INPUT SHAFT SPLINE WEAR

It has come to our attention that many people are experiencing problems with twin disc clutches tearing up the splines on the input shaft.  Shown below are two input shafts; the photo on the left is an EVO-9 that had a triple disc clutch and the photo on the right is a 97 DSM FWD that was ran with a twin disc clutch. Both input shafts were new and had less than 2000 miles on them. This sort of spline damage is terrible and causes the clutch to not disengage properly, clutch and transmission chatter and eventually the splines will strip out.

       

The spline wear is the result of the clutch disc not enough having enough spline length making contact with the input shaft to keep the splines from yielding from the torque and the fact that the transmission was never designed for the strain of a multi-disc clutch. This problem is compounded by the lack of a sprung damper assembly and low mass flywheels that don't carry enough momentum to keep destructive 4th order harmonics from beating up the transmission parts.  Other contributing factors that will damage the input shaft are: stroker engines, low mass flywheels, engines that have poor idle quality, sloppy worn-out engine mounts, excessive backlash in the drivetrain, general abusive dumping of the clutch, time in general and ultimately a clutch that either doesn't have enough area of spline to handle the strain.

Other components that get ruined are: 

• Synchronizers

• Hub & sleeve assemblies

• Load bearing surfaces

• Synchro keys & springs, etc...all things that will effect how well the transmission shift.

If your application truly requires a twin or triple disc clutch, please select a clutch that has a one piece splined section or a clutch  that has enough surface area to handle the strain and keep the input shaft splines from getting destroyed as this sort input shaft spline damage is not something that is not covered by the warranty. It is your responsibility to do the research and find what clutch is truly best for your application. Both Exedy and Tilton make clutches that has a one piece splined section and other manufacturers of twin disc clutches will hopefully be releasing their much improved designs in the future. 

GEAR DAMAGE

Excessive torque will not only damage gears in your transmission but nearly everything that transmits power to the pavement. You can usually get away with shoving a ton of torque into a transmission that wasn't designed for it but eventually you're going to find that nothing is truly bulletproof.  Click here for more info.

RECOMMENDED TORQUE CAPACITIES

 

When choosing your clutch make sure that you choose a clutch that has an appropriate torque capacity for the application. This value should be about 20% more torque than what your engine makes at the crankshaft but no more than 50% higher than the fatigue/endurance limit of the transmission. Using a clutch that is past the recommended torque capacity will greatly reduce the service life of certain drivetrain parts.

Listed below are the fatigue limits for some of the Mitsubishi transmissions. The fatigue limit is also known as the endurance limit and it is considered to be where fatigue related failures will not happen for at least 100 million cycles as long as the transmission is in good working order with proper bearing preloads, correct oil and with gears that aren't worn out or making abnormal contact patterns. It is important to note that while most automotive transmissions can be subjected to loads that are 50% greater than their rated capacity these shock loads must be kept to a minimum for long life.

Rated torque capacities:

• AWD  W5MG1 = 440 ft.lbs

• AWD  W5M6A = 415 ft.lbs

• AWD  W5M51 = 375 ft.lbs

• AWD  W6MAA = 290 ft.lbs

• AWD  W5M33 = 245 ft.lbs

• AWD  W5M31 = 228 ft.lbs

 

• FWD   F5M51 = 375 ft.lbs

• FWD   F5M42 = 300 ft.lbs

• FWD   F6MBA = 280 ft.lbs

• FWD   F5M33 = 245 ft.lbs

• FWD   F5M31 = 228 ft.lbs

• FWD   F5M22 = 160 ft.lbs

• FWD   KM210 = 150 ft.lbs

• FWD   KM176 = 130 ft.lbs

 

Again the fatigue limit is where there won’t be a failure of gear teeth pretty much regardless of how many cycles the parts is subjected to, assuming the transmission is in good working order with proper bearing preloads, correct oil and with gears that aren't worn out or making abnormal contact patterns. This torque rating is determined by the overall design of the transmission, gears, shafts, shaft spacing, structural integrity of the transmission case, size & capacity of bearings, the choice of steel being used to manufacture the gears, tooth count, helix & pressure angles, root radius quality, the manufacture's ability to hold tolerance on the parts and to what AGMA or DIN that they cared to produce in the first place. Then ultimately by doing destructive load testing and long 100-200 million cycle tests, the endurance limit is defined. To better understand what Mitsubishi has built, we've sent several gear samples out to have burn offs performed in order to know what choice of steel they used in their drive-train products. We have built load cells to conduct destructive testing to determine the amount torque at which plastic deformation occurs. Plastic deformation is when the material yields and now has begun to fail. We have measured shaft flex and how much axial deflection the transmission case has in relation to how many ft.lbs of torque in each gear, produced FEA's and have defined the S/N probability curve.  One of the best things that can be done to improve strength is to shot peen the gears.  It has proven itself invaluable when it comes to increasing the amount of abuse your transmission can withstand before failing. More about shot peening.

The above text is merely the tip of the iceberg of what should be done when calculating the realistic probability of survival when it comes to answering the infamous “how much torque is it rated for” question. Yes you can put more torque into the transmission but the overall life expectancy of the transmission will be shortened accordingly.

For more information regarding which clutch to use and what is an appropriate torque capacity for a Mitsubishi transmission click here.

 © 2010 TRE