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    Brake Hyd. cylinder too weak??
    #1
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    I'm really new at all things buggy/automotive. But I recently replaced the master cylinder on my buggy. The old one was a 1980s 3 wheeler rear master cylinder. It was totally seized/corroded. I replaced it with this - Hydraulic Master Cylinder : Go Karts Parts: Racing Kart Parts: Engines: Frames: Tires: Versailles, Ohio: USA: Indoor Track: Tips: Chassis: Kits: GoKart: Briggs: Yerf Dog: Manco: Comet: Torque

    After bleeding etc. the new cylinder wouldn't even budge the piston on the caliper!! SO I took apart the caliper(from a 1983 Honda 250r), cleaned it up, added new seals and tried again. Still nothing.

    Is it possible that the new(and cheap) master cylinder simple doesn't have enough pressure? Could someone recommend a "good" budget one?
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    Re: Brake Hyd. cylinder too weak??
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    Keeper of the Asylum K-fab's Avatar
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    Hard to say. Do you know what the bore size is? If it's 10mm or larger, it should work.

    Are you sure you got it bled fully?
    Take the master cylinder (m/c) off and the caliper off and let the caliper hang below the m/c.

    Pump the m/c a few times - releasing it very slowly. This might help the bubbles rise to the top.

    If the piston isn't bottomed out in the caliper body, push it back into the body as far as it will go - all while keeping the caliper down low - and if you can make the banjo bolt where the line attaches the highest point, this will help. Doing this will displace the majority of the fluid back to the m/c, along with any bubbles that my be present.

    Pump the m/c again, slowly (it is full of fluid, right?) and see if you get any piston movement. If you do, pump it until pads are touching and then push the piston back in again. Do this a couple of times and it usually displaces any air that may be caught.

    Not knocking on anything, and I know you're working on keeping things as inexpensive as possible, but the stuff that YerfDog and the likes did was pretty shoddy equipment, so there's a chance it's just junk. If it sat on a shelf for an extended period, there's a chance the seals in the m/c are dry and not doing their job well.

    Two things to NEVER skimp on or try to save money on are safety equipment and braking components. One trip to the ER will often more than pay for the best safety equip available, so keep that in perspective. Always wear a helmet, always use your seat belts. Always. There are more than one of us on this board that can tell you about being hurt just doing a little "test" or giving someone a ride in the yard (that one was PAINFUL and expensive).

    Hop onto Flea-Bay and search for something along the lines of a Honda CRF (insert size - they all use the same pieces) master cylinder (Nissin is some of the best) and maybe even the caliper if you're willing to adapt something new to your ride.

    As old as the parts your working with are, you'll probably be best off and just replacing the stuff with newer parts.
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    Re: Brake Hyd. cylinder too weak??
    #3
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    I don't know the bore size, I had a friend help me bleed them, we used a piece of fuel line attatched to the bleeder valve and a clean bottle with brake fluid in it . Since its the first time I have ever done it I can't be SURE its bled, but the bubbles came and went like my friend said they would before closing the bleeder with pressure on the cylinder. We added fluid like 3 times to the res during this.

    I know the master cylinder works at least a little but since you mentioned age I did notice the rubber started to crack within days of just being installed.. Probably old as well as weak.

    I don't think the caliper is at fault, the piston popped right out under pressure from a grease gun. ( I did clean it very well after) The seals didn't even really NEED changing and the metal was rust/corrosion free. The caliper and MC were from different atcs, hence the difference.

    I'll use your advice and get a new(er)bigger than 10mm unit.
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    Re: Brake Hyd. cylinder too weak??
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    Millenium Member Xbird's Avatar
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    the yerfs and nearly all motorcycle and atv masters are 1/2 in. bore diameter. I will guarantee you that you have air in the master. they are a royal pita to bleed. i tried a single 1/2 master to dual calipers and it wasn't effective enough, so i went with a 5/8ths master. through the process i put days of research into these and got my hands on a variety of different bike/atv masters--pretty much all the same.
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    Re: Brake Hyd. cylinder too weak??
    #5
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    5/8 would be like 16mm? I sure don't want to get another MC only to have the same problem. Sounds like something newer/better built with a larger bore..Thanks for sharing your experience X , it'll probably save me some headaches.
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    Re: Brake Hyd. cylinder too weak??
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    Millenium Member Xbird's Avatar
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    if you search under "golf cart 5/8ths master cylinder" you should find it. it's part of a kit made for golf cart modders setting up dual disc brakes. available separately, about $40. uses a different thread pitch than the yerf/chinese buggies, so you'll need the correct banjo bolt for it. However, it's the same design, just larger. all of the small master systems are a pain to bleed. if yours has a torn or dried out seal inside, that would be a definite problem. probably all of $5.00 for a rebuild kit. if you're only running a single caliper, the 1/2 inch should be plenty.
    Last edited by Xbird; 01-09-2014 at 04:02 PM.
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    Re: Brake Hyd. cylinder too weak??
    #7
    Keeper of the Asylum K-fab's Avatar
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    Larger bore is not necessarily the way to go.

