Master cylinder leakage

[redzap]

Noticed a small leak coming from the master cylinder on my '83.  I took it apart and cleaned it, put it back together, and am now noticing the leak starting again.  Do I now have to buy and install a rebuild kit or is there another solution?  Also, any thoughts on replacing the stock brake hose with the stainless type?

[Rob Valdez 79 R65]

There may be a sealing ring available that goes between the reservoir and the body.

Have you looked at the microfiche?

Nope, no sealing ring on the fiche...

[nothing]

Do I now have to buy and install a rebuild kit or is there another solution?  

It's worse than that - most leaking MCs on these bikes are too far gone to be rebuilt. The inside bore of the housing often degrades as much as the piston, meaning rebuilding doesn't fix any leaks. To save yourself a lot of hassle and wasted effort, I would recommend a whole new master cylinder.

[Bob_Roller]

Can you tell where the leak is coming from?

If it's coming out of the piston seal area, you may get lucky, and replace the piston and seal assembly, but if the aluminum bore is pitted or corroded, it's a master cylinder replacement.

There is an o-ring between the rectangular resevoir, and the metal body of the master cylinder.

I replaced my OEM rubber hoses with braided stainless lines, and I won't ever go back to rubber again, it makes that much of a difference.

The stainless lines are a bit more costly than OEM, in my opinion, it's worth it.

[nhmaf]

My M/C was leaking on my '82, and I bought and installed a rebuild kit.   The bore was somewhat corroded, but I tried to
carefully clean it with some fine emery cloth.   The fix lasted for about a year, and then I ended up buying a whole new M/C.

[Yikes]

I just completed replacing the piston on my severely leaky '82 master cylinder and it is working fine now and dry as a bone.  The piston assemly was just plain worn out and leaking on the right side behind the brake lever.  The fix was a straight replacement of the piston which came with a spring and washer.  The master cylinder was pretty gunked up, but not visbly corroded or scored on the inside bore.  It took a little effort to get the old washer out.  The leak had ruined the finish all the painted surfaces on the perch assembly, the front fender and probably did in the starter switch which was no-go when I got the bike.  The finish on my riding boots also did not like the application of brake fluid.  Denatured alcohol cleaned everything up real nicely and with a little sanding and paint, everything came back together better than ever.

Replacing the piston is a pretty easy job except for separating the master cylinder from the throttle body.  They were so tightly sealed together that I wondered if they were actually one piece.  But they did eventually come apart without breaking and once cleaned up, went back together without a hitch.  Hopefully it'll last a while.

[redzap]

Thanks for the feedback.  I'll let you-all know how things turn out.

[billygoat]

 There is one o-ring, about the size of a nickle between te plastic housing and the metal brake body. Try replacing that first just to see. My LBS (local bmer shop) was hot to sell me a rebuild kit eventhough my po just installed one.
 I see there is synthetic brake fluid now. Don't mix types, if you have reg. use reg. brake fluid not synthetic. Try to get DOT 4.