Adjusting Mafac Centrepull Brakes
Buy a vintage French bike and it will likely have Mafac centrepull brakes. These brakes are very adaptable with their long reach arms, and earned a reputation over the years for providing reliable and effective brakes. With their classic design and superb functionality, it’s no wonder they were such a popular brand and installed on so many bikes back in an era stretching from the 1950’s to the late 70’s .They are still stopping many vintage bikes today so adjusting Mafac centrepull brakes is an important part of your bike’s maintenance. Here is how to do without using any special tools.
You’ll need three tools: a 9mm spanner ( or an adjustable spanner if you don’t have the correct size ), a 9mm socket wrench to adjust the hanger bolt, and a 10mm spanner for adjusting the main brake bolt attached to the forks or brake stay. Why a socket wrench? Because the hanger bolt has a shallow purchase on its front side, so the socket wrench makes the job of holding it easier when you are loosening or tightening it. Indeed, as the hanger bolt does the crucial job of gripping the brake cable it may have rusted or seized into its position over the years, and it can often be tricky job to release it. The last thing you want is to round the shallow flats on the front of the bolt by failed attempts to loosen it.
There’s no one-step approach to adjusting Mafac Centrepulls, and it’s generally a process of minor adjustments until you feel you’ve got the best positioning for the calipers and blocks. The first step is to tighten the brake bolt just enough so that the brake itself won’t move as you make you initial adjustments. The brake should be aligned as centred as possible to the rim, so both brake blocks travel the same distance from the rim wall. Once you’ve threaded the brake cable through the hole in the hanger, you are ready for the awkward bit of tightening the hanger bolt as you raise the hanger. Before tightening the hanger bolt, make sure the whole cable runs without any slack from the brake lever. It is very easy to overlook the fact that brake nipple may not be sitting snugly in its hole within the lever. Also, check for any friction within the housing too, as this will affect the performance of the whole set up.
Keeping the Tension
An important part of how well these brake perform lies in the position of the hanger, relative to the calipers. The higher the hanger sits above the calliper, the less effectively the whole mechanism works. As the idea is to not have the hanger cable pulled into a really high triangular shape, so the hanger cable should not be cut short or stretched so it is pulled very high. But neither should it be really slack, making the mechanism ineffective. Next, put a thumb or index finger under the hanger and pull it up until the blocks are close to the rim. Get the blocks close, as you’ll find that the cable will nearly always slip back a little as you tighten the hanger bolt. You may find that by the time you have tightened the hanger bolt, the brake cable has slipped back slightly and the blocks have slackened away from the rims. If so, try it again: pull up on the hanger, pull the brake cable downwards so there’s a little slack as possible, and keep the tension as you tighten the bolt. Any slight release may mean having to do it again. When you’re happy with the positioning of the brake blocks tighten it down hard using the 9mm socket and 9mm spanner on both sides of the hanger bolt.
Trial and Error
If you get it close and the blocks are centred first time, it’s your lucky day. It often doesn’t work out as gloriously smooth as the Park Tool videos. Generally you’ll find that once the cable is tight and you’ve got about the right distance between rim and blocks, one arm may not as spring back as well as the other. This causes one block to rub on the rim when the wheel spins. This problem, however, can also be caused by the hanger not being aligned to the centre of the caliper. If the hanger is centred in its cable, the caliper will need centring from the rear, using the brake bolt. Adjust its position by loosening the bolt and applying some lateral pressure, while pressing the brake lever until you see the two arms springing back equally. Once you’ve find the best position, tighten the brake bolt.
On the Road Issues
The only way to properly test the functionality of any brakes is on the road, when the brakes have to cope with stopping a fully laden bike at speed. Mafacs always have a tendency to be squeaky, they’re known for it, which can ruin a jolly nice ride. Toeing-in is a good way of resolving this problem, which is quite simple to do. The brake blocks can be adjusted independently by releasing the bolt that attaches them to the brake arms, allowing you to adjust their height and angle to the rim. Toeing-in is simply angling the blocks so that the the front of them ( being the part which hits the rims first ) comes into contact first. Looking down the wheel from the handlebars, the blocks should point slightly inwards towards the rim and the frontwards. This should stop squealing, but it doesn’t always do the trick. It may be necessary to buy new pads, and since new Mafac pads are long gone from the shops, a pair of Kool Stops is a good way of resolving the problem and adding extra stopping power.
With some patient adjustments, you should be able to get the following results:
- The brake levers don’t feel spongy and shouldn’t travel too far to stop the bike.
- Both arms of the calipers should be equidistant and make the blocks come into contact at the same time
- The brake cable should move smoothly from lever to hanger, with no friction from the housing.
- The caliper arms should have good spring tension, which should be felt in the levers; you should have confidence that the brakes will keep you safe on the road.