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308 Brake Bias

Discussion in 'Technical Q&A' started by Steve King, Nov 15, 2003.

  1. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,353
    NY
    I have been noticing that my rear brakes have been more effective then my front ones.Right after I got the car a few years ago I needed to have the Bias valve rebuilt (by white post) . I have not opened up the front brakes yet but am suspect that 1 of the cal. is sticking. But regardless of this it appears that the rears are more effective then the fronts.Does anyone know what the pressures are for front and rear?
     
  2. donaldh2o

    donaldh2o Karting

    Nov 10, 2003
    143
    Irvine CA
    Full Name:
    Don
    Your brakes should operate just the opposite of what you're experiencing.

    To keep the rear ends of their rear engined cars from breaking loose on curves, Ferrari includes a rear brake delimiting valve in the brake system. This valve lessens the amount of braking to the rear wheels. It also works when traveling in a straight line. On my 1976 308 when I slam on the brakes at about 30 mph, the front wheels lock up but the rear wheels do not.

    I just finished a brake pad and fluid change on my car and the brakes are terrific (see thread: Wow! Great Brakes!).
     
  3. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,353
    NY
    [QUOTE= Ferrari includes a rear brake delimiting valve in the brake system

    I don't see this valve on my 77gtb. There is a bias valve in the front located behind the steering rack. This is the one with the brake warning switch on it and it splits the brakes from front to rear. When I trace the lines to the back of the car there is nothing but 1 line splitting to each rear brake. I am starting to think that maybe my front brakes are frozen and are not moving or the brake hoses are blocked or aged and preventing flow. I'll most likely pull the front calipers and rebuild them over the winter. I'll also put on the braided hoses just to finish it up. I was considering replacing the bias valve with an adjustable one so I could dial in the bias so I was wondering if anyone did this and what were your best pressure settings.
     
  4. Ferrari_tech

    Ferrari_tech Formula 3

    Jul 28, 2003
    1,527
    UK
    Full Name:
    Malcolm W
    Ferrari do not give any values for the braking values restricted by the balance valve - however they donot recommend it being "serviced" and that if faulty it should be replaced. The easiest way to see if the valve is faulty is to put the car on an electronic brake tester and this will show if the balance front to rear is wrong - it will also pick up if the front calipers are under-performing.

    I would expect that the front to rear brake ratio for a standard car of your car's age to be in the region of 65% - 35% depending on the condition of the rotors, pads and rubber hoses.

    MW
     
  5. pma1010

    pma1010 F1 Rookie
    Silver Subscribed

    Jul 21, 2002
    2,556
    Chicago
    Full Name:
    Philip
    Steve
    I've had sticking (F) calipers - you'll notice it as a distinct pull to one side when you press the brake with gentle or moderate pressure. Typically you'll not notice it when you nail it - you'll overcome any resistance caused by the caliper that's sticking.

    I've had the "junction box" balance valve up near the steering rack go before. In theory you can have it serviced (cleaned, lubed etc) but as I recall Ferrari produced an upgrade to the bar with a different contact switch for the failure light. I don't believe this valve does any proportioning.

    I thought F to R bias is driven by the master cylinder.
     

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