[09_Blade]

I have a 2009 ABS model and have some insight.

1. It is not a matter of properly bleeding the system. I did two full flush/bleed cycle including the power unit under the headers using a vacuum pump and did not notice a difference.

2. It is not the stock master cylinder. I replaced it with a brand new Brembo RCS19 and there was no difference.

3. It is not the stock rubber brake lines. I replaced them with a full Galfer stainless kit and there was no difference.

The problem is the caliper piston retraction by the power unit combined with the stock caliper piston extension/retraction distance.

Above a rolling speed, the master cylinder is disconnected from the calipers and goes instead to a pressure sensor. As a result, the "brakes" feel firm and the lever travel is great. Lets assume you apply the brakes and keep the brakes applied until you get below the ABS cutoff speed. As long as you keep the brake lever applied, the actual braking pressure is supplied by the power unit even though you are now in a situation where the ABS system normally would not engage. Now when you release the lever at below the ABS cutoff speed, the front power unit has to retract and the system must pull fluid away from the system.This is fine if your brake lever is fully released and fluid can flow from the master cylinder reservoir. The problem is if your lever is slightly squeezed (not fully released), the ABS power unit still has to retract and draw in fluid which means it will retract the caliper pistons more. Fluid cannot come from reservoir because master cylinder piston is past those fluid ports. Then, the calipers with pistons retracted more than usual are connected back to the front master cylinder, which is already partially compressed in this situation. When you go to apply the brake lever now, the lever travel is significantly greater than expected because the master cylinder is already partially compressed and the calipers are more retracted than normal by the power unit. This is why pumping the lever lets you regain pressure.

Replacing the stock calipers with a pair of Brembo GP4-RX was the very expensive solution. The GP4-RX calipers have less piston retraction by nature of the seal groove design and consequently also less fluid required to engage than the stock calipers. There is significantly less lever travel required to engage the pistons compared to stock calipers, which makes the ABS slop minimal because the power unit piston does not have to extend as much to engage the brakes and consequently does not have to retract as much to disengage the brakes.

 

[09_Blade]

I have not tried any other calipers, but what you are going for is a set of calipers with a smaller outer chamfer than the stock caliper. You can examine this with a small mirror with the caliper piston removed. I have circled this in attached picture. These are typically race calipers because it's a compromise between lever travel before engagement and caliper drag.

If you have access to other bikes with dual 108mm calipers i.e. GSXR's with M4 calipers, squeeze the brake lever to get a feel for how far the lever moves. For reference, on the GP4-RX with light 1-finger pressure the tip of the standard length bar moves only 23mm before it meets firm resistance (not forcing it). Don't remember what the stock calipers were but it was way more than 23mm for sure.

I understand your frustration, prior to addressing the issue, I had to put the stock lever way out to avoid a situation where the lever hits my knuckles. That made it very uncomfortable when downshifting because the lever was so far away from the grip.

 

[09_Blade]

Hey so finally my dealer said that they can have a look at the bike, and it will be on warranty still, is it worth for them to still have a look at this issue or there is no way it's the brake lines that need flushing? I think that's what they are willing to do, flush the brake lines. They obviously are not willing to cover these parts to solve the issue.
Also after speaking to them they told me it would only take 1.5hrs to do the brake flush on the bike, but it's with an ABS module, seems a bit quick

Flushing the brake lines will not make a difference at all for the lever going way down. Nor will changing the brake lines. It's an inherent flaw in the system. If your ABS is flashing then have a go at it sure since it's under warranty. Don't expect it to fix the lever feel.

1.5 hours is about right. It's nowhere as bad as people make it seem. You just short this red jumper under the battery, tap the brake levers in a certain pattern, bleed from the right port, and repeat. It's just annoying to do yourself the first time because if you mess up any part of the sequence you have to start all over.