Ok yamaha fj 1200 master cylinder prob. Replaced with new piston kit because rubber boot was leaking fluid out onto lever. Now having real prob bleeding,cant get fluid out from cylinder down line,let alone to bleed nipple.Any tips thanks Pete

did you completely replace the fluid or just add to it?

Did you get a good bleed with fluid coming out at all four wheels? If they bled good, and the pedal still goes to the floor, you need to check the brake master cylinder-it is probably shot with an internal leak. An internal leak will not let fluid pressure build up, so no brakes.

Did you keep the brake fluid reservoir from going dry while bleeding? If it went real low, air might have got back into the lines.

It is not uncommon when bleeding brakes on an older vehicle for the master cylinder to suddenly develop an internal leak and require replacement . Here's why: pushing the pedal all the way to the floor causes the master's piston to push in farther than ever before. The rubber cups then travel over a section of the cylinder not usually touched by the cups-old fluid can develop a crud there and when the piston pushes over it, the cups can get ruined. To avoid this when bleeding brakes, put a short piece of 2X4 wood block under the pedal. Then the pedal will not extend the master's piston beyond it's normal travel. Of course on a new master cylinder, you do not have to do this. A new master cylinder does require bench bleeding before installing, however, to ensure no air pockets develop from there.

The brake hose is clogged. When under pressure from applying breaks, the piston is forced tight to the rotor. When released the fluid will not return through the hose because there is no real pressure. Replace the hose.
murf427

the only reason you would need a new one is if the bore where the piston runs in is badly corroded or damaged,i would personally fit a rebuild kit to it but i would also check the salve cylinder is leaking first as its much more likely to be that.the master cylinder is easy to rebuild it has a pushed in rubber boot so pull that out carefully and then there is a circlip inside it get that out and the rest is self explanatory as it will pop out.

if this is seized then the seals will also have deteriorated, i would suggest replacement or repair . you should be able to get a repair kit for it. you will have to carefully dismantle the unit and maybe warm the housing to release the piston. depends upon your personal mechanical skills. good luck

It operates exactly like an automotive system. DOT 3/4 brake fluid is put into the reservoir on the handle bar left side master cylinder assembly and bled out at the slave cylinder on the round clutch cover on the backside of the motor in front of the rear wheel. Both the master cylinder rebuild kit and the rear slave cylinder kit are available from a Honda if needed. Some times a simple bleeding will fix the problem. If you can not build pressure in the master cylinder , try loosening the banjo bolt and pump the clutch lever until you get fluid pressure causes leaking past the copper washers. Then tighten the banjo bolt on the master cylinder and bleed the slave cylinder. On some Goldwing's the clutch cover can be removed and the clutch plates can be replaced with the engine still in the frame. Unfortunately. the spring towers can easily be broken if you are not extremely careful.

You have a leaky clutch master cylinder, or a leaky brake master cylinder.

The fix to to find out which one is leaking and to replace it. The new fluid will need bleeding out at the slave cylinder, but first pull back the rubber boot on the end of the slave cylinder (assuming it's the clutch). If there is fluid there as well, the the slave cylinder must also be replaced. if it's the break master cylinder, then you'll need to check the seals on the rear wheel brake cylinders and the front wheel caliper pistons. If any leak, they must be replaced.

If you're an experienced mechanic (your question suggests not) then you may be able to dismantle, assess, and if appropriate rebuild any leaky parts using new seals/pistons. The parts are usually cheap, but the very high labour costs and higher chances of a post-repair fault mean that most garages just replace the entire assembly with new and guaranteed parts as it's far quicker, easier and less likely to come back for remedial work.

If your clutch will not engage when the piston is pushed in fully, you probably have air in the slave, the line , or the master cylinder. Place a piece of plastic and an old towel over the bike to catch any drips. Remove the top master cylinder cover and take an old, clean, lint free, cotton sock and gently soak up all the old brake fluid in the master reservoir. Place the sock into a used zip lock bag and discard. DO NOT touch the clutch/brake lever or you will draw air onto the system. Now fill the reservoir with DOT 3/4 brake fluid and bleed the slave cylinder. Warning: be careful not to spill DOT Brake fluid on your paint or plastic. Place a tube on the bleeder screw (slave cylinder) and loosen the bleeder screw. now pump the lever to push the air out of the system. Hint: if you do not have pressure in the master, loosen the brake hose banjo bolt enough to burp the air out of the master(2 or 3 pumps of the lever). Retighten the banjo bolt and bleed the rest of the system.
Bleeding the system should restore clutch performance. If you notice fluid leaking from the master or slave cylinder , replace the o-rings in the slave cylinder piston and rebuild the master cylinder. A master cylinder kit and slave cylinder o-rings are available at your local Honda dealer.

Just remove the lever, gently pull rubber boot out of the body, take a snap ring pliers,and remove the circlip, and pull the piston out of the body. Use the piston as a reference to install the seals correctly on the new piston. Be sure to take out the screw in the reservoir, remove the reservoir, and clean the fluid return pin hole ( Must Be Clear) , next to the large fluid feeder hole. Also using a dowel covered with a lint free cloth gently wipe out the piston sleeve being careful not to scratch the walls ( Do Not Hone The Master Cylinder or it will be ruined). Coat parts with brake fluid before reassembly in reverse order. Cover bike with plastic and put some old rags under master cylinder. Before tightening brake hose bolt, fill the master cylinder with dot 3/4 brake fluid and pump the lever until the master cylinder is pushing fluid out the end where bolt and hose are loosely connected, now tighten bolt holding the brake line on. This will aid greatly in bleeding the system.

Yes, you can buy a master cylinder rebuild kit. If you can't find a rebuild kit the whole thing can also be replaced.