front brake reservoir hose

My front brake reservoir hose (the one between the reservoir and the master cylinder) has a hole in it.

If I replace this hose do I have to replace the fluid and bleed the whole system at the caliper?

Can i get away with fitting a new hose, refilling the reservoir with fluid and lettting the fluid leak out of the bottom of the hose before pushing it onto the master cylinder and refitting the clip? If I did get a wee bit of air in here would the bubble just work it's way back up into the reservoir?

thanks.....

I would think you need to refill & bleed the system.
I take it you have an S with the round resovoir?

[Sid Squid]

As the hose in if effect part of the reservoir - it's prior to the cylinder, not on the pressure side - if you're careful, you can fit a new one without needing to bleed the brakes, as long as the plastic elbow on the m/cyl stays full of fluid.

[Stu]

A related question then. Bleeding brakes consists of getting air out of the calipers from the bleed nipple right? what if there is air in the lines? It would rise up to the master cylinder does it just escape naturally when you use the brake lever?

(same as zip tying the brake lever on overnight)

Yes, its an SVS with a round reservoir.

The master cylinder and brake lever are unbolted from the bars and hanging from the bike by the brake line, the reservoir is off the bike completely, so I doubt there is still fluid in the unpressured side of the master cylinder, it will have poured out with gravity.

If this were water it wouldn't matter because as you filled the bottle and the fluid went down into the cylinder, the air would come up, but if I refill from empty now I'm worried the viscosity of the brake fluid would just trap the air and leave a bubble. If I poured fluid into the master cylinder first after I've remounted on the bars before fitting new hose and and reservoir, would I get away with it?

[DarrenSV650S]

Why did you take off the master cylinder?

Originally Posted by Stu

A related question then. Bleeding brakes consists of getting air out of the calipers from the bleed nipple right? what if there is air in the lines? It would rise up to the master cylinder does it just escape naturally when you use the brake lever?

(same as zip tying the brake lever on overnight)

No it wouldn't because it's a sealed and pressurised system, the master cylinder is effectively a one way valve, fluid can go down through cylinder from the reservoir into the brake lines, but nothing can come back up, so the air bubble would definately stay where it was. Bubbles in a brake line can only go down, hence bleeding from the caliper.

I'm not sure even above the cylinder that air will rise and escape due to the viscosity of the fluid. Even with something as fluid as water you get small bubbles trapped in small spaces due to the viscosity and surface tension of the fluid being stonger than the bubbles bouyancy.

[DarrenSV650S]

I was bleeding a m/c off a naked sv today. I was just swapping the old m/c for the sv one so the system already had fluid in it.
I connected the hose and filled the reservoir. Then I found that if I moved the lever very slightly air bubbles would come up. I kept doing that until there was no more bubbles coming up. There was a little bite to the lever but not enough so I bled the system.
So the master cylinder must allow some air to pass back up

Originally Posted by DarrenSV650S

Why did you take off the master cylinder?

Alomst everything forward of the bars is being replaced. Had an accident recently and I'm just rebuilding the bike. The forks had twisted in the yokes so I needed to get my socket set & torque wrench into the pinch bolt on the top yoke.

Since the seal between master cylinder and reservoir was already broken, I decided just to remove the whole assembly and get it out of the way to give myself space to work. In hindsight given Sid's comment about the fluid in the master cylinder perhaps I should have just left it in place and rotated it round the bar a bit.

Originally Posted by DarrenSV650S

I was bleeding a m/c off a naked sv today. I was just swapping the old m/c for the sv one so the system already had fluid in it.
I connected the hose and filled the reservoir. Then I found that if I moved the lever very slightly air bubbles would come up. I kept doing that until there was no more bubbles coming up. There was a little bite to the lever but not enough so I bled the system.
So the master cylinder must allow some air to pass back up

Was that just air from the unpressurised side of the cylinder though? I don't really know for sure, but maybe a brakes expert will be along soon.

Even though my cylinder is not bolted to the bars, my system is intact from the cylinder to the caliper, so the brakes work fine. If bubbles will rise from the unpressurised side of the system into the reservoir as you describe then that may answer my question and I don't need to bleed my brake lines.