February 24, 2021

Gear Oil FAQ’s

Gear Oil Capacities

  • Transmission: 2.4 qrts
  • Transfer Case: 0.5 qrts
  • Rear Differential: 0.9 qrts

DSM, 3S, and EVO transmissions require 2.5-3 quarts of oil. For our DSM / 3S transmission rebuilds, we recommend factory Mitsubishi transmission gear oil. For stock or mildly modified vehicles, you can just use the standard Mitsubishi MTF. For higher hp, tracked, or extreme condition driven cars, we recommend the Diaqueen 6-speed manual transmission gear oil from the 2005 Mitsubishi EVO MR. This is the best oil to use as it has the perfect blend of friction modifiers to keep the transmission shifting smoothly and helps to prevent gear failure.” -Jack’s Transmissions

“There are several gear oils that will work depending on horsepower or intended use. For most transmissions we recommend Redline MT90 or Pennzoil Synchromesh.” -Sheptrans

“The Redline MT90 may feel a bit notchy when used in colder climates. Once the fluid warms up, it should be smooth.” -Jack’s Transmissions

“Gear oil choice is very important and varies based on preloads and synchro blocker ring design, therefore, it is strongly recommended that you stick with this fluid for your transmissions.  As an alternative, Redline MT90 gear oil will also work” -Jack’s Transmissions

For Transfer Cases and Rear Ends

DSM / 3S: 

  • “Use Redline Lightweight Shockproof in Transfer Case and Rear Differential. DSM: If you have an EVOIII rear diff, do NOT use Shockproof as the LSD will not work with it. In these applications, we would recommend you use Mitsubishi LSD oil.” -Jack’s Transmissions

EVO 8-10: 

  • “For an ACD T-Case, the recommended fluid is the Mitsubishi LSD gear oil. If you have a Non-ACD T-Case, we highly recommend using Redline ShockProof Heavyweight (Red).” -Jack’s Transmissions
  • “For the rear diff, we recommend the factory Mitsubishi LSD oil as the clutch packs for the limited-slip will no longer work correctly if you use Shockproof.” -Jack’s Transmissions

For Transmissions

ALL Mitsubishi:

“DO NOT use Synchromesh, BG Synchroshift I or II, or Royal Purple. These fluids will destroy synchros and gears!” -Jack’s Transmissions

Shockproof in transmission:

“Absolutely DO NOT use Redline Shockproof in your transmission!” -Jack’s Transmissions

“Shockproof is designed for ring and pinions found in T-Cases and Rear Diffs. If you use it in your transmission, you will break gears and ruin your synchros!” -Jack’s Transmissions

“The pic above is of an EVOIII 1st gear which only had 6 months of use with Shockproof oil. Shockproof causes odd gear failures like this one where 1 tooth in your 1st or 2nd gear will end up breaking off and missing. We have seen a bad rash of odd failures like this with Shockproof users.” -Jack’s Transmissions
“Shockproof can also cause fretting with gear teeth in your trans. This is a picture of an EVO 9 1st gear and input shaft after using Shockproof.” -Jack’s Transmissions


Shockproof also has no friction modifiers, which means that synchros will be unable to work correctly and will have to work serious over-time in order to synchronize your trans correctly.  Synchros need friction in order to properly operate.  When there is no friction, they are under a large amount of pressure and will wear out very quickly.  They will also feel notchy and unpleasant to shift.  

The wax found in Shockproof oils will also plug up your small oil passages found in the synchros, shafts and center diff in your trans.  Just please don’t use it!

Shockproof oils are an unbelievable achievement in engineering and a miracle oil, but only if used as intended.  Use Shockproof in your T-Case and you will never have to worry about worn ring and pinions again.  Use it in your trans, and you’d be lucky to get 6 months out of it.  It is clearly stated on Redline’s instructions to NOT use Shockproof in your trans.  Take their word for it, they are the people who engineered it and know best.

Take our word for it, use the factory Mitsubishi oil in your trans at any HP level!  We don’t see gear failures like this when people stick to the factory fluid.  Yes, we know, many people believe that you must have some kind of aftermarket oil for your trans if you are to push a lot of power through it.  The Mitsubishi transmission fluid is pretty amazing and will give you the cleanest gear wear, and shift possible.  

