Hydraulic Flaring Tool Kit, GM Transmission Cooler Line

This is a hydraulic flaring tool for the bench and the lift, built around a ram and a stabilizing arm instead of a screw-type yoke you have to lean on. It forms seven flare profiles: 45 degree single and double, ISO bubble, push-connect, GM fuel line, GM transmission cooler line, and standard hydraulic flares. Tube range is 3/16, 1/4, 5/16, 3/8 and 1/2 inch, plus 4.75mm, 6mm, 8mm and 10mm metric. Model MU-CT-410, 32 pieces in a blow-molded case with a tube cutter and deburring tool included.

The reason this earns a spot in a transmission bay is the GM cooler line die. Factory cooler lines on GM trucks and vans run steel from the case to the radiator cooler and to an auxiliary cooler, and they rot at the crimp and at the frame rail long before the transmission does. A screw-type flaring bar will not reliably form the GM cooler-line profile on hard steel line, and a flare that is not seated square weeps fluid at the fitting the first time the line sees line pressure and heat. That leak shows up as a low-fluid, delayed-engagement complaint that gets blamed on the transmission.

On the bench the sequence is short: cut the line square with the included cutter, deburr the inside and outside edge so the die does not tear the wall, clamp the tube in the die at the marked height, then pump the ram. The auto-return spring pulls the punch back so you are not fighting the tool between flares, and the pressure relief valve keeps you from over-forming and cracking the flare. Dies are stamped with their size, which matters when you are working under a truck with a flashlight and four die sets in front of you.

Use it for cooler line replacement, brake and fuel line fabrication, and any hydraulic line repair where you need a leak-free seat the first time. Cutting and flaring your own line off a roll is also how you get out of waiting on a discontinued OEM pre-bent line for an older truck.