Now for a different head scratcher.....front master cylinder.

[John Schmidt]

I rebuilt both m/c cylinders, clutch and brake, and used them on my 1200 project bike. The clutch works fine, the brake....not so much. The only way I could get the fluid to draw down in the reservoir while bleeding the system was to use a MityVac, even though I have speed bleeders installed. When I pump the handle, there simply is no resistance so the speed bleeders are of no value. Today I finally pulled the brake m/c and tested it on the bench, moving the handle to see if there's any pressure coming out....NONE. Do you suppose it's possible the rebuild kit was simply mislabeled and is slightly undersized? Over the years I've had a couple cases where the cup was defective and tore one edge shortly after installing, but this one isn't damaged so I'm kinda scratching my noggin. Guess I could order another kit, just didn't want to spend the $$ if not necessary. Any thoughts, suggestions?

[Paladin528]

One of the seals is directional.  Did you get it the right way around?

[John Schmidt]

Yes, it has two cups. One is mounted on the piston with the open face pointing forward. The other sits on the return spring with the open face pointing forward and is pressed forward by the piston when you squeeze the handle. And....when I took it apart for the rebuild, I laid it out on the bench and put the new stuff in exactly the way the old came out. Guess I'll order a new kit and see what happens.

[Pete]

You did check that the piston is full travel, especially rear?
And you did check the small hole or holes that they are clear to feed the fluid to the piston?

Those two things being true then it must be the cups!!!

[da prez]

  John , we have run into this often. Sometimes on a rebuild , the plunger is not fully returning. We take out the clevis pin and put in a smaller bolt or small shank screwdriver so it is a sloppy fit. This allows the plunger more room to return. It is a fast check to isolate the problem. If the cylinder builds pressure  , the problem is not returning far enough to get the fluid in to the plunger. If no difference , then probably a bad kit. We have run into this with factory new master cylinders.

                                       da prez

[John Schmidt]

Ross, another problem seems to have developed now. I pulled the m/c apart and all seems fine, but when I tried to reassemble it the piston now is so tight it won't return and takes a lot of force to press it in. It's as though the cup mounted on the metal piston has swollen to the point it doesn't move in/out unless forced. I've only seen that a few times and traced it back to what appeared to be some bad material for the cups. Guess I'll order a new kit and hope for the best, this one wasn't a Honda kit but will do so this time around. Strange....the same brand worked fine on the clutch.

[Paladin528]

for parts like that I always go with the Honda kits.  The OEM kit worked for 15 years which is pretty good in my books