A Birfield joint. So what makes this part so significant on my Toyota truck? Well, without it, power to the front wheels would not be possible while turning. So what's special about this joint? Well a Birfield joint is a true 100% constant velocity joint. Unlike a Universal joint, which vibrates and spins with unequal power transfers, a Birfield joint produces an ultra smooth and constant transfer rate of torque. This makes for a smooth operation with less stress on the axles. Then why do Birfield joints fail? A Birfield joint, like the Universal joint found on a Dana 44, fail because from the factory, it was only intended to turn 29" tires. And we all know that a tire size greater than 29" is a definite requirement on the trails.    33-inch and greater are most common on the trail today. And with the lower gear ratios needed to spin these huge tires slowly comes a lot more torque to pass through each Birfield joint. But I've got 33" tires and I have never broken a Birfield joint. 90% of the time, Birfield joints fail when the vehicles wheels are turned all of the way to the steering lock, and maximum torque is delivered to the joints. Consider yourself lucky.    Shown in the sketch to the left is a Toyota style Outer and Inner Axle assembly (the outer axle being the Birfield). Sketched first is an axle and joint positioned at 0 degrees, or straight. At this point, maximum torque can be transferred through the Birfield with the least possibility of joint failure.    But below it, is an example shown at a maximum steering angle. This is when the torque transfers are carried to the outer most ridge of the unit. It is here where a failure is most likely to occur. And since torque figures are * greatly increased with lower gearing, joint failures become more and more common.    To resolve this affair of high torque transfers failing stock Birfield joints, Marlin Crawler has invented the Marfield. The Marfield is an all American made 100% direct bolt in new replacement joint for your live axle Toyota Minitruck or 4 Runner. This joint is 125% thicker at its weakest spot, shown in the picture to the right. Although one has never been tested, test results from previous inferior Marfields have us to believe that this new Marfield, design UM4, is more than 200% stronger then a factory Birfield joint, and we want you to put it through the test! *139% more torque with a differential ratio of 5.71:1 compared to a 4.11:1, and 300% more torque when comparing a stock crawl ratio of 36:1 to a moderately-advanced crawl ratio of 108:1. Marlin Crawler Marfield Factory Birfield Close this window