Topic: '77' cb550k master cylinder rebuild, searched but no luck. 2 questions pls

[steam-powered man]

stuck caliper/brake pad wouldn't retract so i cleaned/polished the caliper bore and piston, and replaced the piston seal.  still stuck, so i disassembled the m/c and found 2 of three ports on the piston end (under the star-shaped thingy) were plugged as was the tiny hole in the bottom of the reservoir.  cleaned everything up, confirmed tiny hole is clear and reassembled as i found the parts but now can't get the system bled.  no in-your-face stream from the reservoir, just a few bubbles. 

removed the m/c from the bike and pumped the lever with the brake line removed - nada. 

had plenty of pressure to move the caliper piston before, so i figure somethin's put back together wrong or missing. 

on disassembly i noticed that the "secondary cup" was installed onto the piston (about midway) and the "primary cup" was resting against the spring.  this doesn't match the search info and pics i've found but did seem to work.  did a PO reassemble this wrong?  also i do not have the item labeled "check valve".  i read this item was not included on later model cb550's - just want to make sure.

am gonna take a break from this for awhile, and thanks for any help,
bobp

[honda750k]

can you post up a pic of how it goes together?   I had mine apart awhile ago and just put it together a few days ago. didnt get pics, but I should have.  I could tell you if its ok or not.

[Trav-i]

Sounds like it's put together right.  From everything I've ever read the 550 master does not use the check valve, it was only for the 750s.  I rebuilt a master not too long ago and had the same problem (just an air pocket), I hooked up a vacuum bleeded to it and held the lever back until I saw fluid in the tube.  Once I saw fluid I released the vacuum and the master worked perfectly.

This is just my 2 cents, good luck.

[steam-powered man]

here's a pic of the assembly as i disassembled it.  no check valve, with primary cup on spring having open end placed in the spring and secondary cup is installed on piston.  "skirt" faces spring.  look ok?

maybe all i need to do is some research on bleeding a system after full disass.  thanks,
bobp 

[JohnG]

without vaccum assist tools I have always found it a slow process.  There is air down around the caliper and you are trying to get it out the top of the MC.  I sit next to it playing with the lever and watching the resevoir, as well as tapping the line and caliper with a small, rubber mallet.  Every so often a trail of bubbles appears in the resevoir.  I kind of feather the lever back and forth, about 1/2 of the possible travel.  It demands about as much patience and persistance as anything.

What do you guys like for a vaccum assist tool???

[Bill/BentON Racing]

Mity vacs work well,If you make sure fluid is coming out of m/c before install,point hole up after filling to proper level pour a little fluid in hole pull lever sloooowlyair will bubble up, soon no air,install,fluid out of caliper 10 pumps or less!! This is with or w/out Mity Vac,Bill I call it priming the M/cylinder.Sure seems to work.

[BeSeeingYou]

here's a pic of the assembly as i disassembled it.  no check valve, with primary cup on spring having open end placed in the spring and secondary cup is installed on piston.  "skirt" faces spring.  look ok?

maybe all i need to do is some research on bleeding a system after full disass.  thanks,
bobp 

That looks correct.  I think the check valve was not used after 76.  Here is a picture of mine from a 76 750.  Now that it is apart I would put a rebuild kit in.  The cup on your piston just looks a little "flat" on the flared end.

[steam-powered man]

thanks very much!  excellant help as always.  have been on my enduro for the last coupla days and will try the brake again on the next rainy day. later,
bobp