jlaw

Hello BF,

I know that other Trek 620 owners have successfully installed 700c wheels on a Trek 620 that was originally spec'd with 27" wheels. As an experiment I mounted some 700c wheels that I have and took the photos below. The canti brakes are the original Dia Compes and they actually work well with the 27" wheels and were pretty easy to set-up.

In the photos the brakes remain in the position adjusted for the 27" wheels and I don't want to mess with them without some reassurance that it's worth the effort.

Do you think that adjusting them downward to the 700c rims will work?

Thanks.

The Golden Boy 

Some people say that DC 960s work fine for 27 to 700c conversions... There's no slot to move the pad arm holders up and down- the 960 only has a hole.

If you can adjust those brakes to the rim- it looks like they'll be angled more downward than inward by the time they strike the rim.

There's lots of other brakes to use.

PhotonDon

Don't know the specific differences, but I converted my '87 Trek 520 from 27" to 700 with no problemo. My brakes however were Shimano MB60 or something like that. Good luck!

Classtime 

The front looks like 700c is a better fit. Rear looks good enough for the rear.

Road Fan

If your 620 did not have canti posts changing to 700c would be no problem at all. As it is, I don't know what kind of canti or linear brake would be workable. You might be stuck with what Trek chose. But is that a bad thing?

crank_addict

I had no issues fitting 700c with the DC cantilevers on a 1987 520 Cirrus. Looking at the OP 620, the brakes should work with 700c though the only means to confirm is to actually try it. The negative to those particular brakes are not having spring balance adjustment.

The lower portion of the brake cantilever arm and relation to the pad post work well if at 90° when at contact to the rim. Also, length and adjustment of the straddle cable will reflect leverage. The advantage of cantilevers are in its many adjustments and tuning to users preference. You can make them over powering with single digit control or to less power in locking up and more modulation. There are conditions such as icy or rain season when I prefer a less likely to lock up.

Other consideration:
One of the best setup improvements is adding a Suntour 'Power Hanger' pivot. Trek also had the same concept as an accessory item. Rare and I've only seen one in all the years. They are time consuming to setup but once done, are fantastic. I've loaned my 520 out and its fun to hear others comments about the brakes. Hydraulic disc are overhype - lol

jlaw

Interesting. The Suntour version of this can be found on ebay. Tektro also made (makes?) their own (photo).

My existing cantis work well, but this might be fun to try. Some users say that the set-up for a Power Hanger requires a higher spring tension on one side than the other - I'm out of luck there because the Dia Compe 960s only have one spring setting.

tiredhands 

These have always looked interesting to me as maybe a way to get v-brake levels of stopping power out of an old narrow-post frame. Do you have an idea if the front power hanger would work with a fork-crown mounted rack, like a Nitto M12?

crank_addict

Unfortunately it would not.

I use a front rack but with mount that attaches to the rear of the fork crown, a design that also wraps around the crown.

madpogue 

It *MIGHT* help to trim/sculpt the brake pads so that, when hit the rim at that funny angle, the contact surface is parallel to the rim wall (or at least closer to it).

dddd

Goes without saying that this will be necessary, though to be fair, one has to do this on certain other setups unless a beveled OEM pad is chosen.

Shaping the pads to the rim can be done in-situ, using belt-sander stock facing the pad as it moves with the rim with the brake applied (see below). This hastens the perfect break-in where the surfaces have worn and stabilized against in-use forces and geometry. Sometimes a second round of adjustment might be warranted if a lot of material is being removed, but this is not usually needed to get the brakes working well.

When going from 27" to 700c wheels, the pad-dive angle becomes closer to vertical, which increases leverage of the braking action considerably.
Using wider rims helps a lot here, since the pads move closer to horizontal so leverage is moderated and their is less tendency for the pad to touch the tire sidewall as it retracts.

I've used these exact canti's with 700c rims on my Miyata Grand Touring, they worked perfectly even with the original pink pads, no issues at all.

Salamandrine 

Since no one else mentioned it, the only way to 'lower' pads in this type of brake is adjusting the pad post length. Push them in. This pushes the caliper farther from the rim, and lowers the position slightly. Readjust the other things like straddle wire as necessary.

You want the brakes to hit the rims at as close to perpendicular as possible. Angled down is to be avoided.

