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1963 Super Hawk with power brakes that won't stop well at all

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  • Brakes: 1963 Super Hawk with power brakes that won't stop well at all

    Now that I have gotten the shop manual, read it, understand the system, followed the directions, I feel qualified to ask for help. This 1963 super hawk with power brakes, front discs, rear drums (not self adjusters) has not been used for at least 3 years. The brakes were very soft even 3 years ago.
    We have replaced the master cylinder, replaced both rear wheel cylinders and shoes (turned the drums), have not done anything to the front calipers except inspect them to see the pads are a little skinny, and we have determined that they do clamp down on the rotor when applying the brakes while spinning the front wheels (rust on the rotors showed signs of wearing off), but we are not really shure how well they are working. The power brake unit is the type shown on page 19 of the brake system section of the shop manual (with 2 bleeder valves). We followed the testing procedures on page 28, and determined the following:
    When the brakes are applied during 20 mph stops, they do not pull, but barely stop the car. The pedal will go to the floor the first time down, but pressurize and hold that pressure if you pump the pedal. Still does not stop the car quicly at all (slows gradually to a stop). The test for determining if the power booster is working is to pump the brake with the engine off, then hold the pedal pressure while starting the car. The booster kicked the pedal down further, which should mean the booster is working. The brake pedal will hold, not slowly drop, if you pump it up first.
    We took the new master cylinder off, bench bled it, and found a lot of air in it. I thought we had found the problem. After reinstalling the master cylinder, we bled the booster first as outlined in the manual. I thought we would find air at the booster, since the master was pumping air before we just bench bled and reinstalled it. We did not see air, and bled about 4 oz of fluid without air from each of the bleeders on the booster unit. Then we bled the rear and front brakes, and readjusted the rear shoes. The pedal never got better.
    I am lost for where to go next. I know the front brakes are not 100%, but we can't afford to change them out and still not have the problem solved.

    Has anyone else ever had this problem. I know it sounds like we still have air in the system, but I have no idea where it is coming from.

    Any help is greatly appreciated.

    Steve Ewbank

  • #2
    The rear shoes might need to be matched to the turned drums.
    Allen

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    • #3
      they actually sat in the drums very tightly.

      thanks anyway.

      steve

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      • #4
        The Bendix/Dunlap Calipers have "Stops" that are on top of the Pads that touch the Rotor when the Pads are too far gone. You will have to replace the Pads, before you drive the Car and ruin the Rotors.

        PM me for a New Pad Set.
        StudeRich
        Second Generation Stude Driver,
        Proud '54 Starliner Owner

        Comment


        • #5
          I have noticed on my disc brake Studebakers that even if the front pads show lining but worn pretty far down that their ability to stop the car is very bad. I dont know if there is a minimum thickness for the pads but they wont stop before they reach metal to metal. New pads arent expensive. I would replace them first and replacing all the brake hoses too at this time wouldnt be a bad idea either. If you still have a problem I would remove the front wheel calipers (any shims removed should be put back in the same position too!- very important) and inspect them for operation, perhaps with some low pressure compressed air being careful not to blow them apart- maybe rig up a hand pump. Keep us informed on your progress.
          59 Lark wagon, now V-8, H.D. auto!
          60 Lark convertible V-8 auto
          61 Champ 1/2 ton 4 speed
          62 Champ 3/4 ton 5 speed o/drive
          62 Champ 3/4 ton auto
          62 Daytona convertible V-8 4 speed & 62 Cruiser, auto.
          63 G.T. Hawk R-2,4 speed
          63 Avanti (2) R-1 auto
          64 Zip Van
          66 Daytona Sport Sedan(327)V-8 4 speed
          66 Cruiser V-8 auto

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          • #6
            Steve, I sent you a pm.
            Joseph R. Zeiger

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            • #7
              The most important issue first, is why you have to pump the pedal. That usually means air in the line, but you say you bled everything. So..one question, where did you get that master cylinder? NOS, new Chinese, rebuilt? The pedal should be firm with the engine off and only be able to be depressed a little bit before becoming firm, like an inch or two. It used to be rare but in recent years I have received two defective master cylinders from auto supply stores.

              Did you measure the drums before they were turned to make sure they are within limits, and are the rotors in front within thickness limits? Brake repair people will tell you that out of limits old drums and rotors can make the pedal have to be pumped up like that. I am still trying to figure out why that would be, since if everything is adjusted right, I would think the pedal would travel no farther than with all new parts.

