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Rock Crawler Driveshaft Buildup - 'Shaft Science

Posted in How To on July 1, 2010 Comment (0)
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If you like to crawl in boulders you've probably sacrificed a driveshaft to the ravages of rock. Whether it be a simple bend, dent, or a complete collapse, such damage is all too common. As such, driveshaft shops are used to re-tubing or replacing what we destroy.

To further understand what it takes to assemble a driveshaft from scratch, we took a trip to Phoenix Rack & Axle, a driveline specialty shop located in Phoenix, Arizona. The shop builds standard and custom driveshafts for all types of vehicles. We were interested in the construction of one of its long-travel 'shafts.

Owner Bernie Thompson showed us the steps his shop uses in constructing a 'shaft from base components. While a standard auto driveshaft may use tubing as thin as 1/16-inch-wall thickness, shafts for rock-crawlers are often built from 0.120-inch to 0.250-inch-wall tubing for added strength and the ability to be dragged across boulders as needed.

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Driveshaft Balancing
Four-wheel-drive vehicles with large tires and lifts may suffer driveline shakes for a number of reasons. However, one item that is often overlooked is driveshaft condition. Consider the fact that you're cruising down the road with the engine spinning at 2,500 rpm in top gear. Your driveshaft is whirling away just as fast. That's a lot of speed for a spinning shaft and a couple of joints flexing through steep angles.

Driveshaft balance plays a big part in how smoothly your driveline operates. Just as an unbalanced tire can make one corner of your truck shake, an unbalanced driveshaft can send a shimmy all through your vehicle. This makes for an unpleasant ride and increases driveline wear throughout the vehicle.

Driveshaft balance consists of a number of separate components. First, in order for the shaft to be stable when spinning, the CV joints or U-joints must have no play in them. Any joint looseness may cause the driveshaft to snap back and forth when it rotates. This can cause vibration and further rapid wear of the joints. All joints should move freely and be well greased.

Second, dents or other damage to a driveshaft can greatly upset its balance. A shaft that is not straight or true will wobble when rotated and cause driveline vibration problems. Generally, a damaged tube must be replaced. A qualified shop may be able to true a slightly bent driveshaft by heating sections of the shaft and causing it to straighten. However, this can only be done for slight misalignment.

Finally, variations in the yoke components and tube welds can cause a newly built driveshaft to be slightly out of balance at high rotation speeds. Most driveshaft shops are equipped with electronic balance fixtures and can fine-tune the balance of a shaft. Balance is typically achieved by welding small steel weights on a driveshaft tube as needed.

Sources

Phoenix Rack & Axle
Phoenix, AZ 85034
602-252-8255
www.phxrack.com

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