Road Bike Brake Cables

Hey guys

i'm trying to install new brake cables on my trek 2300, and i'm having trouble with the rear brake. the cable and housing are supposed to travel inside the top cross tube and out a hole before it meets with the downtube. i can't get the housing or cable to come out that little hole, and it seems like they get hung up inside, or they hit where the top tube and downtube connect inside. does anybody have any ideas/suggestions as to how i can this cable to feed through the tube properly? thanks!

Route the housing first, then run the cable through the housing. What I have done is thread the housing a few inches onto a stiff piece of wire that is about three feet long and tape it securely with some electrical tape. Use the tape to make a taper from the edge of the housing to the wire, that way the edge of the housing won't hang up on anything inside the frame. Put a gentle bend (about 30 degrees) in the wire a few iches from the end and then fish the wire through the top tube, twisting it until the tip comes through the hole at the far end. Grab the end and use it to pull the housing through. Once the housing is through, the cable passes easily.