The EVO input shafts have weak ball bearings from the factory. They are so bad that there is a service bulletin about replacing them from Mitsubishi. If they are breaking in stock cars, imagine if your car is modified!
How do they break?
As you can see from the picture below, all bearings can not withstand thrust load. In a constant mesh helical transmission you are putting the shafts under thrust load anytime you accelerate or decelerate the vehicle. If you launch the car hard, or have a lot of power, the thrust shock to the bearing also increases. Eventually the bearing will fail or become very loose. When the bearing is loose, this will allow the input shaft to wander away from the intermediate shaft and break gears or cause synchro issues with 3rd and 4th over time. Just about every EVO transmission we have rebuilt had loose or damaged input shaft ball bearings.
We have made our own tapered roller bearings for the EVO input shafts. These tapered roller bearings will not be affected by shock load – they can take launching and shock load all day long. With the tighter preloads they hold the input shaft very well making the gears and input shaft stronger. The tighter the input shaft can be held in place, the more power the gears can withstand.
Another benefit of this upgrade is that we have have calculated the best preload for the bearings making your up-shift at high RPM far faster than you could ever get from the factory ball bearing units everyone else uses. The preloads are a little tight when cold, so the trans will be a little stiff when cold on a cold day (people usually never even notice this), but this means incredible shifting once warm! This upgrade will make it so that your transmission can shift faster than you will be able to move the clutch pedal and shifter, and at any RPM with the proper clutch.
Advantages to our tapered roller bearing upgrade:
■Bearings will be less likely to fail due to high shock loads
■Bearings will have longer life
■Input shaft will be held tighter in place
■Gears will last longer
■3rd and 4th gear synchros will last longer
■No wandering input shaft
Disadvantages to our tapered roller bearing upgrade:
■Shifts will feel a little tight when cold