GL-4 Gear Oils

We only recommend using a GL-4 spec transmission oil your Mitsubishi manual transmissions. There are several GL-4 gear oils on the market for you to choose from. I highly recommend REDLINE MT-90 gear oil as it has proven itself a worthy oil for those who are making lots of torque, shift fast, and wanting long service life from their transmission. Another impressive oil is the Motul 300 Gear. This oil appears to have excellent film strength, making it a good choice of oil for your Mitsubishi transmission. Amsoil Manual Transmission Gear lube (MTG) is API GL-4 rated and it will work in your transmission. And another transmission oil that is readily available at the Mitsubishi dealership is DIAQUEEN SUPER MULTI gear oil part # MZ313376. 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.

There are concerns about using REDLINE SHOCKPROOF type gear oils inside manual transmissions. While this is truly an excellent product, it has been found that the heavy Teflon-like particles are quickly centrifuged out of the oil and will 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. Also this oil is has too high of a viscosity for winter use. Therefore we do not suggest using SHOCKPROOF in the transmission unless the transmission is to be serviced often or a dog box.

Remember that proper viscosity is important when it comes to splash type lubrication; certain parts require enough viscosity so that the oil get thrown far enough so please check out the viscosity chart and choose an oil for the operation temperatures of your transmission.

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 long gear and bearing life for the Mitsubishi transmissions.

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. Transmissions that call for Synchromesh type gear oils are designed with wide gear shaft spacing which greatly reduces the force on the gear teeth and large bearings so that they can used these low film strength oils. The reason behind it is to reduce parasitic frictional losses and to improve shift quality.

If you have a weak synchro, you may want to try the “Synchromesh/Synchroshift” type oils. However, it is our strict recommendation that you use the proper GL rating that the transmission was designed to use.  Check your owner's manual for this information. 

Use of GL-5 spec gear oil is not recommended in your manual transmission.  The EP (Extreme Pressure) additives found in GL-5 will reduce the effectiveness of your synchronizers making the transmission shift poorly and tarnish them over time. How quickly will it eat up the synchros?  This is dependent on both time and temperature but it's a gradual process. However, it should also be noted that if you are wanting an oil that does provide higher film strength and added protection against gear & bearing wear, you may consider using a GL-5 spec gear oil. Just remember that it will not shift as good at the high rpms and that it will oxidize the synchros over time.

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 production parts are less that perfect. What does this mean?   It means that it will require some drive time to fully bed-in the gears 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 8,000 miles to fully wear themselves in, allowing for full & proper contact and the most strength. It is wise to drive any new or recently rebuilt transmission gently so that the gears bed-in before pushing them 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. I find that my transmissions shift well around 500 miles and feel damn good after 1500 miles. Take your time and read this page.

By design, synchronizers will either block the driver from completing their shift or possibly grind during shifting 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.

 © 2010 TRE