Evo 4/9 Limits


The amount of torque the clutch holds is proportionate to the damage it can do. Choose your torque capacity wisely and don’t deviate too far astray from the OEM design. OEM did all the hard work of finding out what is best suited for your drivetrain and what will help make it last a long time. If you bought the meanest race clutch expect it to have nothing to do with what is best for long transmission life and everything to do with not slipping. If the clutch doesn’t slip then the input shaft must take the brunt before passing it to the next gear.  Here is a classic example of too little length of spline trying to do the job of getting power into the transmission.

1st gear features a pretty high pressure angle in order to keep the teeth from breaking off. However the high radial thrust loads are generated from the pressure angle and caused brinelling of the inner diameter of 1st gear.  This is caused by the gear pressing against the needle bearing rollers during those big clutch dumps.

Also note that this 1st gear was not properly heat treated. When the gear was shot peened it brinelled the surface. This is commonly found on 1st and reverse gear but not exclusive to these two gears.


The inner sleeve and roller bearing both suffered damage from the extremely high radial thrust load exceeding the material strength.  This is not commonly seen on the older DSM AWD transmissions because the pressure angle isn’t as high.

TRE offers a HD 3rd/4th to fix this.


There is more than one way to drop the transmission out of a high power EVO.  This way used a triple plate carbon/carbon clutch that held over 800ft.lbs of torque, a Motech ECU set-up with the bang-bang anti-lag @ 6500rpm and a rookie dumping the clutch.  The quickest time that this EVO owner had ran this day at the dragstip was mid 13’s.  It takes more than money to get an 800WHP EVO into the 9’s.


Notice again what too much axial & radial thrust load can do to an EVO transmission. This transmission didn’t need to be unbolted to get the internals out of it. Be careful getting it from a dig.


The EVO-4/91st gear is narrow. it’s .080″ narrower than a 90-99 DSM 1st gear but it holds up pretty good because of the high pressure angle.  However, it’s also the reason the case split in the photo above.  The radial thrust loads generated by the pressure angle will yield the transmission case and cause 1st gear to crack at or above the pitch circle.

Note the cracks.  Yes it’s bad.

Here is the input shaft 1st gear teeth that ran with the gear above.  Notice how worn out the teeth are, there is .010″ worn off the face of the teeth and yes these teeth are also cracked.

Make sure to use the correct transmission oil in your EVO.  Synchroshift/mesh type oils are NOT to be used regardless of what people may tell you. Recommended oils can be found on the FAQsection of this site.

These are pinion gears. 

The gear on the left is from a Ford Mustang with an 8.8 rear end.  Yes, people do manage to break them.

Note the size of the gear teeth when compared to the pinion gear inside of an EVO transfer case. You will want to learn how to let the clutch out gently, avoiding shock loading, if you want the transfer case to live.

A flimsy transfer case housings and poorly adjusted contact patterns will crack a ring gear in a hurry. We machine the housing square and shot peen our gears improve durability.


The front differential works great for road racing, autocross or just daily driving but it has 3 things wrong from a design stand point that keep it from being worthy for drag racing:

1. Crappy cast housing with lots of stress risers.

2. Tight corner radii.

3. The above two flaws are also located directly on the gain boundary of the induction hardening for the splines and these are all things that we can fix.

Some people will find that a wheel barrow’s worth of pricey items can and will get destroyed if the hollow splined transfer shaft shits the bed.  There are stronger transfer shafts out there and we recommend them however, there are many other parts that can and will fail besides that transfer shaft if you use a clutch that holds too much torque.  When choosing your clutch make sure to read this page.

It has been said that shit rolls down hill…and when it comes to the EVO it’s an avalanche until you learn how to get the car off the line without killing it. Use your head when it comes to a realistic launch RPM. If you have to drive it home and don’t have a spare car let me be the first to tell turn it down.

We machine our own parts to repair this and it’s way cheaper than an aftermarket front limited slip differential.











Just because you can doesn’t mean you should….

Some people understand that you don’t want to launch the balls off the EVO but think that no-lift-to-shift ECU mod was ok to do over and over and over again.   Be careful when using NLTS.

Both input shaft and output shaft were bent a combined .043″

Your EVO transmission has pretty good synchronizers and can take it’s share of fast shifts.  However, if your clutch isn’t releasing, the blocking teeth on the synchro will block the shift from being completed until speeds of the various components are going the same speed.

If you’re hell bent on sending into a gear before speeds are synchronized you will break off the blocking teeth like this guy. You don’t need to shift hard if the clutch is working.

Here is a text book example of what the 1st/2nd synchros will look like if your clutch is not releasing properly.  Note how the synchro stops are deformed.  Tapering the stops does not work as it’ll only have less material to mush out of the way.

This is the 3rd/4th synchro assembly from an EVO.  Notice that the hub is busted.  This mainly happens when running a solid hub clutch disc. Over time the harmonics from the engine damage the synchro stops. If the transmission blocks the shift you need to fix the problem.

Having trouble with the 5th gear synchros grinding?  New parts alone will not fix this problem, it requires some trick machine work.  TRE has the machines, tooling and the know-how to make the corrections so that all your synchros will work their best providing long service life.


2003/4 EVOs were plagued by chipped teeth on the final drive gear.  A new part number gear exists but this gear still needs corner rounding to make it live in a high power EVO that lives a 1/4 mile at a time.


Make sure the little O-ring is between the transmission and transfer case when installing the transfer case. If you don’t oil will leak out of your transmission.  Also, don’t wrap your downpipe past the oil pan because it can soak with oil and act like a wick, burning your car to the ground.


If you are leaving oil drips in your parking spot and the underside of your car is getting an oil bath you should find out where it’s leaking from.

This is reverse gear from an EVO that was driven will low on oil.

Yes that is a tapered roller bearing on top of the gear. One would think that the driver would have stopped instead of trying to drive home just to avoid having to be towed.


It took so much power to turn the transmission that the driver had to downshift to 4th gear and get into the boost just to drive home.

Eventually 4th gear started to slip but they couldn’t downshift to 3rd gear because the hub & sleeve had pair bonded.

 Don’t be afraid, just use your head.