Replacing transmission cooler lines
 

Since my radiator is leaking I figure while I'm in there it's a good time to replace the transmission cooler lines. My truck has the towing package so in addition to having the radiator it also has the smaller transmission cooler that sits in front of the radiator. All 4 of those cooling lines need to be replaced. I crawled under the truck yesterday to see how hard is is to replace the lines. Well the Cat and exhaust in general makes just seeing where the lines connect to the trans difficult let alone trying to get to them with a wrench. The good news is those 2 lines are in good condition from about the engine crossmember to the transmission. So I'm thinking the easier repair is to cut the lines somewhere along the healthy part of the line before it hooks up to the transmission and then install some type of coupling and run the new lines to the radiator and trans cooler.

If I do this how should I go about it? I was thinking I would cut the lines with a hacksaw or angle grinder and then plug the lines with corks. (I'd like to change these lines without draining the transmission). Then buy some standard metal tubing at the parts store and bend and install the fitting myself. Does this sound feasible? What type of couplings are used for these transmission lines? Do they need to be double flared like brake lines? Or would I get some type of brass coupler from the parts store to connect the new line and old lines? By chance does anyone know the size of these cooler lines?

The lines are 3/8 I believe. You can use trans cooler hose and hose clamps, but be sure to double clamp them, they can blow off and make a big mess. A compression union would be better and a double flare union would be better yet

The lines are 5/16" You can use 5/16" preflared brake line from the parts store. Easy as pie. I recommend replacing the entire line to save aggrivation down the road, only use rubber if necessary for a couple inches at each coupling if they are not flared fitting on the coolers. Use two clamps on each coupling, and it doesn't hurt to put a flare on the line before you slide the hose over, to help retain it. Also you could use compression fittings to couple the two steel lines together if you don't replace the whole line, which would be preferable to rubber.