Master Cylinder O-Ring Seal?

[mattardi]

Hello All,

I'm new to the forums, new to riding and new to maintenance/repairs.  I just picked up an 1987 R65 a few weeks ago and the problems are already starting...or at least I'm already finding out about them.  

After I took the bike out for it's first ride I got back and noticed that the Front Master Cylinder was leaking.  I cleaned it up and let the bike sit over night, and the next day more leakage was apparent.  I'm not entirely sure where the leak is coming from, whether it's the piston or reservoir, but I first suspected the reservoir, so I took the master cylinder apart and inspected everything.  Lot's of gunk and dirty brake fluid (I suspect this bike sat for awhile).  

Anyway, my Clymer Repair Manual says that I should replace the O-Ring Seal on the Master Cylinder Reservoir O-Ring, regardless of the condition of the O-Ring.  The O-Ring looks fine, but I ordered another one anyway, but I can't find any information on an O-Ring Seal.  The place I ordered from said that I would only be receiving the O-Ring, no seal.  What is this seal?  Is this some basic shop knowledge that I don't know about?

I'm fully aware that my problems probably lie with the Piston, but either way I will (supposedly) need an O-Ring seal.

Thanks for any help.  I'm glad I found this forum, I imagine I'll be spending a lot of time here.

Mike

[Yikes]

Hey Hyphen and welcome!  

The most important thing to know about a leaky master cylinder is not to let the fluid drip onto your painted fender or you will have another job to do - repaint your fender.  What you will most likely have to do is remove and replace the piston assembly which comes with the new spring and seal.  As with every job you do on an older bike, a good bit of the work is cleaning up the years of dirt and grime, and you will have to clean out the crud that has built up in your piston cylinder.  If you are unlucky the cylinder will be scored and the piston won’t seal and will continue to leak, but chances are the new piston assembly will be all you need.  

It is really not a difficult job, except for separating the piston cylinder from the throttle body.  That can be a bear.  It was one of the first things I had to do in my bike when I got it a couple of years ago.  The second job I had to do was repaint my fender, but Monte here is the guru to learn from for that job.  Let us know how it goes.

John Mc

[Bob_Roller]

Welcome hyphen, you need to get the master cylinder out of the handlebar housing to see what the problem is .

Most likely the cup seal on the master bake piston is wore out, there is no o-ring, unless you know of a source for the seal itself, you're probably going to need to purchase the piston and seal as an assembly .

Another possibility, is that there is pitting and corrosion in the  bore of the master cylinder .

No way to know for sure, until you get it taken apart .

[mattardi]

Hey Guys,

Thanks for the replies.  I've already disassembled the master cylinder and cleaned it out.  Everything looks pretty good, maybe a little wear on one of the piston seals, hard to say as I've never seen a fresh one.  I'm prepared to get a new piston if necessary, but first I want to reassemble it with the new O-Ring on the reservoir.  And thats what my question is,

What is the O-Ring Seal on the brake fluid reservoir that the Clymer repair manual is talking about?

[Bob_Roller]

The master cylinder reservoir is removable, after removing a Phillips head screw from the bottom of the master cylinder, it's got an odd looking thread .

After removing the screw, you need to twist and turn the reservoir to get it separated from the metal part .

[mattardi]

Yep, I've removed the reservoir.  In the process I removed a clear film, not sure if it was plastic or rubber, but it came off in pieces.  This was around the O-Ring on the reservoir.  I assume this is the O-Ring seal.  The Clymer Manual states:

"Remove the O-ring seal from the reces in the reservoir neck.  Discard the O-ring seal as it must be replaced every time the reservoir is removed, regardless of the condition of the O-ring."

I've got the O-ring being shipped to me, but I don't know what to do about replacing the seal.

[bruce_launceston]

Pretty sure it is just a weird way of saying 'replace the 'O' ring'. I don't believe there is another seal you need to find.
The 'O' ring and the O' ring seal are one and the same item.

I wouldn't worry about the clear film you found, i don't recall ever seeing this and I have rebuilt my master cylinder twice.\\When you clean all the gunge out of the master cylinder make sure the very tiny fluid return hole in the alloy base is not blocked with gunk.

There is also a seal hidden behind a washer that sometimes gets missed in the lever end of the piston.
You will get a new one with the piston kit but might have trouble finding where it goes if the old one is stuck against the lever.

Cheers

[mattardi]

Excellent, thank Bruce.  I was beginning to suspect that that may be the case.

Thanks for the tips, I don't remember seeing that seal behind the washer, I'll have to take another look tonight.

Mike