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  •  » Brake issues after disc conversion

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    6/29/2017 3:49 PM  #1

    maxelsson
    Unregistered

    Brake issues after disc conversion

    Hi
    Have some trouble with the brakes on my car after disc / disc conversion.
    As I bleed air, the pedal becomes hard and the brakes seem to work properly. Does not find any leakage either. When you start the car then the pedal drops a bit seems to be normal when you have a brake booster. But when driving, it seems that the brake only takes a little bit on the first 1/4 of the pedal stroke and then nothing happens (impossible to lock the wheels). Seems like it does not get more pressure than it gets at first 1/4 of the stroke. However, it feels like when you get up at higher speed, the brakes work better. Had trouble with a broken brake booster due to leakage so had to replace it with a new one so no more leakage in booster.

    Vacuum related ? internal bleed trough in MC ? 

    Does anyone have any idea?

    Best regards Marcus

    Mustang HT 1967
    C4 trans
    302 with .030 bore
    Edelbrock carb and intake manifold
    Edelbrock E-street heads
    Howard cam
    intake    Valve.lift .501    Duration 275
    exhaust    Valve.lift .501    Duration 285

    Mustang 2004 Cobra front brakes
    Mustang GT rear brakes
    Master cylinder PB-6.2
    Booster kit PB - 6770
    Proportioning valve PV-100-CHR
     

     

    6/29/2017 9:46 PM  #2

    Bullet Bob
    Senior 24-7 FYI Addict

    Offline

    From: Montrose, Colorado
    Registered: 4/01/2013
    Posts: 4,780

    Re: Brake issues after disc conversion

    I have the GT 12.5" fronts with Explorer 11 (or so) rears.  5.0, EFI, AFR 165 heads, Comp XE 266 which has a little more timing than I think I want and 550 lift.  At my 6000' elevation it only pulls 9.5 inches at idle and at slow speed the brakes were very poor.  Coming down from speed it felt much better which indicated it wanted more vacuum.  After verifying that the most line pressure I was getting was 750 psi with the engine running,  I finally installed a mechanical vac pump which pulls 17.5 inches at this elevation and that made a huge difference and I was able to measure 1400 psi.  I have yet to make it lock the wheels but it seems to be right on the edge from about 40 mph.  Had it down at 1500 feet last week and didn't panic test it but it felt really good...very little pedal effort. 

    Sounds like you may be experiencing the same issue.

    And...welcome to the best place on the web.  Hope we can help and maybe you can make it to the annual bash some day...like this Oct. in Fort Walton Beach, FL.

    BB
     

    Last edited by Bullet Bob (6/29/2017 9:48 PM)

    "you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
     

    6/30/2017 1:10 AM  #3

    mcfade
    FYI FORD Member

    Offline

    Registered: 6/22/2017
    Posts: 17

    Re: Brake issues after disc conversion

    That makes sense if the mechanical vac pump would correct the pressure. Let us know

     

    7/03/2017 12:37 PM  #4

    maxelsson
    Unregistered

    Re: Brake issues after disc conversion

    Thank you for the reply Bullet Bob and mcfade. Tried with a vacuum tank (4" PVC pipe 😀) between the brake booster and the intake yesterday it made a big difference but not good enaugh. Will connect an electric vacuum pump (Hella UP28 from a Volvo) to also. Think it will work well.

    Thank you for your welcome. There is a plan to visit the United States sometime in a few years. And then it would be fun to travel around a bit. So who knows 

    Last edited by maxelsson (7/03/2017 2:31 PM)

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