It’s hard to believe that oil from the factory is best, but it is and the reason why is due to the poor engineering of the EVO 6-speed trans found in the 9 MR.  The trans broke synchros and gears at factory HP levels.  Mits had this fluid developed to allow that horrid trans to survive.  Due to this, it is the best trans fluid on the market today!

Next question we always get is: Can I use a mix of Shockproof or some other aftermarket oils with the factory fluid?  The answer is NO!  Please get away from the mentality that you must have some kind of aftermarket fluid in your trans!  Use 100% Mits fluid mixed with nothing but more 100% Mits fluid.  It works great as it is and will give you the best life and performance possible. 

We don’t know who has been starting the rash of Shockproof in your trans or mixed with other fluids as a good thing, because it’s not.  Please don’t do it!” -Jack’s Transmissions

Gear Oils: TRE Recommendations

TRE recommends using the following manual transmission oils listed below for use in your Mitsubishi manual transmissions including the EVO-X manual transmissions. We critically question the validity of Mitsubishi’s recommendation of a GL-3 oil specification for the EVO-X manual transmissions as this oil clearly lacks the proper EP additives to keep the center differential spider gears from seizing to the cross shafts and shearing the retaining pins. Listed below are a few of the gear oils on the market for you to choose from.

MOTUL GEAR 300 75W90- This oil has incredible film strength while still allowing for quick shifts making it another wise choice of oil for your high power Mitsubishi transmission. Part# 100118. Note: We are talking about GEAR 300, not Gear 300LS which is a full GL-5 gear oil and has the friction modifiers that are required by limited slip differentials.

REDLINE MT-90- This gear oil offers good shift quality in most manual transmissions and would be fine for stock power levels. Part# 50304

REDLINE 75w-90NS GL-5- This gear oil is rated NS “no-slip” and is synchro friendly. It provides excellent film strength and reduces the gear wear that we commonly see in modified vehicles that that are making big power while still offering good shift quality. Part# 58304.

REDLINE 75W140 NS GL-5- This is an excellent gear oil that will prevent the gears from scuffing in a high torque application. It’s one of the best oils that we know when it comes to gear protection in those mission impossible applications. Part# 57104.

AMSOIL Manual Transmission & Transaxle Gear Lube 75W-90 (MTG)- This API GL-4 rated gear oil has good stability and film strength and would be fine for near “stock power” levels. Part# MTGQT-EA

MITSUBISHI DIAQUEEN SUPER MULTI GEAR OIL- This oil is rated 75w-85 API GL-4 and it fine for stock power levels Part# MZ313376.



FRICTION MODIFIERS-  Never add a friction modifier to your transmission gear oil as it will make for poor shift quality. Understand that the friction modifier is an additive that reduces friction and is designed to reduce noise that limited slip differentials can make while making tight turns at low speeds. Do not use it in your transmission!

REDLINE SHOCKPROOF- 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. Also this oil is has too high of a viscosity for winter use. Therefore we cannot recommend 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 will get thrown far enough in the proper direct to provide lubrication so please check out the viscosity chart and choose an oil for the operation temperatures of your transmission. Ideal transmissions temps should be between 140-200 depending on what you’re doing.

OIL LEVEL- Oil must be level with or slowly flow back out of fill/level plug. It would be wise to drive the vehicle a short distance and recheck the oil level and top off as required.  Road racing & drag race applications may add an additional pint of oil to the transmission for added lubrication and cooling.

EVOLUTION OWNERS TAKE NOTE- It is of utmost importance that the transmission oil be checked again after driving the vehicle 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. Driving the EVO with the transmission oil level too low will drastically shorten the service life of the 3rd & 4th gear synchros and gears.

CHANGING THE OIL- New or recently rebuilt transmissions should have the oil changed after the initial first 500 miles and then every 5000 miles. Vehicles that are being road raced require race car maintenance and all drivetrain oils should be inspected after each race and preferably changed.


Synchromesh/Synchroshift Gear Oils (TRE)

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 use 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 but it is our recommendation that you use the proper GL rating that the transmission was designed to use and prepare for a rebuild.   


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.

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.