Rear brake MC...rebuild time?

[wapam]

When I first got my bike ('80 SG) the rear brakes were seized. Took the MC apart, cleaned the "spooge holes", new fluid and bled the brakes.

All seemed ok until I was riding today and noticed that sometimes when I pushed the rear brake pedal it went all the way down without actuating the brakes. If I pushed it down again, all was fine. Almost like the brakes need one push of the pedal to build pressure then all is ok.

Sound like MC to you?

Thank you.

[rman]

Air

Sounds like air in the lines. Try bleeding the brakes again.

Oh, almost forgot make sure you read my disclaimer below.

[wapam]

I've bled the rear brakes multiple times, still does the same thing. Still seems to be losing pressure. Sometimes I'll be sitting at a light with my foot on the rear brake and all of a sudden the pedal will lose pressure and sink all the way down.

I'm no mechanic but if there is a leak in the system allowing air to get it wouldn't the brake fluid be leaking out the same place? I see no evidence of brake fluid leaking at all.

Thanks to all.

[randy]

wapam,

Did you replace the piston seal when you had the MC apart? A tired seal may be the culprit? Always a good idea to replace the rubber parts when doing brake service. It's not always necessary, but a good idea.

How did you bleed? with the pedal or with a vacuum bleeder? I've found the rear MC is almost impossible to bleed properly with the pedal. A vacuum bleeder can work wonders.

If your seal is new, then I'd agree with rman, even though he claims to be an idiot. People often claim to be something they're not!

[XSPastor]

Wapam,

If no fluid is leaking from the system, then you have fluid leaking past the seals on the Master cylinder piston and back into the reservoir. You will need to rebuild the Master cylinder. It's very easy and the parts are not that expensive; about 25 bucks. Should take an hour or so if you're fairly handy. You can buy the kit from Georgefix on ebay.

Tim