General Category > ABS related issues

Brakes still squishy after GS-911 bleed on 2003 F650GS Dakar:

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questhe:
I just got done with master cylinder disassembly.


The pressure cup looks fine.  I think it might be a bit hard to tell if it was failed since it is required to hold huge pressure.  So, I am ordering a new one as a 24k maintenance. 

The lever will slowly pull in, even with a little force.  When riding, I have to pump it to get braking, and then also pump it to keep braking.  It releases in about 1/4 second from full brake to no braking.

If I run the gs-911 brake cycle, it will sometimes result in a hard lever (it appears to work correctly) until I use the brakes a few times.  After that, the symptom is always present.

-current path is to buy a used ABS off fleabay and R&R. 

Jughead:
Doubt very much the ABS is at fault.  The fact that the lever slowly creeps toward the grip indicates that the master cylinder is leaking back into the reservoir.

The entire system is sealed so if the lever is creeping as you say and there is no evident brake fluid leak onto the ground, the brake fluid is going somewhere.  This "somewhere" is past the pressure seal on the master cylinder piston and back into the reservoir.

questhe:
Thanks - I have the master rebuild kit coming.

Have you had this happen to yourself?

GS Jim:
I've had it happen on MX bikes and also on hydraulic cylinders many times. Usually caused by contaminants in system but also wear and tear in industrial settings, in your case probably something in the fluid nicked the edge of the seal. After disassembly totally clean master cylinder and install new kit being careful with the seal. Good luck.

questhe:
awesome!, thanks again  8)

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