also looking for long service life from their transmission.  There are concerns about using Redline's Shockproof type gear oils inside manual transmissions. While this is truly an excellent product, it has been found that the heavy paraffin-like particles are quickly centrifuged out of the oil and build up inside the center diff housing and around the synchronizers and inside of the gearshafts. After several oil changes this build up may block oiling passages inside the gearshafts that lubricate the needle bearings and can reduce the overall effectiveness of the synchronizers, leading to poor shift quality. Therefore we do not suggest using Shockproof in the transmission unless the transmission is to be serviced often or a dog box.

Amsoil offers an excellent manual transmission gear oil called Manual Transmission Gear lube or (MTG) that is a 75w-90 API GL-4 oil and it will work very well in your transmission.

Another transmission oil that works very well is Diaqueen Super Multi part # MZ313376 and it available at the Mitsubishi dealer.  Mitsubishi strictly specifies this oil for use in the 05/06 EVO-MR 6 speed manual transmission but it can be used in the 5 speeds. This oil is a 75w-85 API GL-4 and  we recommend that you use it if you can't find the other oils that we recommend.

Synchromesh/Synchroshift gear oils

While it has been found that the Synchromesh/Synchroshift type oils can sometimes improve the effectiveness of the synchronizers, allowing for faster shifts at higher rpms, this oil does not have enough film strength to ensure the longest gear and bearing for the Mitsubishi transmissions that lives behind a high torque engine. Synchromesh/shift type oils are used in transmissions that are found in low torque applications that don't ask much from the oil in regards of film strength. If you have a weak synchro, you may want to try the “Synchromesh /shift” type oils. However, it is our recommendation that you use the proper GL rating that the transmission was designed to use.  Check your owner's manual for this information.   OIL VISCOSITY INDEX CHART

Transmission gears

A short word about transmission gears. Transmission gears are exceptionally strong and generally have a hardness of 58-62HRC. It is because of their hardness that the gears will take quite a while to fully bed-in together before ultimate power handling capabilities can be obtained. The are several reasons for this and they all revolve around the manufacture's ability to hold tolerance on the parts and to what AGMA or DIN that they cared to produce in the first place. In a perfect world, everything is machined right on the money and you have full and proper contact of the gears that are in mesh but I can assure you that parts are less that perfect and will require some drive time to fully bed-in before you go out there and explore the limits of how much power they can handle without failure. Transmission gears can take as many as 5,000 miles to fully wear themselves in allowing for full contact and the most strength and it's wise to let any new or recently rebuilt transmission gears bed-in before pushing the gears to their material limits regardless of what people may tell you.

Synchronizers

Transmission synchronizers, like brake pads, will require some time for their surfaces to fully bed-in. Do not shift a new or freshly rebuilt transmission fast or at high rpms for this bed-in process requires that you drive the car gently and shift slowly. You want to allow the synchronizers a little extra time to develop their full contact finish which provides the most friction and ultimately the best shift quality. This process takes a few hundred miles of city driving, where you are shifting through the gears often. Rush this process by shifting the hell out of it and your transmission will not shift as well as it could have. Take your time!

By design, synchronizers will block the driver from completing their shift into any gear, and for that matter, even make shifting into any gear in the first place difficult if the speed of the clutch disc, input shaft & various other components doesn’t match the speed of the gear they are shifting into. It is crucial that your clutch is operating properly, with sufficient release to allow the clutch disc, input shaft & various other components to be “free” from the engine’s rotating speed thus allowing them to slow down and match the speed of the gear you are shifting into. Synchros are not designed or capable of dealing with a clutch that doesn’t have enough release.  If you are having trouble getting into any gears while the car is running or are experiencing blocking or “notchy” shifting; you must check your clutch, making sure that it's properly adjusted or you will cause damage to the synchronizers. It is sole responsibility of the driver and/or installer to make sure that the clutch is properly adjusted so that is has sufficient release to allow the synchros to do their job without the clutch disc dragging on the flywheel/pressure plate assembly.

Filling the transmission with gear oil

Oil must be level with or slowly flow back out of fill/level plug. 

EVOLUTION OWNERS TAKE NOTE: It is of utmost importance that the transmission oil be checked again due to the oiling circuit for the front differential. You must to drive the car a few miles at speeds over 25mph to fill the front differential housing and then top of the transmission oil level.

Change the transmission oil every 5000 miles. Vehicles that are being road raced require race car maintenance and all drivetrain oils should be inspected after each race and changed if the oil is dark or stinky. Road racing & drag race applications may add an additional pint of oil to the transmission for added lubrication and cooling. New or recently rebuilt transmissions should have the oil changed after the initial first 500-1000 miles.

 © 2008 TRE