microcord

The pair of Mafac "Racer" centre-pulls on my bike do their job tolerably well. I don't sense that stopping has deteriorated during the circa 1000 km of use. But recently the front right pad has sometimes rubbed on the (Al) rim. Today I thought I really ought to take a look.

As I squeeze the brake lever, the left shoe moves in till its (Koolstop) pad contacts the rim. And then it seems that it keeps going, pushing the rim over till the rim closes on the motionless right pad.

As I release the lever, the left brake shoe/pad releases the rim from the right, and eventually retracts farther out to the left. The brake then looks symmetrical; the wheel spins freely -- though after dozens of instances of braking, the brake comes to list to the left, the right brake shoe rubbing the rim.

(I bought the brake together with a matching rear brake. Both appeared clean and in good condition. The rear brake doesn't have this problem of imbalance.)

The "period" books I have about maintenance suggest for centre-pulls in general that one should clean away any obvious dirt, and lubricate the pivots and perhaps also the areas where each end of the spring rubs against a brake arm. And that it's seldom a good idea to delve any further. (The authors are too polite to add "especially if you're a klutz", which I am.)

Is there anything I should try before dismantling the brake, cleaning its ingredients, and attempting to reassemble it?

non-fixie 

They are not difficult to disassemble and get back together again. One at the time, so when in doubt you can check the other for reference.

Kabuki12

Mafac brakes are a bit more challenging to get just right but once aligned they modulate very well. You may check the straddle cable and guide to make sure they are free from any grime or oxidation. Other than that, it is all about the set up. The Racers I have on my Mondia took some time to get right but they are fully adjustable so once centered should come together equally. If it pushes the wheel to one side it just means more adjustment is needed.

microcord

non-fixie , Kabuki12 , thank you both for your suggestions. I've already promised friends (and am looking forward to) a ride tomorrow; I'll do this on a newer bike with three-year-old 105 brakes. And then it's going to be a particularly busy week. But I'll find time somehow. Memo to self: make careful notes and photos, use box wrenches wherever possible, and keep all the parts in jars with their lids screwed on. Somewhere I even have one of those elaborately-bent wire contraptions that used to be sold as "third hand"; I'll see if I can find it.

ehcoplex 

Having rehabbed a set of Racers and a set of Raids recently, as long as you have the right wrenches it's simple and easy. The shallowness of the heads of the pivot bolts and the mounting bolts can be a little bit tricky to get a good grip on, and be careful if/when you take the plastic bushings off- the flat ones on at the bottoms of the pivot posts are tight, they're (probably) old, and can crack. I'm not sure if you can get 'new' ones, and the brass replacements from Rene Herse are $$. A little 0000 steel wool and some Simichrome or Mother's and Mafacs shine up really nicely.

And of course, if you run into any trouble there's always help here.

microcord

ehcoplex , it's not just the price of Compass's "Rene Herse Brass Thrust Washers for Centerpull Brakes", it's the extraordinary rates Compass can charge for airmailing their stuff (plus the unavailability of their "Rene Herse Centerpull Bushing Tool"). "Thrust washer" is a new term for me; it seems to mean something like "washer that's sacrificed so that more expensive bits aren't". My brake is probably doomed as long as it's me who's tinkering with it; still, the man who assembled the bike is skilled and resourceful and I'd be able to ask him.

markk900

While the best thing is complete disassembly and thorough cleaning, I have been successful in resolving similar problems with Mafac Racers by lubrication and light cleaning. They're pretty robust. By design they are self-centering in use so your observation indicates there is enough friction somewhere that the forces are moving the one arm more than the other. As suggested, straddle cable and straddle cable holder, and pivot points are easy to look at, lube and perhaps solve the problem without disassembly (until you have enough time to "do it right").

As a reference, I just checked the Mafacs on my Peugeot: slowly operating the lever, one arm moves a bit first, the second arm starts to move a bit as well but slightly more slowly, the leading edge of the first arm's pad just touches the rim surface and seems to "pause" a bit, the other arm moves slightly more rapidly until its pad just touches the rim, then both arms move evenly as the brakes are applied.....

obrentharris 

I will add to the other good advise here that the straddle cable can sometimes cause this problem. If it has a slight kink in it the stirrup will sit slightly off to one side causing the pad on that side to activate first. A little lube in the stirrup groove where the straddle cable sits can also help.

If the problem persists after everything is cleaned and lubed you can gently bend the springs to make them stiffer or softer.
Brent

Road Fan

As far as care and feeding of Mafacs, I would add to put a dab of grease between each spring end and the part of the arms it bears against. In addition, a similarly small dab in each pivot surface, once they are all squeaky clean.

gugie 

Lots of good advice above.

Disconnect the springs when adjusting the pads. It's a loooooooooooooooooot easier that way.Use a flat blade screwdrive to disconnect them, those pesky springs hurt like heck when they pop off and hit your finger. To put them back on, file a groove in the middle of an old flat blade screwdrive to catch the spring and push them back.

