Front Brake - First Lever Pull feels soft

I continue to do research on the lever travel/feel and found the below in another forum.

http://www.ducati.ms/forums/56-superbikes/149120-brembo-m50-panigale-callipers-999-a.html

When you design a hydraulic system it's important to have good feedback from the lever as to how much lever force to apply to achieve a desired braking rate. Having good feel, sensitivity and control is the major factor influencing braking quality.

The main factor in designing good braking modulation characteristics is the ratio of the total area of the caliper pistons to the area of the master cylinder.

The Panigale calipers have a total piston area of 5655 sq. mm and has a master cylinder area of 201 sq. mm. This gives a hydraulic ratio of 5655/201 = 28.1.

The RCS brake master cylinder has an area of 284 sq. mm. Used with the Panigale calipers you get an hydraulic ratio of 5655/284 = 19.9.

A general design rule-of-thumb for twin rotor brake systems is as follows:

30:1 - soft feel
27:1 - sweet spot for design
23:1 - firm feel
20:1 - wooden feel

So the use of a RCS master cylinder isn't going to blow your piston seals but it will result in a lever that gives almost no feel, so braking will be extremely hard to modulate.

1098 monoblocs have a caliper piston area of 7263 sq. in and used with the RCS will give you a very nice hydraulic ratio of 7263/284 = 26.6.
....

The 16mm piston actually creates more pressure and has to travel further in its stroke, hence more feel and control to your fingers.

....

The rc19 would pump lower PSI into the calipers than say the rc16

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Basic Hydraulic Formula,
Force/Overall Area= PSI
For instance well use 100lbs Force,
So 100lbs/ 0.439 SQ IN (rc19 Area) = 227 PSI
Where as
100lbs/ 0.309 SQ IN (rc 16 Area) = 323 PSI

Some more information to share:

My Dealer told me that Ducati does not recommend nor does it approve of keeping the front brake lever cable tied under pressure overnight. I was told that Ducati suggests that the sustained pressure could damage the ABS unit.

So, if you have been using that method to help a spongy lever, do not, according to Ducati.

Thoughts?

Interesting read about how the ABS units interact with the regular braking system:
http://www.stoptech.com/technical-support/technical-white-papers/bleeding-abs-brake-systems

Searching for any supporting opinions that prolonged pressure on the brake system can cause damage:

In regards to your question about zip tying the brake lever back to the grip: There is some truth to the madness. However, it really only works if the air bubbles are trapped up near the master cylinder. Anything lower than that and not too much is going to happen for you with this method. In the many years we have been at the race track, and helped racers bleed brake lines, we have followed this method....Bleed out the master cylinder first, then the left side line followed by the right side...then back to the master cylinder. This is topped off by zip tying the lever back for about an hour or so. Anything beyond that really doesn't help and can cause damage to your system. Another technique that we use is bleeding the system with the motorcycle in different angles. Lean it on the kick stand, over on the right side, bounce the forks a bit and so on. All these methods help to knock the air bubbles out of the corners and crevasses of the master cylinder.

Another reason why the zip tying method works is because as you lean the bike (depending on your bike) the fluid in the reservoir moves around causing air to be trapped many times over. Some systems can allow this trapped air to be exposed to the tube that leads the fluid into the master cylinder. When this happens, the air bubbles rest in the master cylinder and can cause that, oh too familiar feeling of a mushy brake lever. Zip tying the system alone doesn't also do the trick. When the system is under pressure, using a plastic pen to tap on the brake lines helps to create vibrations which will aid in getting the air to the top. We also use a small rubber hammer and will knock around on the master cylinder body to achieve the same effect.

Either way, giving your brake system regular flushes is the best way to keep air out of the system and your brakes working like they should. Remember that your brake fluid should look like apple juice and not coca cola. If there are any other questions, please feel free to contact me: [email protected] .

Best Regards,

Sergio Garcia
Sales Manager / Sr. Tech
Galfer Braking Systems USA
[email protected]
www.galferusa.com




One question I have about the assertion that maintaining overnight pressure in the brake lines could cause damage.

How then can it be safe to maintain the parking brake set on a car with hydraulic brakes and ABS?

Dingo said:

I’ve got to replace my pads...


Sent from my iPhone using Tapatalk

Click to expand...

What pads are you considering?

I am thinking of changing mine as well, but not because they are worn. I think the issue of sponginess (which is back BTW) may be just the result of the feeling from increased lever travel to engage pads to disk.

Would another pad from stock change this perhaps? Likely NOT because if the pistons are retracting too much after every release of the lever, the problem of too much lever travel will remain no matter what. Perhaps the piston seals will break in with more mileage and the pistons behave better?

I was observing the piston/pad movement on the first pull of the lever this morning. Using a flashlight, it could be seen that the right side pistons on the right side calipers had to travel a visible distance to engage the rotor.

My Dealer saw this as well last time the bike was in the shop. Ducati said it was normal.


I could not recreate this observation on the second pull. The pads stayed flush with the disk and did not retract to their previous gap.

This could be why there is a feeling of having a long lever pull which can also be described as spongy.

When I get the bike up on a headlift stand, I will be able to rotate the front wheel to recreate this phenomenon and I will try and capture this on video.

I am assuming that the spinning rotor helps push the pistons away from the disk, something that a static pull on the lever on a stopped wheel does not recreate.

On the other hand, perhaps the calipers are not true to the rotor. I may loosen up the calipers and re torque them in place with the lever under pressure.

The rotors may also have a slight warp.

The investigation continues.

Interesting stuff.

https://itstillruns.com/fix-brake-rubbing-wheel-motorcycle-7820564.html

Locate the two mounting bolts that hold the brake caliper onto the front fork. Remove these bolts using a socket and wrench, or hex wrench depending on your model motorcycle, and pull the brake caliper away from the rotor and front wheel. Use a tire lever or similar strong and slender object to push the brake pads toward the outside of the caliper. This will force brake fluid back into the main reservoir, essentially resetting the brake pad alignment.

Set the brake caliper back in place and reattach the mounting bolts you removed previously. Do not tighten them fully. Only tighten them enough to hold the caliper in place. Squeeze the front brake lever multiple times. If will feel soft at first, and will slowly regain its usual firm pull. Use a zip tie to secure the brake lever in the closed position.

Return to the front brake and tighten the front brake caliper bolts securely using a socket and wrench or hex wrench. Because you have the brake lever held shut, the brake caliper should not move or swivel as you tighten the mounting bolts. When you are finished, cut the zip tie on the brake lever and take your bike out for a ride.

@Pard, What you're experiencing is normal as far as the difference in piston extension with your calipers. They are never completely even. It is also normal for your pads to stay right up against the rotors. They will retract somewhat as the rotor spins, but you should never see a visible gap between the pad and rotor. You will almost always feel a slight drag (especially on Ducati's) when you spin the front wheel. "Full-Floating" rotors will aid in the "free wheeling" but they too usually have some drag. Also, my guess is changing brake pads will not aid this situation. It sounds like perhaps your issue is more to do with lever adjustment. I'm sure you're aware, but there is a knob on each lever that allows you make adjustments to the lever travel. You might want to play around with that.

Aside from faulty or leaking components, there are really only a few issues you can possibly have with a hydraulic brake / clutch system.
1) Contaminated fluid (air / moisture / dirt / age)
2) Excessive heat build up (rotors / pads / fluid)

Dingo said:

@Pard - I think I'm going to get EBC EPFA pads, unless someone can suggest a better one for less cost that's not strictly racing

Click to expand...

You might give these a shot... CL XBK5