Yet another master cylinder question!!

I have been posting on the brake bleeding topic but one last question....I hope. I have removed the lines and they are clear and not clogged or anything, but my question is about the master cylinder. With everything disconnected with everything I mean the line, and the cover off, when I pull the brake lever, shouldn't fluid run out of the threaded part where the line connects?? :? It just dribbles out and then stops! Could the 'smaller' hole be plugged up? I ask this because you can see the piston working through the bigger hole. Thanks!

 

From my recent rebuilding experience I found that the master cylinder does not work well with air in the system, including the hole where the banjo bolt goes. The little hole you speak of is a pressure relief hole. You will definitely know if it's clear, as it will shoot a stream of brake fluid, and if you're not careful, will get fluid all over the place :-D

I had to use a tiny (and I mean tiny!) sewing needle to clear mine, as it was clogged with 20 year old coagulated brake fluid. If it's not clear, your brake will drag. If you have to clean the hole, be careful not to touch the plunger with the needle (or whatever you decide to clean it with).

Re-attach your brake lines, top off the master cylinder. Put some teflon tape on the bleeder valve threads (thanks Rick!), attach a length of clear tubing to the bleeder valve, and attach the clear line to a vacuum pump with a ball check valve (mighty vac or something similar). Back out the bleeder valve a bit, and pull vacuum on the line. To help it along, squeeze the brake as you go, and remember to tighten the bleeder valve every time you're letting go of the brake lever.

Make sure you keep the reservoir full, cause if you get an air bubble in it you'll have to do it all over again.

You will see fluid coming through, along with some bubbles. Once the bubbles are gone, you should be very close!

Hope that helps.

 

that helps a lot....however, what if I am not getting fluid to 'shoot' up when I pull on the lever???? You can see fluid back up, but not shoot up

 

so I took off work early to try this out and nothing is working!! I am assuming my master cylinder is plugged up. When I took it apart there was coagulated fluid in it. Can I use some brake cleaner to clean out the cylinder? :? I know this is not difficult and it is making me crazy! Thanks!
:evil:

 

Not clean enough then. You'll know once it's clean as you will have to reach for a shop towel

Or.... something's wrong with the plunger and/or o-rings... Wouldn't hurt to pop that snap ring out and inspect everything, worst case scenario.

 

that was my next question....how do you get that plunger out?? Any easy suggestions for 'popping that snap ring out? Thanks!!

 

The end of the brake plunger points out the rear of the MC (The thing the handle presses against). There is a rubber boot on it. The top of the boot has a lip that goes into a groove in the plunger. The bottom of the boot has a lip pointing outwards that engages the MC housing. Remove the boot (I would try popping the bottom out first then pulling the top off the plunger. When I did mine I pulled it loose from the plunger first and tore it).

With the boot removed and looking down the plunger you should be able to see the circlip that holds the plunger in. You need to remove the circlip. In my case I was able to get my smallest snap ring pliers just on it if it was rotated the right direction.

Now the plunger will pull right out. Behind it is a spring with a rubber cup on top of it. Pull all that out and start cleaning.

If you don't have a snap ring pliers that will fit, I'd suggest grinding the tips on a HEMOSTAT for the job.

 

MiCarl is right on with disassembly directions. I ended up gently grinding the tips of some needle nose pliers. Went slowly with a dremel tool until the tips fit in the little circlip hole. A single strand of small gauge copper wire will help clean the little holes inside the master cylinder. Proper cable adjustment when you reassemble the unit will ensure the plunger travels the full distance.

 

Have a close look at the plunger.

Some models have really tiny fluid passages drilled through the base that let brake fluid pass through and replenish the volume needed to make pressure down the lines.
Not just having the fluid move out and back a short distance.

They are there to keep the volume constant, to allow the MstrCyl to act as a pump and compensate for brake pad wear and for bleeding.

If those passages are blocked; you won't get the pressure build-up you need and the movement of the fluid -- out -- as the plunger will only be acting on the fluid in the cylinder ... and NOT ~~> PUMPING fluid down the lines to the caliper ... and displacing air in the lines as fresh fluid is pumped down and out.

 

Since I think I have a similar issue, I think I'll just tag onto this post. I had my front brakes lock on me the other day because the plunger in my master cylinder stuck completely. As the brakes heated, I assume the fluid heated, and eventually the wheel locked from the pressure. Just to get this out of the way.....Yes, I knew it was binding before it locked; yes, it was not smart to continue; and no, the thing I was hurrying home for was not worth the risk. Good news is that I didn't drop as I was boarding a ferry and when into a front wheel skid. Once on the ferry, I was able to release the pressure at the calipers and continue with only the rear brake.

The plunger is still stuck in the "all the way in" position. Knowing that this is obviously the main problem, I bought a master cylinder rebuild kit and plan on doing that today. While I am doing that, are there other things that I might be missing that could have caused the problem? Should I also replace seals in the calipers? I doubt either has been done in the past, and the bike is 21 years old. Any suggestions on using aftermarket vs OEM seals for those repairs? Thanks!

 

You need to service the Caliper.

The Caliper seals are in Channels that accumulate the nasty stuff that water, brake fluid and dust create.

You need to remove the seals and do the required "Dentist-type" cleaning-out of that stuff with a scraping tool.
An Extra-large paper clip works great ... because you can bend it to hit awkward angles in the confined space.

If you have "Traveling-type" Calipers. Clean-up the rods, bores and O-rings.
Synthetic waterproof grease on them.
Lube the Piston and seals with CLEAN Brake Fluid -- Only!