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308 Hand Brake

Discussion in 'Technical Q&A' started by John Peel, May 5, 2006.

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  1. John Peel

    John Peel Rookie

    Jun 22, 2005
    18
    Portsea Victoria Aus
    Full Name:
    John William Peel
    #1 John Peel, May 5, 2006
    I know this subject has been done to death but I dont understand what been said in the past and I would appreciate some member setting me straight. Andy 308 Gtb wrote a very detailed description of adjusting the brake in Jun 2004, which seems to get more or less universal agreement. He describes the first step in setting the clearence between pad and disc by adjusting the pin that presses against the piston on each caliper to get a .004 clearance. Why is this so? The piston has a rubber ring which distorts in operation which lets the piston move forward [and returns it] so excessive clearence indicates piston sizeure or other malfunction. The Work Shop manual does not mention this move. If the rotating shaft on the caliper, that is operated by the hand brake, moves the piston forward, then operation is by achieved by that caliper only as no oil is driven into the mating caliper. Is this how it works only on one caliper? If so what is the purpose of the adjusting pins that Andy refers to. I would appreciate a comment. Thank in advance.
     
  2. Andy 308GTB

    Andy 308GTB F1 Rookie
    Lifetime Rossa

    Jun 2, 2004
    2,666
    Essex, UK
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    Andy M
    #2 Andy 308GTB, May 5, 2006
    John - please note these were Ric Rainbolt's instructions

    I merely reposted them...

    regards
    Andy
     
  3. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,022
    Groton, MA
    Full Name:
    Verell Boaen
    #3 Verell, May 5, 2006
    The range of motion allowed by the rubber seal is pretty large as it has to accommodate the wear range of the pads.

    The initial clearance adjustment's purpose is to position the pads a precise distance from the caliper so that t

    1) the master cylinder travel required for stopping is precisely controlled.

    2) Position the adjuster pins so that they can automaticly compensate for pad wear. As the pads wear, the adjusters inside the pistons reduce the piston's inward (away from the rotor) travel to compensate for the wear.

    I believe the parking brake actually pushes against the adjuster pin rathar than directly on the piston (It does in the 914 rear caliper which I believe is identical to the 3x8 other than the center spacers). The adjuster pin has a flange on it with an o-ring seal. When the pin moves into the cylinder, it may act like a piston and displace enough fluid to partially actuate the outer piston.
     
  4. John Peel

    John Peel Rookie

    Jun 22, 2005
    18
    Portsea Victoria Aus
    Full Name:
    John William Peel
    #4 John Peel, May 6, 2006
    Thanks Andy and Verell. Another piston in there that is operated by say a camm on the handbrake spindle would explain the whole operation., and for that matter the procedure for setting up the system up.My parts manual which has of course an exploded view of the calipers does not show such a piston or for that matter whats at the end of the spindle. Thanks fellas.
     

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