Topic: desperate for front brake help!!!

[ezranz]

so i've rebuilt the caliper and the MC countless times, carefully bled the brakes and the caliper still has a problem with releasing the pressure on the rotor... i honestly know very little about hydraulic disc brakes which may be why i can't figure why the pressure isn't releasing.  the bike is a 1973 honda cb500k2, and the original front caliper was toast, so i'm using a donor caliper from a '75 cb550, i checked the part # and they match meaning they should be the same part, but is this my problem or is lack of disc brake knowledge my problem?

~Ezranz

[Mach-5(50)]

are the brake hoses original, or have they been replaced?

[manjisann]

Also, where are you located? If you are anywhere near me, I would be happy to help. I spent a few months trying to figure mine out, turned out I had put them back on incorrectly once and that was he issue. It goes fork, brake, then fender. 

Brandon

[BobbyR]

This has been covered before so a search give you more detail. There are two small holes at the bottom of MC. You need a fine strand of copper wire to rod them out. If they are plugged, the cylinder will not retract. If you have a hose that is collapsing, that is a possibility. Check the holes first. If you have an old hose you should replace it anyway for safety.   

[DaytonGuy]

+1 on the tiny return hole in the MC.

Also, make sure you got all of the crud from behind the round rubber seal inside the caliper.  Remove seal and clean groove really well.  I assume you know this already.

Also......BobbyR you have the best collection of "babe" pics on the forum.  I really dig Santa's little helper.  I'm sure she takes good care of him....

[ezranz]

those two holes are pretty clean looking, no visible crud... and i went in and cleaned the piston cylinder but did not remove the seal... perhaps that could be where my problem lies... btw i'm from the bay area, walnut creek area...

[Deltarider]

Are you sure you placed the round rubber seal (inside the caliper) the right way around? So that it helps to retract the piston, when pressure is relieved.

[ezranz]

also, they are the original hoses, but they look to be in pretty good shape IMHO...  but given that the problem plagued the last caliper that was on the bike, and pretty much everything but the hoses has been either replaced or rebuilt so that logically leaves the hoses as the culprit... we'll see
 

[ezranz]

Are you sure you placed the round rubber seal (inside the caliper) the right way around? So that it helps to retract the piston, when pressure is relieved.

so how do i know if that seal is on in the correct orientation?  i'm about to roll up my sleeves and spend my afternoon hunched over the front wheel, so all your help is much appreciated!

[Deltarider]

The rim of that rubber seal is a little bit higher on one side. That side should be on the diskside.

[Bob Wessner]

those two holes are pretty clean looking, no visible crud... and i went in and cleaned the piston cylinder but did not remove the seal... perhaps that could be where my problem lies... btw i'm from the bay area, walnut creek area...

The one hole, the smallest, is at the bottom of what appears to be an incomplete drilling. It is very small. The only way I was ever able to determine it was clear, was to shine a bright light down the M/C piston bore and check for a speck of light. If you don't see the light, it's plugged.

[BobbyR]

+1 on the tiny return hole in the MC.

Also, make sure you got all of the crud from behind the round rubber seal inside the caliper.  Remove seal and clean groove really well.  I assume you know this already.

Also......BobbyR you have the best collection of "babe" pics on the forum.  I really dig Santa's little helper.  I'm sure she takes good care of him....

Thanks, it is a community effort. Now you know why Santa is always so jolly.