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Post by roninrun on Dec 15, 2015 15:46:59 GMT
I've read somewhere that the front brake calipers can cause the piston to catch and make the bike flip. They say that if you have the piston past the tiny fluid return hold (because lever is adjusted improperly) that as the break fluid heats up, the brake fluid expands and cannot bleed off the pressure. Basically the bike might have a front brake issue that can be quite dangerous. I've seen recommendations to replace the master cylinder with the GSXR or CBR to prevent this. They also said to make sure you have about 1mm of space between the adjuster screw and piston to prevent this from happening. Anyone have any information on this?
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fz989
New Member
Posts: 24
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Post by fz989 on Jan 3, 2016 10:48:06 GMT
This is possible on any hydraulic master cylinder. At rest, the master cylinder piston cup seal is exposed to a tiny port which feeds from the mater cylinder reservoir. The first few mm of brake lever travel will not pressurise the hydraulic system, until the master cylinder piston cup seal travels past the tiny port. The reason for this, is so that as the brake pads wear, more fluid can enter the system via the port to make up the extra volume where the caliper pistons have moved toward the discs.
Now, if the preload is adjusted incorrectly at the brake lever, so that the master cylinder piston has been preloaded far enough for the cup seal to be past the tiny port, bad things will happen.
As you have read somewhere, the slightly dragging brakes will develop heat, which will transfer through the caliper and into the brake fluid. The fluid expands, which exerts more hydraulic pressure, applying the brakes harder which creates more heat... the cycle continues.
It is unlikely that you will flip the bike over, but it will feel that someone is applying the brakes harder and harder.
In my first year of riding, lacking the knowledge I have now, I did exactly this, with the rear brake of my RZ250. I was wondering why it felt my bike was slowing down (at approx. 80 km/h), so down changed a gear and got back in to the powerband. Again it slowed, so I pulled the clutch in to pull over and found the bike was braking quite hard with no input. Once I stopped, I found smoke coming off the rear brake and the disc was a dull orange colour!
Backing off the lever, let the master cylinder piston return to where it should have been (exposing the tiny orifice) where the brake fluid could return to the reservoir, relieving the built up pressure.
There is no need to replace the master cylinder to prevent this - just make sure there is no preload on the master cylinder piston at when the lever is at rest.
If the lever is no springing back to rest, you need the overhaul the master cylinder.
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