Maintenance and diagnosis
Most of you know the symptoms of a slipping clutch. If you don't then you will eventually. A broken output shaft, stripped output shaft/TC input spool, popped center VCU, striped VCU/sun gear/pinion shaft splines, broken or popped out front CV axle, broken rear third section of the OEM drive shaft, and/or a busted TC housing will give similar symptoms. The difference is that a clutch usually goes out gradually while these parts usually go out all at once. The only exception is if you are using a puck style clutch, which can also go out all at once. These failures are often misdiagnosed as failed clutches and members end up spending time and money for a part that won't correct the problem. Listed bellow are symptoms of these failures.
TC failure
You will usually know when your TC housing explodes because they literally go out with a "bang" during a hard launch. Most members report that they felt a thud by their feet when it happened. Of course with the case busted wide open all the fluid inside will spill out on the road. At the least, the front housing will have to be replaced. The extent of the damage will very on a case-by-case basis and can include the bell housing, TC middle casing, and the TC gears. Most members just buy a new TC from Kormex or another member and put new seals in it. The part number for the reseal kit from Mitsubishi is MN156006. Be sure to use the metal washer to press in your TC input spool seal so that the washer is flush with the housing. Failure to do so will result in the seal being flush with the housing (not recessed in the housing like it should be) and it may pop out, leak out all of the fluid, and cause your TC to lock up potentially causing an accident.
Output shaft and TC spool failures
If you are pretty sure that your clutch is good and your TC housing is intact then the next step is to remove the TC from the car and inspect the condition of the output shaft and the TC input spool. You should be able to tell right a way if the output shaft has broken or if some thing is striped. The splines on the shaft and spool should be trapezoid shaped not triangular. Usually the splines on the shaft will strip but they can damage the spool in the process. If you striped something then it is a good idea to replace the spool and the shaft at the same time. If you broke an 18 spline shaft then the most cost effective repair (and upgrade) is to get a Mark Williams 300m 18 spline shaft an 18 spline spool from Kormex. In either case, inspect the splines on the shaft and the spool to be safe. If they are triangular shaped then they are worn and about to strip. It they are trapezoid shaped then they should be good to go. Be sure to clean the splines and then apply grease or another rust inhibitor to the splines to help keep them rust/corrosion free.
VCU failure
Usually when the VCU in the center diff pops, it pukes the viscous goo out into the transaxle's gear oil. If you drain you tranny fluid, then look to see if it is blackish/brownish in color. The VCU goo will usually separate from the gear oil if it is sitting for a couple of hours. If you found goo in your gear oil, then you have a failed VCU. The car will still be able to move but members have reported that they get a lot of front wheel spin on a launch and their 60’ times increase as much as half a second or more.
Another more rare VCU failure is that the splines that mesh with the sun gear and/or the pinion shaft will strip. You will usually hear a clicking/ratcheting type of sound along with the usual slipping clutch like symptoms. You do not experience any wheel spin however. These symptoms are most prevalent in the lower gears.
Front CV axle failure
A front CV axle failure or a front CV axle that has popped out of the tranny can be easily diagnosed by looking at your speedometer when the “slipping” symptom occurs. If your speedometer registers an increase in speed, then inspect your front CV axles first. The reason your speedometer registers more speed is because the front diff carrier drives the vehicle speed sensor. The carrier will spin if an axle popped out or if an axle broke and thus drive the speed sensor faster. A front axle failure/popping out puts a lot of stress on the VCU also. So drain and inspect your tranny’s gear oil if this happens to you.
Drive shaft failure
The OEM drive shaft is made of three shorter drive shafts splined and bolted together. The rear third section is made up of three parts. There is a smaller diameter tube inside a larger diameter tube with a layer of rubber in between that holds them together. With enough power (estimated around 500 AWHP) or enough age to dry rot the rubber, the outer tube will separate from the layer of rubber that holds it to the inner tube and the tubes will slip against each other. This will heat up the rubber in between the tubes and partially melt it. It will then cool and hold the tubes together again but it will never hold them as strongly as it once did. It will hold them together strong enough so you can’t turn the tubes against each other by hand but the engine will be able to get them to slip with the greatest of ease. Here are two things to look for if you suspect this failure. First, it will be easier to induce slipping in the lower gears. Secondly, when slipping occurs it will feel like you are in a RWD vehicle that is stuck in the mud. You can feel the drive shaft spinning but you are not going any faster. You may hear a grinding sound from the rear during slipping but this symptom is not always present. This type of failure is also very hard on the center VCU and you should inspect the tranny’s gear oil for signs of VCU goo.
Rebuild manual and recommendations
To replace the output shaft and/or VCU you have to open up the tranny. I recommend you remove it from the car and put in new seals, synchros (if needed), and a clutch (if needed or stock) while you are at it. I highly recommend against pulling the end cover with the tranny in the car. I have had way too many members calling me up or sending me PMs/e-mails for advise about shifting problems, grinding noises, leaks, and cracked housings as a result of this practice. These tranny’s were designed to be taken apart bell housing first while out of the vehicle. Any other disassembly method can (and often does) result in further damage. The Getrag 440 (five speed) and 446 (six speed) rebuild manual can be downloaded from the thread linked bellow. Special thanks to Gatecrasher and all who helped in the translation for the hard work in making this information available to all 3Si members.
Getrag Rebuild Manual - 5 and 6 speed models - 3000GT/Stealth International Message Center
The torque spec for the input shaft lock bolt is for the 12 mm hex bolts only. It does not list a torque spec for the 7 mm hex bolt found on earlier 5 speeds. I have been torqueing them to down to about 20 ft-lbs with thread locker myself with out any problems.
Other commonly and not so commonly failed parts include the synchros, seals, and the occasional bearing and shift fork. These are almost always related to previous owners neglecting to change the gear oil on a regular basis and/or the clutch dragging for any number of reasons. The driver’s inability to properly shift gears fast will also cause a burned synchro or a broken fork (I know even I am guilty of poor driving abilities). While fluid and clutch issues will be addressed in other threads/topics I would like to caution members about tranny installation. When attempting to line up the input shaft with the clutch hub, DO NOT VIOLENTLY JIGGLE THE TRANNY. This will result in the input shaft beating against the clutch hub and warping the disk. A warped disk will drag and greatly increase the chances of synchro and shift fork failure.
Here are a few tips that have made mounting the tranny to the engine much easier for me. When installing a new clutch, you will notice that the clutch alignment tool has some up and down play in it when holding the disk against the flywheel. If you hold the alignment tool midway in it’s range of up and down play before tightening the pressure plate bolts, then it will better align with the tranny input shaft so you will not have to fight the shaft into the clutch hub.
The easiest way to get the tranny into position to mount it to the engine is with an engine hoist if available. Bolt the chain of the hoist to the shift cable bracket holes in the bell housing. This will balance the tranny and generally only requires you to slightly push it side to side to clear the cross member and any hoses or splash shields. The closer you get the tranny to it’s final position on the engine, the more it will naturally align it self to the engine. You should find that the tranny will slide easily against the engine once the input shaft splines are aligned.
This is just a small portion of the writeup on the AWD Drivetrain on 3si.org. For more click here:
Everything you need to know about your AWD drivetrain - 3SI Wiki.
