Choosing the Proper Clutch

From the guys at TRE


TORQUE CAPACITY

90-99 AWD DSM: 

The factory rated the W5M33 89-99 AWD transmission for roughly 250ft.lbs of torque.  You can put over 700ft.lbs of torque through our top shelf DSM AWD transmission, these guys have but we don’t expect it to last forever on the OEM gears. It should be noted that a customers have successfully put over 600ft.lbs of torque through our transmission for two seasons of drag racing while another customer is reporting over 750ft.lbs of torque without issue but it is expected that fatigue cycle failure will eventually happen because the factory parts were never designed to handle this kind of torque.

We have done destructive load cell testing on the DSM AWD transmission. Listed below are the average peak torque numbers at which failure occurred immediately during a static load test of a factory new AWD transmission.

        1st gear = 1000 ft.lbs caused the intermediate shaft to crack teeth on the primary reduction gear.

        2nd gear = 1200 ft.lbscaused the intermediate shaft to crack teeth on the primary reduction gear.

        3rd gear = 980 ft.lbs caused the teeth on the synchronized 3rd gear.

        4th gear = 950 ft.lbs caused the intermediate shaft to crack teeth on the 4th gear.

        5th gear = NA*

During the testing the input shaft splines began to yield and crack where the splines end at approximately 1100ft.lbs. of torque but it is common to find them failing when used with clutches that hold above 700ft.lbs. when driven long enough  Multi-disc clutch warning!

While the numbers may appear to be impressive, understand that failure was immediate and that the endurance limit is approximately 1/3 of peak torque values listed above. To put things into perspective a new off the shelf 4th gear & intermediate shaft from  the DSM AWD has an approximate life of less than 500,000 cycles per tooth @ 450ft.lbs of torque. The number of cycles can be increased substantially by detailing & shot peening the gears.

I recommend using a clutch that holds around 450ft.lbs of torque for the daily driver who street races and occasionally goes to the drag strip. This will provide you with the best service life for the gears because shock loading is kept to 450ft.lbs.  Shockloading a set of gears with excess torque will severely reduce the number of cycles before the teeth fail and must be kept to a minimum. Sure you can run whatever you want but these recommendations should be adhered to if you’re looking for long transmission life.

90-99 FWD DSM: 

I have not done any destructive testing on the FWD transmission but it should be similar to the AWD and I recommend us a clutch that holds the same amount of torque maybe a little less. An ACT 2100 works fine in most applications. A customer reported making over an impressive 700ft.lbs of torque is using one of our FWD transmissions for the past three years without failure.

TYPES OF CLUTCHES

DAILY DRIVER:

OEM style clutches are best for daily drivers who are looking for the longest clutch & drivetrain life. Clutch life will vary with how you drive. The torque capacity must properly chose so that the clutch slips before parts break.  More about clutches can be found here. Sprung hub type clutch discs are good because they reduce transmission chatter from the 4th order harmonics of the engine making their way into the transmission. This is done because 4th order harmonics will make the transmission chatter. The chatter is caused from the backlash between the gear teeth. 4th order harmonics will oscillate the gears in a manner that tends to wear out the gears and splines on the input shaft as well. This is why OEM clutches use sprung hub damper assemblies.  However, sprung hub assemblies are not designed to cushion the drivetrain from shock loads and the damper springs can get damaged from hard clutch dumps.  This is also compounded when aftermarket clutch manufactures increase the clamp load of the spring plate without doing anything to strengthen the damper assembly. To avoid damaging the sprung hub assembly one must learn the classic slip-dump method.

ROAD RACING:

Single disc puck style clutches shift the best for road racing or autocross period.  Don’t even think that a twin disc can outshift a single disc when it comes to road racing unless you are willing to spend 4x’s more for an uber high-end racing clutch than what a well-designed single disc clutch would cost. The reason for this is due to the low mass clutch disc, it reduces the amount of work the synchronizers must perform making them last longer. They can be driven on the street and offer decent service life as long as you’re not launching the balls off the car. When choosing a single disc puck style clutch, the less number of pucks the less rotational mass the disc has. Don’t get too caught up in how many p.s.i. the pressure plate has, instead be more concerned that the clutch has the proper amount of torque capacity for you application.

DRAG RACING:

Torque capacity is as stupidly high as you dare to use. Carefully make your decision when choosing the torque capacity and pay attention to the torque capacity data provided as they are important when it comes to the life of your transmission, transfer case and rear differential assembly. Racing type clutches are intended for hard core racers, where all that matters is winning the race and rebuilding or replacing parts often is part of the game, not daily drivers where it needs to last tens of thousands of miles. If you drive it on the street you should consider using a full face organic clutch disc for longer service life. Puck style clutch discs can be used in a daily driver but don’t expect it to last.

RULE OF THUMB:  THE CLUTCH IS SUPPOSED TO SLIP BEFORE DRIVETRAIN PARTS BREAK. IF YOU DRIVE IT ON THE STREET, USE A CLUTCH THAT IS SIMILAR TO THE ORIGINAL EQUIPMENT.

RACING TYPE CLUTCHES ARE FOR RACE CARS, NOT DAILY DRIVERS. CHOOSE YOUR CLUTCH WISELY AND REMEMBER THE MORE YOU ABUSE IT THE SOONER THEY WEAR OUT.

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