Use a derailleur cable for the straddle cable. They're typically just a tad bit too large of diameter to fit into the little thimble bit (MAFAC article 59), just sand/file/carefully grind until they fit into the counterbore on one side, otherwise over time they'll creep into it, and you may suddenly lose braking power (don't ask how I know). Counter-intuitively, you don't want a thicker, stiffer cable.



There's a lot of interchangeable parts on MAFAC centerpulls (Racer, Competition, 2000, RAID, etc.) They're really a brilliant and elegant design. Set up properly, they have good stopping power and excellent modulation. Set up wrong, they can be the crappiest brake you'll ever use. If you take the time to learn and tame the beasts, you'll be quite happy with them.

microcord

Good morning (my time), all! Thank you for your comments. I'm in a rush to go on a bike ride (on a different bike) that was arranged back when I had fewer worries; this evening I'll be too exhausted to contemplate faulty brakes, but I expect to reread your comments on Sunday and to do some exploratory cleaning, etc, trying not to break anything. Till then.....

zukahn1 

One thing you can do on Mafacs or pretty much any center pull to help this is to run short section of modern thin cable liner over the center of the straddle cable.

tiger1964 

Brilliant! Gotta do this! (Partly because I had to buy a gazillion feet of that stuff )

leftthread

What are the differences between the Racer and the Competition models?

79pmooney

Mafacs that have lead hard lives may have a spring or two that has been tweaked so the two are now unequal. Centering the pads and having them hit equally can now be a challenge. I have used straddle clamps with the set screws for the straddle cable and pushed it off center to get the pads to sit equal distances off the rim. Not ideal and the brake may now push the rim to one side (like every dual pivot I've ever owned though that's a no-no to talk about). I now always use those straddle clamps with Mafacs. Very useful at 4:30 am when you see that the commuter's pad is rubbing.

My wish - that someone would find the old tooling and start making the Racers again. Yes, Pauls are nice but I'd much rather trust my life to forged arms that care little how many times they've been scratched or how deep those scratches are. I've never heard of one of those Mafacs breaking and I've been riding them 55 years. (No, not the same ones. Eventually the play gets so bad I cannot live with it though they've been just fine as stoppers when I've replaced them for more respectable. Haven't gone the bushing replacement yet because finding a pair in good shape used to be so easy. Near NOS for $50 at garage sales with a UO-8 attached. That source is drying up.)

79pmooney

Never had a Competition but the differences are, I believe, shorter reach and a straddle cable with fittings at both ends whereas the Racer has the fitting at one and a clamp at the other. The Competition is neater, cleaner but lacks the ease of fine-tuning straddle cable length for custom feel.

gugie 

Racers use a derailleur cable as a straddle cable, you can adjust the length for more power or more modulation.
Competition models have a fixed straddle cable length - proprietary

Competitions have a nicer finish, and come with a tire guide.

Racer


Competition


Over the years there were variations of both, but these are the most common representations.

gugie 

Mostly correct, but there were reah variations on reach for both.

gugie 

Hmm, I just bought a lot of 4 sets complete for $80. Racers can be found for cheap. File off the casting marks, sandpaper at various grits, polishing wheel and they can pop.

oldschoolbike

Some Competitions had brass bushings. Those were great brakes.

oldschoolbike

El Chaba

One note….the calipers of the Competition model have a shorter reach than the Racer ( or 2000). The chart that shows those models in short, long and adjustable reaches reflects differences in the stirrup only as the caliper arms remain the same. The Competition has slightly better mechanical advantage than does the Racer or 2000…The difference is not huge, but noticeable. I think it’s worth getting the shortest reach model that will clear the largest tire/fender combination that you will use. If you ditch the stirrup via brazed on pivot mounts, you get a huge bonus in the clearance department whatever the model. If you look closely, you can see the difference in caliper length between the Competition and 2000 model.

gugie 

Good info, did not know that! I had to re-read your post a few times to fully understand. What you call a stirrup I've always called a backing plate, but that's just semantics. I've only come across a few Competitions and one 2000 model, but changing out the "stirrup" to make for more reach makes a lot of sense. Why make a different forging for both arms?

I've done a few dozen 650b conversions, most of them with brazed on posts. As you mention, you do get a lot more clearance without that plate in the back. Almost all of them used RAIDs, which have the longest arms of all the MAFAC brake family. I typically braze them on so that the calipers don't bottom out on the fender to allow them to swing open wide enough to allow the fully inflated tire to clear the brake pads. This varies a bit depending on the fender used and placement on the frame, but usually means the brake pad is roughly centered on the adjustment slot properly adjusted for the rim.

repechage

These guys don't have what is needed?

https://cyclesgrandbois.com

tiger1964 

I could have sworn that back in the 1970's I saw Mafacs, and I recalled they were Competitions, that had the not very Mafacy technology of pad holders attaching to the arms with something like a ball and socket arrangement. Was I dreaming? A Google Image search only shows that on a model called Tiger, which appears really, really old to my eye. No idea what the reach is for such a thing.

gugie 

Amir Avitzur has several Flickr albums that are extremely useful for researching all things MAFAC.

MAFAC Top 63



Here's the MAFAC Tiger you mentioned:


I couldn't find a Competition model with the ball joints.