Master Cylinder/Bleed Problems, Question

So I was out bleeding the front brake after a caliper rebuild. I'm not able to get any real pressure in the brake. I hear the pads grab the rotor about half way to the bar but I am able to pull the lever to the bar with little issue.

There is no longer any air coming from the bleeder and I ran an additional half bottle through the system, but the situation has not changed.

I did notice that if I grab the lever too quickly or pump rapidly, the fluid will shoot out of the upper (smaller) hole in the reservoir. I read somewhere on here that this is a sure sign that the MC is in need of a rebuild. This true?

I'm hesitant on buying a rebuild for $25 while a whole in MC costs $80.

The funny thing is, the piston was so stuck in the caliper that I could not blow it out with 120 PSI, BUT I was able to push it out by pumping the MC and now it's working like garbage.

Thx

-Rob

 

Bet you still have air in there somewhere. Keep tickling and feathering the lever, don't pull it all the way in til it IS fully bled otherwise you just keep compressing the air and shoving it right back down the tubes.

Dave Fox

 

Welp, I ended up buying a rebuild kit for the MC. The way I see it is that if I'm going to spend hours bleeding this system, I might as well make sure that I will not have to take it apart in a few months to rebuild the MC and undo everything.

I will keep trying to bleed it after I do the rebuild with your suggestion.


Thanks

 

Look at the Bore of the MC before throwing the kit in there.

Aim a Penlight Beam in there and look for Pitting and Foreign Matter.

You got to get rid of Pits and Crab before rebuilding it with the New Kit.

 

guess I assumed you had already done the MC rebuild. My bad.

Dave

 

I just bled my brakes for the first time. Don't know how much experience you have but the bleeding part took no time until I had no air bubbles and clear fluid however it seemed to take forever to build up enough pressure for my pads to grab. Even once they reached the disc it took many pumps to get the pressure right. So many that at first I thought I must have done something wrong or something was loose/damaged.

 

Thanks for the heads up... I just got done reading the MC rebuild FAQ. Doesn't look like a bad job at all.

Rick, how do you typically clean up the bore? I would assume it its pitted then you have to remove material which will run the risk of ovalizing it.

 

In a perfect world, you would ream out the hole and hone it but if the holes/pits are small enough, a quick hone is all it takes. If you can't get the pits out with a hone job, I'd opt for the new M/C.

 

You have to Improvise.

Fabricate a Hone.
Use a Wooden Dowel or a Fiberglass Rod.

Affix Finishing Paper to the Rod with Textured Duct Tape
Roll the Paper around the Dowel.


Moderator


Joined: Jun 22, 2006
Posts: 10913
Location: Massachusetts, Billerica

PostPosted: Wed Jul 26, 2006 11:26 pm Post subject: Re: front brake problem.

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 commercially 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 sketch 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 oxidation is to BURN it off. Use a propane torch with a PENCIL POINT flame and get right in there and turn it into dust. The crap WILL turn to dust -- long 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 have 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 rebuilding a Yamaha Brake Master Cylinder.