456 brake booster problem | FerrariChat

456 brake booster problem

Discussion in '456/550/575' started by rviani, Mar 15, 2013.

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  1. rviani

    rviani Karting

    Jun 22, 2005
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    Ron Viani
    #1 rviani, Mar 15, 2013
    The hudraulic brake booster (rear of the master cylinder) on my 1995 456GT appears to have quit working. The electric booster pump assembly appears to be working properly as there is sufficient pressure at the accumulator and no brake light. However the pedal is extremely hard and appears to have no boost.

    Anyone familiar with this problem?

    I intend to remove the booster and send it out for repair but before I dig into it two questions:

    1) looks like I can just pry the resevoir straight up off the master cylinder after releasing the small bracket - YES ?

    2) looks like perhaps the master cylinder can come off the front of the booster without dicconnecting the brake lines to avoid getting air into the system - Yes?

    3)Anyone have a recommendation on a shope with experience rebuilding 456 hydraulic parts?

    Any help grately appreciated.

    Ron
     
  2. tazandjan

    tazandjan Three Time F1 World Champ
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    Jul 19, 2008
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    #2 tazandjan, Mar 15, 2013
    Ron- Assume you have a 456 workshop manual since you know you have a hydraulic boost system.

    Interesting. Turn off battery and pump brake pedal at least 25 times to ensure no pressure in the system before maintenance.
     
  3. rviani

    rviani Karting

    Jun 22, 2005
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    Ron Viani
    #3 rviani, Mar 18, 2013
    Thanks Taz - unfortunately with my problem pumping the brake pedal does not depressurize the system. Which is part of the reason I know the booster is not working. Unscrewing the pressurized accumulator does - and also results in a torn O-ring and a big mess - ask how I know.
     
  4. tazandjan

    tazandjan Three Time F1 World Champ
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    #4 tazandjan, Mar 18, 2013
    Ron- Quite a bit of pressure in that accumulator, so I can see how that would happen, but cannot see any way to prevent it if the pressure will not drain. Really messy, but at least it is only highly corrosive brake fluid. Lucky none got in your eye.

    Sort of like letting down a clock spring. You know bad things can happen, and just hope for the best and no damage. Ask me how I know about damage.
     
  5. 166&456

    166&456 Formula 3

    Jul 13, 2010
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    #5 166&456, Mar 21, 2013
    Yes be careful with that fluid. It will damage your skin (and permeate through it, I heard - don't know if that is true but that can't be good) as well as any paint it sits on for a longer period.

    As for the hydraulic booster, I think this system is identical to systems used by BMW and Jaguar (on the XJ40). Not sure if they're identical on the inside but that might help with finding parts and avoid the "Ferrari tax".
     
  6. rviani

    rviani Karting

    Jun 22, 2005
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    Ron Viani
    #6 rviani, Apr 1, 2013
    Thanks guys. In fact I believe the 456 hydraulic accumulator and pressure switch are interchangable with parts supplied by AC Delco (#25528382 - accumulator) and #25533700 pressure switch) which are the parts most prone to failure. However I have not personally verified this.

    My problem is apparently a bit more complex. Has no one on the list done this type of repair? Any help appreciated.

    Ron
     
  7. rviani

    rviani Karting

    Jun 22, 2005
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    #7 rviani, Oct 7, 2013
    An update for general info:

    1) I managed to repair this without resorting to sending the unit out for rebuild or ( heaven forbid) buying a new part from Ferrari. The process was in fact not too difficult and my suspicion that the brake booster was malfunctioning turned out to be correct.

    2) the brake fluid reservoir comes straight up off the master cylinder once the small torx screw hidden underneath it is removed from the bracket holding it to the master cylinder.

    3) the master cylinder can in fact be pulled forward from the booster by carefully removing the two large torx bolts holding it. The booster mechanism can then be removed after pulling the MC forward without the need to disconnect the brake lines and bleed the system.

    4) Once removed, the booster mechanism is not too difficult to disassemble - in my case the slide valve was stuck in the "closed position" therefore not allowing any boost to get to the master cylinder.

    Can't believe I am the only person on the list to encounter this problem - and would be happy to provide further details if requested. Now on to rebuilding front calipers - anyone have a source for seal kits for these original ATE calipers as installed on a 95 456GT ??
     
  8. 166&456

    166&456 Formula 3

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    #8 166&456, Oct 8, 2013
    It's the first time I have heard of this problem, so it could be an exception. What was it that stuck the valve, was it some sort of dirt or debris?

