Cool Transmission

After running the fuel line there was one more major line – the second transmission cooling line.

Automatic transmissions need to cool the transmission fluid, especially under hard operation. The typical way of doing this is to pipe the transmission fluid to the radiator and through a liquid/liquid heat exchanger inside the radiator.

The transmission cooler lines are routed from the radiator, down the block, through the suspension, around the starter and bell housing, close to the exhaust, around the shifter and kick-down lever, and up into the transmission. In other words a twisty turny bendy chunk of 5/16″ line about six feet long. And, of course, this involves working under the car…

I managed to successfully remove one of the lines when taking the engine out – this line went back in with little difficulty. Unfortunately, on the other line one of the tubing nuts was frozen to the line and twisted the last several inches of the line into a mangled spaghetti knot.

My plan had been to cut out a foot or so of the second line and insert a new chunk of line with a coupler. I had never been happy with this plan – couplers are additional sources of leaks, and a coupler failure would be catastrophic for the transmission. In addition, I was having trouble getting the coupler I wanted to use.

After installing the new gas line (see previous article) I had about eight feet of 5/16 copper nickel line left over. I think you can see where this is going…

After finally resigning myself to actually tackling this project, I unrolled the leftover new line and cut off a piece about a foot longer than needed. Remember this, we will come back to it…

The next hour or so was spent trying to make the new tubing match the old one bend for bend. There was no hope of matching it exactly, so the goal was to get it close enough to allow final tweaking on the car. Since the end of the old line was completely mangled the new line was just left straight at this point.

To test fit I needed to install a nut on one end. These lines use double flares like brake lines do. I’ve documented my travails with creating double flares. Since the special flaring tool that makes this easy is only for 3/16″ line, I had to use the standard flaring kit. Being extra careful with alignment of the die seemed to make a difference – or perhaps 5/16″ is simply more forgiving. In any case I was able to produce a decent double flare on my first attempt.

With the nut installed, I threaded the new line from the radiator, down the block, through the suspension, around the starter and bell housing, close to the exhaust, around the shifter and kick-down lever, and up into the transmission, tweaking the bends as I went along.

It actually fit and the only thing left was to make a 90 degree bend near the end to bring it to the inlet fitting on the transmission. Remember the earlier task where I cut the new line “a foot longer than necessary”? This is usually the point where you discover that it is 1″ short.

After all the bending and fitting I ended up with 5″ – 6″ extra. Perfect! Mark the location for the bend on the tubing, undo it from the transmission, and work it out.

With the line out of the car, carefully figure out which direction this last bend needed to go (it is really easy to bend in the wrong direction when it is out of the car!) and bend it. At this point all that is left is to cut it to length and install the nut on this end.

The inlet fitting on the transmission is very close to the transmission tunnel, so the distance from the bend to the end of the tube needs to be as short as possible. A certain amount of space is needed for the nut and the flaring tool. The process is to work the nut as far into the bend as possible, determine how much space is needed for the flaring tool, and cut the tubing.

The result is that you have one chance to make the flare. If you mess up this flare you will have to either remake the whole tube or cut it and insert a join. Fortunately the flare came out fine. And there was much rejoicing!

For the last time thread the new line from the radiator, down the block, through the suspension, around the starter and bell housing, close to the exhaust, around the shifter and kick-down lever, and up into the transmission. Carefully tweak, adjust, bend, and massage the line so that it fits as well as possible and doesn’t interfere with anything. Carefully line up the end of the line on the inlet fitting and try to start the nut. After a few tries, the nut actually went on!

Previous efforts had only run down the nuts finger tight. Since this was the final install the nuts had to be tightened all the way down. Due to the tight fit around the transmission, these nuts could only be tightened 1/32 of a turn at a time. With a bit of patience and perseverance everything was properly torqued and another task completed.

Next: Coming Together