I'm having some serious issues with my rear brake fluid.. basically, for awhile now (after I bleed the brakes initially, unsucessfully) when I push the pedal down, it just slowly floats down to the bottom. If I pump it a few times it sometimes works.

After reading on here, I did the proper bleed technique. (Open the secondary thingy, bleed right front caliper, left front caliper, lower rear, upper rear) I've almost gone through a complete jug of fluid and its still doing the same thing...it just feels spongy. What am I doing wrong?

 

Hi there! I have a 1995 CBR1000F and am having the exact same problems....

I've bled the system about 10 times now - no bubbles appear to be coming out,but the rear brake pedal is spongy and never holds the pressure.

Like you,if i pump it a few times then it works - but that ain't no good if you need to stop quick!....thing is i can't figure out what caused this.

I'm relying on the front lever at the moment,which does give partial braking to the back - but i would still like to get the rear pedal working...

a couple of people have told me that it could be the seals in the rear master cylinder that have gone,allowing the fluid to travel through it
and not holding pressure - but i ain't sure..

I'm seriously thinking about de-linking the brakes with callipers and parts from an older CBR but don't really want to do this if i can get the
linked system sorted as i'm used to it now!

 

Mines also a '95. I don't get any bubbles coming out. I don't think it would be anything but air in the system, since it worked fine before I bled it originally. Is there anything you have to do the master cylinder while your bleeding it? (like opening the secondary one, for example)

 

Hi - I've recently done my '99 F-X model. Used the traditional method (ie I didn't used a vacuum pump or one-way valve etc). Instead I just attached clear tubing to the bleed valves and opened/closed them as appropriate. Make sure the other end of the tubing is secured in a glass jar and submergered under some brake fluid. The correct procedure is below. It requires a helper and a prearranged method of communication between the both of you in order to get lever/pedal pumping and valve opening at the correct times:

Undo secondary master cylinder orifice bolt (counter-clockwise) until it seats against circlip.

Remove both reservoir caps.

Use a syringe to remove as much old brake fluid from the reservoirs as possible without exposing the small hole at the bottom to the air.

Fill reservoirs with fresh fluid. I loosely fit the covers back on in case of brake fluid spurts out, although this has never happened.

Right front caliper, upper valve - using front lever (keep front reservoir topped up)

Left front caliper, upper valve - using front lever (keep front reservoir topped up)

Right front caliper, lower valve - using foot pedal (keep rear reservoir topped up)

Left front caliper, lower valve - using foot pedal (keep rear reservoir topped up)

Rear caliper, rear valve - using foot pedal (keep rear reservoir topped up)

Rear caliper, front valve - using ring spanner on secondary master cylinder linkage bolt (keep front reservoir topped up, although it will go down slowly as not much fluid is expelled at the valve with each 'pump' - infact, none came out on the initial pump)

Tighten valves to correct torque (5 Nm)

Top up reservoirs and fit diaphragms, covers etc

Tighten secondary master cylinder orifice bolt (5.4 Nm)

I like to flush around 1.5 - 2 reservoirs of fluid through for each valve to make sure the pipes have been cleared of old stuff.

I periodically tie back the front lever tight with a zip tie over night to bleed any bubbles remaining from the system to give a firm feel to the lever. Haven't yet worked out a way to hold the foot pedal down over night in order to do the same that circuit.

Sorry if I've told you stuff you already know. My rear brake pedal and front lever for that matter do not have the firmest of feels (say compared to my CBR954RR), but they are not spongy. If your rear pedal is working correctly, it should stop the front wheel from turning. Just put he bike on the centre stand, get a mate to sit on the pillion seat and lean back until the front wheel is off the ground and try the pedal. Might be worth checking that all the banjo bolts at each caliper are correctly tightened to 35 Nm before you start. One other thing with the rear pedal is that it can feel a little like an on/off switch in slow moving traffic. This is simply due to it activating the front caliper and causing some fork dive (this always catches me out when I switch to riding the 1000F from the 954RR.

Hope this helps, if I've missed anything, hopefully somebody with point it out!

Good luck

 

I agree with Nelson. You have to push fluid from the rear master cylinder all the way to the two front calipers for bleeding and all the way back through the secondary master cylinder (with orifice bolt opened) through the proportional valve and finally to the rear outer pistons. The rear center piston is a direct line to the rear master cylinder and bleeds quicker.

Do not over tighten or over loosen the orifice bolt.

When I bleed mine I replace the yellowish DOT 4 with a clear DOT 5 so that I knew that I had pushed the fluid all the way. Keep topping out the reservoir or you start all over.

If you ever decide to de-link you can use your parts but you need to make two brackets to hold the front left caliper and get two front break lines. You also need to drill the calipers to link the pistons. It's an easy job.

Nelson, how about hanging a paint can on the pedal when on the center stand.


[IMG]local://upfiles/8473/5C55F231D3EF44328AA56168DB889122.jpg[/IMG]

 

Thanks for the tip with the paint tin TimBucTwo. The simplest ideas are always the best!

 

A quick update. I fixed the problem, I wasn't paying enough attention to the rear brake and one of the lines wasn't bled properly. I spent another 45 minutes on it and everythings all bled. I fear after all my efforts the pads are worn out though, even strongly stepping on the brake it barely slows it down. It doesn't fall down to the bottom anymore, though..so I'm happy.

 

Roughly 75%-80% of a bikes stopping power comes from the front brake. A hard squeeze on the front brake lever can easily lift the rear tire off the ground [:-], or worse, lock the front tire. The rear brake will slow you down, but it often seems like you have "Coaster Brakes" like on a kids bicycle. The stopping ability of the back brake is not that impressive IMO.

 

It depends on the bike.

The longer the wheelbase on the bike the better the rear works.

Look at a goldwing. The size of the rear disc is the same as the front. Where as on a CBR1000RR the rear disc is tiny.

The whole DCBS systems on the CBR1000f is designed to prevent the rear lifting under brakes making it more effective at stopping tke bike compared the a non-DCBS bike.