Brand new master cylinder not producing any pressure.

S

scottyfunj

Been Around the Block
I recently bought this master cylinder:
http://www.dimecitycycles.com/vintage-caferacer-cafe-racer-bobber-brat-chopper-custom-motorcycle-brake-parts-aluminum-universal-hydraulic-front-brake-master-cylinder-perch-lever-kit-717-602.htmlv

I hooked it up today, along with a new brake line, and tried filling the line and bleeding it. No matter what I do it isn't producing any kind of pressure. I'm pretty sure it has nothing to do with the line or the caliper, because even when I pull the line off and press my finger over the hole in the master cylinder and squeeze the lever I don't feel any pressure against my finger.

Any ideas?
 
I know when you hook them up after cleaning/replacing parts in a master, the first place I bleed is the banjo that comes right from the master cylinder, not at the bottom (caliper) like you would think. I don't really remember feeling any "pressure" if you plug it with your thumb either. Try bleeding it at that top banjo bolt (a billion times, or so it feels ::)) And see if that helps.
 
I had that problem when I rebuilt my mc and when I rebuilt the caliper. I had to use a vacuum bleeder to get it flowing.
 
scottyfunj said:
There is only a bleed valve at the bottom on the caliper. How do I bleed it from the master cylinder?
Click to expand...

Just loosen the banjo bolt to let air out, just as you would on a bleeder valve.
 
Alright. I just went through this with my build. I bought new lines, MC and rebuilt the calipers and when I bled the brakes I would get ZERO pressure. Got a vacuum bleeder, nothing.

What I ended up doing is this. Take the caliper off with the line still attached. Pump the handle and see if the piston moves. If it does, pump the piston out as far as it will go. Then open up the bleed valve and push the piston back in until it will fit over the brake pads. Then bleed the brakes by squeezing the brake handle a SHIT load of times building pressure, crack the bleeder valve real fast and close it up again. Rinse & Repeat. Within a few times, you should have a fist full of brakes.


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I know that seems really unorthodox but it worked. Try it out.

Also, to clarify, close the bleeder back up once you have the caliper back on the mount. Then bleed the brakes like I mentioned.


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sxecafe, in your post it sounds like you're saying the problem had something to do with the position of the piston in the caliper, is that right? I'll try it and see how it goes. I appreciate all the input - I now have 3 or 4 different things to try.
 
I used the "bench bleed" method that I use on car master cylinders.

I took the caliper end of the brake line and put it in the master cylinder reservoir (careful, don't get brake fluid on any paint), and then pumped the brake lever until bubbles stopped coming out of the end of the line and the relief holes in the bottom of the master cylinder reservoir.

I then pinched the end of the line between my fingers to prevent it from dripping (careful around the paint again) and quickly reattached it to the caliper. From there on out, bleed as normal.

If you've ever had to replace a car master, you probably got a kit of plugs and rubber lines to "bench bleed" it before you hook up the steel brake lines - this is the same idea.
 
Ok when I'm free tonight I'll try all these solutions until I find one that works. Thanks so much for the info.
 
For what it's worth, I highly recommend a vacuum bleeder - I bought one for approx. $25 from a speed shop when I needed to do some brake work on my classic Mini Cooper, and have ended up using it SEVERAL times on bikes as well, mainly because it's so freaking easy to do a one-man bleed on basically any system.

Just hook it up, turn on the compressor, push the handle on the bleeder unit, then wait for fluid to smoothly flow into the catch receptacle. With cars I usually stand by the reservoir with extra fluid, just in case it takes a while for bubbles to work themselves out of the pipes. For bikes, I find this is seldom necessary - just top it off, bleed until no bubbles, then re-top off. Test the brakes with actual operation (the pedal/handle should be firm from the get-go, or within 1-2 pumps tops), then re-re check the level in the reservior just to be absolutely certain). No more pumping - gotta love it.
 
I am searching about how to increase the top speed of my kh 125, do anyone have any idea how to increase my power and efficiency, my bike goes upto 120kph, i want to increase its top speed, please give me an idea
 
Ok I have tried everything except the vacuum bleeder, and have had zero success. Now I'm just trying to decide whether I want to buy a vacuum bleeder or a new master cylinder. Tough choice.
 
Vacuum bleeder! I got one a few months ago and have used it multiple times. Wouldn't be without one now.
An additional tip is to tap the master cylinder as you're blending it will unlock more bubbles.
Are you seeing bubbles in the resovior as you are pumping? If not maybe a master cylinder issue?
 
I'm not seeing any bubbles. I'm thinking it's a master cylinder issue. I've bled lots of brakes before and this is the first time I've had this problem, so I'm assuming there has got to be something wrong with it.
 
Ok then have you tried the "reverse" method? Get a large syringe (turkey baster hahaha) open up bleeder on caliper and PUSH the fluid up into the reservoir! I use a large syringe with some small fuel hose to make it work, but that's the method I use on the Aprilia because for some reason they don't bleed well unless you do it this way. Worth a try eh? :eek:
 
Yeah I tried that. I'm totally stumped, so I'm just going to replace the master cylinder and hope that solves my problem.
 
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