Mafac centrepulls are some of the most common type of centrepull style brakes on bikes from the 50's all the way through the 70's until they started to fall out of favour and gave way to sidepull caliper brakes. They came on all kinds of bikes from Peugeot mixtes all the way to Jacques Anquetil Tour de France bike.
This review is based on my own experience using the Dural Forge model on my commuting/touring bike Mr Ramen, they are more or less identical to the ubiquitous Racer model which came a bit later.
Construction & installation
The brake consists of three main parts, the two arms pivot off a central bridge which then is bolted through a standard road brake hole. As far as I know all Mafacs are a nutted fitting instead of the recessed fitting which became popular in the 80's. They are named Dural forge because the arms are forged from the then new alloy called Duraluminum. The arms pivot on red plastic bushings on this model which are replaceable. The bridge can be done away with if the are installed on a frame with cantilever mounts meant for centrepulls, whilst I haven't ever tried this myself apparently this greatly improves the feel of them.
The arms are joined by a straddle cable which is pulled upon by a yoke which is connected to the brake lever by a brake cable on a hanger usually attached to the headset on the front and by a hanger either on the frame or attached to the seatpost bolt. The standard Mafac front hanger is somewhat flexy and a stiffer brake feel can be obtained by changing the hanger for something stiffer.
Mafacs are commonly used on touring bicycles because of their large clearances and generous brake drops to fit around larger tyres and mudguards The frame I originally had them installed on was a 27" to 700c conversion. The conversion to the smaller 700c size increases the brake reach by 4mm. The maxiumum reach of the dural forge models is 70 something mm. I did find though that when the calipers were closed the inside of the arms would touch the 48mm wide velo-orange mudguards I had installed.
I fitted velo-orange adjustable smooth stud pads and holders to the Mafacs to allow me to have a large choice of modern pads. I had to mile down the spacer on the pads to get them to sit properly on the Mafacs, otherwise they pushed the arms out too far open.
The lever feel is reasonably stiff and brake modulation is better than most sidepulls. However I found under hard braking the arms tended to flex forward in an arc and hit the tyre sidewall. This necessitates angling the pads to compensate for this flex, so under light braking only a small part of the pad comes into contact with the rim which causes uneven pad wear. See the picture below for the typical flex.
At full effort the braking power is adequate, let's say if 10/10 is a modern dual pivot caliper then the Mafacs would be a 6 or a 7. It's enough to slow you down but not really much to really haul you up in an emergency. They didn't have enough power to lift up the back wheel, braking from the hoods could be best described as speed attenuation.
There seems to be a lot of variation in braking power with Mafacs, everyone has their opinion on them. This is my own experience running them over the course of a year for about 3000km or so. I suspect that with braze on fittings the flex would be reduced a lot and the braking power improved. I was using BBB techstop pads which work well on my Cinelli with Campagnolo dual pivot brakes, so I doubt it was poor quality pads which are at fault for the average braking performance. Over the last year I have had a few close calls where the braking power simply wasn't up to scratch, one time I bumped very lightly into a taxi which was what convinced me to go to sidepulls on the Mr Ramen refresh. As a comparison the Shimano 600 sidepulls with kool stop salmons are able to pop up the back wheel under hard braking, and although they do flex, are nowhere near as severe as the Mafacs. Funnily enough, they also completely clear my mudguards unlike the Mafacs.
In conclusion, the Dural Forge Mafac centrepulls are limited in stopping power by the flex. If you can get around the flex somehow, either by using braze on cantilever studs or possibly using one of the later models which have beefier arms you could probably improve the performance significantly.