Looks kind of borderline to me, but maybe worth a try. Personally I'd look at a different caliper with an adjustable slot location. As has been noted, there are other brakes. Dia Compe 988 and the new version 980 for example.

There's some chance you may be stuck with 27.

Miyata and Univega typically had their posts in a sort of neutral position, and you could go from 700 to 27 pretty easily. That Trek looks more biased to 27.

madpogue 

I wouldn't make that presumption.
+1; this appears to be one of Trek's first forays into cantis, and before the historical push from 27" to 700C was in full swing. If only they'd had a crystal ball......

dddd

That's a good point, it looks like the pads are already pushed in pretty far, which gets the swivel mount out further from the rim.

So angling the pads down at this point looks like it will not have a drastic effect on the angle of the pad against the rim, though with a narrow rim one shouldn't expect the pad to contact the rim squarely without some accelerated break-in of the pad surface having been done.

Remember that these canti's came from the factory with beveled pad surfaces, and that was for optimal setup on bikes equipped with their original wheels!
But even with modern pad surfaces needing to be "dressed" to use them, these are nonetheless excellent canti's from my experience using them extensively both on and off-road.

I agree about Trek's canti posts perhaps being slightly lower than on an equivalent Miyata. I switched from 27" to wider 700c rims on my Trek 720, and I perceived a great increase in leverage/power. But I had previously much-shortened my front straddle cable, which in itself had given the brakes more leverage than stock, and the switch to non-anodized rims and premium pads seemed to increase the friction even much more.

Salamandrine 

Yeah, I agree, there's not much more adjustment left, but there is a little. Like I said, worth a try, it should help a little. Maybe not enough.

Might be close enough. Best practice is that the posts should be perpendicular to the rim flats obviously. You can fudge a little. If you fudge too much it can cause problems, especially as the pads wear in. I couldn't really make a judgement on it without the bike in front of me on a stand. Judging by the photos, I'm skeptical, and as I said I'd lean toward new calipers with vertical adjustment.

I remember when a lot of brake pads came stock with beveled surfaces. It only occurred to me recently that most newer younger cyclists think this is weird and have never seen it. Generally the angled pads were for rims that had angled sides, which used to be pretty common.

SurferRosa

What's the point? You can still buy new 27" Sun rims. You can still buy new 27" paselas in 1" and wider sizes.

palincss

The Pasela is about the best tire you can find in 27" these days. There are lots better choices in 700C. If you could make the transition easily, it might be worth switching. On the other hand, if you can't, Paselas are at least OK. I switched my 1963 Jack Taylor Sports to 700C because I had the wheels already and the Mafac Racer brakes I wanted to use so that I could use the TA mini-front rack that fits on them had enough reach to make the conversion work. Moving cantilever posts is a lot more complicated. There are other cantilever brakes that provide more vertical adjustment that might make the swap easier.

The Golden Boy 

Of course it's possible- dozens, if not HUNDREDS of people have done this with this particular bike, and hundreds if not THOUSANDS have done it with similar frames.

If it doesn't work with the stock DC 960 brakes, use other brakes.

The DC 960 just has a hole- there's no "up-down" traverse for the arm holder. Later brakes such as the Shimano MT-62 and M732 and the Suntour XC Pro brakes have slots, so the arm holder can come from a higher or lower arc.


MC70M732MT62 by Dave The Golden Boy, on Flickr

jlaw

I adjusted the DC 960's to the 700c wheels with no issues. I was considering getting a new(er) set of brakes as suggested by others, but these seem to be ok. The cable yoke angle is getting a bit steep, but if they work they work. Even without any adjustment mechanisms the DC 960s have been pretty simple to set-up.

Also, I was at my LBS the other day and they have a 'specials' table - picked-up a set of unused Shimano 4600 brifters for $20. I'm not a huge fan of the shift cable exiting the inside of the lever - limits handlebar bag choices - but hey, 10 speed brifters for $20! I'm not loving the bar ends that I installed or the original DT friction shifters.

Converting to 2x10 was the whole reason I wanted to fit 700c wheels on this bike.






I'm also going to get a diffrent handlebar. The Daija Far Bars - that I love on my Trek 410 - don't really work on this bike because the geometry is more slack and I need a drop that is more parallel to the road. I feel like I'm sliding off the inclined drop section of the Far Bars because I sit further back than on the 620 than the 410.


I might try the short-drop Velo Orange Nouveau Rando Bar or maybe the Soma Condor 2.