Replaces the failure-prone plastic quick-connect cooler line fittings on 2011-2014 LML Duramax Allison 1000 trucks with 1/2 in. braided line.
Owners of 2011-2014 Chevrolet Silverado and GMC Sierra 2500HD and 3500HD trucks with the LML Duramax tend to find this part the same way: an oily film on the front crossmember, a puddle under the radiator, or a fluid level that keeps creeping down with no pan leak. On the LML, the weak link is usually the factory cooler line plumbing and its plastic quick-connect ends. This kit replaces that plumbing with kink-free braided line, a 1/2 inch inside diameter instead of the 3/8 inch factory line, and all-metal AN-style fittings.
Fluid leaves the Allison 1000 at the To Cooler port, travels forward along the frame to the cooler section in the radiator and the auxiliary transmission cooler, and returns to the From Cooler port, where it feeds lubrication to the gears and bearings. On the LML, those lines snap into their ports with plastic quick-connect retainers and O-rings. Years of underhood heat make the plastic brittle and harden the seals, and the connection that was tight at the factory starts to seep or lets go under pressure. The larger braided line also gives the fluid a less restrictive path, which matters most when you are pulling a trailer and the cooler circuit is working hardest.
Clean the connectors and lines, drive the truck until it is fully warm, then trace any fresh fluid back to its highest wet point. A leak at a quick-connect will show at the joint itself, not at the pan rail or output shaft seal. Check the fluid level hot. If the truck already threw a code or went into a reduced-gear mode while the level was low, use our Allison 1000 limp mode diagnosis guide to sort out whether low fluid was the only cause.
This kit is listed for 2011-2014 Chevrolet Silverado and GMC Sierra 2500HD and 3500HD with the 6.6L LML Duramax and the Allison 1000, rear-wheel-drive models as stated in the listing. If your truck is four-wheel drive, a 2015-2016 LML, or anything other than an LML, send us your year and VIN before ordering so we can confirm the routing matches. Earlier 2006-2010 LBZ and LMM trucks use a different layout; for those see our braided cooler line kit for LBZ/LMM. All Allison parts we stock are on the Allison 1000 parts page.
Since the fluid is partly drained anyway, many owners add a magnetic spin-on pre-filter and change the filters at the same time. Our Allison 1000 service guide walks through it.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
The listing covers 2011-2014 LML trucks. The 2015-2016 trucks changed the cooler setup, and aftermarket kits are sold separately for those years, so send us your VIN before ordering for a 2015 or 2016.
The kit uses 1/2 inch inside diameter line in place of the 3/8 inch factory line. The larger passage reduces restriction in the cooler circuit, which helps when the truck is towing and the fluid is hottest.
No. The kit replaces the plastic quick-connect ends with all-metal AN-style fittings, which is the point of the upgrade. The old lines and clips come off the truck.
Refill with an Allison-approved fluid, start the engine, and check the level hot at 160-200 F sump temperature. Recheck after the first drive and look over every fitting for seepage.
If the slip came from low fluid, correcting the leak and the level usually restores normal shifts. If it still slips with a full, hot level, there is internal clutch or valve body trouble that needs diagnosis.
