3rd gear in the 8-9 units had some lubrication issues, but Mits added more oil holes to the input shaft and more oil channels through the 3rd gear hub to lubricate and cool the 3rd gear synchro more for longer life:


The EVO 8-9 units have a single synchro 4th gear. If that wasn’t bad enough, they were also on the small side. Mits engineered a nice large double synchro to 4th gear eliminating all of the previous synchro issues the 8-9 had. 8-9 on the left, X on the right:

Same deal with 5th. The 5th gear synchro was a tiny single synchro with a high failure rate. The new 5th gear was moved over to the input shaft side of the trans (where there was more room for a bigger synchro) and not only did they make the synchro huge in the X, but they also installed a double synchro! 8-9 on left, X on right:

The reverse gear synchro assembly is no longer on the output shaft, but its own assembly as a 3rd cluster to the side of the unit integrated to the idler gear. This looks to be a better assembly over the previous design as well as this way the synchro can work more efficiently as a brake in the idler than on the heavy output shaft. IOW, the gearing in the idler makes the synchro do its job better. This adds a little more complexity to the trans, but well worth it.


We now see Mits did the exact same thing to the EVOX trans! Great minds think alike!! Their tapered roller bearings obviously fixed all of the old issues involving the ball bearings. Pic of X input tapered roller below. Looks very similar to our 8-9 upgrade doesn’t it?

It appears Mits did a lot to improve on the 8-9 with the X unit, but the X also has some problems. The center diff spider gear pins have an issue of working their way loose and going through the case causing a lot of damage. All of our X rebuilds include a fix to the center diff so you never have to worry about it again. If your center diff had this failure and damaged the trans case don’t give up on the unit and spend a fortune on a new one! We have the ability to repair most case damage here with our equipment, and if we can’t, we can get any part needed for your trans, so your unit is repairable! Please email us at sales@jackstransmissions.com
Another issue we had pop up on a recent unit here is excessive 3-4 shift fork wear. The fork wore so badly that the unit would no longer stay in 3rd gear. We added lubrication channels to the fork and so far all seems to be well.
Last issue we found is Mits is still using the same weak fork pins as the previous years. We modify these in all of our rebuilds also so you never have to worry about them backing out.
We have not seen any other issues involving the X trans. They look to be the best shifting and strongest design we have ever seen from Mits, but if abused, raced on, or not maintained they will need service like with anything else. Feel confident that Jacks Transmissions has the knowledge and equipemt to do it right with all of the latest updates to make a unit that is better than new when you recieve the unit back from us!
Thanks for reading! If you have any questions please feel free to email us at sales@jackstransmissions.com