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Brake Failure light

Discussion in '206/246' started by scotgm, Jun 15, 2007.

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  1. scotgm

    scotgm Rookie

    Mar 12, 2005
    16
    #1 scotgm, Jun 15, 2007
    I'm driving through upstate NY today when I notice the brake failure light has come on. I tried the brakes and they seemed to work ok. I need to diagnose the problem before driving again. Does anyone know where the sending unit for this light is? Could the rear brakes be out of service? Any advice most welcome-thanks-Scot
     
  2. John Corbani

    John Corbani Formula 3
    Honorary Owner

    May 5, 2005
    1,153
    Santa Barbara, CA
    Full Name:
    John Corbani
    #2 John Corbani, Jun 15, 2007
    Might be vacuum leak. Check soon. Cracked vacuum hose?
    Brakes still work with a small leak. If it grows, no brakes.

    John
     
  3. John Corbani

    John Corbani Formula 3
    Honorary Owner

    May 5, 2005
    1,153
    Santa Barbara, CA
    Full Name:
    John Corbani
    #3 John Corbani, Jun 16, 2007
    Forgot one more thing. If vacuum line leaks, you loose an exhaust valve on #3 as the mixture goes lean on that cylinder. Found out the hard way.

    John
     
  4. scotgm

    scotgm Rookie

    Mar 12, 2005
    16
    #4 scotgm, Jun 16, 2007
    Losing an exhaust valve is scary-I didn't find a leak under the bonnet, but was unable to find the hose coming off the engine. No luck in the workshop manual, but I will look near cyl #3 based on your post-certainly appreciate the advice.
     
  5. PAP 348

    PAP 348 Ten Time F1 World Champ
    Lifetime Rossa Owner

    Dec 10, 2005
    100,220
    Mount Isa, Australia
    Full Name:
    Pap
    #5 PAP 348, Jun 17, 2007
    Might be a silly question but have you check the brake reservoir fluid level, most master cylinders have a pressure switch on them, maybe the level is just a little low because your brake pads are slightly worn thus your piston requiring extra fluid to apply your brakes, I have seen/repaired many "Brake Failure Light" faults just from the above ;) Worth a shot :)
     
  6. sowest

    sowest Formula Junior

    Aug 18, 2006
    899
    #6 sowest, Jun 17, 2007
    The brake failure light on a 246 is turned on by a switch that senses a pressure differential between the front and rear brake systems. The sending unit is in a unit mounted to the frame under the front compartment floor. It is accessible by removing the belly pan under the front area that has the spare tire. You will see a block with four hydraulic brake lines and a small switch with a single wire. The front circuit is on one side of the switch and the rear circuit is on the other side of the switch. If a pressure differential exists, a small piston is moved and the switch is closed. You can see this in action by cracking a bleed valve on a rear or front caliper and applying light pedal pressure.

    If there is no external leak, the cause will likely be a leaking seal on one piston inside the master cylinder.

    I do not think that Dinos have a brake fluid level warning device.

    It is also possible that the switch itself is bad.
     
  7. Kliz

    Kliz Karting

    Mar 6, 2005
    77
    #7 Kliz, Jun 19, 2007
    I had this same problem a couple years ago. I replaced the pressure differential sensor, rebuilt all the calipers and replaced the pads and performed the usual bleeding. By the way, Porsche 911S rebuild kits work and are much cheaper than those with "Ferrari" labels on them. I've been told that F dealers stick a Ferrari p/n label over the Porsche p/n and charge twice as much - probably just a rumor! Right!

    Anyway, the "warning" light is coming on again. The fluid levels are OK. I'm going to re-bleed the system and see what happens but, on following this thread, I'm beginning to suspect the master cylinder and/or the brake proportioning valve may need rebuilding; not something I'm looking forward to during our prime driving season. Hmmm, I wonder if Porsche master cylinder rebuild kits will work here also!?

    I'll let you all know if I learn anything startling but that may take awhile, due to all the other automotive projects I'm into at the moment.
    Bill
     

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