front brake problem

recently i had the front wheel off and dpressed the front brake lever. the piston/caliper stuck. a friend seperated it by wedging a screwdriver betwen the plate and the pad and banging it out. not the best way to do it but too late now.
anyway i bled the line and it was working ok until the other day - i rode it one and and went out the next and the brake lever pulled all the way back in with no pressure at all - all free play. bled it again a few times and nothing happened.

any idea what could be wrong?

 

Good chance that the caliper piston seal was damaged and fluid leaked out. This can be confirmed by checking the brake fluid level in the reservoir and seeing if it is very low. If too low then there won't be enough fluid to compress the piston. If you checked the level when you rebled the brakes then check for fluid leaking at the caliper and then check the operation of the master cylinder by looking into the reservoir and see if fluid appears to move.
How did he get the piston back into the caliper? If it was forced without removing the reservoir cover this could have damaged the master cylinder. It is still possible that air is trapped. If you know anyone with a Mity-Vac I would bleed the lines with it. It gets the trapped air out when nothing else does.

 

yeah sounds like u dont have any fuild in the system , if the seal on the caliper was broken then there should be fluid on your brakes and pad , so it might just be low on fuild or still have massive air in the system. ive open up heaps of cailpers with screw drivers lol , havent broke a pair yet
good luck

 

If there's fluid in the system ... and, you've bled it a few times ... and, the process of bleeding it is somewhat tedious and slow ... then, ... you probably need to rebuild the Master Cylinder ... the Master Cylinder fluid seals are probably done-for ... and, all the bleeding in the world isn't going to make them better, again. Kits run about 35-Bucks.

 

Don't know which bike you have but try these guys for a rebuild kit. That's only about $24
https://www.partsnmore.com/cat_index.ph ... ry=chassis

 

thanks all,
yeah i guess a key point i didn't mention was that the master cylinder was pretty much empty. didn't notice if the fluid had leaked out of the seal because i didn't real know too. not sure off the top of my head where the seal even is, i'll check my clymer manual.
so maybe its the master cylinder isn't sealing correctly??
is it pretty easy to rebuild? i would think just from looking at it it can't be too hard.

 

The seal is around the piston on the caliper. The piston actually slides through it when actuated. I haven't personally rebuilt a master cylinder but I do know that it isn't that hard. Some of these guys who know will chime in about that for you.

 

Rebuilding the Master Cylinder is a fairly straight-forward adventure. Only moderately frustrating. Get the MstrCyl on the bench. Remove the dust boot. Now, the fun begins. Remove the circlip. After doing the job a couple of times "the hard way" ... I just made myself a tool by spending a few minutes at the bench grinder with an old pair of needle-nosed pliers. (The commertially available circlip tool can't make the squeeze between the plunger and inside diameter of the cylinder.) Anyway ... remove the circlip -- taking precautions not to allow it to fly away and hide! After you get the clip out ... keep tapping it on the your bench or vice to allow "The Guts" to work their way out of the cylinder. Catch the assembly and remove it ... laying it out so you can see the proper order for everything when its time to re-assemble it and button it up. Note the position of each of the internal parts. Make a skecth and put the sketch under your pillow!
Don't do anything to those parts you just pulled out of there, yet. Shoot some Disk Brake Kleen into the bore. Rinse the bore out -- real good. Now, hold up the bore to a light and inspect the walls of the cylinder, in there. If the bore is clean ... you can relax and get ready to rebuild a master Cylinder. If there's "Stuff" in there ... or, the cylinder walls are pitted ... you deal with that; first! The ugly stuff needs to go away. The ugly stuff does not want to go away. It's an ugly situation. DON'T scrape!
The easiest way to get rid of that moisture-related oxyidation is to BURN it off. Use a propane torch with a PENCIL POINT flane and get right in there and turn it into dust. The crap WILL turn to dust -- looong before the aluminum begins to melt. Wear gloves. Burn it out. Let the Master Cylinder cool before handing it to an assistant. OK, its cool now. More brake cleaner. The cruds gone. Now you see "Pits." If the pits are within the "footprint" of the travel of the seals ... you need to remove the pits. If the pits are below the footprint of where the seals travel ... it's nothing to worry about. But, it ain't your lucky day. The pits are where the seals travel. Now there's two things to do. If the pits are really small ... you'll haave to "HONE" them out before rebuilding the cylinder. If the pits are LARGE and DEEP ... you need to take the Master Cylinder outside and see how far you can throw it! (I can still heave one 80-yards ... and, I'm getting old!) OK ... Let's say you luck-out and the pits are small and not too deep. Remove the pits ... HONE the cylinder out a couple-'a-thousandths. Piece-'o-cake! Go buy a foot of 1/4" hardwood dowel. Duct-tape some terrycloth to the dowel and roll it on the dowel until you get a snug fit into the bore. Then, duct tape some # 400 Wet-'O-Dry sandpaper to the terry cloth. Stuff this Special Tool -- down into the bore -- lubricating the sandpaper very, very lightly with clean brake fluid. After you get the fabricated tool stuffed in there ... chuck the dowel into your drill and HONE the cylinder wall for about 10 - 15 seconds. Remove tool. Clean bore with brake clean. Inspect. Pits? Do more. New 400. Hone. Check. Pits? More of above. No? Finish honing bore. Use #800 Wet-'O-Dry with brake fluid used as wetting agent. 15 - 20 seconds of finish honing. Clean. Inspect. Looks good in there? Yes? OK ... lets wrap-up this motor-scooter. Note the position of the cup-seal on the plunger. Surgically remove them with a razor blade. Inspect plunger. Clean, clean clean! All the tiny holes; too! Clean it again; until it is perfectly clean. Get out the new seals. They have to go where the ones you removed were. Lube them with brake fluid and s-l-o-w-l-y ... and, c-a-r-e-f-u-l-l-y work them to their channels ... using NOTHING but your fingers -- after you've trimmed your fingernails. Use ALL the new parts in the kit. Go get the sketch under your pillow and put it all together; nice. Lube as you go using virgin brake fluid! Yes, it does fit. When it does ... you make sure that the circlip is firmly seated. Then, you put on the brandy-new dust boot. Then ... you "Bench Bleed" the master cylinder. Then you put it back on-yer-bike! Then you bleed the system, again! Then, you have brakes ... and, you get to put a gold star on your toolbox for rebuillding a Yamaha Brake Master Cylinder. Congratulations!!! Practice saying it like Elvis .: "Sang gue verra mush!"

