Allison 1000 Braided Transmission Cooler Line Kit LBZ/LMM

A wet front crossmember, a red drip under the radiator, or a dipstick that reads a little lower every week: on a 2006-2010 Chevrolet Silverado or GMC Sierra 2500HD or 3500HD with the 6.6L LBZ or LMM Duramax, those clues usually lead to the transmission cooler lines. This kit replaces the factory steel-and-rubber lines between the Allison 1000 and the coolers with braided hose and the adapter fittings needed to connect it.

What the cooler lines do on an LBZ or LMM Allison 1000

Hot fluid leaves the Allison through the to-cooler port on the case, runs forward to the cooler built into the radiator tank and to the front-mounted auxiliary cooler, and comes back through the return port, where it feeds lubrication to the gear train. On a truck that tows, that circuit is the only thing keeping the fluid out of the temperature range where it breaks down. The factory lines are formed steel tubing with short rubber sections and clamps, and they run low near the oil pan and frame rail where road salt and water sit on them. Pinholes in the steel and tired rubber sections are the usual failure. A line that lets go at speed can empty the transmission quickly, and an Allison run low on fluid will slip and burn clutches in a hurry.

The hose in this kit has an oil-resistant synthetic rubber liner, a textile braid for reinforcement and an abrasion-resistant cover. It is rated 840 PSI working pressure and 3,360 PSI minimum burst, and for continuous use from -40 to 257 degrees F.

Symptoms of leaking cooler lines

• ATF on the front crossmember, the oil pan or the inside of the driver-side frame rail
• Rust scale, pitting or a wet spot on the steel sections of the factory lines
• Seepage at the crimped rubber joints or at the fittings on the radiator and auxiliary cooler
• Low fluid level, followed by flare shifts or slipping once enough fluid is gone
• Higher transmission temperatures when towing if a line is kinked or crushed

Confirm it before you buy

Clean the lines and fittings, run the engine to temperature and look at the full run from the case to both coolers with a light. Many apparent pan leaks are actually cooler line drips that ran back along the pan rail. Then check the fluid level hot, the way our Allison 1000 fluid and filter guide explains. If the truck has already been run low and now shifts harshly or goes into a fixed gear, read the Allison 1000 limp mode guide before the lines are your only repair.

Fitment

This kit is listed for 2006-2010 Chevrolet and GMC 2500HD and 3500HD trucks with the 6.6L LBZ or LMM Duramax and the Allison transmission. That covers the late classic body LBZ trucks and the 2007.5-2010 new-body LMM trucks. It is not for gas trucks or for the LML; 2011-2014 trucks use a different line layout and quick-connect ends, covered by our LML cooler line kit. If you have a 2006 truck, confirm the engine is an LBZ (VIN 8th digit D) rather than the LLY before ordering, or send us the year and VIN and we will check it. More parts for these trucks are on our Allison 1000 page.

Install notes

• Work with the engine cold on a lift or jack stands, and have a drain pan under both ends of each line.
• At the radiator, change one fitting at a time. Line kit makers warn that removing both radiator fittings at once can let the internal cooler shift inside the tank.
• Some radiators use M22 x 1.5 fittings with a large integral nut; check what your radiator has before you start.
• Route the hoses with a little slack at the transmission end, keep them away from the exhaust, the sway bar and anything that turns, and secure them so they cannot rub.
• Refill with an Allison-approved fluid such as TranSynd 668, run the truck to temperature, recheck every fitting for weeps and set the level hot.

If the fluid was low or dark, plan a filter change with a filter and pan gasket kit, and recheck the fittings after the first few heat cycles.

Will this kit fit my 2011 Duramax?

No. It is for 2006-2010 LBZ and LMM trucks. The 2011-2014 LML uses different lines and quick-connect ends, so it needs the LML kit.

Does it fit a 2006 LLY?

The listing covers LBZ and LMM trucks. Some 2006 trucks have the LLY, so check the engine code in the 8th digit of the VIN and send it to us if you are unsure.

Do I need to replace both lines?

The kit replaces both the feed and return runs. If one factory line has rusted through, the other has seen the same salt and age.

What fluid should I use to refill?

An Allison-approved fluid. TES 668 is Allison's current recommended specification, and TranSynd 668 meets it. Check the level hot after the install.

Can I drive with a leaking cooler line?

Not for long. A line that fails completely can empty the transmission quickly, and running the Allison low on fluid causes slipping and clutch damage.

• Allison 1000 Fluid and Filter Service: Real Capacities, Intervals, and the TES 668 Change
• Allison 1000 Limp Mode: Causes and How to Diagnose It
• Allison 1000 Transmission Service Guide: Fluid, Filters, and Common Issues
• Allison 1000 Torque Converter Shudder: Diagnosis and Fix