shipwreck

Working on getting cantilever brakes that fit a 1990 Davidson sport touring bike.
The posts are only 1.4cm from the center of the post to the middle of the 700c rim.
This bike was found NOS, so it never had parts on it.
Made some Dia-comp brakes work, but have to lay them almost flat out to get the pads to hit the rim.

Thought it might be for a 27" wheel, but that does not bring the center up enough, and would have to run a 1" tire as the frame is very tight. Will barely fit a 32mm 700c tire in there.

Kind of at my wits end, what was the builder thinking? If it wasn't the most amazing riding bike that could have been built for me, I would just get rid of it.

Any suggestions on what might have been available in the late 80's early 90's with that short of a reach? Thanks for any help.

fietsbob

OK what do they Measure? Center of the Brake Post , to the center axis of the dropout ..

You tell Us and then some comparisons can be Made >>

Remember the brake Pad sits Above the pivot, so a measurement of that distance on the caliper will Help As Well.

Fwiw I n The new Imported MTB Boom 80's once the Calipers had a Pad height adjustment .. the Factories got a 'Good enough, Ship it' attitude
to the Post location , where Before with Mafac's cantilevers , It had to Be in the right spot, Period.

dabac

Could it be intended for an U-brake instead of canti/caliper brakes?

shipwreck

30cm from the center of the dropout to the center of the canti post. As stated in the OP, its a 1.4mm reach from the center of the canti post to the center of the rim.

there is no brake caliper to measure. I am looking for one that will fit. I have been using some old dia-comps that can be made to work by adjusting them down very far, putting the brake pad post at full extension to hit the rim. This works, but is not ideal. The reason these dia-comps are the best is the exposed spring. there is only one spring hole on the mount instead of the three that most have for tension adjustment, so every other cantilever brake I have will not engage the spring enough at the angle it has to be run to make the pad hit the rim.

shipwreck

the posts are below the rim. I though u-brakes needed the posts above the center of the rim;/

dabac

But you also say it's a tight fit for the wheel even with a narrow tire. Maybe meant for another wheel size as well?
Anyway, it's just a thought. Don't see many U-brake bikes, but I know it has had me stumped before, until I figured out what was up.

FBinNY 

Yes, what I was thinking, but that would have to be for a 26" rim (if the math works) since U-brake posts are above (outside) the rim, and Canti-s are below.

The critical distance is the radial distance from post/pivot to center of brake track which is typically 25mm or so. So if your posts are at 300mm from axle, it would argue for a rim that's 325mm in radius, or 650mm in diameter. So I strongly suspect canti's were not the intent.

Estimating the same 1" drop for a U-brake (don't have one to measure) then the rim would have to be at 275mm or a 550mm diameter, which sis reasonably close for a 559mtb rim.

So based on that my best guess (roling dice) is that the frame was made for 26" wheels with a U-brake.

(someone, please check my math)

shipwreck

Hopefully these help explain. I have boxes of cantilever brakes. Old richey logics, lots of shimanos, suntours, and the like. None of them fit, requiring a post drop of at least 2cm. Its only by laying these brakes down to this angle that I can hit the rim. For what its worth, they stop it really well, Ive done some loaded touring with this setup.

Dabac, that's an interesting thought, 650 something wheels taking a u-brake. I doubt it, as it looks right with a 700c, and the BB height is low with 700s, and the chain stays are pretty narrow where a 650 tire would be.. The front posts are placed pretty good for a 700 as well.

fietsbob

For comparison, I get 288mm on my 700c Cross Bike fork 257mm on my 26" wheel Trekking bike.. aprox (tape Measure)

Modolo Cross caliper are about 23mm from pivot bushing to brake post.

FWIW..

shipwreck

And in this case its 15mm. Very frustrating.

shipwreck

Measured my Univega gran turismo frame, and its about 28.8cm from center of the dropout to the center of the post. Everything works fine on that bike, exept it does not have the magic ride of this problem frame...

FBinNY 

Re-read my post no.7 which I was editing as you were posting. 300mm - 25mm drop for U-brake (estimate) = 275mm rim radius, which is very close to the brake track diameter (halved) of a 26" rim.

shipwreck

And thanks to everyone for the input so far, have to go do heart day stuff, should probably wash the bike brake crud off first!

shipwreck

Its a little beyond my bicycle knowhow off the top of my head, but if this is true, holy crappp. It changes everything!
Will mess with this tonight.
And in all my crap, I don't have any Ubrakes to see

FBinNY 

My visual memory isn't a mile off, so it's a reasonable guess that it's for 26" U-brake. Especially since no other combination of standard brakes and tires works out.

You'll have confirmation within the hour when somebody with a U-brake measures the Post to Shoe drop and posts it. Fietsbob where are you when we need you?

And don't mess with this tonight if your lady is in the house. I'm sure there's a better way to spend your time. (my lady's in Cozumel, so I have an excuse).

Andrew R Stewart 

Sure looks to me like a wheel diameter change was made at some point. Also the pivot boss C-C distance is likely less then is usual these days. (For rim outer widths of about 24mm a C-C distance of around 80mm is typical).

How much do you love this bike? It's not hard for an experienced frame guy to remove and reattach bosses in a far better location. Andy.

shipwreck

had a hell of a time finding a 130mm hub on a 26" wheel. But by god I had one in the parts shed!
The drop seems to be about 150mm from center to center on a 26" wheel.

And this frame was never changed. I found it like this.

Never assembled. Never even taken out of the box. The man who ordered it passed away before it was built. According to the guy I bought it from, he was almost exactly my size. It does ride like a freaking dream on 700c, and everyone it fits agrees.

If it does actually take a smaller wheel, I will deal with that. THanks again everyone...

fietsbob

Davidson is still a a Seattle based Builder (?) perhaps they have a record of the original build order?

I'll be slaking my thirst , soon ..

shipwreck

Tried to contact them several times, but they never got back to me. He has closed his shop now...

fietsbob

I'll vote with andrew then .. Pick a New color you like , have the braze-ons Moved, add a few new ones too, then have it repainted..

JohnDThompson 

Try this:

faustocopious [at] gmail.com

shipwreck

Update and todays thoughts.

I have put about 1,000 miles or so on the bike with the brakes pictured, and they do stop a 220 pound guy with four panniers. The rear will actually lock up with these brakes, and the modulation and feel is fair.
I wanted to run a little narrower rim, and was doing some test fits. This is the only reason it is an issue, really. I have decided to build a wheelset for it using a wider rim, using these brakes. As a clyde, a bigger rim is not really a bad thing.

There is no way its meant for 26" wheels. The fork fits a 700c to well, and the geometry changes far to much. BB height with the largest tire that would fit the chainstays is far to low. That and the 150mm drop to the center of the rim is to short for a U brake.

Thank you John for the address, I have sent an email off and await an answer with interest.

nfmisso

Couple of comments:

* A 32-559 tire on a 18x559 rim fits nicely in a Bianchi rim intended for 23-662 tires. A Tektro R559 brake properly engages the braking surface on the rim too.....
* Between 559 (aka 26") and 622 (700c, 29er, 28") there many diameter rims currently available: 559, 571 (650c), 584 (650b, 27½er), 587 (700d), 590 (650a), 597 and 622.

unterhausen

did you try some MAFAC canti's?

Slash5

I wonder about a set of Dia Compe 983 brakes? Also ran across a page with a similar problem and the bike was designed for Dia Compe XCE - they look like they would adjust very low.
Any chance a V-brake would adjust lower? Raises all kinds of other problems of course.