The order of parts within my master cylinder?

[Guest]

Hi guys,

I'm getting so close to a fully functional bike, much of which came from this forums help. One of my last tasks is to repair the front brake master cylinder. I've done this well I believe, in that its very clean and I'm using a good repair/replacement kit.

However, I'm getting some bleeding of the fluid coming through the back of the piston where the brake lever pushes it in to activate the brake. Does anyone know the order of the parts within the cylinder, from left to right? It's a 79, GS550 E.

I followed the order of the old piston when removed, but I'm wondering if I missed something or put a rubber washer the wrong way etc?

Many thanks

[chuck hahn]

Spring in fat end toward the line.
Cup in with the flat side facing the lever..in other words, the spring end goes inside the cup
Then the brass disc.
Then the piston with the star shaped end thing against the disc.

[Wes51st]

Spring in fat end toward the line.
Cup in with the flat side facing the lever..in other words, the spring end goes inside the cup
Then the brass disc.
Then the piston with the star shaped end thing against the disc.

Chuck to the rescue! That you for always helping me.

My system seems a little different- here's how I have it:
.Spring with wider end far left.
.Rubber pusher fitted to small end of spring
.Brass solid washer
.Piston
.Rubber bush on piston, widest point facing the left making this kind of shape )
.Brass washer
.Pin clip.

Still when I push the plunger lots of times I'm getting fluid leaking out, it's only slight but can't be right.

[chuck hahn]

Yeah. the best I could describe which end of the piston that went down bore was by that star looking end thing on it. never mentioned the retainer washer and circlip as I thought you were smart enough to realize that...HA HA

But yes, the rubber cup on the piston is toward the lever end of the bore. be sure the tiny pin hole inn the bore ( under the reservoir cup itself) is open. Poke a fine wire in it to be sure..thats the pressure return port that allows the fluid to back up the line and release pressure on the pads.

[chuck hahn]

As for the leaking..is the rubber cup on the piston new??? Thats the one that stops fluid from escaping the bore. Helps to make pressure too, but its most important function is to stop leaks.

EDIT...is the bore perfectly free of scratches, pitting or any other obvious damage??? Imperfections can let the rubber seals leak too.

[Wes51st]

Yes it seems spotless, and yes the rubber cup is brand new. Still when I fill the reservoir with fluid then turn sitting upside down so that the fluid is against the rubber cup, fluid does leak out slightly. I think the rubbers fit but be the problem

[chuck hahn]

Some will a vent channel machined ( molded ) into the reservoir cup. Take a look and see maybe that whats leaking. I was under the impression it was leaking out from around the piston where it goes into the master cylinders bore...least that the way your initial post seemed to me

So where is the fluid coming from??? The piston area or the reservoir cup cap area??? what bike is this..may wish to edit your profile and add that to your signature for a clearer understanding.

[Wes51st]

It's a 79, 550E (I'll change my profile soon)

It's leaking from the plunger side that the brake lever pushes. The leak physically happens when I pump the plunger an number of times and it flows from around the pin clip.

Does that add anything?

[chuck hahn]

Seems to me the piston rubber seal is the wrong size maybe. If the bore isnt scarred up I cant think of anything other than the rubber being bad and not seating correctly. Look and see if there are some numbers molded into the body on the bottom when it was cast at the factory...if there are then what are they????

Where did you get the rebuild kit..are you for sure it was the right size for the bore of the cylinder???

[chuck hahn]

#1 on the parts fiche is what you should have installed. Still have the packaging to check the part number against the fiche number???

http://www.partsoutlaw.com/oemparts/a/suz/50d3f5a2f8700230d8b4c70d/master-cylinder

[Wes51st]

#1 on the parts fiche is what you should have installed. Still have the packaging to check the part number against the fiche number???


http://www.partsoutlaw.com/oemparts/...aster-cylinder

I think you're right Chuck, the rubber bush nearest plunger is snug, but not quite creating a seal. I've stretched it a little in my hand and warmed it up to make sure it takes it's maximum natural size, but it's still not a complete seal.

However, I found another fix I think is even better. I've added a thin rubber grommet behind the bush so that there's a second seal point. The profile of the two pieces of rubber together looks a little like this within the cylinder: )~|

The seal is much better yet it still slides back and forth smoothly. Question is, do you see any issues with this mod?

[chuck hahn]

Throw up a picture...........but if it were my butts safety at issue there would be a new OEM Suzuki kit going in there. Brakes are NOT an item worth gambling on.

[Wes51st]

Throw up a picture...........but if it were my butts safety at issue there would be a new OEM Suzuki kit going in there. Brakes are NOT an item worth gambling on.

Hi Chuck,

I think you're right and brakes aren't something to scrimp on. Thought I'd show you the added rubber grommet on the back and how it helps keep the pressure that little bit better. So rather then change what's there, I've just reinforced the seal.

IMG_4953.jpg

[chuck hahn]

It may work temporarily but I still would get the hew one soon.

[bobgroger]

That cup is definitely too small, the small end should be about the same diameter as the piston.