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Hydrovac- What causes them to fail?

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  • Brakes: Hydrovac- What causes them to fail?

    Trying to decide which way to go, my "F" type booster is weak and has been for many years but brakes have always worked fine regardless. I have a spare on the shelf and I also have an upgrade rebuild kit, so I am thinking about rebuilding the spare. I know you can get new offshore made boosters, but I'm curious about what actually fails in the "F" boosters and if anyone here has successfully rebuilt theirs. What part(s) commonly fail and is it a maintenace issue or just crappy design? Also, any good tricks to bench testing a Hydrovac?

  • #2
    Is the "F" Type the single Diaphragm type for Drum Brakes, or the DUAL for Disc.?

    I guess it should not matter as they are both the same basic design by Bendix Hydrovac, but I thought it was almost always the Leather Diaphragm that is just TOO OLD.
    And they were/are? very hard to get, so many "Rebuilders" do not change them, unless they are completely Toast.
    Last edited by StudeRich; 10-25-2017, 05:38 PM.
    StudeRich
    Second Generation Stude Driver,
    Proud '54 Starliner Owner
    SDC Member Since 1967

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    • #3
      I have had success by spraying in copious amounts of WD40 into the mesh (filter) end of the booster. I suppose it softens up and lubricates the leather diaphragm mentioned above.
      Bill.

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      • #4
        I recently had one fail, but could still 'hear it' trying to work. Air was coming out of the mesh/screen. Removing the spring clips that hold the filter/mesh on the front of it revealed that the spring inside failed. I used a spring from a wheel cylinder, cut it to fit and it repaired it for now......

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        • #5
          Thanks, I think I'll give those ideas a try, maybe I won't have to spend a big sack of money getting it to work better....

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          • #6
            My experience with Hydrovac reliability involves two things: Rebuild with new non-leather diaphram which does not need neets foot oil, Replace check valve when replacing Hydrovac. This way no oil gets into the manifold and the unit is much more durable.
            Randy Bohannon
            52 commander starlight
            63 R2 gt super hawk
            64 daytona convert

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            • #7
              Most every failed hydrovac I have seen fail is because the the actuating part gets corroded. The rubber diaphragm behind the top filter is actuated by a small hydraulic cup just like a wheel cylinder. The bore gets corroded, and leaks onto the diaphragm, and then the diaphragm rubber fails. The shaft that connects the main leather faced piston to the slave cylinder passes through a leather faced seal. They also fail, and corrode the shaft and the seal gets further chewed up. The slave cylinder gets rusty just like a wheel cylinder. The vacuum check valve gets hard, and no longer seats, and it's spring can get rusty, and weak further causing it not to function. All of the problems are due to not flushing out the dot 3 brake fluid every year, and not servicing the leather every year like in the shop manuals. There is NOTHING inherently wrong with the design.
              Bez Auto Alchemy
              573-318-8948
              http://bezautoalchemy.com


              "Don't believe every internet quote" Abe Lincoln

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              • #8
                Originally posted by bezhawk View Post
                Most every failed hydrovac I have seen fail is because the the actuating part gets corroded. The rubber diaphragm behind the top filter is actuated by a small hydraulic cup just like a wheel cylinder. The bore gets corroded, and leaks onto the diaphragm, and then the diaphragm rubber fails. The shaft that connects the main leather faced piston to the slave cylinder passes through a leather faced seal. They also fail, and corrode the shaft and the seal gets further chewed up. The slave cylinder gets rusty just like a wheel cylinder. The vacuum check valve gets hard, and no longer seats, and it's spring can get rusty, and weak further causing it not to function. All of the problems are due to not flushing out the dot 3 brake fluid every year, and not servicing the leather every year like in the shop manuals. There is NOTHING inherently wrong with the design.

                Thanks for pointing me in the right direction. I pulled the control valve apart and, as you mentioned, it was corroded and stuck. Diaphragm was still soft and pliable so I cleaned up the pistons and cups, honed the bore with some #1200 and reassembled everything with some Apezion high vac grease (left over from my days working on helium mass spectrometers) and VOILA! I now have great power brakes! I don't think the booster has ever worked since I've owned the car. I had been feeding the vac servo neetsfoot oil periodically, even though I really didn't have power brakes so it seemed to work OK once it got used to functioning again. Gave it another dose of neetsfoot oil and lost the stupid rubber bung plug trying to put it back in. Lucily, I have a big box of rubber grommets & plugs, etc and found a better replacement.

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                • #9
                  On the 1963/64 Hawks were two different Hydrovacs.
                  One for disk brakes an one for drum brakes.
                  The disk brake Hydrovac was unique and was not used anywhere else.
                  They had flaw and a modification kit Studebaker part number 1565515 was offered.
                  This kit replaced most of the original insides.

                  Robert Kapteyn

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                  • #10
                    Originally posted by rkapteyn View Post
                    On the 1963/64 Hawks were two different Hydrovacs.
                    One for disk brakes an one for drum brakes.
                    The disk brake Hydrovac was unique and was not used anywhere else.
                    They had flaw and a modification kit Studebaker part number 1565515 was offered.
                    This kit replaced most of the original insides

                    Robert Kapteyn

                    I have a mod kit for the "F" (disc) type Hydrovac, but it's missing a few pieces and the hard chrome finish on the pushrod has a spot where the chrome is damaged. Any idea if any of these kits or any parts are still available?

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                    • #11
                      anyone have the service manual from Lockheed for the HydroVac? My big truck has one....2R17A.....got a few twenties in paypal waiting....

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