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Prop Valve 4 Whl Disc Brake Avanti/interim update

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  • #16
    Running a 13" rotor with a two piston PBR caliper up front with an 11"
    rotor with single piston caliper rear. Using a Chrysler dual master
    from the early 70's application (Avanti II). No proportioning valve
    seems to be needed at this point. I'm waiting to see what Karl finds
    out with the same setup on the Twin (he will use the 12" rear, but the
    caliper is the same - marginal effect on stopping according to the Ford
    guys).

    Tom

    '63 Avanti, zinc plated drilled & slotted 03 Mustang Cobra 13" front disc/98 GT rear brakes, 03 Cobra 17" wheels, GM alt, 97 Z28 leather seats, soon: TKO 5-spd, Ported heads w/SST full flow valves, 'R3' 276 cam, Edelbrock AFB Carb, GM HEI distributor, 8.8mm plug wires
    '63 Avanti R1, '03 Mustang Cobra 13" front disc/98 GT rear brakes, 03 Cobra 17" wheels, GM alt, 97 Z28 leather seats, TKO 5-spd, Ported heads w/SST full flow valves.
    Check out my disc brake adapters to install 1994-2004 Mustang disc brakes on your Studebaker!!
    http://forum.studebakerdriversclub.c...bracket-update
    I have also written many TECH how to articles, do a search for my Forum name to find them

    Comment


    • #17
      I finally got to the point where the brakes were ready to be bled. Bench bled the Master, carefully set the pushrod depth and began to bleed. All lines are free and clear, hoses are new, rear brakes are adjusted.

      I plumbed the adjustable prop valve in the rear lines and opened it up all the way. No more than 600 lbs of pressure to the rear brakes. Air is out and pedal is up, not as high as I would like but it's hard to tell with the car up in the air how much travel I would need to stop the car under normal circumstances. MP Brakes says I need a minimum of 800lbs.

      I'm going to order a gage to pumb into the mastre to check pressure at the outlets. Just because the stream is strong doesn't mean I have enough pressure to the fronts either.

      I'll post once I have it sorted out any guidance is certainly welcome in the meantime.

      ErnieR

      Ever since the initial dual master installation, even before the Turner front brakes, I didn't feel the back brakes were doing anything. When bleeding the drum brakes the fluid just didn't stream out like I'm accustomed to seeing on non-modified systems. Front brakes will shoot a stream two feet from the caliper and the rears maybe 3 inches.

      Right now I'm starting to think that the factory booster either doesn't build enough pressure for a dual master let alone 4 wheel discs or total piston travel is not sufficient.



      This may be the reason no one seems to have any rear brake lock up issues.



      On its way to a 15.097 Island Dragway Great Meadows NJ Spring 2006.

      Comment


      • #18
        Just remember....
        The bigger the bore on the master cylinder, the less pressure you will develop in the lines (all other things being the same)..
        You said you were running a 1&1/8" bore...
        Most disc/disc setups (ie: Corvette) run a 1" bore on the master cylinder.
        HTIH
        Jeff[8D]
        HTIH (Hope The Info Helps)

        Jeff


        Get your facts first, and then you can distort them as much as you please. Mark Twain



        Note: SDC# 070190 (and earlier...)

        Comment


        • #19
          Hey Jeff, (trying not to hijack the thread) How about a Lark with Turner Discs all around with a 64-66 pb booster. 2 stud master cyl mount. Would that Corvette master cyl fit this booster? Or is there a master just as good that can be off the shelf at my FLAPS? As it is now I have a 70 Chevelle Disc/drum m/c not yet installed..that I guess will not work..Any ideas? Thanks!!

          Making resverations at the poor house parking lot for me and my 62 Lark..

          Comment


          • #20
            I do understand that. More pedal travel with the smaller bore also. I won't know until I take pressure at the front brakes but there is a visual difference between fluid forced out from the front and the back when bleeding. That sympton has existed through a couple of different size dual masters with factory brakes, Turner Front Discs/drum and now disc/disc.

            I'll be able to take pressure readings next week and see for sure.

            ErnieR

            quote:Originally posted by DEEPNHOCK

            Just remember....
            The bigger the bore on the master cylinder, the less pressure you will develop in the lines (all other things being the same)..
            You said you were running a 1&1/8" bore...
            Most disc/disc setups (ie: Corvette) run a 1" bore on the master cylinder.
            HTIH
            Jeff[8D]

            On its way to a 15.097 Island Dragway Great Meadows NJ Spring 2006.

            Comment


            • #21
              You can get that 'Vette master as a rebuilt at your FLAPS.
              I got mine from Discount Auto Parts for about $30
              IIRC, you tell them it is a late 60's, early 70's 'non power' disc brake master cylinder.
              Try this....
              [urlhttp://tinyurl.com/mr7cve[/url]
              HTIH
              Jeff[8D]


              quote:Originally posted by prager

              Hey Jeff, (trying not to hijack the thread) How about a Lark with Turner Discs all around with a 64-66 pb booster. 2 stud master cyl mount. Would that Corvette master cyl fit this booster? Or is there a master just as good that can be off the shelf at my FLAPS? As it is now I have a 70 Chevelle Disc/drum m/c not yet installed..that I guess will not work..Any ideas? Thanks!!
              HTIH (Hope The Info Helps)

              Jeff


              Get your facts first, and then you can distort them as much as you please. Mark Twain



              Note: SDC# 070190 (and earlier...)

