The brake pedal slowly sinks to the floor

Discussion in 'The whoa and the sway.' started by Chatarina, Nov 30, 2017.

  1. Chatarina

    Chatarina Well-Known Member

    We restored the rear brakes with new cyl and bled the system.The brakes works fine BUT the pedal slowly sinks and you have to brake again.No leaks front/rear. My question: Could it be the mastercyl? Worn out inside?
    It`s Power Drum brakes.

    1968 GS 400 Conv.
     
  2. Chatarina

    Chatarina Well-Known Member

    Also need some help which mastercyl to use. Raybestos,AC Delco,What #number? Rock-Auto?
     
  3. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

  4. Chatarina

    Chatarina Well-Known Member

    Okey,will bleed again. If it is the master cyl,Centric # 13062024? The rest is for manual or disc brake in front?
     
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Yes, that is what it looks like.
     
  6. CJay

    CJay Supercar owner Staff Member

    Very common for the master to go bad when bleeding brakes
     
  7. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    what happens is the plunger in the master only travels an inch or so in normal use. a ridge forms within the bore and when you're bleeding you force the pucks past that ridge and they tear. very common. it seems aluminum master cylinders suffer more from this. when i do a brake job and pump the pedal up to seat the pads i won't push the pedal more than the normal travel amount. that eliminates the risk
     
  8. TexasT

    TexasT Texas, where are you from

    I always put a block of wood under the pedal to keep my "helper" from over stroking the mc.
     
    dan zepnick likes this.

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