    As for the seal kits, I have done some research because the brake pads are so outrageously expensive for these calipers (600 for a set of pads is simply out of this world). I had the feeling that these ATE brakes are nothing but a nicer casting of an existing design, made for Ferrari. And I have come to the - however yet unverified- conclusion that these ATE/Teves brakes are identical to the 420/500SL/500E of the time.
    I have bought a set of performance Mercedes pads for these calipers, however have not yet installed or tested them yet on my car. This might give you a lead of where to start looking though.
    For caliper seal kits, the most important thing you need to get right is piston size, so I would start by measuring that on your 456.
     
    F456M likes this.
  9. 360modena2003

    360modena2003 Formula 3

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    #9 360modena2003, Oct 8, 2013
    Fantastic and very useful - could you add some pictures? Would be very useful.

     
  10. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
    2,399
    #10 360modena2003, Oct 8, 2013
    If you look on ebay.co.uk you will find very cheap brake pads for the 456, I believe they are the same as the Porsche 964 Turbo and 928.



     
  11. Mr. V

    Mr. V Formula 3

    Oct 23, 2004
    1,247
    Portland, Oregon
    #11 Mr. V, Oct 8, 2013
    Last edited: Oct 8, 2013
    delete
     
  12. 166&456

    166&456 Formula 3

    Jul 13, 2010
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    #12 166&456, Oct 8, 2013
    The later models indeed use those pads, but not the 93-96 models.
     
  13. 166&456

    166&456 Formula 3

    Jul 13, 2010
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    #13 166&456, Oct 11, 2013
    Last edited by a moderator: Sep 7, 2017
  14. rviani

    rviani Karting

    Jun 22, 2005
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    #14 rviani, Oct 15, 2013
    Interesting post. The BMW system is functionally similar but the hardware for the booster it self is clearly completely different. In my case the slide valve piston had become stuck in the position where it blocks admission of the high pressure fluid. It's not clear what caused this other than a build up of old fluid - the clearances are extremely tight, and I suspect the piston and bore may be individually lapped together. Removal of the slide valve assembly and cleaning the valve piston and bore to restore free movement solved the problem. Unfortunately I did not take pictures during the repair but am more than willing to help anyone experiencing a similar problem.

    As an aside I wonder what in the world made Ferrari adopt this system rather than the traditional vacuum booster use by EVERYBODY else. I guess they returned to the traditional vacuum system in later years. Still having problems locating seals and dust boots for the ATE calipers.
     
  15. tazandjan

    tazandjan Three Time F1 World Champ
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    #15 tazandjan, Oct 15, 2013
    Ron- The 456M has a typical vacuum booster. Ferrari did a lot of experimenting with the 456 and 456M. Many experiments (hydraulic boost, automatic torque converter transaxle, different firing order, eccentric adjustment of suspension settings) did not survive and all were eliminated for future models when the 612 went into production.
     
    F456M likes this.
  16. BWSmith

    BWSmith Rookie

    Jun 9, 2014
    1
    #16 BWSmith, Jun 9, 2014
    As per previous chat I have a 95 456 Ferrari GT, I have rebuilt the brake booster, bled all the brakes, still have a hard pedal and no brakes. I have unplugged the pump, it has blown the two center fuses, I have 12 volts going to the pump but it shows the motor shorted. I'm going to remove the pump and run 12 volts to the motor section tomorrow to see if it runs. Any ideas?
     
  17. Mikaferrari

    Mikaferrari Rookie

    Sep 6, 2011
    5
    #17 Mikaferrari, Jun 26, 2018
    I have a similar situation with a hard pedal and no brakes. I replaced the accumulator, but no luck. Any suggestions? Thank you, Mike.
     
  18. Craig Bonham

    Craig Bonham Rookie

    Dec 1, 2017
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    #18 Craig Bonham, Sep 17, 2018
    I have a similar problem to, I have taken the booster system apart because I had a leaky seal and now when I put it back together I get great brakes but no assistance, is there a special way to reassemble the power booster piston?
     
  19. jcbam

    jcbam Karting

    Nov 30, 2019
    79
    New York
    #19 jcbam, Nov 22, 2020
    Hi, may I know which shop did your brake booster rebuild for your 456? Mine has hissing noise inside the cabin when I pump the brake, noticed the seal on the plunger is gone with no dust cover neither. Brake is not good with poor response, perhaps due to air leak in the booster. Not sure if your brake boost rebuild addressed the seal issue. Thanks.
     
  20. tazandjan

    tazandjan Three Time F1 World Champ
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    Terry H Phillips
    #20 tazandjan, Nov 22, 2020
    That was 6 years ago and he only had one post.
     

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