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  • Spongy Brakes

    Howdy,

    I got an issue. I push the pedal down and i get pretty weak brakes. But, on the second push, i have great brakes.

    I've totally rebuilt entire system, all rubber seals,etc. I did convert to synthetic brake fluid.

    I was wondering if I should go back to DOT 3...

    Anyways, I did a rebuild on the engine and just about every system on the car. I was wondering if "vacuum" from for the booster may be at issue... Do the unsealed ports on the sides of the two ZS carbs need to be plugged in order to affect proper vacuum?

    I am about to change out the master cylinder and booster with a spare that I have just to see what's what. if no good I am stumped.

  • #2
    Originally posted by Rajun Cajun View Post
    But, on the second push, i have great brakes.

    I'm not absolutely sure this is the problem, but to me this says "air in the fluid/lines".

    Walt
    CC80954U '72 TR6 original condition/sold 16.500.
    poolboy rebuilt the Z-S Carbs. Philstr6 rebuilt both rear hubs.

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    • #3
      Originally posted by SapphireBlue72 View Post


      I'm not absolutely sure this is the problem, but to me this says "air in the fluid/lines".
      +1...Might check other threads on this subject. My understanding is that DOT 5 readily retains air that is slow to dissipate.

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      • #4
        When i converted to silicone, i bench bled the master first, then had to bleed the entire system several times over a couple of days until i was happy with a firm pedal. As previously stated, silicone holds air bubbles more readily.

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        • #5
          When I redid my brakes with stainless flex lines, I bled about 5 times over a week to get the pedal feel I wanted. All good now.

          SR
          73 TR6. HT/AC/OD
          86 930
          91 535i

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          • #6
            When you step on it the 2nd time, does it grab really well but slowly continue to depress? If so, could be master. Otherwise, yeah keep bleeding.
            So much rust, so little time

            64 TR4 Overdrive Surrey
            67 GT6 Mk1
            68 TR250 Soon to have Overdrive & Surrey
            71 TR6 Hardtop Soon to have OD
            81 TR8 Injected Automatic...the LAST Automatic

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            • #7
              Try this: hold a towel under the MC and crack the lines coming out of it. Have an assistant push down and hold while you tighten the lines. Do this a couple of times. Basically you are bench bleeding while in place. If that does not work, I would suspect the booster. We had a car where everything was replaced from front to back and we could not get a good pedal. Turned out to be the booster. BTW, you can replace the booster without taking the MC out. Just remove the bolt holding the PDWA valve to the body and it will allow you to slide everything forward without disturbing the system. You need the PDWA tool that my buddy Cliff was making, but he has the Covid and is not making any right now. Good luck, Mike

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              • #8
                Does this happen repeatedly, say over the course of a drive? That is to say, first push is spongy, and 2nd is firm.

                Or just the first time you get in the car for the day?
                Keith, Huntsville AL, 1971 CC66559U
                10.0:1 CR gasflowed head | Weber DCOEs | CP "150hp" Cam | Distibutor by Advanced | Lightened flywheel | Phoenix SS Exhaust System | HVDA 5-Speed | Good Parts R200B Diff and CV axles | Good Parts suspension and anti-roll bars | Good Parts Dual Brake Master Cylinder | Konig Rewinds | Boyd 15 gal tank | Miata Seats and Mr Mikes covers | Carl Visser dash | Mohair hood | Gas-strut bonnet and boot lift kits

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                • #9
                  Flush, fill with DOT 3/4 and bleed, bleed, bleed.
                  '74 w/Overdrive
                  Answers to the name Winston
                  Far from perfect but still running, we're a good match.

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