700s on an Old Trek 720
 

Hey all. I'm on the brink of buying a 1983 Trek 720 bicycle. I know this is a gorgeous bike, but there is one thing tripping me up. The original Dia Compe GC960 Canti brakes were set up to work with the stock 27" wheels. I want to put a set of 700c wheels on this bike, but I have heard rumors that this might be a huge problem. Has anybody out there actually ever tried this on this bike? I'm not sure if it will be possible to adjust the stock cantis enough to reach the 700c rim or if canti brakes are made that have enough adjustment to make them work.

I don't think I can buy the bike if I can't put 700c wheels on it, but I would love to turn it into a vintage touring masterpiece if I can.

Any advice / experience on this subject out there?

I have tried it. And heard from many on these boards who also have tried it.

I did it to a Trek 620. No problem on the rears for me. But the front bosses were much closer together than current standards and so I had some trouble getting the pads to angle down enough to hit the rim. I finally got some older, smooth studded pads/calipers to work. Still not great braking power, but it works.

It is an issue, but one that seems to be solveable.

jim

Thanks Jim,

Do you happen to know which pads/calipers they were, and if there are any others that might work?

They were old (like mid 80's) Deore I lifted off an old Bridgestone MTB. Nothing very special, but they met three criteria:

-relatively short reach (of course, this is required)
-There was some up and down adjustment. Many cantis just have the fixing bolt in one place, this may not be flexible enough of a set up for what you want it to do. Look for the fixing bolt to be in a slot, not a hole.
-Smooth brake pad stud, not threaded. Threaded ones have only a little angle flexibility because the way the cupped washers work. In my case, not anywhere near enough. Smooth studded pads can be set at radical angles. This is the feature I most needed since the bosses were so close together; The pads had to hit the rim before the caliper moved very much.

jim

hi, i have a similar situation here. apparently i have some spare parts like scr-3 brakes, levers, etc...so i just wanna update my old schwinn le tour to a bad weather bike, which is for 27" wheels. but i can't put the front brake on as the bolt is too short to be secured. and i will make a Sheldon's drop bolt for the rear one.

so my question is can i just change the fork for an easier job like that? or is there anything that i should aware of when buying a new fork? thanks!

My advice is to try and find some Weinmann or Dia Compe centerpull brakes. They typically have a lot of reach adjustment, usually plenty for the 27" to 700c conversion. They're nutted brakes, so keep that in mind. There are usually some on ebay for very reasonable prices-

I think I was the beneficiary of dumb luck. I was given an old 620 frame (grey, stamped lugs version) and never used 27" wheels in it during the five years that I had it. 700c rims fit just right with Mafac cantilevers. I used the short-armed Mafacs, not the long tandem ones. What one also needs on an old touring frame like the Treks being discussed, is a front cantilever that will work with more closely spaced posts than current forks. A current Avid or Shimano canti won't work--but Mafacs, Suntours, and old Deore LX or XT brakes will.

how about i change it to a fixie and only use the front brake? can i just get a new 700c fork? coz i don't want to spend more for brakes and leaving my spare parts alone...

Assuming you have the long tubular looking bolt that goes on the caliper bolt then what you need to do is drill out the hole in the rear ONLY to 5/16 diameter so the tubular shoulder bolt can pass through and catch the threads of the caliper. This assumes that you actually have a correct front caliper. On the front unit the bolt is around an inch long vs the 1/2 inch bolt on the rear caliper.

Same on the rear actually. The front hole in the brake bridge needs to be enlarged to let the tubulr nut to fit. I said "enlarged" rather than drilled because you won't be able to get a drill in there.

One person did this job using drill bits held with a pair of visegrips.

thanks for the info...actually the front caliper is a short reach type and it's not able to reach a 700c wheel, that's why i wanna change the fork as there're some good deal on craigslist and online...and i am wondering if i change it, will the bike be unbalance as it's designed for 27" and the wheelbase will thus not be aligned? (will it be like lower in the front when the wheels are on?)

I doubt you'll be able to find a fork with the same amount of rake as your le tour fork unless you find one off another le tour of the same vintage. As I said, get yourself some old centerpulls, problem solved-

ok thanks, i will just find some centerpulls then

Or some long reach side pull or dual pivot brakes. How much reach do you need?