Spongy front brakes.

[erik]

My front brakes are spongy, I've tried bleeding them, replacing the lines with new (rubber) lines, bleeding them some more.

The last trackday I went to I was starting to loose confidence in them as the lever was almost touching the handlebar. It got worse during the day. I'd replaced the lines and bled them the week before the trackday. After the trackday I tried bleeding them some more, I might have got a single bubble of air out of the left caliper, but that was it.

I've read a couple of other threads on here where people suggested tilting the master cylinder and/or the splitter block thing while pumping the lever a bit to try to get any stuck air bubbles free. I'll try that.

But I've also been wondering about the master cylinder size. Mine says it is 5/8. El Dopa's one says it's 3/4. He's also got braided lines, but I reckon the 3/4 cylinder must be making a difference as well since.

Anyone else with a twin disc bandit know what size your master cylinder is? I'm thinking about looking for a 3/4 one at a wrecker, but I should really figure out how to bleed my brakes properly first in case that's what's making them spongy.

[Banditmax]

Having the 5/8 master cylinder would mean your lever would travel further but should not make your brakes "spongy" Are you sure you master cylinder is sealing properly though?

[Forde]

braided lines could make a good difference and theyre not too dear, rubber ones suck under hard braking especially on track conditions.

Maybe some high temp race brake fluid too?

[gsxr400 racer]

braided lines could make a good difference and theyre not too dear, rubber ones suck under hard braking especially on track conditions.

Maybe some high temp race brake fluid too?

good idea but some break fluids dont mix with others

[PitterB4]

Steel lines make such a difference.  I didn't realize it until I got my Kawi.  My steel line equipped B4, even with the single disc stopped better than the Ninja.  The CBR with steel lines and race pads is just crazy.

[turbofb]

My FZR suffered from a spongy feel too.
At first,it was just stubborn bleeding,so I got a bleeder screw banjo for the MC.That turned out to be a very helpful little part BTW,I put one on all my bikes now since it makes one-man bleeding much easier and quicker.
After a couple years,the spongy feel came back and I couldnt get rid of it.I rebuilt the MC,changed the MC,bled the hell out of it and even upgraded to 94'  6-piston front calipers...but it still didnt feel well.So I slapped on some nearly brand-new Ducati rotors I got for a steal,and that solved it.Even though my old rotors were still pretty thick,they had become concave on the friction area,and I guess it was making the pads contact in a rocking fashion,rather than hitting the surface dead on.

[gsxr400 racer]

just slap a gsxr, sv, or hyabusa master on and run with it

[Forde]

braided lines could make a good difference and theyre not too dear, rubber ones suck under hard braking especially on track conditions.

Maybe some high temp race brake fluid too?

good idea but some break fluids dont mix with others

i wouldve imagined that you would change the brake fluid so the high temp one was the only one in there.  anyway definitely get steel lines dude, theyre awesome and cheap too!

[Red01]

If you decide to change the fluid again due to steel lines (+1) or just as an experiment, I've heard good stuff about Valvoline's DOT 4 SynPower fluid.




I learned of it during the brake fluid debate of a few moths ago. When I put steel braided lines on my B12, I chose this stuff. There are a few better fluids for the racer, but they are harder to find, will have to be changed more frequently and cost substantially more than this stuff - which can be found in most any auto parts store.

[CWO4GUNNER]

It would help to know how old your bike is hence the cylinder. I know only one thing from experience, when a brake cylinder & piston gets old and starts acting up I just find it easier to replace it new then rebuild or replace with a junker which usually repeats the problem. But your right, you need to bleed them correctly and hopefully with someone who has allot of experience if your not sure how.

[land-warrior.rus]

My bet is on the master cilinder, i had same problem. when i rebuilt it everything was spot on.

[erik]

I tried bleeding them some more, this time taking the brake system off the bike and putting the calipers above the master cylinder and moving things around in the hope that any trapped bubbles would get out. It didn't help though.

A friend suggested plugging the master cylinder with a bolt to test if the seal was ok, I tried that and pulling on the lever with the bolt in the lever only moved a few milimetres and was rock solid, so I'm guessing there's nothing wrong with the master cylinder?

I'd really like to know what other people's twin disc bandit brakes are like, and what size master cylinder they have. the only thing I can think of now is that the master cylinder isn't big enough to cope with moving all 8 pistons + the expansion of the rubber hoses.

So as I see it, I could either get braided lines or try a bigger master cylinder... hmm

[tomacGTi]

On stubborn brakes, I use a syringe and reverse-bleed the system.

Pretty much, fill the master cylinder so it isn't entirely topped off. Connect a syringe filled with fluid to the bleeder and push the fluid up towards the master. If there is air in the system, you will see bubbles in the master. Actuate the lever several times and this will pump the fluid back down into the syringe and if there is air there, it will bubble into the syringe. Close off the bleeder and try the brakes then.

Also, if you've cracked the system open before, you may need to replace the bronze bushings on all of the banjo bolts. I've had that happen before as well.

I used to work for an Italian disk brake manufacturer that build bicycle disc brakes as well as moto (not Brembo). Little secret we used to do to speed up the process....

[Red01]

I used to work for an Italian disk brake manufacturer that build bicycle disc brakes as well as moto (not Brembo). Little secret we used to do to speed up the process....

Campagnolo?

[tomacGTi]

Formula.

The owner was an avid motocross and trials guy. Got into MTB and has won several world championships. It was a great company to be involved with helping develop and test product for race/market.

Campy never did anything with hydraulic