Hi

Right up until recently,the linked brake system on my '95 CBR1000F has been working faultlessly and gave no problems.

Problem is now,the rear pedal is very spongy and travels all the way down when pressed....It's ok if you give it a few pumps
first off,then it responds and works - but leave it few a few seconds and it'll lose all its pressure.....

Now the front brake lever works fine and is operating the brakes as it should.I've tried bleeding the rear brake,through both
the bleed nipples on the rear calliper - a few bubbles seemed to come through but nothing too bad,but doing this hasn't made
any difference....I've been through the haynes,which recommends taking it to a honda dealer as they have the proper pressurised
brake bleeder,but i want to fix this on my own if i can.

Why would it be after bleeding the rear,would the pedal still not be holding it's pressure?would it mean the proportional valve has given up,
or maybe just the rear master cylinder?If the front levers working ok,i don't really want to touch it but if there was a problem with the linked
setup surely i'd be experiences front problems too?

Have any of you running linked brakes experienced problems with bleeding?

 

I bled my brakes according to the Honda service manual. While it says it's recommend to bring it to a dealer, they do give a garage setup instructions to bleed the brakes on your own. Also, ANY air bubbles will screw with pedal / lever feel.

 

Hmmm....what i meant to say was that a few bubbles came through initially but i have bled the rear until NO bubbles came through!

 

From what I understand about the LBS, both levers activate both brakes. If your front brake lever has good pressure, that must mean the problem is not in the rear brake but somewhere between the rear brake pedal and the master cylinder. Hope that helps.

 

Yes,that is correct Chesthing,cheers - I've also just discovered that the rear calliper won't come on with the front brake lever squeezed like it should,
however even though the rear brake pedal is playing up and needs umpteen pumps before it'll work,it'll operate the front and rear brakes.......i just don't get it....

 

No, from what I understand, the rear and front brake are not linked in that way, the front handle does not activate rear brake directly, the front caliper (left) can move in its brackets during braking which activates a lever connected to a smaller "caliper" that transfers the brake force back to the rear caliper via (I think) a regulating device. The rear works in a similar way.
To cbrlover: this forum has a few treads about bleeding brakes and more, try use the search option and see if you get any help to your problems.

I just wen´t out and checked my theory, and yes, rear wheel still spins even how much I pressed the brake handle. I have a -97 year model.

 

That is strange...I would figure this problem out before riding the bike again, don't want to mess around with a failing brake system. I also hate the idea of paying a dealer but that option sounds worlds better than losing your brakes while riding, good luck.

 

To bleed the rear, you need to loosen the secondary master cylinder orifice bolt.
Also read this thread;

https://cbrforum.com/m_123770/tm.htm

 

Steps are as follows;

loosen the orifice bolt by backing it out against the snap ring and then stop.

using the lever:
bleed the right front caliper from theupper bleed valve.
bleed the left front caliper from theupper bleed valve.

using the pedal:
bleed the front right caliper from the lower valve.
bleed the front left caliper from the lower valve.
bleed the rear caliper from the lower bleed valve
bleed the rear caliper form the upper bleed velve.

tighten the orifice bolt. Do not over tighten it.

Note: You need to keep adding fluid to the reservoir or it will run dry. If this happens you start all over.

Edit: added a step

 

I'm not sure his problem will be resolved by bleeding...the brake pedal suddenly started doing this - I would be inclined to think some component has failed.