Allison 1000 Transmission Cooler Line Kit, L5P Duramax

This kit replaces the factory transmission cooler lines on 2017-2019 Chevrolet Silverado and GMC Sierra 2500HD and 3500HD with the 6.6L Duramax L5P and the Allison 1000. It is the later-generation routing, not the 2011-2016 LML or the 2006-2010 LBZ/LMM setup, so match your truck year before ordering.

The factory lines on these trucks are a mix of hard line and quick-connect sections, and they leak at the crimps and the connector seals once the miles and the heat add up. A weeping cooler line on an Allison is not a slow problem: the whole cooler circuit sees pump pressure, so a connector that lets go drops the fluid level fast, and the 1000 does not survive long without fluid going to the converter. Towing makes it worse, because that is exactly when the circuit is hottest and flowing the most.

Instead of patching one section, this kit replaces the run with three 5/8 inch ID reinforced hydraulic hoses terminated in -10AN fittings, which is a larger flow path than the stock line. Six 7/8-14 O-ring to -10AN adapters thread into the factory ports at the transmission and cooler, so no cutting or fabrication is needed. Large OD washers, double hose clamps, locking cable ties and fir tree clamps are included to route and secure the hoses away from the exhaust and driveline. Plan on refilling and rechecking the level hot after the install, since the longer hoses hold slightly more fluid than the lines they replace.