Wet brake disc

[Jerbear]

So finally, after weeks of waiting for the right time, I took the bike out for the first short 100 mile test run, since working on the carbs. She ran great!

Couple days later I noticed that the front right disc is wet, not dripping but it had a thin film of something on it. I did not ride since that day. I did mention the “woody” feel of the front brake last year before the winter came. I did strip the calipers when I got the bike, as a part of the general: let’s see what we’ve got here” routine when buying a used bike. I remember replacing/installing the master cylinder rebuild kit as well as replacing the piston seals. Pistons looked ok then, so I didn’t bother replacing them.

I have yet to remove the caliper and try to pinpoint the leakage. The brake lever felt very hard to squeeze and the braking wasn’t impressive. Would a leaking brake piston seal cause a hard lever? Is there possibly something else, somewhere that would cause the brake piston seals to leak? I used a fleabay master cylinder rebuild kit but used Honda piston seals. I would welcome any ideas before I fork out $200 for new pistons and seals. TIA.

 

[Obo]

A stiff lever wouldn't be expected with a leaky seal unless the lever was bound up somehow (at the pivot point or the plunger)

Another option for the wet disk could be a leaky fork seal and what you are seeing isn't brake fluid at all - or the neighborhood dog lifting it's leg?

 

[pmatulew]

The caliper piston bores corrode behind the piston seal and jam the pistons. May have gotten bad enough to start leaking. Unless you have a fork seal going bad.

Time to get those calipers stripped down and cleaned out.

 

[Jerbear]

A stiff lever wouldn't be expected with a leaky seal unless the lever was bound up somehow (at the pivot point or the plunger)

Another option for the wet disk could be a leaky fork seal and what you are seeing isn't brake fluid at all - or the neighborhood dog lifting it's leg?

Good idea, I'll take a good look at the fork seal. Thanks!

 

[jfheath]

Brake fluid is not nice to get on your hands, but you can easily tell the difference between it and fork oil by the feel of it.

The antidive plunger may be on your right fork leg - depending on whether or not you have Abs - that is worth looking at.

The radiator cap and hoses are also possible sources of fluid down the right hand side. Its a bit if a jump to the forks but who can tell what direction the air and fluid flows behind the fairing ?

 

[Jerbear]

It looks like Obo was right, there is a significant amount of oily film on the right fork lower. Blackish in color, wonder when was the last time that was changed. Darn it (not the words I'd usually use at a time like this) was hoping for a brake job at this point. I'll continue with this under the suspension theme. Thanks for your input guys.

 

[Obo]

If it's just a leaky seal from some dirt etc you might get lucky and use a SealMate fork sealer tool to fix it (or make your own out of a plastic milk jug. You may still need to top up the fluid but may save from needing to remove the wheel, forks etc.

 

[pmatulew]

I did the "make your own seal cleaner" thing a couple years ago and it did stop the leak. Just cut a curved part out of a plastic container. Make a sort of hook on one end. Slip it in and wipe the dirt out.

If it doesn't work you're only out a few minutes of time and a plastic container that you were going to dispose of anyway.