Replaces rusted or leaking steel cooler lines on a GM 4L60E with 20 ft of 6AN braided hose, AN swivel ends and 1/4 NPT and 9/16-18 flare adapters.
A wet frame rail under the front of a Silverado, Sierra, Tahoe or Yukon, a red drip at the radiator, or a transmission that suddenly flares between gears after a long highway run often traces back to one thing: the steel cooler lines rotted through. On the 4L60E they usually let go at the frame clips and at the crimped joint where the steel tube meets the short rubber section. This kit gives you 20 feet of 6AN braided hose and the ends to build both lines new, with enough length left to route out to a front-mounted auxiliary cooler instead of only back to the radiator tank.
Fluid leaving the torque converter is the hottest oil in the transmission, and the 4L60E sends it forward through one line to the cooler, then brings it back through the other. That returning oil is not just dumped in the pan. It feeds lubrication to the bushings and the gear train. So a leaking or kinked line does two things at once: it lets the fluid level fall and it starves lube flow. On a unit whose best-known weak spot is the 3-4 clutch pack, heat and low fluid are exactly what you do not want. Sonnax traces most burned 3-4 packs to low line pressure and leaks in the third-gear circuit, and low fluid from a cooler leak lowers pressure across the board.
Clean the area, run the engine to temperature and look with the truck in gear on the parking brake. A leak at the case fitting or the radiator tank is sometimes just the fitting or an O-ring, not the line. If the fluid is already low, top it off and drive it before you assume the transmission is hurt; slipping that stays after the level is right points inside the unit. Shift codes such as P0741 or P0748 are a valve body or solenoid problem that lines will not fix. Our 4L60E common problems guide walks through what each symptom points to, and the Astro van 4L60E guide covers the hot fluid check procedure from the owner manual.
The hose and fittings suit GM 4L60E and 4L65E transmissions and any other unit plumbed with 6AN line. Inside the box: 20 ft of 6AN hose (about 0.31 in inside diameter and 0.56 in outside), 2 straight and 2 90-degree swivel hose ends, 2 adapters from 6AN to 1/4 in NPT, 2 adapters from 6AN male flare to 9/16-18 inverted flare (1/4 in NPSM), 2 separator clamps and a tube expander. The NPT adapters suit most aftermarket coolers. Ports on factory radiator tanks vary by year and supplier, so pull one line and check the thread before you cut any hose. If you are unsure, send us the year and VIN. More parts for this unit are on our 4L60E parts page.
The hose is a CPE rubber liner with a 304 stainless reinforcement layer and nylon outer braid, rated 750 PSI working, 2250 PSI burst and -22 F to 248 F. If the old lines died after an overheat, look at the pump and clutches too: a 1995-2003 4L60E pump or a 1997-2003 master rebuild kit is often the real repair, and new lines keep it from happening again.
| Transmission | |
| Hose size | |
| Length | |
| Construction | |
| Pressure rating | |
| Temperature range | |
| Includes |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
On a typical full-size GM truck or SUV it covers the supply and return runs from the case to the radiator tank with length to spare. It is also enough to run both lines to a front auxiliary cooler, or to loop through an auxiliary cooler after the radiator on most trucks. Measure your planned route with string first if the cooler sits far from the transmission.
The kit has 6AN to 1/4 in NPT adapters and 6AN to 9/16-18 inverted flare adapters. Factory radiator tank ports differ between years and radiator makers, so remove one line and check the port thread before you start. If neither adapter matches, a single correct adapter is all you need.
Yes. The line carries hot oil away from the converter and the return oil lubricates the gear train. A leak drops the fluid level, which lowers line pressure, and the 4L60E 3-4 clutch pack is the first thing to slip and burn when pressure and fluid are low.
GM 4L60E and 4L65E units take Dexron VI, which GM uses in place of the earlier Dexron III. Check the level hot with the engine running in Park, and recheck after the lines have filled.
If the transmission failed or the fluid was dark and full of material, yes. Flush the cooler and do not reuse a cooler that will not flow clean, because trapped debris will travel straight into a rebuilt unit.
