How to Fix Radiator Line Leak in a Transmission

by Max Stout

Fluid contained in automatic transmissions becomes heated while driving due to friction created between the various moving parts. To cool the transmission fluid, a pump circulates it through a length of steel tubing connected to the car’s radiator. Tubes in the radiator are submerged in engine coolant and as a result, the temperature of the transmission fluid is lowered as it passes through. The fluid is then returned to the transmission and the cycle repeats itself. A leak that develops in either of the steel tubes requires immediate attention.

Step 1

Locate the area of the transmission line where fluid is leaking. If necessary, place newspaper under the lines and start the car. After 30 seconds, turn the car off and look for leak traces of red transmission fluid on the paper and the steel lines.

Step 2

Open the hood of the car and check the transmission line fitting connections at the radiator to ensure they are secure and not the source of a telegraphed leak.

Step 3

Park the car on a flat, solid surface.

Step 4

Place wheel chocks behind and in front of the rear tires to prevent the car from rolling. If ramps are to be used, put chocks in place immediately after the vehicle is secure on the ramps.

Step 5

Raise the car using an approved jack. Place jack stands beneath solid frame surfaces only. Check the vehicle owners manual for specific jacking instructions.

Step 6

Check the fitting connections at the transmission and verify that they are secure and not the source of the leak.

Step 7

Cut the transmission line on both sides of the rupture using a circular tubing cutter.

Step 8

Clean both ends of the line thoroughly with #400 emery paper.

Step 9

Ream the inside walls of the cut transmission lines with a reamer. Apply light pressure to remove any burrs caused by the tubing cutter.

Step 10

Install the two union nuts onto each line with the open threaded ends facing towards each other.

Step 11

Install a compression ring onto each line.

Step 12

Insert one transmission line end into the union coupler. Be sure that the end of the line is fully seated in the coupler.

Step 13

Slide the compression ring and the union nut forward and turn the nut in a clockwise direction onto the threads of the union. Hand tighten.

Step 14

Insert the other transmission line into the other end of the union coupler. Be sure that the end of the line is fully seated in the coupler. Slide the nut and the ring forward. Thread onto the union hand-tight.

Step 15

Tighten the two union coupler nuts 3/4 to 1 full additional turn using the adjustable wrench. Turn each nut in a clockwise direction.

Step 16

Start vehicle and allow engine to operate at least 30 seconds. Turn engine off and leak check the coupling.

Step 17

Remove jack stands, jack and wheel chocks. If ramps were used, remove chocks and lower vehicle from ramps.

Step 18

Check transmission fluid and add appropriate amount if necessary. Install fluid recommended by vehicle manufacturer only.

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