Front brake bleeding
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Has anyone had a problem with filling and bleeding the front brake when the system was completely empty to start with? I can’t get any fluid to pump through although the piston seals look flexible and I’ve blown through the holes. Am I missing something or is the master cylinder buggered!
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I had this exact problem when I changed over a new master cylinder after an accident ruined the original.
If there hasn’t been any fluid in the system for a while you will probably find the chevron seals in the master cylinder have gone hard.
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The new front brake master cylinder piston arrive very quickly (interestingly, from Madrid!), but I still can’t get fluid to flow down to caliper. Looking at a flow diagram of master cylinders, one says there should be a check valve at the output end of the cylinder, but there is nothing in mine. Is this right? Can anyone shed light on my problem?
It looks like I’ll have to buy complete front brake system if no-one can offer a solution.
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Another trick, get your CALIPER pistons out, ultrasonic clean the body and carefully refit the pistons back in with their seals (caution that you may need new seals again) (Common Hyosung item to resolve when servicing brakes or if pistons have gone bad , which allows air to get in to system sometimes.)
Before you fit the pistons in fully, put them about 10% inside the caliper.
Now fill brake fluid in the master cylinder (check washers are good for the hoses or may hiss or leak air, or fluid out)
Once the master cylinder is filled in.
Put brake pads inside the caliper.
Now press the pads so that they compress the caliper pistons down fully inside the caliper
The master cylinder should be hissing and bubbling up at the top, suggesting most air is leaving the brake system
Then as usual, try to pump your brakes and bleed a little then pump your brakes , if it fails , it could actually be the piston itself not being suitable or strong enough.  it could then mean time for a master cylinder replacement
Keep us posted!
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Tried that and got bubbles out top, but decided to look closely at caliper. One piston very difficult to get out and badly pitted, so I’ve decided to get new master, caliper and pipe-line! Looking on ebay it’s nearly as expensive to get repair kit as to buy new complete caliper from Hyosung.eu. One thing though, the master doesn’t show the stop light switch. Is this transferable from mine, or will it come with it?
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Tried that and got bubbles out top, but decided to look closely at caliper. One piston very difficult to get out and badly pitted, so I’ve decided to get new master, caliper and pipe-line! Looking on ebay it’s nearly as expensive to get repair kit as to buy new complete caliper from Hyosung.eu. One thing though, the master doesn’t show the stop light switch. Is this transferable from mine, or will it come with it?
i hope you get the correct parts , otherwise i can always help you as usual. I even sell stainless pistons.   You can keep your old caliper. No need to replace it,  its downfall is always the cheap axle pins and pistons, hence we do stainlesss so you won’t worry about that again.
Master cylinder , the GV uses a different switch that’s like a cylinder which goes in the GV master cylinder.  Others will be a switch box under the lever with 2 spade terminals. So it may mean cutting up your GV brake switch wires.
Don’t cut the main bike harness (very difficult to get one) .
You can get
2x spade connectors (to connect the aftermarket brake switch box if using Non Hyo master cylinder)
2x speaker wires
1x harness jacket or a long shrinkwap to encapsulate the 2 wires like what hyosung does with their 2 wire cables.
1x tape (waterproof up those wires!)
2x “bullet” connectors (to join main bike harness)  (if i remember correctly! as i am a little drunk as its weekend!)
I would have done this while i was getting you a master cylinder so you can just fit and play.
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