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  •  » Brakes

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    9/16/2013 4:52 PM  #1

    frozen2long
    Unregistered

    Brakes

    Hello everyone, I have a '67 Mustang GTA 390 and I cannot get the brakes to stop hard in an emergency stop. All it will do is slow down quickly, but not lock up. I have had the booster out and bench tested and the push rod set up to factory standards, new master cylinder, new brake pads, new brake hoses, checked boost at 16 psi at idle, bled front and rear breaks, new rear brake cylinders, caliper pistons working and installed a aux. vaccum canister and I still cannot stop hard and I run out of pedal before I slow down to a stop. Any Ideas?

     

    9/16/2013 5:20 PM  #2

    MS
    Forum Originator

    Offline

    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 12,499

    Re: Brakes

    Hard pedal can be attributed to a master cylinder with too large a bore.  If over 1" (original size for your car) you will not be able to push hard enough, even with the booster helping, to build enough pressure.

    Other issue might be the pads.  If you bought lifetime warranty pads or ceramic pads, take them off and buy some cheapo OReilly house brand pads.  They will stop alot better.

    Other issue is breaking in the pads.  It is quite common for folks to install new brake pads and then go out and stomp down on them to see how well they work.  Doing so will immediately ruin the pads.

    Also, a master cylinder with too small a bore can result in the master cylinder piston bottoming out before the brakes are fully applied.

    Those are a few things to check.  Lots of times it is the booster, especially if it is a Midland Ross type.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    9/16/2013 6:10 PM  #3

    frozen2long
    Unregistered

    Re: Brakes

    Thank you for your reply. The booster is a Midland, and as far as I know it is the original. I did replace the pads with what I was told were the mid grade, but I'm going to check around and see if I can get the cheapo O'Reilly pads you suggest. And yes, that is the first thing that I did too, was to tramp down as hard as I could when I replaced the pads. Also, what make of booster do you think I should replace that Midland with, if as a last resort that I do this? Also the rotors are polished like a new bumper, but when I told the mechanic to turn them, ( to give the pads a bit of rough surface to bite into ) he advised me not to as this would not make any difference and be a waste of money. What do you think? Also someone suggested getting the brake pressure measured at the rotors to see if they are putting out the correct pressure. What do you think about that? I appreciate all of your tips.

       •Thread Starter
     

    9/16/2013 7:11 PM  #4

    MS
    Forum Originator

    Offline

    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 12,499

    Re: Brakes

    Checking system pressure at a caliper bleeder is a good diagnostic tool.  You need around 1,000 PSI to do the job.  Sounds like the rotors are glazed pretty good,a long with the pads, if the rotors are polished.

    I don't take chances when working on brakes.  If something is suspect, I replace it.  If the rotors have never been turned before, it would be worth doing so the new pads seat to the rotors.  If the rotors have been turned before, new ones are not that expensive.  Just break them in gently for about 300 miles before you try to burn them up.

    I prefer the Bendix boosters over the Midland.  If your car has the original booster, that may be part of the problem.  Inner diaphragm is probably as hard as a rock, even though it may still hold vacuum.  If you buy a Bendix, you also need the formed steel plate that goes between it and the firewall.  Most rebuilts do not have it.  I have the boosters and the plates if you need.  Just email me or PM.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

     

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