Re: master cylinder rebuild
I've got three master cylinders and all seem to be kaput. The plunger won't come back out after engaging. I was able to get one working but I had to tear away the rubber dust cover (I think/hope it was a dust cover). Should it be possible to successfully rebuild one master cylinder from the three I have? (Unless of course the same thing is wrong with all three). Is there somewhere I can find basic methods and modis operandi for this procedure? Also, is that a dust cover I ripped away from the external portion of the plunger?
You can rebuild master cylinders but you need a combination of tools, parts and patience. I have recently rebuilt two front and two rear master cylinders and can offer these general guidelines.
Take care in disassembly, note the order of things. You don't want to cause damage to what may be salvagable parts. Most master cylinders (MC for shorthand)have a simlar design. I am describing the disassembly of a GS1100 MC.
Diconnect banjo bolt at caliper, drain brake fluid.
Disconnect banjo at MC, drain any additional fluid.
Remove brake lever or pushrod lever in the case of rear MC.
Remove filler cap and drain remaining fluid.
Remove rubber dust protection boot.
On front caliper there is snap ring clip which needs to be removed using special snap ring pliers.
You can remove using a small hook like tool and a ice pic like awl. Not easy but possible.
Same type of clip on the rear caliper.
Remove any washer(s) next.
I believe there is an o-ring seal next, I'll check tonight, I have a spare plunger set sitting in a jar of brake fluid. Remove without damaging, or leave it. Checked, this is the right order.
If the piston hasn't fallen or pushed it's way out at this point things have gotten a bit more difficult.
The pistion is frozen in the bore, stuck in place by dried brake fluid.
For rear MC hook up a slide hammer and gently tap it out.
For front MC.
The first thing I try is lube, teflon type, penetrating. Spray the plunger side, remove brake fluid reservoir and spray in feed holes, spray in the banjo opening. Soak it and set it aside. Make sure you set it so that if the plunger pops out when your not there you don't lose parts. Also it's good to preserve the order of things.
If the piston hasn't popped out, normaly it doesn't, relube to ensure coating.
Take MC in hand and slam down on wooden surface. The side of the MC that the brake lever pushes piston plunger into MC is the area to slam against the wood. Slam and hold down. Don't lift at the moment of impact or the plunger may fly out and you may lose parts. Try this a number of times. If it doesn't work lube and set it aside and try again later.
If the above hasn't worked you can try hooking a compressor to banjo opening and blow out plunger. Never had to do this, just a suggestion.
Another thought, though I haven't had to do it this way either, is to hook up another working MC and line to the banjo of the bad MC and pump the plunger out. Messy but should work.
If you don't have compressor you can center drill plunger piston rod and use screw extractor to twist out plunger. You will have to replace plunger with this method.
As long as you don't damage the plunger bore your good to go. Remember to note how everthing comes apart so you can put it back together.
One last thing, when putting the plunger in the bore with new snap ring, use a deep socket to press clip and plunger into place. Alternate method is hold down plunger body with a long screwdriver and use special pliers to compress and install clip.
