Topic: Help me with a master cylinder rebuild!

[Chippy569]

Hey guys,

I'm trying to figure out how to rebuild a master cylinder. (The shop wanted like $170 to do it... I don't think it's that much work...) So, here's what I'm trying to do. Tell me where I'm going wrong! I only have my Clymer manual to work off of, and this is all it says.


I have the MC cleaned out and my rebuild kit package open, so here's all the parts in what I believe is the order they go in according to the manual.


So I started by putting the little valved cap in the open end of the spring...


...and then the valved end goes in first, correct?


Next are these two little rubber caps. The left one is closed, the right has a nice hole.


All I can figure to do is stick them together and put them in the cylinder closed-end first.


Next is the plunger assembly, which I believe goes this way?


the washer and the the ring go on the open end of the grey plunger, then the dust cap slips over and fits into the ridge on the plunger.


...and that leaves me with an extra piece.



So I'm pretty sure I screwed up somewhere... any ideas?

[ev0lve]

I feel your pain   Didn't use the last piece either. I think the kit fits multiple masters or something.

http://forums.sohc4.net/index.php?topic=38242.msg416346#msg416346

[Chippy569]

That makes a little more sense, got the spring in, then the closed cap, slipped the open cap over the plunger like yours. How does the washer/spring clip/dust boot attachment go?

[Joel]

Washer first, circlip second, dust boot third, semi-circular wire last.

[ev0lve]

Wire clip holds the dust boot on? Makes sense cause I skipped the dust boot.

[Joel]

Wire clip holds the dust boot on? Makes sense cause I skipped the dust boot.

Has so far on mine.  I pumped the lever a couple times with the boot on and the wire clip off and the boot popped up.

[GK]

It's a little hard to explain so here is a step by step video to follow

http://dotheton.com/index.php?topic=4114.0

[Laminar]

I rebuilt my master cylinder yesterday, and I'm getting brake fluid slowly seeping out of the lever end of the master cylinder, and a lever that won't completely firm up. The brake works and it grabs the rotor well, but I can pull the brake handle all the way to the bar the first time I pull, then after that it stops a centimeter or so away from the grip

I thought I cleaned the bore well enough, but I suppose it's possible there's still some crap in there. Besides residue in the bore, what else would cause a leak on a fresh rebuild? I believe I followed the correct steps, but I'll probably pull it apart again just to be sure.

[Chippy569]

I got it together -- thanks guys!

[Chippy569]

Well, actually, I thought I had it together. All the parts are in place, but it does not pump fluid.

So, a question for everyone. In the bottom of the cylinder reservoir, there are 2 "dimples" in the bottom. In mine, the one closer to the handle is open to the cylinder below it, and the 2nd dimple is closed (and feels very, very solidly shut). Are they both supposed to be open? I don't want to damage it.

[BeSeeingYou]

The one closest to the outlet has a very tiny opening.  Use a very thin wire, like a piece cut off a wire brush or a small gage guitar string to open the hole.  Some have used needles but be very careful if you try that as it is easy to break off the tip in the hole.

[Chippy569]

thank you! i used a wire brush bristle, and it seems to work. The cylinder now pumps fluid through.



Unfortunately I'm missing a washer for the banjo bolt outside of the handle. Off to the hardware store tomorrow... *sigh*

[BeSeeingYou]

Just in case you are not aware that these are copper crush washers so a steel washer from the hardware store will not work.  You may have to go to a bike shop or someplace that services hydraulic equipment.  Or get them online from the usual suspects if you can wait several days.

[BeSeeingYou]

I rebuilt my master cylinder yesterday, and I'm getting brake fluid slowly seeping out of the lever end of the master cylinder, and a lever that won't completely firm up. The brake works and it grabs the rotor well, but I can pull the brake handle all the way to the bar the first time I pull, then after that it stops a centimeter or so away from the grip

I thought I cleaned the bore well enough, but I suppose it's possible there's still some crap in there. Besides residue in the bore, what else would cause a leak on a fresh rebuild? I believe I followed the correct steps, but I'll probably pull it apart again just to be sure.

I would guess the only thing that should cause a leak would be a scored cylinder bore or a damaged cup.  Make sure the cups are orientated the right way and everything is clean.  Check the cup for nicks or scratches.

[Chippy569]

It seems that my brake lines themselves are frozen, somewhere between where the rubber tubing connects to the metal banjo eyelets. I was able to feed a piece of wire through the eyelet hole, but it only made it about as deep as the rubber.


More money... *sigh*

[BeSeeingYou]

It seems that my brake lines themselves are frozen, somewhere between where the rubber tubing connects to the metal banjo eyelets. I was able to feed a piece of wire through the eyelet hole, but it only made it about as deep as the rubber.


More money... *sigh*

This seems to be pretty common if it has sat for a long time.  I used a piece of 1/16 multi strand wire rope and was able to get it through. It is flexible and stiff enough to push through. Sometimes it would hang up on the opposite banjo but just go in from each side.  The best solution is to replace with braided stainless lines but for me it is not in the budget for now and the old lines are working fine.

[Chippy569]

I was able to free up one line, the lower line, so now i'm just working on the upper. I don't really have any wire that can easily get in through the eyelets.



I do have a MC question. If I fill up the MC with liquid and squeeze the handle (disconnected, no banjo, off the bike) should fluid squirt out?

[mcpuffett]

Yes definatley  , cheers Mick.

[Chippy569]

hmmmm, #$%*. Not sure what I did wrong then. It makes sucking sounds, but no fluid comes out.

[Laminar]

One thing I always do is to fill the brake lines before hooking up and bleeding the master cylinder.

I have a funnel whose small end is exactly the size of a 10mm banjo bolt, so I put the funnel over the banjo bolt and open the bleed screw on the caliper. I put some brake fluid in the funnel, and eventually it flows through the brake line and out the bleed screw. I close the bleed screw and connect the banjo bolt to the master cylinder. It makes bleeding go much quicker.

[nobody]

I do have a MC question. If I fill up the MC with liquid and squeeze the handle (disconnected, no banjo, off the bike) should fluid squirt out?

I'm having this same problem right now. I just threw all the guts back in generously coated with brake fluid (no gloves  ) and all it does is pump and make noise but no squirting. When I initially disassembled it that little valve piece wasn't in there and it didn't come in the kit so I assumed that maybe it wasn't necessary. Is this valve the reason mine isn't working?

[nobody]

Upon re disassembly I discovered that the rubber boot was swelled and full of fluid (which sprayed everywhere and destroyed the new black paint on my master cylinder... GAH!!!!). So what do I do? I know how to take things apart and put them back together but it's the trouble shooting that I'm not so great with. HELP!

[Gorms]

My kit from Honda did not include the check valve and I dont remember seeing it when I took the original pieces out.  Its a '77 cb550.   Now I worried.  Does every master cylinder have that piece???

[Gorms]

I feel better now.  The microfiche shows the check valve on the 750 but not for the 550.  Whew.

[nobody]

that doesn't make me feel better!