365 GTB/4 Daytona break warning lamp („FRENO“) | FerrariChat
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365 GTB/4 Daytona break warning lamp („FRENO“)

Discussion in 'Technical Q&A' started by Ferdinand Mayr, Jun 20, 2021.

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  1. Ferdinand Mayr

    Ferdinand Mayr Rookie

    Jun 4, 2018
    22
    Full Name:
    Ferdinand Mayr-Melnhof
    #1 Ferdinand Mayr, Jun 20, 2021
    Hi everyone,

    my Daytona‘s „FRENO“ lamp is lighting up whenever I perform a hard breaking. The light remains off when I just break „normally“.

    The break performance is definitely not as good as it should be, but it‘s not dangerously bad. I just have to use significantly more force.

    The user manual says that the FRENO lamp appears when there is a pressure difference between the two break-circuits.

    The manual gives three possible reasons for a pressure difference between the two circuits:

    1. Fluid leak (I‘m pretty sure there is no leak because the reservoir remains stable at „max“)

    2. Reservoir without break fluid (not the case)

    3. One of the hydraulic master cylinders binded or with compensating hole obstructed.

    I guess it will be reason number 3 in my case, but the translation seems to be a bit off. Does any one have a clue what reason number 3 means?
    Any other ideas or faults I should be looking out for?

    Best wishes,
    Ferdinand
     
  2. garybobileff

    garybobileff Formula 3
    Sponsor

    Feb 5, 2004
    1,180
    San Diego CA
    Full Name:
    Gary
    #2 garybobileff, Jun 20, 2021
    If it is a car after chassis # 14307, there are only 3 switches that can indicate that problem:
    1. handbrake switch, but that has nothing to do with depressing the brake pedal
    2. reservoir float switches, if the reservoir is full, and the switches function normally, that would not be a factor
    3. The shuttle valve switch could be your problem, as it cuts off the front or rear circuit incase of a brake fluid and pressure loss. The shuttle valve needs to be centered in the housing, and if not, it will move slightly and activate the switch. That is probably the source of your problem
    Gary Bobileff
     
  3. Ferrari Tech

    Ferrari Tech Formula 3

    Mar 5, 2010
    1,217
    Georgia
    Full Name:
    Wade Williams
    #3 Ferrari Tech, Jun 21, 2021
    I agree, most likely the shuttle valve. You need to find why the valve is not staying centered. It sounds like it is doing its job properly and warning you of a brake imbalance between front and rear.
     
  4. jimmyr

    jimmyr Formula Junior

    Oct 10, 2004
    342
    Scottsdale, AZ
    Full Name:
    Jim
    #4 jimmyr, Jun 21, 2021
    Had the same problem, rebuilt the master cyl., and all back to normal.
     
  5. Ferdinand Mayr

    Ferdinand Mayr Rookie

    Jun 4, 2018
    22
    Full Name:
    Ferdinand Mayr-Melnhof
    #5 Ferdinand Mayr, Jun 21, 2021
    Thanks for your reply. However it can‘t be an imbalance between front and rear breaks, because each break-circuit works for all 4 wheels (see diagram attached -> red is circuit 1 and yellow is circuit 2). The lamp means that the two circuits don‘t have the same pressure.
     

    Attached Files:

  6. Ferdinand Mayr

    Ferdinand Mayr Rookie

    Jun 4, 2018
    22
    Full Name:
    Ferdinand Mayr-Melnhof
    #6 Ferdinand Mayr, Jun 21, 2021
    Thanks Jimmy. What exactly did you have to fix in your master cylinder?
     
  7. raemin

    raemin Formula 3

    Jan 16, 2007
    2,341
    Lyon (FR)
    Full Name:
    R. Emin
    #7 raemin, Jun 21, 2021
    Last edited: Jun 21, 2021
    Let's assume your fluid is fresh.

    It could also be one "stuck" proportioning valve. 6 and 8 in diagram?

    If one is working it leaves room for 1 or 2 cc of fluid, while the other locks the circuit. This is more than enough to move the needle of the warning valve. On hard break you would lock the rear wheel and lack some bite in the front.
     
  8. garybobileff

    garybobileff Formula 3
    Sponsor

    Feb 5, 2004
    1,180
    San Diego CA
    Full Name:
    Gary
    #8 garybobileff, Jun 21, 2021
    Technically, you are correct, you have a upper and a lower brake circuit, not a front and back circuit. But, the same solution to your problem exists, and that is to center the piston in the shuttle valve.
    Gary Bobileff
     
  9. jimmyr

    jimmyr Formula Junior

    Oct 10, 2004
    342
    Scottsdale, AZ
    Full Name:
    Jim
    #9 jimmyr, Jun 25, 2021
    The master cyl. was clogged with rubber debris and had worn seals. The braking was not up to spec as it did not seem to have full braking. Replaced all seals, bled the brakes and no more red light and full braking restored. I agree the shuttle valve is a suspect, but in my case the imbalance between the two systems caused the shuttle to react with a red light.
     

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