Front master cylinder not holding overnight pressure

[ilanr1]

Hi , i'm feeling that my front brake lever is a little spongy like there is air in the system.

I tried to bleed the system and it's much better , i saw in youtube that if i put overnight pressure on the front brake lever the air bubbles that trapped inside will go up in the morning when i release the pressure and that will improve the braking action.

So i have done that and in the morning i saw that the front lever is not holding presure and it went all inside , no leaks in the front brake tubes or connections.

Do i need a rebuild kit to the front master cylinder ? or what ?.

Thanks

Edited July 26, 2023 by ilanr1

[johnmark101]

I had this same problem with my Kawasaki.  Can't say that yours is the same issue but rebuilding the master cylinder solved mine.  

[ilanr1]

Thanks .

[TomTracer]

What bike?

[Brentinpdx]

First up brakes are brakes doesn't matter what bike it is. They all use the same parts. A spongey lever means there is air in the fluid. It could also be old. Brake fluid should be changed every 2 years. 2015 is 8 years old. Has the fluid been changed regularly?  Brake fluid should not be cloudy, brown, or black. If it is, it is old and has water in it. Water causes the cups to swell and they begin to deteriorate.
A spongey lever means that air has gotten into the system. Find out why and correct it.  A rebuild can be it. If it gets rebuilt and you still have the issue. Find it. Also, the crush washers that mate the lines to the cylinder are one-time use only. They are cheap so it pays to use new ones. Also, your OEM rubber lines could be needing a replacement. Braided lines will help improve braking and are not subjected to the same issues that rubber lines get. Like sunlight. This ages the lines due to UV rays.

[ilanr1]

The bike is Tracer 900 GT 2019 , i should update my picture...

 

Edited July 27, 2023 by ilanr1

[TomTracer]

Snark not appreciated! Lots of people do lots of things to bikes that can allow air to get into the system inadvertently. I'll ask anytime I like and no one needs your permission or approval.

[duckie]

Yeah……leave the snarky remarks to me…..

In this case, air in the system is not the issue, but the brake master cylinder plunger isnt make a good seal with the housing letting brake fluid go pass back into the reservior. 
 

Too just assume its air in the system      is bad troubleshooting and shows not fulling understanding how the components of the brake system operate. 

[duckie]

Oh yeah……..improved braking means what? I think some clarification is in order. 

What steel braided lines do is change the feel of the lever but does not increase the actual braking force being spplied. It may feel like it cause of no rubber expansion, but they dont. 

Braking force being applied is a ratio between the master cylinder bore size and total brake caliper piston surface area. 

If ya want more braking force, the most common method is to change the bore size of the brake master cylinder. 
 

[johnmark101]

For what it is worth, rebuilding the master cylinder is very simple.  Usually it is just a coupe of seals and a piston.  You will probably need a small pair of snap ring pliers.