    A larger bore will give you a stiffer pedal and less travel and require more pressure to get your desired brake feel.
    A smaller bore will give you a softer pedal, more travel (better modulation) and require less pressure to get your brake feel.

    It's hydraulic leverage ratios that causes this.

    If you like what you had, stick with the same size or similar to what you already have.
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    Re: Brake Hyd. cylinder too weak??
    #8
    Millenium Member Lug-Nuts's Avatar
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    bleeding your brakes can be made easier.

    I use a big 'ol horse syringe and a flexible clear hose attached (glued) to the end of it. You dont want the hose to come off or leak.

    The hose should fit over your banjo bolt dont go too big. The hose doesnt need to be really tight either.

    Then fill up the syringe with new braked fluid, and get all the air out. Hold up the hose and squeeze till all the air is gone.

    make sure your master cylinder is open, and have a buddy watch it.

    Connect the hose to your banjo bolt, open the bolt.

    Now gently push the brake fluid till your buddy say's the master is full.

    If you are about to run out of fluid close the banjo while applying just a little pressure to the syringe to ensure no air gets in.

    Repeat this until no bubble's come out the master side. Also dont spill or over fill the master this stuff eats paint and is messy.

    I suck out the extra with my other syringe from the master till I'm finished.

    This is a easy way to bleed those stupid brakes. Its also a lot less expensive than MIGHTY-VAC.
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    Re: Brake Hyd. cylinder too weak??
    #9
    Millenium Member Lug-Nuts's Avatar
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    You might want to break down the brake caliper and make sure its in good shape. They come apart really easy and if you have worn, or cracked or O-rings get a rebuild kit (cheap)

    If all the seals look good put it back together. I have found rust in some brake calipers before and the fluid was NASTY.

    Clean everything with some solvent and tooth brush. Brake cleaner works good too!
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    Re: Brake Hyd. cylinder too weak??
    #10
    Millenium Member Xbird's Avatar
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    Quote Originally Posted by Lug-Nuts View Post
    bleeding your brakes can be made easier.

    I use a big 'ol horse syringe and a flexible clear hose attached (glued) to the end of it. You dont want the hose to come off or leak.

    The hose should fit over your banjo bolt dont go too big. The hose doesnt need to be really tight either.

    Then fill up the syringe with new braked fluid, and get all the air out. Hold up the hose and squeeze till all the air is gone.

    make sure your master cylinder is open, and have a buddy watch it.

    Connect the hose to your banjo bolt, open the bolt.

    Now gently push the brake fluid till your buddy say's the master is full.

    If you are about to run out of fluid close the banjo while applying just a little pressure to the syringe to ensure no air gets in.

    Repeat this until no bubble's come out the master side. Also dont spill or over fill the master this stuff eats paint and is messy.

    I suck out the extra with my other syringe from the master till I'm finished.

    This is a easy way to bleed those stupid brakes. Its also a lot less expensive than MIGHTY-VAC.
    I tried mity vac and went to the livestock syringe method. I do believe lug is referring to the bleeder screw and not the banjo bolt though (the banjo bolt is the hollow and cross drilled bolt that goes through the line end fittings, holding it to the caliper and master.) I also use a variation of the above technique and attach a very long line to the caliper's bleeder, run it about 6 feet in the air into a bottle and use the syringe to force the fluid from the reservoir down through the system until i have fluid all the way up the hose to the hanging bottle. When you remove the syringe from the reservoir inlet, the fluid in the lines above at the other end gravity bleeds it in reverse. Makes the system gets bled in both directions and helps get out air trapped in turns/bends and under the master seal.
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