              Comment


              • #22
                Hey Jeff,Its Rich. RE: Vette master cylinder. We ( Prager and I ) are looking at a second generation Firebird master cylinder with disc-disc brakes,and a 1-1/8ths inch bore. It would appear to bolt onto the 64-66 power brake booster Wes installed on his 62. Whatta ya think??? Thanks for all the tech help too! Helps to review someone else's issues and fixes instead of reinventing the wheel!

                Comment


                • #23
                  DUH!!-And another thing.Is it necessary to install a proportioning valve? Would a single adjustable valve in the rear lines be ok?
                  I am not running any proportioning valve in my 61 with Turner front disc and Stude rear drums. I did install a Wildwood adjustable proportioning valve in the rear supply line,but it is wide open and that works best.I really feel as though it is not needed. I read a drum to disc swap story in Car Craft and the basic idea was a proportioning valve was not necessary except in certain instances in the rear line,which is why I did mine like I did. Opinions?

                  Comment


                  • #24
                    I would stick to the 1" bore master....
                    But....
                    If you are running a power booster, it will/should make up for the increased pedal foot pressure required.
                    I know of a lot of people who only run the Wilwood adjustable on the rear and it works ok. It is used as a tuning aid, and once you get it set where you like your brakes, it most likely will never get touched again.
                    One way to test your setup is to do a max effort panic stop.
                    If you can't lock 'em up (no anti-lock).... Then you probably could go with a smaller diameter master cylinder to raise the brake psi.
                    If, when you do lock 'em up, see if the fronts lock first, or last...
                    The fronts should lock up first.
                    The MP Brakes site has some good tuning info.
                    HTIH
                    Jeff[8D]



                    quote:Originally posted by ChampTrucking

                    DUH!!-And another thing.Is it necessary to install a proportioning valve? Would a single adjustable valve in the rear lines be ok?
                    I am not running any proportioning valve in my 61 with Turner front disc and Stude rear drums. I did install a Wildwood adjustable proportioning valve in the rear supply line,but it is wide open and that works best.I really feel as though it is not needed. I read a drum to disc swap story in Car Craft and the basic idea was a proportioning valve was not necessary except in certain instances in the rear line,which is why I did mine like I did. Opinions?
                    HTIH (Hope The Info Helps)

                    Jeff


                    Get your facts first, and then you can distort them as much as you please. Mark Twain



                    Note: SDC# 070190 (and earlier...)

                    Comment


                    • #25
                      Many thanks Jeff and Champ..Good info..I think my mission is clear now..What were we talking about again???? I think I'll go with the 79 Trans Am disc/disc with power set up..1 1/8 bore..after your idea on the booster making up for it I'll give it a shot..Thanks again!

                      Making resverations at the poor house parking lot for me and my 62 Lark..

                      Comment


                      • #26
                        Years back I purchased a hold off valve from Master Power.

                        Very simple.....when you hit the brake, there is an initial delay line.....in other words, the rear brakes become energized first, then the front disc's come on....works great and eliminated the front nose dive on Avantis when hard braking is employed.

                        Comment


                        • #27
                          The question is...since no one has posted that they needed a proportioning valve are the rear brakes working as they should on any of these dual master conversions?

                          This was my concern from the beginning and the impetus for the disc brake swap. I'm wondering if the simple single to dual master swap is not so simple and results in reduced rear braking power. I'm going to do a pressure test with the commonly used replacement master cylinder just as an FYI.

                          ErnieR

                          quote:Originally posted by ChampTrucking

                          DUH!!-And another thing.Is it necessary to install a proportioning valve? Would a single adjustable valve in the rear lines be ok?
                          I am not running any proportioning valve in my 61 with Turner front disc and Stude rear drums. I did install a Wildwood adjustable proportioning valve in the rear supply line,but it is wide open and that works best.I really feel as though it is not needed. I read a drum to disc swap story in Car Craft and the basic idea was a proportioning valve was not necessary except in certain instances in the rear line,which is why I did mine like I did. Opinions?

                          On its way to a 15.097 Island Dragway Great Meadows NJ Spring 2006.

                          Comment


                          • #28
                            Yes, is the prop valve a requirement bar none? I would just as soon not run one, but as soon as I leave it out i'll need it...Let us know on the test if you can..Thanks!!

                            Making resverations at the poor house parking lot for me and my 62 Lark..

                            Comment


                            • #29
                              I took the valve I bought apart just to see what's inside. If yours is like mine it's a simple deal that has a heavy spring inside pressuring a plunger of sorts. As you scew the knob in it increases pressure on the sping requiring more pressure to overcome the plunger and thus limiting the output pressure.

                              When the valve is screwed all the way out I doubt there is any pressure reduction going on. The spring in mine was loose enough to rattle around and 100 lbs of shop air just blew right through. So a guess on your system right now is that it's operating the same way it would without a valve.

                              I will update as I work through this.

                              quote:Originally posted by prager

                              Yes, is the prop valve a requirement bar none? I would just as soon not run one, but as soon as I leave it out i'll need it...Let us know on the test if you can..Thanks!!

                              Making resverations at the poor house parking lot for me and my 62 Lark..

                              On its way to a 15.097 Island Dragway Great Meadows NJ Spring 2006.

                              Comment


                              • #30
                                Yes, you SHOULD run a proportioning valve.
                                For some enlightened reading, go to....
                                http://tinyurl.com/m7jujg
                                HTIH (Hope The Info Helps)

                                Jeff


                                Get your facts first, and then you can distort them as much as you please. Mark Twain



                                Note: SDC# 070190 (and earlier...)

                                Comment

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