Front Master Cylinder...

azuqui · Full Member Joined: Mar 30, 2008 Posts: 88

Hey guys, I just rebuilt my front master cylinder. But before installing, I put some fluid in it, and pumped it, nothing comes out, I do see tiny tiny bubbles, in the resevoir, but nothing. I did it by the book. The only thing I can think of is that banjo bolt has to be on, and somehow squeezes the spring inside?????? I don't know....... Is it true. Do you have to have it air tight for it to work???? any input is appreciated Thanks,, Carlos

Tomterrific · Posted: September 9, 2008, 8:10 am Post subject: Re: Front Master Cylinder...

Put your finger tip over the outlet hole and try pumping again. You must understand that the MC isn't a pump to flow fluid it is to build pressure. The only reason the MC needs extra fluid is to take up brake pad wear. It is very difficult to get a strong flow of fluid through a brake system to remove all the air.

Since the MC and caliper are so close you can do the - open the bleeder and pump the MC then close the bleeder- operation by yourself. Best to use a MityVac or some sort of vacuum or pressure device so the initial frustration of getting fluid to start is lessened.

Tip: Before you start use a thin wrap of Teflon tape on the bleeder threads as this stops air from leaking through the threads during bleeding.

Tom Graham

azuqui · Full Member Joined: Mar 30, 2008 Posts: 88

Tom, so in other words, when I put my finger on the opening, and try pumping fluid, I should feel pressure, rather than liquid?

Jake68 · 650Rider Supporter Joined: Mar 23, 2007 Posts: 841

Hey, just thought I could help here...

Ideally, try getting a vacuum brake bleeding setup..but...failing that do this...

Get some latex mechanics gloves, they'll protect your hands from the fluid which is nasty stuff, but more importantly, if like me, you arent that worried, they make a perfect seal when doing stuff like this.

The master cylinder is a pump, and like any pump, like an oil pump it will need to be primed up. Especially as you are pumping liquid with a high viscosity. In this situation the bubbles you see are the pump chambers trying to fill I would think...

Do like this ...connect your hose, might as well do the whole lot at once. Right?

Now hold the bango end between two fingers effectively sealing off the end of the hose. Now close the level. You should feel an expansion or pressure between your fingers or a slight puff of air if you remove your fingers.

Now leaving your fingers off, close the lever, hold the lever down and place your fingers over either side of the banjo, release the lever. Doing this draws fluid. Repeat this as fast as you can, after a while however, leave your fingers lightly over the banjo as you close the lever allowing the fluid to pump down the master cylinder and hose. Dont worry you wont be able to hold it back when the fluid comes into play.

So long as your re-assembly is good, this method will never fail. Make sure you dont get fluid on paint and you wash it off your skin. Its 'orrible stuff Smile

Retiredgentleman · Posted: September 9, 2008, 1:21 pm Post subject: Re: Front Master Cylinder...

Since the master cylinder does not move any volume of fluid, it really helps to prefill the brake line before bleeding. I have used a syringe ( like the type used to refill ink jet cartridges) to inject brake fluid into the line and then takes very little time to build up pressure.

What Happened to 650rider.com?

Yamaha xs650