I have a bike with 27 x 1 - 1/4 wheels (630 mm). I am considering switching to 700's (at least at the back).

My understanding is that it is not recommended to switch wheel sizes on a frame because brake reach could be come an issue? Are there other pitfalls i could run into?

If i swap the back wheel for a 700 should I also switch the front if I don't what issues will I face? Thanks guys, hope this question made some sense.

-Jeff

Swapping both will keep everything level, just about 4 mm lower at the BB.
You'll have to work out some brake mods or swap to move the pads off the tire, though.

Many 27" bikes have brakes with long enough reach that they can be adjusted to work with 700c rims. Try it and see, if the brakes won't reach, there are calipers out there with more reach.
I doubt you'll notice any difference running 700c on the rear and 27" on the front, you're talking 4mm difference in axle height over the wheelbase of the bike, you can probably make it up with tire choice if you're that fussy about it.

You already covered the one issue that might cost the most - brakes. Swapping out one or both for 700c and having them mismatch is not a problem. Do as your budget allows.

I'm running a 700c rear with 27 front. Kept the front stock so I didn't have to worry about getting a long reach brake, and just put a 28 tire on the rear for a little extra height. No problems at all.

You can often put a small spacer behind the brake to push it forward and keep it from scrubbing the tire. That's why my wifes FG conversion ended up with a bottle cage up front.

That is the most ridiculuous hack mechanic solution I have EVER seen. If you were going to do it properly, why the hell didn't you just stick a regular spacer there? Or hell, even filed out the pad slot. I really hope nobody goes home thinking this is an adequte solution to a brake reach problem.

You have no idea what you are talking about. The "spacer" I used was the stock front reflector mount. I was going to remove it becasue the bike used the not-so-awesome 3" diameter round orange reflector that was popular on many bikes of the late 60's. When I removed the mount it pushed the brakes back to where the pads were scrubbing on the tire. I took off the reflector, mounted a bottle cage, and the problem was solved. This isn't a hack mechanic solution- this is how the brakes were set up from the factory, all I changed was replacing the reflector with a bottle cage. Thanks for playing though....

You can purchase new 27" rims and there are still a number of 27" tires available. If you go to 700c, there are the Tektro R556 long reach brakes(Rivendell has a version called "Silver" which has Kool-stop brake pads) or the Dia-Compe 750 centerpull brakes.

Sometimes you still need long reach brakes on older frames even for 27" wheels. I used the Rivendell long reach brakes and 27" wheels on my Raleigh Sprite.

Handsome Ryan, if your wife has to have the saddle at that angle, there's needs to be some other adjustments for a proper fit.

Your existing brake may fit, or you can buy the Tektro R556 brake(s) and they should fit.

That saddle isn't even on the bike anymore but it was very softly sprung so when you sit on it, it was horizontal. It just looks weird in the pictures, but if it were adjusted to be level when the bike is just sitting you'd slide off the back when you actually sat down. The saddle was original to the bike and I'm not sure if the springs just gave up over the last 40 years or if they were always that soft but that saddle went to live in the parts box and a new modern saddle has since replaced it.