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Racers old and new, and a brake snappage story

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Racers old and new, and a brake snappage story

Old 06-27-19, 04:45 AM
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mboro1876
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Racers old and new, and a brake snappage story

A quick story. I started with a pair of Weinmann 737 (the solid straddle model)

A nice and quite stiff design.

Suddenly the front cable pinch started slipping. No clear reason although the 'channel' for the cable seemed rather wide. Perhaps enlarged through years of use.

While I thought about what to do, I improvised a way to get proper clamping (this routing is shown in the first picture above, too -- I don't have photo from the 'correct' cable routing that was slipping):


All looked fine, and I went out and tried a few heavy, front-loading stops to make sure. The cable didn't slip, perfect.

However, the arm of the front brake snapped clean in two and flew off sideways.



It's tempting to blame this on the unusual 'twist' in the caliper arms on these brakes. I shudder to think that this was waiting to happen all that time.

My solution has been to go back to old-faithful Racers. For the front, though, I picked up a new-in-box Paul Racer for a nice price -- I'd always worried about how the flexy Mafacs would threaten to send the shoes into the sidewall. Perfectly good and useable, but in my case it was really hard to arrive at a setup that worked well in normal use and did not threaten the sidewall in extreme use.

So, old Racer:


New Racer:


I'm not convinced the Paul Racer is worth full retail, especially in the UK, unless one has the braze-on mounts. But I have to say it's fun to work with a brake that has all the elements of the Mafac design with excellent build quality, tolerances, and Allen bolts
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Old 06-27-19, 07:12 AM
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Originally Posted by mboro1876 View Post
However, the arm of the front brake snapped clean in two and flew off sideways.
I think I've seen every possible part on a bike break, except that one. Scary!
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Old 06-27-19, 10:42 AM
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Maybe I should add this to my usual pitch to never bend the arms on Weinmann/DiaCompe centerpull brake calipers!

The pivot design (using a thin steel stand-off spacer against the softer arch), and the use of plastic bushings, are my usual reasons, since the caliper will never be quite the same and may then bind if the bolts are so much as snugged up. Not easy to fix, the spring-loaded pivots can be a bear to reassemble.
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Old 06-27-19, 11:08 AM
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that is scary. I'd love to get some Pauls but the prices are high ($300 a pair); you can pick up dia compe 610 for half the price but it's a different design.
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Old 06-27-19, 11:08 AM
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Originally Posted by mboro1876 View Post
....

My solution has been to go back to old-faithful Racers. For the front, though, I picked up a new-in-box Paul Racer for a nice price -- I'd always worried about how the flexy Mafacs would threaten to send the shoes into the sidewall. Perfectly good and useable, but in my case it was really hard to arrive at a setup that worked well in normal use and did not threaten the sidewall in extreme use.

...
The only times I have seen Mafac Racers touch the sidewalls have been when I've tightened the cables to compensate for pad wear and not adjusted the pad heights. That in around 80,000 miles of Racer use (on my most neglected bikes, the rain/winter/city ones).

Funny, I implicitly trust the Racers more than the Pauls because the Racer arms are clearly forged and not machined much whereas the Pauls are milled from stock material. So the Racers have the "grain" flowing with the curve of the arms like the cells of a piece of wood and the Pauls do not. This means the Mafacs are probably less subject to cracking from imperfections and minor damage. And I have used many pairs up to the point where the pivots were really sloppy and never broke one. I suspect the Pauls' pivots hold up better. Does this mean the failure that retires them is breakage? Does anyone retire perfectly working Pauls?

I'm hoping to learn the Pauls are indeed made from forged arms. I love the Mafac geometry and the supply of near new UO-8s to pull them from is diminishing and the price is going up.

Ben
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Old 06-27-19, 11:51 AM
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Originally Posted by 79pmooney View Post
The only times I have seen Mafac Racers touch the sidewalls have been when I've tightened the cables to compensate for pad wear and not adjusted the pad heights. That in around 80,000 miles of Racer use (on my most neglected bikes, the rain/winter/city ones).

Funny, I implicitly trust the Racers more than the Pauls because the Racer arms are clearly forged and not machined much whereas the Pauls are milled from stock material. So the Racers have the "grain" flowing with the curve of the arms like the cells of a piece of wood and the Pauls do not. This means the Mafacs are probably less subject to cracking from imperfections and minor damage. And I have used many pairs up to the point where the pivots were really sloppy and never broke one. I suspect the Pauls' pivots hold up better. Does this mean the failure that retires them is breakage? Does anyone retire perfectly working Pauls?

I'm hoping to learn the Pauls are indeed made from forged arms. I love the Mafac geometry and the supply of near new UO-8s to pull them from is diminishing and the price is going up.

Ben
Good points! Iím pretty sure the Paul are not forged, though they are relatively chunky. Agreed it is a great geometry!
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Old 06-27-19, 12:25 PM
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I tend to disregard judgement of a product based on it's material specification, simply because the use of adequate testing standards and quality control is so much more relevant and conclusive.
Field reputation is another consideration, though less relevant with newer designs (and in product categories which tend to redesign every few short years).

There is however the consideration of the corrosion-resistance of certain alloys, as I found out when tightening the cable pinch bolt recently on a SRAM RED caliper. The particular alloy bit had lost strength over only a few years in use, so the arm cracked/split in half right at the threaded bolt hole. I'm guessing that the alloy used in the super-light RED calipers is something like a corrosion-prone 7000-series alloy, but these are cutting-edge racing parts so their durability might have been compromised in the interest of lighter weight. I'll never know if accelerated environmental testing was sufficiently emphasized in the creation of this part's testing standards, but this single example suggests perhaps not.

Last edited by dddd; 06-27-19 at 12:30 PM.
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Old 06-27-19, 04:53 PM
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And letís just say I hope not to find out whether a Paul or Mafac is more durable!

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