 

Excellent write-up RickCoMatic, color me impressed. Two points to offer in addition to your post. I bought the cheap snap ring plier kit from Harbor Freight for about $7 USD and they worked very easily for the snap ring (yes, I fought with this one too, it is a bear!). I would also suggest using a brass (not the steel) Dremel brush or ScotchBright "cross" buff to remove corrosion in the absence of said heat (some people were not meant to play with fire). Dang, with this kind of writing skill available, small wonder we haven't written a how-to manual for the XJ's!

 

Thank you very kindly for your nice compliment. I try to keep the "How-to" in my instructionals comprehensive, yet ... not to technical -- so that the first-timers get a "feel" for what they might encounter and what to do if they decise to dive-in. I've always thought that an extremely "User friendly" series of articles would benefit those intent on doing some maintenance and repairs. I do enjoy getting a little "light" when I post these write-ups of mine. I try to place myself in the position where I attempted projects the first time. Make it fun; not complicated! I plan on having a bid debut of the 750 Max priject I have been working on for a couple of years. The final piece of the puzzle is the fuel tank is having the freshly painted tank -- clear coated -- before rolling it out onto the Red Carpet -- Friday or the following Monday! Every keep save and smiling!

 

its weird i took a short spin on it the other day and the brake worked a little bit. then a day later it worked fine.
i doubt the problems solved but could the bleeding have just taken a few a day or two to take?
the master cylinder also (when i was saying master cylider in my response the other day io was thinkning of the resevior for some reason) seems to move a little bit, like its loose.

 

Actually the master cylinder is in the bottom of the reservoir. Where is it loose? If the brake cable coming into the back is loose then by all means tighten it. If it is just loose on the handlebars then I would tighten the perch but that would not be the problem. It wouldn't take the bleed timet o take. Something else is loose allowing air to get in/fluid to escape or the master cylinder is not working and needs rebuilding.

 

not to hate on your wonderful write up. (it is a very good lay mans guide to rebuilding your master cylinder!) but it is generally frowned upon to hone a master cylinder. The reason for this is that since aluminum when machined is not quite porous, but it does have millions of little pits that are microscopic. after a master cylinder is manufactered it is then put through a process of sealing up all those little pits. So if you re-hone the cylinder, you have taken the finish off the cylinder walls, and it is now riddled with microscopic pits, that will in time wear the seals down on the piston.

However this is all automotive knowledge of recent cars. I dont know how much of this holds true to 80's bikes. And with that said, some seals down the line, are cheaper then a new master cylinder.

just food for thought, nice post!

 

Ok Brian, you got me thinking. What would you suppose they would have used to seal those cylinders? They might have hardened the surface, but I personaly find it hard to believe that a coating was used. Coatings do not last forever and I'm not aware of to very many (make that zero, but by no means do I have the whole picture so I'm giving room for wiggle) that are even recommended for use in a brake system. Could you educate us with more info??

 

i remember that sort of thing but i no remember how , sort of like anodizing but not , great help this is and a complete waste of typing it even hardened the surface too [in microns]

 

Running some 800 grit sandpaper around, in there, if far from honing. It does the job on ridding the surface of small ... that word being SMALL ... pits. Given the chose of buying 3 sheets of 800 and a new Master ... its worth the shot giving the mster cylinder inside diameter a new life. It might be a waste of time for some ... because the concept of "Centrifugal sanding might not be fully understood and the cylinder could get slightly "out of round" ... Generally, for a light resurfacing ... it works like a charm. The l;ittle bit of 800 work and a cleaning might save it. Not just for a little while, either. You might find that the cylinder is fully repaired and the new seals will push the brake fluid as athey should; giving the calipers what they need to bring the bike to a halt. Remember, the cylinder needed to be a candidate for it ... otherwise, you get entered in the Master Cylinder throwing contest.

 

Hmmm... I'm going to have to dig. You caught my fancy with that question. Anodizing is possible, and can be done at home. I'm going to experiment (right after I contact Nissin and pick their brains).

 

I agree, i remeber being told it was not so much a coating, as a process similar to anodizing that fills in all those little pits. Let me check my automotive chassis & Brakes book for more info when i get home....