4L60E 6AN Braided Transmission Cooler Line Kit, 70 in

If the steel cooler lines on your Silverado, Sierra, Tahoe, Camaro or S10 are weeping ATF at the radiator, or you are adding a stand-alone cooler before the truck starts towing, this kit gives you two 70 inch runs of 6AN hose and the adapters to tie a GM 4L60E into it. Seventy inches is the middle length: long enough to reach a front-mounted cooler from the case on most full-size trucks, without the extra coils of hose a 15 or 20 foot roll leaves you to cut and re-end. The hose is PTFE inside a stainless braid, and the kit includes the straight and 90-degree adapters most installs need.

What cooler lines do in a 4L60E

The 4L60E sends converter charge oil out one case port to the cooler and takes the cooled fluid back through the other, where it feeds the lube circuit for the bushings, planetaries and the rear of the unit. That makes the lines part of the lubrication path, not just plumbing. A kinked, restricted or leaking line raises fluid temperature and cuts lube flow, and heat is what glazes the 3-4 clutches and the 2-4 band and hardens the seals in this transmission. A line that loses fluid slowly also drops the level below the pump pickup, which shows up as slipping and flare on hard acceleration or in turns.

Signs the factory lines need replacing

• ATF drips at the crimped rubber sections, the radiator tank fittings or the case connectors
• Rust scale on the steel tubes along the frame rail, especially on trucks from salt states
• Fluid level dropping between checks with no pan or seal leak you can find
• Dark, burnt-smelling fluid after towing, a sign the unit is running hot
• Slipping or delayed engagement when the level is low, which can lead to the burnt 3-4 clutch pack the 4L60E is known for

How to confirm before buying

Clean the case, the line ends and the radiator fittings, run the truck to temperature and look again before you blame the transmission. Seepage at a rubber section or a fitting points to the lines. Check the fluid level hot as described in our 4L60E Astro van problems guide, which covers the owner-manual hot check. If the fluid already smells burnt and the truck flares between gears, read 4L60E common problems first, since a cooler upgrade will not bring back clutches that are already cooked.

Fitment

The fitting set covers GM 4L60E, 4L65E, 4L80E, 700R4, 200-4R, TH350 and TH400 cases, plus Ford AOD, 4R70W and 4R100 and the TR6060 with the correct adapter. Case ports on the 700R4 and 4L60E family are a 1/4 inch straight pipe thread (NPS), and the kit includes 6AN to 1/4 NPS adapters for them, along with 1/4 and 3/8 NPT adapters for coolers and radiators that use tapered thread. Thread pitch on aftermarket coolers varies, so measure the old fitting or check your cooler's instructions before you start. Measure the actual route with a string from the case to the cooler; if either run is longer than 70 inches, step up to a longer kit. Browse every part for this unit in our 4L60E collection.

Install notes

• Drain or catch the fluid in the old lines, then remove them at the case and the cooler or radiator.
• Seal tapered NPT threads with an ATF-resistant thread sealant. Never put sealant on the 37-degree AN flare; the flare seals metal to metal.
• Use the 90-degree swivels where the hose has to turn right at the case, so the hose itself is not bent tighter than its minimum radius.
• Route both lines clear of the exhaust, the driveshaft and the steering linkage, and clamp them so they cannot rub on the frame.
• Tighten AN nuts snug, then about a quarter turn more. Overtightening crushes the flare and starts a leak.
• Top off with Dexron VI ATF, run the engine to temperature, recheck the level and look over every joint for weeping.

If you are already pulling the transmission for a rebuild, this is the time to fit new lines, since a rebuilt unit is only as healthy as its cooling. A 4L60E shift kit raises clutch apply pressure to reduce slip time and heat, and the master rebuild kit with BorgWarner frictions covers the clutches and band if the old unit already overheated.

Will this kit fit the cooler ports on my 4L60E case?

Yes for the stock case. The 700R4 and 4L60E family use a 1/4 inch straight pipe thread at the case, and the kit includes two 6AN to 1/4 NPS adapters for those ports. The NPT adapters are for coolers and radiators that use tapered thread.

Is 70 inches long enough?

On most full-size GM trucks and SUVs with a cooler mounted ahead of the radiator, yes. Run a string along the path you plan to use, following the frame and avoiding the exhaust, and measure it before ordering. If either run is longer than 70 inches, a longer kit is the better choice.

Do I use thread sealant on the AN fittings?

Only on the tapered NPT threads. The 37-degree AN flare seals metal to metal, and sealant or tape on the flare can keep it from seating and can shed debris into the fluid.

What fluid should I use after installing new lines?

Top off with Dexron VI ATF, the fluid listed for the 4L60E, and check the level hot with the engine running in Park after the lines have filled.

Should I flush the cooler when I replace the lines?

If the transmission failed or the fluid was full of metal or clutch material, flush the cooler or replace it. Debris trapped in the cooler goes straight back into the lube circuit of the new or rebuilt unit.

• 4L60E Common Problems, Symptoms, and What to Actually Do About Them
• 4L60E Astro Van Common Problems and Fixes
• 4L60E Camaro Common Problems and Fixes
• 4L60E Chevy S10 Common Problems and Fixes