Bicycle Tutor

I have an old trek that I'm fixing up (mostly just to learn how to do all this stuff myself). Trying to replace old cantilever brakes with new v-brakes but the spring pin doesn't fit into the hole on the frame brake housing. The front brakes fit but the rear brakes do not. Any tips would be great.

Is the hole to small or not in the right position?

The hole is not in the right position. the spring is a bit too big (diameter) - just missing the hole by a couple milimeters to the outside.

If it looks O.K then I would consider drilling another hole or opening the existing one?
Option 2 would be to bend the spring to suit. It's funny that the front one fits but not the rear.
Try the rear one on the front as I don't think it matters whether fitted to front or back?
Not sure of the spring shape but it is the correct spring? or the right way round ?
I had no trouble with mine when I swapped to V brakes from Canti's.

If I was you I would stay with Cantilever and run salmon kool stops on them.I never did like V-Brakes.

I'm having the same problem with a 1988 Trek 8000 frame. I bought a set of Avid SD-7 V-brakes. when attempting to install the rear ones, I could not get the spring into the hole. (No jokes please)
I didn't try the front but will tonight when I get home. Also, can you move all of the spacers to one side of the caliper? It seems that if (when) the brake caliper does go on, the pads are going to fall short of the rim.

If it is just that the spring is too thick to fit in the hole, there is some variation between brands. It should be fine to drill the hole a little to let the spring fit in. On alignment, sometimes it is also just a tiny bit off and once you get the spring to slide in, everything works fine. I just had this issue putting Avid v-brakes on an early 90's Trek so I could build an Xtracycle. I filed a tiny burr off the end of the new spring and was able to get it to slide in, though it was very tight. All works perfectly.

You should not need to re-space the pads unless you have very unusual tires. Usually the spacers that are on there need to stay in place so you can adjust the angle of the pads correctly.