Successful 27" to 700c caliper brake conversion
 

In preparing to convert my 1981 Miyata 1000 from 27" to 700c wheels, I read through a number of threads on the subject here. There were quite a few suggestions for cantilever brake calipers with enough range to work for that application. But most were more or less speculative--people saying "this often works," or "I would try X, or Y."

Based on one of those suggestions, I took a chance on a $30 set of Shimano BR-M454 calipers from Ebay. When I first bolted them to the fork to (which is out of the frame for headset servicing) to check the fit, my heart sank--the chunky original Shimano pads hit way up on the tire, even adjusted to the lowest position in the slots.

But when I installed a new set of Jagwire Mountain Sport pads I happened to have on hand, they strike the rim
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perfectly, although with no room to spare. The photo shows the pads at the bottom limit of their adjustment. So I'm putting this one in the win column.

Just thought I would share that information with anyone contemplating a similar project. I don't like the look of the new brakes as much as the original Dia-Compes, but I will get used to it.

Koolstop thinline pads are even thinner and will get you more clearance from the tire.

check if mini-v brakes will give you lower adjustment. I don't think you've got enough purchase on the rim with those jagwires at the lowest slot.

It looks like the pad is still hitting the tire. The Thinlines (as per above) might get you to functionality.

Sorry to agree with the above assessment, but I don't think that's safe. It's close but not close enough. Might be OK with a small amount a filing of the slot, or by tweaking the pad stack height by adding or subtracting a washer or something. Or try thinline pads.

Calipers with post type pads really do give you more adjustment options. FWIW I went back and forth between 700c and 27" several times on my Univega Specialissima in the early 80s, using good old Mafac cantis. Pretty sure the frames are exactly the same, though I suppose it's possible Ben Lawee spec'd a slightly more intermediate post position.

Wow, tough crowd! That's what I get for putting the word "successful" in the head.

The photo may be a little deceptive. The pads don't hit the tire. They are close to the tire, but not too close. After they have worn in a bit, they will be a little less close. The face of the pads hits the face of the rim squarely. Everything is fine.

Even so, I had been planning to install some Thinlines, both because I like the compound and because I'm guessing it will give me another fraction of a millimeter of clearance. I don't need the added clearance, but I wouldn't mind having it.

The nature of the calipers would make filing the slots problematic, because the slot is slightly recessed by the approximate width of the stud washers.

Famous last words...

Just make sure the pad doesn't squish too much under heavy braking. We like having you here.

My favorite last words are "What could go wrong?" and "Hey, watch this!"

Point taken about pad squish. A little more clearance would be nice. I suppose I could always file a small bevel on the upper edge of the pad. But I think the thinner pads will take care of the issue you you usefully raised.

This is unfortunately the problem that many people have to account for when trying to get a 700c onto a 27" cantilever frame. I have found that the brake posts are often too high relative to the braking surface of a 700c wheel. Most often this results in either poor mechanical advantage or poor pad to rim contact. If you find that these brakes don't work, I think there are a few other vintage cantilevers (mostly smooth post) that have a longer slot for the brake post bolt. Other more recent options: Shimano BR-CX50/70s, mini-linear pulls from tektro, PAUL components, etc.

Sanding Down Brake Pads
 

Jon,

Another suggestion: I sand down the faces of brake pads before use, both old ones and new.

Most new pads have a hard surface from the mold process that takes a while to wear in. I take them down maybe .2mm to .5mm until the surface feels a little softer. Old pads I'll take 1mm or more off of the face.

You can sand the new ones at the correct angle to get good contact from the get go. Trial and error....

I use 3M 3M Drywall Sanding Screen in medium grit. It's inexpensive and works fast.
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Close up view

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verktyg :50:

After re-examining my pad setup in better light, I am backing down from my premature declaration of victory. I can now see that although the top edges of the pad do indeed clear the tire (though barely), and do meet the rim squarely--that is, the faces of the pads are almost exactly parallel to the rim braking surfaces when the two make contact--they should ideally be a couple of millimeters lower. The current setup is probably adequate, but not ideal.

In other words, I should have put a question mark after the title of this post. It's too bad titles can't be edited. On the other hand, this sort of public admission of error is probably good for one's soul.

Anyway, I don't want to try mini-Vs, partly because of tire-clearance concerns--this is a touring bike, and one of the reasons for converting to 700 is to use fatter tires--and also because I would like to avoid further expensive trial and error. Again, I'm surprised that there's not a solid body of information about what brakes will and will not work for these kinds of conversions. So much "maybe" and "probably" and "sometimes."

Why is that, I wonder? I would have thought that if a brake works for one 27-to-700c conversion, it should work for all. Possibly way over on the edge of the bell curve where such conversions happen, there's a tolerance stack-up effect having to do with the choice of pad and rim, combined with slight variations in where the frame manufacturer positioned the cantilever posts?

