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Discussion Starter · #1 ·
Hello everyone! It has been awhile since the last time I posted, but I have hit a brick wall with a brake issue so I figured I would ask the experts.

I recently rebuilt my front master cylinder (everything labeled 25):
Front Master Cylinder.jpg
However, brake fluid is still leaking from the piston/brake lever and when I apply the brakes I get very little if any response. Also, you can feel the brake lever get softer as you hold the brake. When I rebuilt it there was a small rubber piece left over (I'm assuming it is #27)? When I disassembled my master cylinder #27 was not in it so I dont know if it is made of rubber or metal...it appears to have a hex shape in the manual I have so I'm assuming it is metal.

So basically, I'm wondering if I assembled my master cylinder correctly...
What are find #26 and 27 made from and what is the difference?

When I disassembled, 26 appeared to be a little metal cap with a nipple on it, at least thats how it came apart.

Any help would be greatly appreciated!
 

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Bear with me, as it's been a while since I had one apart. Part #26 is called 'cup, primary', and is what keeps the spring centered, and from damaging, the piston set #11, and also slides in the cylinder to build pressure; pretty sure it has a rubber-like sealing ring, as the service manual warns not to damage it on assembly. Part #27 is called 'check valve', and is assembled to the other, larger, end of the spring, and allows fluid to flow through the banjo fitting when pressure is applied. The unlabeled loose part in group #11 is called the secondary cup, and may have a sealing ring; it may even be the only rubber-like part (I don't recall, exactly. It fits onto the piston during assembly. The order and direction of #26 and #11 have to be right for pressure to build, and not push past the cups. The secondary cup has a kind of nipple that faces the primary cup, and the primary cup is hollow on the side that goes into the cylinder first.

Perhaps your leftover part is the secondary cup?
 

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Discussion Starter · #3 ·
Thanks for replying WintrSol!

So since my original post, I found a different picture and went back and disassembled/reassembled the whole thing, this time putting the extra cup in (color is a wonderful thing!):
Front Master Cylinder_2.jpg
The book I have give the parts the following names:
13 = Stopper Washer/External Clip
12 = Boot
33 = Internal Circlip/Snap Ring
15 = Washer
11 = Piston and Secondary Cap
26 = Primary Cap
14 = Spring
27 = Valve, Check

This time I put the put on the thin end of the spring like shown. The secondary cap was put on in the same orientation as shown.
Since this configuration also has not worked, I am left with two questions:
Which way does the check valve go on? With the nipple (the gold dot in the picture) facing towards or away from the spring?
Does the picture show the correct orientation of the components?

BTW...any recommendations on getting that snap ring out? The pair of snap ring pliers I have are to short and I couldn't find a longer pair at Advanced Auto.

Thanks for your help!
 

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From what I see in the manuals, the domed side of the check valve goes into the spring. As for the snap ring, I use long steel probes, and use one to hold an end of the ring against the cylinder, and the other to pry the other end of the ring away from the groove; plus a lot of special words.;)

The manual says "Install teh check valve to the return spring and install them in the cylinder as a unit. When installing, be sure to install the spring with a end having a larger dia, inward. Take care not to allow the check valve to come out of the spring." The drawing shows the MC held so that the open end is tilted downward, so the valve stays in the spring. All of this is with the cylinder dampened with brake fluid. The drawing for installing the primary cup next shows the MC held so the opening is up, so you can carefully push the cup against the spring; again, dampened with fluid.

One more thing: with or without the check valve, if the piston and cups are installed correctly, there should be no fluid leaking out of the master cylinder, around the piston. If there is, either you got a badly made kit, or the cylinder wall is not able to seal against the cups.
 

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Discussion Starter · #5 ·
I actually figured out what I was doing wrong with a little help from a friend at work who pointed me to the video at the bottom of this page:
Honda CB360 / CB450 Master Cylinder Rebuild Kit | Common Motor Collective

Makes me feel slightly stupid to admit this but the secondary cap apparently slides over the piston over the end with the star shape on it and seats where the groove is about half way on the piston. Whats funny is I put it back together EXACTLY the way it came apart so this tells me the following:
1) there was no primary cap in the assembly to begin with
2) the secondary cap was never on the piston
3) the master cylinder was clearly rebuilt in the past by a NOOB (kinda like me):roll:

Now the bike stops on a dime and makes me feel a bit safer not having a leaking/failing front brake.

Thanks for the help WintrSol!
 
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