How do you overhaul front master cylinder

[koolaid_kid]

I am overhauling a master cylinder from a 79 GS850G.
I have removed it from the bike, pulled the reservoir off and cleaned out the passages with air.
I need to remove the piston/cup set to replace it. Is there a keeper or circlip or something holding it in? I looked at the picture at BikeBandit, it is part #1, but shows no keepers of any sort.
I would expect all GSs to have similar master cylinders, so any help would be appreciated.
Thanks, kk

 

[frosty5011]

There is a circlip in there under the rubber dust boot.

It's probably hidden under a bunch of "corrosion" and hard to see. Clean it up first with some cleaner and a little pick.....should be fairly easy to get to then.

 

[koolaid_kid]

Got it. Now the bling-blang piston assembly won't come out. Grrr.

 

[gspaul]

Mine wouldnt come out either, spent over a day trying.
Then holding the reservoir with the piston faceing down, I smacked the back of it a few times with a plastic malet,the piston just fell out!

 

[koolaid_kid]

Tried that, although I used a rubber mallet.
The little booger is stubborn, no doubt.
Also tried compressed air, whacking it on wood, pulling on it with vise grips. Very frustrating.
Thanks, kk

 

[gspaul]

I actually hit that resevoir as hard as I could with the plastic mallet, but a bit of wood would have the same effect, I reasoned that if it wasnt going to come out I'd have to buy a new one any way.
I also soaked it in penertrating oil the night before ,as I was replaceing all the rubber parts.
Just meant I had to give it a really good clean after.
Good as gold now!

 

[BigMattyD]

When I rebuilt my master cylinder, I used pliers and penetrating oil to loosen up the piston. You have to twist it back and forth and pull on it. Unless it has permanently bonded to the cylinder, I don't see why it wouldn't come out.

Are you 100% sure you took the circlip out? there are two things to remove before you can pull the piston. The first is a rubber boot with a metal ring in the bottom that seals out dirt and water (not that well).

The second is a standard looking circlip with two holes that you can grip with circlip pliers or really long, small needle nose pliers. If that is not totally removed, you will never get the piston out. That is what locks it in place.

Matt

EDIT: It appears from the picture on bikebandit.com that you have a different master cylinder assembly than I do, so there may be more to it than I know of. My master cylinder is rectangular, not round.

Sorry if my info doesn't apply.