Brake master cylinder question... I'm new to discs.

[TheRadBaron]

Most of my bikes have drum brakes, so I'm kind of new to hydraulic discs on motorcycles.  I just got done installing the stainless lines and bleeding the front brakes on my '84 FJ, and I have a question about the master cylinder.  If you're looking down into the reservoir (with the little stainless steel strip removed), there are two holes visible.  A small one on the inboard side, and a larger one outboard.  When the lever is pulled in, fluid squirts up out of the small inboard hole for the first 1/3 or so of piston travel.  This seems weird to me since that fluid is going out of that hole instead of down the lines to apply pressure to the pads.  I don't really like the way the lever feels due to this.
Is this normal behavior for the master cylinder, and if so, what's the purpose?

[FJmonkey]

Most of my bikes have drum brakes, so I'm kind of new to hydraulic discs on motorcycles.  I just got done installing the stainless lines and bleeding the front brakes on my '84 FJ, and I have a question about the master cylinder.  If you're looking down into the reservoir (with the little stainless steel strip removed), there are two holes visible.  A small one on the inboard side, and a larger one outboard.  When the lever is pulled in, fluid squirts up out of the small inboard hole for the first 1/3 or so of piston travel.  This seems weird to me since that fluid is going out of that hole instead of down the lines to apply pressure to the pads.  I don't really like the way the lever feels due to this.
Is this normal behavior for the master cylinder, and if so, what's the purpose?

That dates my experience on bikes. I have had hydraulic clutches exclusively. Does the clutch work properly? The hydraulics just might be new to you and all is good. If the bike is warm and the clutch works properly, what you feel just may be the hydraulic thing vs. cable. check the slave next to the drive sprocket for pealing paint and and DOT3/4 leaks. You might have leaks and some air in the lines that hydraulic clutch owners know as tell tail failure signs. Check for fluid level, with bars turned to full Right hand turn. What color is the fluid? Dark indicates time for a change, too much water/moisture absorbed in the fluid. Should be clear to piss Yellow, brown to dark and you are over due. Plenty of guides and methods for a good flush and bleed on this sight.   

[TheRadBaron]

I'm actually working on the front brakes, not the clutch.  The fluid looked okay when I changed it, but I've got fresh DOT4 in it now.  It seems odd to me that the fluid is squirting up out of the small hole instead of being used for braking force.  After the piston travels in a bit, the fluid stops coming out of the small hole and the brakes feel nice and firm.  Between the specified 5-8mm of free play at the lever, plus the travel of the piston while the fluid is coming out of the small hole, I don't like the amount of travel in the lever before it actually applies the brakes. 

[Kopfjaeger]

my brakes are the same... yes when you squeeze the lever it does "squirt" a little back up in the resevoir... wether this is an issue of bypass..( as in there is sufficient pressure in the line or wether it is to keep the fluid circulating ) im not sure. yeah they are soft, i have an 86 and you need to pull on the lever a bit to get any response... i believe thats why the fellas and ladies here upgrade to  better callipers. remeber they are only single pot callipers, albeit 2 sided, unlike other bikes i have had which have a floating or "fixed" plate and the pistons on one side the FJ has 2 pistons pushing in. the more i think about it the more im inclined to belive the squirt is to circulate the fluid and allow cool fresh fluid into your lines. If the others can clarify this it would be cool.... sounds like they are operating ok if you have bled them and no more air is in the system, then yes that is as far as i know in my expierence they work normally the way you describe. soft and squishy!!!

[racerman_27410]

that is perfectly normal for hydraulic brakes.... what you are seeing is the fluid being pushed back up the bleed hole...this action has nothing to do with the building of force on the brakes its there to allow the piston to move inside the sealed system....... as the lever is pulled, a certain amount of fluid has to come back into the cylinder in order for the piston to move its full distance.... as the lever is released it also draws fluid back in thru the same hole in order for the piston to be able to return.


if you have excessive lever play then you have not finished bleeding the brakes..... move your handlbars so that small bleed hole is up hill and just tickle the lever to see if you can get the last few bubbles of air from inside the master.


KOokaloo!

[Kopfjaeger]

but of course.... i forgot the piston to busy thinking about the lines. thanks