Replacing transmission cooler lines

**Gnat** · 08-09-2011

Hello everyone, I'm a longtime lurker of these forums and have learned a ton of how-to info and saved a lot of money with everyone's help! I'm fairly ignorant when it comes to transmissions and I want to make sure I don't cause bigger issues while doing my own repairs.

I have a 1997 Grand Prix GT, automatic trans, 158K. All factory parts, as far as I know. Two months ago I replaced the transmission filter and fluid. Everything went better than expected, no metal shavings in the pan, etc. Two weeks ago I noticed transmission fluid dripping from the front of the car. Turns out the transmission cooler lines are rusted and leaking. I ordered the parts (had to go through the dealer) and I'm about to replace them. It seems like a straightforward job, but I want to make sure I do it correctly and not cause a bigger problem:

1) Can I drain the trans fluid by removing the cooler lines, or is it safer to drain it by loosening all those bolts around the trans filter pan? It seems to me it would be easier to just drain it by loosening the lines, because I have to remove them anyway, but other threads say to drain through the pan, which is a pain in the butt!

2) Could I somehow have caused this leak when I replaced the filter and fluid a few months ago? I only ask because it seems like these lines rarely go bad and mine are in rough shape for some reason.

Thanks for your time!

**BillBoost37** · 08-09-2011

To swap the lines, just take off the old lines with a pan underneath and swap them out. No need to drain the whole trans. You won't leak excessively while you are doing it. But it will leak a little.

Once the new lines are on and you done, fire it up, check the fluid level and top it off if needed.

IIRC you need a 16mm wrench at the radiator and a 16mm and if they fight an 18/19mm as well at the trans.

When the fittings at either end don't seem to want to thread. Check the angle and keep on trying gently. Once you get the right angle, they'll go right in. Many first timers can get frustrated at how they can be a pain to align.