Converting 27" to 700c
 

I'm meeting the seller today to buy an 83 Trek and am already thinking of putting a 130mm wheelset on it. Although I've owned several vintage bikes before, I have never tried this upgrade and was wondering what complications I was looking at. Is it better to have the rear cold-set, or is it OK to simply squeeze the hub on? Will the caliper brakes line-up properly? How will the chainline be effected? I have a 10 spd group that I'm thinking about using.

Thanks.

try getting a 130 axle wheel in a 126 spaced frame and see if you want to do that with every wheelchange/ puncture repair.
if its a 27" wheel and by 10 speed you mean 5 cogs on the back wheel 2 on the crank it may be a 120, then you are stuck. have to get the frame spread and re aligned.

if you are considering the latest stuff with 10 cogs on the back wheel alone ie a 20 speed if there are 2 in the front,
Buy an entire bike or pour way much cash into this project.

a 120 dropout frame is more suitable for a single speed or an internal gear hub conversion.,
126 was the era of 6 speed freewheels or compact 7, 130 was compelled to get #8 cog on the end of 7 speed spacing.

Whether the brakes work or not depends on how long the reach of the brake arms is...you will need to move the brake shoes a little bit to keep them lined up with the rim. 27" = 630mm while 700C = 622mm.

Yup, 4mm radius, brake slots for the pads to bolt in got 4mm [3/8"] of space
below the current mounting location on the 27" wheel?

For most bikes it's not a big deal to just spread the rear triangle when you install the wheel, but as Bob said, you should try it and see for yourself. I'll just contribute that my primary rider is spaced at 126, has a 130mm hub and I don't think twice about installing it. I do have an old mountain bike spaced at 126 that I squeeze a 135 into, and that is a chore.

As far as the brakes go, if you are close to having enough reach, but not quite there, it's not the end of the world if you file out the bottom of the slot just a little bit.

...I've read this thread with some interest, as I would eventually like to do this very thing with my 1985 P8. It came with Rigida 27" rims; the rear rim got severely warped, and I had to play with the spokes a lot to bring it anywhere near true. Of course, this resulted in spoke tensions being way out of balance and consequently a lot of breakage (thank heaven for that much-maligned Helicomatic hub...naturally, all the breakage was on that side). So I unlaced the wheel and tried to carefully straighten the rim by wedging the rim between pieces of wood and just pushing on it. I didn't take out my 32-ounce ball peen and do the Trondheim Hammer Dance on it or anything like that. But in the process, the rim joint started to separate, and I doubt highly that it is possible to fix that satisfactorily, so I am about to try my hand at rebuilding the rear wheel using a new 27" rim (a Weinmann RM19; not the best, to be sure...I see that Weinmann have done the same as many other once-respected manufacturers and put their name on, well, what the Germans have been known to call 'China-Schrott' (think Grundig radios!)...but at 15 bucks, if I make a complete mess of it, it's not a big loss) as soon as I can get my paws on some 302 and 298mm spokes. If it works out, I'd eventually like to build up a 700c set, seeing that 27-inch is going to be increasingly difficult to replace. I've already measured the brakes; I've got the 4mm difference in reach more than covered (btw, 3/8 inch is considerably more than 4mm...it's actually very close to 10mm...3/8 inch=0.375 inch; 10mm=0.394 inch)...what I would ideally like to do (I know this will sound positively insane to many here!) is to somehow get hold of another Helicomatic hub and build up a 700c wheel on it (the bike came with a Helicomatic and, despite everything that has been said about it, I rather like it...an excellent idea that perhaps wasn't as well executed as it could have been...but perhaps would have been if it had been given a little more time)...of course, I'd need to recalculate spoke lengths to compensate for the difference in rim size, and apparently it wouldn't be as simple as using spokes that are 4mm shorter...
...I'm not necessarily one to run from a challenge...

I'm sorry about the confusion to the earlier responder, but when I said I was thinking about upgrading to a 10 spd from a 6 spd, I meant the cassette cogs. I got home late with the bike and tried squeezing the 130 wheel on the 126 spread. Is there a technique to this? It's like trying to spread a chicken wishbone while trying to stuff a bagel em-between it. I was working outside and it was getting dark so I quit, but it never did fully seat in the drop out. Are there concerns about damaging the brake bridge if you spread too far?

if your frame is steel, do the sheldon brown proceedure.

It's possible to pop out the brake bridge if you cold set, but it is rather unlikely.

As far as technique, just place the wheel so it's sitting with one side of the axle in the dropout, then pull the other side out while pushing the wheel back. Try it again some place warm and well lit, at least until you get the hand of it.

Well, some say straightening a rim is a definite nono, a sacrilege against the cycling gods etc etc. I've done it on numerous times, and although those rims have only gone on beater bikes(hence limited mileage) they seem to be doing just fine. At least far better than they did when the spoke tension was all over the place.

I bet some people would be amazed/horrified if they'd ever see how and how much force that has to be applied to counter-bend a rim. I've laid rims across a 2x4 on edge and stood on them several times.

If the sidewalls starts to flare, then that's bad news. But remember that when the spokes go back on they will all try to compress the rim to a smaller diameter, so the joint will usually close up quite nicely. Again, IME to no significant degradation of rim strength.