Brake problems: 308 GTSi QV | FerrariChat
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Brake problems: 308 GTSi QV

Discussion in '308/328' started by 455Fosbery, Jan 27, 2023.

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  1. 455Fosbery

    455Fosbery Karting

    Oct 3, 2013
    212
    #1 455Fosbery, Jan 27, 2023
    I’m currently experiencing a problem with the brakes on my 1984 Ferrari 308 GTSi QV. When the engine is running at idle and I depress the brake pedal, the idle speed increases to about 1500 RPM. If I release the brakes, the engine speed returns to normal.

    In addition, the brakes don’t seem to be as affective as they used to be.

    Can anyone shed light on the root cause of this problem? For example, Could this be an air leak in the brake booster?

    This being the case, is it possible to repair or rebuild the brake booster?

    Any help/recommendations would be greatly appreciated, including any tests I could do to troubleshoot, and good sources for a new booster or to rebuild the existing booster.

    Many thanks!
     
  2. miketuason

    miketuason F1 World Champ
    Owner Silver Subscribed

    Feb 24, 2006
    15,763
    Cerritos, CA.
    Full Name:
    Mike
    #2 miketuason, Jan 27, 2023
    You may have a bad or crack vacuum hose or the one way valve could be faulty or the brake servo diaphragm can also be bad.
    Does the pedal feels stiff or soft and spongy?
     
    thorn and ProvaMo like this.
  3. ProvaMo

    ProvaMo Formula Junior

    Jun 29, 2004
    347
    Mid West
    Full Name:
    Paul John
    #3 ProvaMo, Jan 27, 2023
    Concur with the questions @miketuason is asking. I'm guessing your brake pedal is hard as a rock(?) When you step on the brake, the booster may be leaking air (vacuum) and the increased air to the intake is a temporarily leaning out of the air/fuel mixture which increases idle speed.

    Also, if the idle increase upon stepping on the brakes is consistent, then a simple test could include disconnecting the booster vacuum hose at the booster, plugging the hose... then running the same "step on brakes" test to monitor the idle speed for change...
     
  4. Brian Harper

    Brian Harper F1 Rookie
    Owner Silver Subscribed

    Feb 17, 2006
    4,078
    San Jose area
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    Brian Harper
    #4 Brian Harper, Jan 27, 2023
    Yes. I brought mine to the local brake booster rebuild shop in San Jose. He knew the part number of the rebuild kit without even looking it up. They redid the yellow zinc plating to make it look like new and rebuilt the master cylinder also. I don't remember the cost but I do remember being pleasantly surprised. I Say Ding-a-ling even has the Bendix Italia stickers in stock to fully make it fully look like new.

    My car is an '83 and I think I had a diaphragm leak for a couple of years, so the age of your car certainly makes it likely as well.
     
    Ron308fromSFBayArea likes this.
  5. 455Fosbery

    455Fosbery Karting

    Oct 3, 2013
    212
    #5 455Fosbery, Jan 28, 2023
    Many thanks guys! I’ll check and report back... @Brian Harper: do you recall the shop in San Jose? It would be great if I could source the rebuild kit.

    As a comment, I’m currently in San Jose, headed to LA shortly, then Dallas right after that. The car is in Dresden (talk about a logistical challenge ).
     
  6. MFlanagan

    MFlanagan Karting

    Dec 21, 2016
    158
    #6 MFlanagan, Jan 28, 2023
    waymar likes this.
  7. Brian Harper

    Brian Harper F1 Rookie
    Owner Silver Subscribed

    Feb 17, 2006
    4,078
    San Jose area
    Full Name:
    Brian Harper
    #7 Brian Harper, Jan 28, 2023
    Yup, that's who I used. I am 100% satisfied with the customer service, the work they did, it was done on time, and I was pleased with the price. I can't even remember the last time I can say that about anything.
     
  8. 455Fosbery

    455Fosbery Karting

    Oct 3, 2013
    212
    #8 455Fosbery, Feb 3, 2023
    Update: it’s definitely the brake booster. After making a few calls (thanks for the leads) and digging, I finally took the decision to buy a “NIB” one that I was fortunate to find. This will ship Monday, so looking forward to getting it fitted and then having the TÜV done. Many thanks again guys!
     

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