A Transfer Case is a fundamental part of the 4WD drive system on your 2004.5-2005 Chevy Silverado or GMC Sierra 2500HD/3500HD. The LLY Duramax trucks came equipped from the factory with either a New Process NP261HXD transfer case or NP263HXD transfer case (also known as a New Venture NV261 / NV263 or GM 261XHD / GM 263XHD). If you've ever gotten stuck and needed 4-wheel drive, then a transfer case is what helped get you out. There are usually two different gear ratio options with a Transfer Case, 4-wheel low and 4-wheel high. Transfers cases typically have two 4-wheel drive settings, a high and low gear ratio for different situations. The transfercase in a 4-wheel drive system is responsible for transferring power to both the front and rear axles. 4-wheel high is used in high-speed settings such as dirt or snow, whereas 4-wheel low is used in low-speed settings like steep rocky hills where maximum wheel torque is required. Bolted to the back of the transmission, a transfer case has two driveshafts connected to it that run to each axle.

It is highly recommended to not engage the transfer case for anything other than off-road or low-traction situations. When engaged in 4-wheel drive the transfer case and drivetrain need some wheel slip to prevent binding or damage. Since transfer cases lock the front and rear axle together, the wheels are unable to spin at different speeds making turning and cornering on dry pavement difficult. Transfer Cases generally are very strong from the factory and do not require internal upgrade unless the vehicle is used for extreme off-roading or racing. In some applications an external brace can be added to increase the structural rigidity of the transfer case to prevent damage from high torque loads or twisting. XDP carries a wide selection of Duramax LLY Transfer Case products available from Zumbrota Drivetrain, Dorman, Merchant Automotive, PPE, Sun Coast Converters, and more.