              Comment


              • #8
                Steve I agree with the others: you really need to replace the pads. As I said on your previous post, its dangerous to be driving a Hawk without the front brakes working properly. Dan

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                • #9
                  Originally posted by Geoff Fors View Post
                  The most important issue first, is why you have to pump the pedal. That usually means air in the line, but you say you bled everything. So..one question, where did you get that master cylinder? NOS, new Chinese, rebuilt? The pedal should be firm with the engine off and only be able to be depressed a little bit before becoming firm, like an inch or two. It used to be rare but in recent years I have received two defective master cylinders from auto supply stores.

                  Did you measure the drums before they were turned to make sure they are within limits, and are the rotors in front within thickness limits? Brake repair people will tell you that out of limits old drums and rotors can make the pedal have to be pumped up like that. I am still trying to figure out why that would be, since if everything is adjusted right, I would think the pedal would travel no farther than with all new parts.
                  I agree with your statement that the first thing I have to figure out is why that brake pedal keeps going down. If the master cylinder was defective, would it still hold firmly after pumping?
                  I did spec out the rear drums when we replaced those, but I have not measured the rotors, and the front pads are likely below the .200 spec in the book ( at least 2 of them). They are not anywhere near the .400 original thickness.

                  I agree that before we go driving, we need new pads, but I really want to figure out this pedal first, both going down on the first pump, and holding after pumping.
                  I don't bleed brakes for a living, but it did seem to me that the amount of fluid that came from each pump was less that I would have thought, especially at the rear cylinders. It probably took 4-5 pedal pumps to produce 2 ounces. Does that sound right?

                  Comment


                  • #10
                    My Hawk had a brake hose that looked perfect from the outside but had a bubble in the inside not allowing the fluid to pass by. I pulled the hoses and noticed a dribble coming out one of the hoses when the peddle was depressed. As for bleeding the system - I thought the procedure was to bleed the furthest cylinder to the nearest and the hydrovac last?

                    Allen
                    1964 GT Hawk
                    PSMCDR 2014
                    Best time: 14.473 sec. 96.57 MPH quarter mile
                    PSMCDR 2013
                    Best time: 14.654 sec. 94.53 MPH quarter

                    Victoria, Canada

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                    • #11
                      bleed thoroughly

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                      • #12
                        Not according to page 28 of the shop manual, and I think it correct since the master cylinder pumps to the hydrovac in a single line, then out to the wheel cylinders. It makes sense to me that the stream of brake fluid must be solid (airless) through the hydrovac before you can get the wheel cylinder lines clear. This hydrovac is designed almost like a second master cylinder with boost assist.

                        Comment


                        • #13
                          bleeding the system backwards

                          Some friends say I need to bleed this system backwards. That is how folks bleed motorcycle brakes today, and it makes sense that generally speaking, if you are forcing air from the low spot (wheel cylinders) to the high spot (master reservoir) it is always going to be easier than forcing air downward (when air will always want to rise to the top).

                          This Hawk has a master cylinder that is under the front floor pan, so the uphill argument seems to fail on this particular car. However, I can see the argument to backwards bleed from the wheel cylinders to the power booster unit (which is up high). That would give me confidence that the air could not be between the wheel cylinders and the booster unit.

                          There has got to be a lot of air in this system somewhere, but I bled it conventionally as best I could figure out how.

                          Has anyone bled their brakes backwards with any luck?

                          Steve

                          Comment


                          • #14
                            I have one question which, may, or may not help, but, here goes. When you pump up the brakes and finally get a solid pedal, does it remain solid if you apply the brakes quickly, but will need pumping if you apply them some time later? My thinking is that you may have a problem with residual line pressure. I think you need 2psi for disc breaks and 10psi for drum. I may be wrong on the psi but, there is a difference, and if the line pressure bleeds back down to zero, you have to pump the brakes a couple times to get a solid pedal again.

                            Scott

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                            • #15
                              To answer your question, I believe the brake pedal would go back down to the floor whether you slammed them on, or gradually depressed them. This of course after letting the pedal back up to the top (ie, not immediately after pumping them up).

                              Having said that, do you believe the brake lines still have pressure in them when the brake pedal is not depressed? I am not sure where you are going with your comment that I may have a problem with residual line pressure.

                              thanks for replying

                              steve

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