Mafac Racer rear brake sticking.

def_defyr
def_defyr Posts: 93
in Vintage bikes forum
Hello, any Mafac experts out there? The rear brake on my daughter's 1978 LeJeune mixte frame is "sticking" from time to time -- it seems to pivot on the frame mount, and get hung up to one side. I've disassembled it, cleaned it, changed cable, checked hanger angle etc -- all seems to be OK.

Is there some kind of magic bullet I'm missing? If I loosen up the frame mounting bolt, which obviously would prevent it from sticking at all, the assembly sags a few mm and looses effectiveness etc. Conversely, tightening the frame mount bolt too much would just freeze everything up, no? Or is there something I could lube?

Sorry to be a bit blind here -- I've got everything else fettled on the bike but the rear brake is driving me batty....

Comments

  • ugo.santalucia
    ugo.santalucia Posts: 28,313
    I do remember these old calipers being problematic... I had a pair of Universal with similar issues. Are all the vashers in the right place? These things rely on minimal friction to work properly... ultimately, if it is a utility bike, you might want to consider a more modern and more reliable caliper...
    left the forum March 2023
  • paulkilbourneassociates
    paulkilbourneassociates Posts: 14
    Am I right in thinking that you are talking about Mafac Driver brakes, the braze on types, not the Racer type?
    If you are, then carefully cleaning, even very carefully sanding down minutely the posts, and greasing them well may help. I’d also take the springs out whilst you do this, and carefully bend a bit more spring into them, then grease the contact with the brake arms.
    They can be very fussy about the division of power between sides, as determined by the length of the straddle cable between the “ pull” and the brake arm.
    Ultimately it can end up by fiddling with cable lengths .
    PS make sure that the rear wheel is centred correctly.
  • def_defyr
    def_defyr Posts: 93
    ^^Thanks, No it's the Racer - the kind that broke hundreds of thousands of French hearts with their horrid squealing.

    It's a center mount bolt. I'm thinking the next step is to replace the straddle cable and playing with the cable length, as you suggest. The cable routing is not very efficient so a lot of energy gets directed in directions that are, shall we say, subobtimal...

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