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Manual brake mod explained (with pics)

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  • Manual brake mod explained (with pics)

    This is the brake pedal side of the booster after it's removed from the vehicle. You'll see, around the edges, that there are "dents" which hold the two halves in place. If you look closely, there will be an arrow and the word "loosen". This is there in case you want to rebuild the assembly without forcing it apart. Our intention is not that, however.


    Here the halves are split. I DIDN'T USE THE BIGGER HAMMER AND SCREWDRIVER LIKE A CHISEL, AND YOU SHOULDN'T EITHER. IT'S DANGEROUS! The smaller hammer is my Festiva hammer. No joke. Anyway, flatten out the dents that hold the two halves together however you like, then gently pry the halves apart. Careful, don't be surprised when the big spring forces them apart as soon as the rubber breaks it's seal on the metal.





    Locate this clip and push it out with your non-chisel screwdriver. It's just got a spring clip holding it in, you can almost push it out with your fingers.



    Once you've pulled that clip back, stick your non-chisel screwdriver into the brake pedal pin hole and pull. That's the part you need for the manual brake mod. Remove the push-in retaining ring, the two foams and the felt. When you get those off, flip it over and notice the swiveling part at the bottom. You'll see that it's been swaged onto the ball end. Drill out the swage marks, being careful not to drill into the ball end or shaft. Nicks are OK. Once that swivel end is off, remove the remaining springs and rubber seal.

    The rest of the disassembly pics:



    Pictured here is the piece you need to be working on. Also, note the swage on the right side of the rod. It's a little dent in the swivel end. There are 3 total.



    Exploded view. This is about as far apart as you can get it without damaging anything thus far.



    When all's said and done, this is what you should be left with. This piece will attach to the brake pedal and slide into the back of the master cylinder to actuate the piston. You may need to smooth the shaft down (remove the ring) with a grinder, I haven't test fitted it to a loose M/C yet.



    You'll still need to make an adapter plate with the pattern for the firewall as well as the M/C pattern, which I'll measure and update this thread. The thickness of the adapter plate is yet to be determined, I'll handle that part when I get around to actually swapping my booster for the plate, because I'll have time to measure it up then for the thickness I need.

  • #2
    The "left over" pieces of the brake booster equal (by feel) about 10 lbs. Not too shabby of a weight reduction for a 1700lb car. You'll add some back with the adapter plate and studs.

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    • #3
      And the explanation is....to take <10lbs off the weight of the car?
      '88 Festiva L, stock carby engine (with exhaust upgrade), 4 speed tranny. Aspire Struts and Springs, Capri 14" wheels, interior gutted, battery in back

      '92 Geo Metro XFi

      '87 Suzuki Samurai

      '85 F150, modded 300cid

      Comment


      • #4
        Aside from the ~9 pound weight reduction (I added one pound for the new adaptor plate and stuff), this gives you "manual" brakes which may or may not be a tactile improvement for your foot's braking pleasure. You are removing the "power" stuff and replacing it with a more direct foot to MC connection. This should be different from the experience of driving a Festiva with a bad power booster, where you would be operating all the broken parts along with the necessary parts.

        Also, I think that you are removing some of the engine vacuum draw which may smooth out your idle in some situations. Not sure.

        Plus, that nine pound reduction comes from a fairly high up area of the car, near the top of the engine bay, not just from the floor area. And you have removed one more part that could (and eventually does) go bad. (My '93GL's brake booster is bad, so I know how that feels.) New Festiva brake boosters run from $80 to $170 at Rockauto. Repeat after me, all you cheapskates: "Ka-ching!"

        To be fair, this is an option which we won't truly know is "worth it" until it's done and can be experienced first hand. Until then, it's mainly theoretical. I've been wanting to see about this mod for a long time now.

        My thanks to Christ for "doing the work."

        Karl
        Last edited by Safety Guy; 05-17-2012, 09:27 AM.
        '93GL "Prettystiva" ticking B3 and 5 speed, backup DD; full swaps in spring!
        '91L "AquaMutt" my '91L; B6 swap/5 speed & Aspire brakes, DD/work car
        '92L "Twinstiva" 5sp, salvage titled, waiting for repairs...
        '93GL "Luxstiva," '94 B6 engine & ATX; needs overhauled
        '89L "Muttstiva," now a storage bin, future trailer project

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        • #5
          I plan to add power windows and a/c, and also plan to lose my power brakes. A non carnut would think that is stupid
          1993 GL 5 speed

          It's a MazdaFordnKia thing, and you will understand!

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          • #6
            The last part Christ shows above is the diaphragm actuator rod. Does it mate directly to the M/C push rod?

            Another way to ask this question, "Is the input stroke the same length (or distance) as the output stroke"?

            Why not just remove the clip/bracket that goes on the brake pedal arm, and then substitute a metric bolt of the length you need? You'd just have to form the bolt head into a half ball, wouldn't you?

            I may have to do this mod.
            '88 Festiva L, stock carby engine (with exhaust upgrade), 4 speed tranny. Aspire Struts and Springs, Capri 14" wheels, interior gutted, battery in back

            '92 Geo Metro XFi

            '87 Suzuki Samurai

            '85 F150, modded 300cid

            Comment


            • #7
              Big - Yep, that would also work.

              The part that fits the pedal fits directly into the rear of the mc. You may need to grind that ridge off. If someone gets to this before me, the way to determine spacer/adapter thickness is to measure the overall thickness of the booster with both rods included, then subtract the length of the actuator eod you save, as far out as it sticks from the mc.

              The other way is to put the rod into the mc, hold it temporarily against the firewall, and figure out where the pedal needs to be on the rod. Everything past three center of the mounting hole in the pedal is spacer thickness.

              You can cut the rod down and ball the end again if you want to mount the mc to the firewall. I wouldn't recommend it, because the force spread isn't very far. Use at least a reinforcement plate. The firewall is VERY flexible as is.

              You can also make a custom rod, to the oal of the booster, and gut the booster if you want things to look stock still.
              Last edited by Christ; 05-17-2012, 09:48 PM.

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              • #8
                Originally posted by Christ View Post
                The part that fits the pedal fits directly into the rear of the mc.
                But it's two seperate rods, one pushing on the other, in the stock booster, Right? That's what I see in your pics, but maybe, I'm wrong.


                It's called Ockham's razor...cut away anything unnecessary...I'm on board.

                I would probably use a 1" thick aluminum block to adapt from the 4 holes in the firewall to the two studs on the M/C. I won't be getting to this anytime soon, however.
                '88 Festiva L, stock carby engine (with exhaust upgrade), 4 speed tranny. Aspire Struts and Springs, Capri 14" wheels, interior gutted, battery in back

                '92 Geo Metro XFi

                '87 Suzuki Samurai

                '85 F150, modded 300cid

                Comment


                • #9
                  Yes, two rods, connected by a diaphragm.

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                  • #10
                    I'm waiting to get my suspension swapped and squared away before doing this to my car, but I will be doing it.

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