Sudhanshu Sabharwal

Front Brake Master Cylinder – fitment & spongy lever after upgrade 3

Forum|Forum|2 months ago
December 2, 2025
17 replies
162 views

Replacing stock master cylinder with an aftermarket unit. Lever feels a bit spongy even after a quick bleed. Looking for best-practice on piston size, banjo/crush washers, ABS compatibility, and bleed order.

S

Sudhanshu

Inspiring

Did you match piston size to caliper piston area? Oversize MC can feel firm but weak; undersize can feel long/spongy.

S

sudhanshu.sabharwal

Known Participant

If ABS bleed is painful, a dealer ABS-cycle routine saves time

sudhanshu_sabharwalAuthor

Sudhanshu Sabharwal

@sudhanshu_sabharwal Realtime? EDIT*

S

Sudhanshu

Inspiring

Re-seat copper crush washers (new ones) and torque the banjo to spec. Micro-leaks = soft lever.

S

sudhanshu.sabharwal

Known Participant

Full bleed order matters on ABS bikes: MC → ABS module → calipers. Vacuum + reverse bleed helps.

S

Sudhanshu

Inspiring

Did you match piston size to caliper piston area? Oversize MC can feel firm but weak; undersize can feel long/spongy.

sudhanshu_sabharwalAuthor

Sudhanshu Sabharwal

Confirm caliper pistons slide freely; sticky dust seals retract pads too much.

S

sudhanshu.sabharwal

Known Participant

Master cylinder push-rod free play: a hair of slack prevents port blockage.

S

Sudhanshu

Inspiring

If switching to radial MC, ensure lever travel clears handguards/fairing.

sudhanshu_sabharwalAuthor

Sudhanshu Sabharwal

Spongy after a session? Heat-soak + old fluid → boil. Flush thoroughly.

S

Sudhanshu

Inspiring

If brake light switch is hydraulic, confirm correct thread/pitch.

S

sudhanshu.sabharwal

Known Participant

Verify ABS bleed screws (if present) were actually cracked.

S

Sudhanshu

Inspiring

Quick test: pump lever, hold firm—if it creeps back, there’s air or a leak.

sudhanshu_sabharwalAuthor

Sudhanshu Sabharwal

Check rotor thickness/runout; warped rotors knock pads back.

sudhanshu_sabharwalAuthor

Sudhanshu Sabharwal

Re-seat copper crush washers (new ones) and torque the banjo to spec. Micro-leaks = soft lever.

sudhanshu_sabharwalAuthor

Sudhanshu Sabharwal

Nested reply

sudhanshu_sabharwalAuthor

Sudhanshu Sabharwal

If switching to radial MC, ensure lever travel clears handguards/fairing.

sudhanshu_sabharwalAuthor

Sudhanshu Sabharwal

f switching to radial MC, ensure lever travel clears handguards/fairing.

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