I can't offer much help just commiseration.

I feel you on the lack of certainty. I have a 1986 Schwinn Voyageur with canti brakes. I have a 700c touring wheelset that is BOMB PROOF! I absolutely love them. Had them laced up almost 10 years ago and still going strong. Love them! They don't work on the Voyageur. A slightly thinner rim does work better. Better is the key word, not great. Tried a few different brakes. I haven't tried the Koolstop Thinlines though. Just called the LBS. Got a couple pairs in stock. Gonna pick em up today.

The thing I hate the most, aside from the up to this point failure with the conversion, I found someone on social media with an identical, EVEN the frame size is the same!, 1986 Schwinn Voyageur that made the conversion work. It makes me mad he did it and I can't figure it out.

On a side not, I might have access to a different mid 80's Schwinn canti brake touring bike. I'm a gluten for punishment! I haven't jumped on it because of the problem with the wheels. Resignation to 27" wheels isn't certain at this point but I can see it as an option. Even been keeping an eye out for good hubs/hubset for a new 27" laced wheelset. Single wall rims with a freewheel instead of a cassette isn't my favorite option.

Too many variables. The pad thickness, the pad "squishiness," the rim thickness and the post spacing, all mentioned so far in this thread, are all pretty important. How far back (away from the surface of the rim) any given model of caliper can swing, and whether swinging all the way back gives you bad geometry that reduces the braking power to unacceptable levels. The thickness of the washers between the caliper and the pads count, too. An individual's tolerance for "close enough" fittings. Probably a few more variables I'm not thinking of ...

ive done several of these and i believe i fall into the close enough catagory. What i tolerate many wouldnt, but it works for me. I set up an 81 miyata 1000 with 700c actually. I found that thin after market pads and cr18 rims worked well for me. However when i put some mavic cd4 rims on it, it was much tougher to make it work. I used the stock brakes.

Well, I will point out that I never expected this to come out perfectly on the first try. So at least I was right about something.

Don't forget "Hold my beer!"

Yeah that photo shouts out "too close for comfort". At that position, and the way the arms swing, and the way the tire bulges, there's a good chance the upper edge of the pad will graze the tire as it swings past. A narrower tire would help, but a thinner pad would help as well. Looks like you're at the limit of the angle adjustment of the stud, too.

When I swapped my Miyata 110's 27" wheels with my wife's Kettler Alurad's Mixte 700-23's a few years back, I left the existing Dia-Compe brakes as-is. Just had to re-align the pad position slightly.

Sorry, can 't upload a pic...

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On second thought, now that I have angled the pads downward a bit, I'm re-declaring victory. It appears to me the tire is beyond the reach of pad squish now.

Of course, this isn't the set of wheels I'm actually going to use. Possibly building up a new set of 36/40 rims on Sun Rhynolites will change the picture again. But I've still got the change to Thinline pads in my back pocket if it does.

By the way, that's my sauna in the backround. I shows up in my photos now and again.

That ^^^^^ does look better.

I've ridden sidepulls that I set up like that (short reach dual pivots on a longer reach frame). Keep it clean and it'll do.

^^^ That looks good now. Victory is yours. :)

FWIW my standard for this is that the top of the brake pad cannot be above where the radius at the top edge of the rim starts -- if that makes sense.

LOL! IMO, it's "close but no cigar!" They look like they will wear down and start rubbing the tire.

Options

1. Shave down the tops of the pads - bevel them so the top angle downwards. Shave the rear of the pads, too, while you are at it to make them toe-in.

2. File the bottom of the washer to allow the pads to sit lower in the brake arm. If it is the brake bolt that's limiting downward travel, consider filing the slot a little bit longer (not a lot, just a smidge).

3. Do a little bit of both.

Another millimeter (0.040") would probably fix it completely.

Don't get me wrong; I have maybe a few bikes where everything is set up textbook-perfect. But most of my bikes, and especially the ones with cantis and racks are firmly in the "Eh, close enough" camp.

Example: My Cdale ST with pretty narrow rims and Tektro 720 calipers that barely fit and have some ugly cable geometry. :eek: It's kind of a complex mess. Everything is really tight and little wrong, but it all works fine together with the racks and fenders, etc. And you can tell from the dirt, it gets a lot of my miles.

Victory declared.


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I believe that the clearance between brake and tire will increase as the pads wear.

My experience - the main part of pad wears and forms a "lip" that reaches over the radiused upper edge of the rim and works its way towards the tire.

My suggestion of chamfering is to remove that material before the lip forms.

Lowering the brake pad moves the upper edge onto the flat sides of the rim, below the radius.

Both options are meant to stop wear from allowing the pad to contact the tire.

It's up to you.