brake rubbing against rear brake disc

[tiku]

Hi.. not too sure whr to post this exactly... I have this problem recently... rear brake auto been applied even uf pedal not depressed. .. went to one of my usual shop, mech found out rear brake pump faulty as sometime I kick up the brake pedal the braking effect is gone sometime not..

 

So mech say change rear pump n service caliper.. after I go home problem return.. braking effect is there.. basically the disc is hot but not hot till change colour... today went back that shop n do it again... today went back that shop n say bout the old prob... mech manage to reduce the braking effect but not all.. but after I travel 2km prob back again.. now my disc got one line on both side.. mech tried to file my brake pad n put back n try...

 

After I reach home I call mech.. mech say try runninh a few day let the pad n disc wear evenly first.. if cannot then go back.. he say worse come to worse is change new pad n disc. . Not too sure how much is one rear disc.. my ride is cbr250r. .

 

Guyz got any idea how to solve??

[Tachnicolour]

Hi.. not too sure whr to post this exactly... I have this problem recently... rear brake auto been applied even uf pedal not depressed. .. went to one of my usual shop, mech found out rear brake pump faulty as sometime I kick up the brake pedal the braking effect is gone sometime not..

 

So mech say change rear pump n service caliper.. after I go home problem return.. braking effect is there.. basically the disc is hot but not hot till change colour... today went back that shop n do it again... today went back that shop n say bout the old prob... mech manage to reduce the braking effect but not all.. but after I travel 2km prob back again.. now my disc got one line on both side.. mech tried to file my brake pad n put back n try...

 

After I reach home I call mech.. mech say try runninh a few day let the pad n disc wear evenly first.. if cannot then go back.. he say worse come to worse is change new pad n disc. . Not too sure how much is one rear disc.. my ride is cbr250r. .

 

Guyz got any idea how to solve??

Make sure that the caliper hasn't seized on the caliper sliding pin. Rear brake should be a single pot slider. If the caliper seizes on the pin, it can drag.

 

Can try to ask him to service the calipers. Either the brake pump at the pedal is in need of servicing, or the caliper piston seals need servicing/replacement. Brake dust can get past the seals when changing pads, if it's not cleaned off before retracting the piston. Can form a paste that causes the piston to gum up in the bore, won't retract when you let up the brake pedal. Rear caliper, 1 piston, should be cheap to change the seals and flush.

 

From what you're describing though, it may be the master cylinder pump. There is usually a small opening, the compensating port, which allows fluid in the system to flow back into the reservoir when the spring retracts the pump piston. If the port is blocked by dirt/debris, the pump may not be able to release pressure from the system. Also, if the brake pedal is adjusted too far "down" or "on", the piston might not be able to retract the cup back past the compensating port. To diagnose, release the lever and then open the caliper bleed valve (make sure to have something to catch the fluid), if the brake fluid forces itself out without pressure on the lever, you might have residual pressure in the system.

 

Just my 2 cents worth. If any of my assumptions are wrong, please do let me know. Always wanting to learn more.

 

Have you adjusted the brake pedal downwards recently? If so, can try adjusting up a little. Since you mentioned that when you kick up the brake pedal, the effect is gone. Might be the case of the MC pump. Or the return spring on your pedal not strong enough to fully retract the brake pedal.

 

P.S.: You mentioned you have changed the brake pump and service caliper already? Btw, it's not uncommon to have a light drag against the brake disc, but the wheel should still spin freely when jacked up and spun by hand.

 

Oh yea, CBR250R, can bring to bro Raptor workshop. He races that bike, should be able to sort you out easily.

Edited November 22, 2014 by Tachnicolour

[tiku]

Thanks Tachnicolour for the reply.. yup I changed the pump n serviced the caliper..the wasnt unable to service like front brake pump so need to change as told by mech... not cheap wor... t

As for the caliper service part , the mech did not really remove the caliper and dismantle it into pcs to service so felt that the mech never do a good servicing on it...

 

And yes the bike has drag when reversing it feels like a cls2 bike...lol. wheel stil can rotate but wif force applied.. as what mech say he said that my brake pad is now uneven n mayb brake disc.. changing new pad wil not solve the problem... mech ask me to ride witht the drag on until the pad got wore off while moving...after I rode to work today, the drag effect lesser

 

I was considering racewerks or planet for alternate advice ..mayb can include rapper and raptor...

[Tachnicolour]

Not too sure about not serviceable.

http://www.motosport.com/sg/motorcycle/oem-parts/honda/2011/cbr250r/rear-brake-master-cylinder-%28cbr250r%29

Doubt there'd be a parts list if it was non-serviceable. Maybe can't see he compensating port easily eh.

 

Yep, sounds like good choices for shops you have there. Can always ask them to have a look see. It'll take a while for the pads to wear into the calipers, give it a bit more. Just keep an eye on the disc if it shows any signs of bluing. Make sure that the brake fluid isn't overfilled also. If it's pass the full line, extract some.

[tiku]

Hmm.. seems like serviceable seens there are parts.. but now after multiple depress of rear brake the drag increase back to the usual pressure. ..

 

Now my disc got a line v obvious as the line rusted.. is it fine to ride with it?? Think I should avoid using rear brake for now as the pressure seems to build back up after using a few time... will update here again once prob solved but not today as got stuck at work.. thanks Tachnicolour

[Tachnicolour]

Hmm.. seems like serviceable seens there are parts.. but now after multiple depress of rear brake the drag increase back to the usual pressure. ..

 

Now my disc got a line v obvious as the line rusted.. is it fine to ride with it?? Think I should avoid using rear brake for now as the pressure seems to build back up after using a few time... will update here again once prob solved but not today as got stuck at work.. thanks Tachnicolour

 

Np bro. You're saying that the pressure builds up after a few pumps, then if you leave it alone for like half and hour or so the pressure will lessen? If that's the case, it's rather likely that the fluid isn't returning to the reservoir via the compensation port when the pedal has returned to home. Which is unusual, if the brake pump is new.

[tiku]

None the pressure wont lessen but remains. . Sounds like caliper ??

[Tachnicolour]

Could be. 1st, check the reservoir, make sure it's not filled past the full line. If it is, remove fluid till it's below the full line.

 

if that don't work.

 

1) place papers towels around bleed nipple to absorb fluid. don't apply brake pressure. crack open bleed nipple on the caliper, if fluid flows wait for flow to stop, then tighten back up. roll bike and check if brake pressure releases. If it does, then it's brake pump. *caution, don't apply brakes at all or anything when bleed nipple is open, can cause air to enter system*

Ideally you should be carrying out a normal bleed when you check so that the tubing attached to the nipple prevents air ingress.

2) If brake pressure doesn't release and no fluid flows out, possible caliper / caliper slide pin.

 

If not comfortable with the above, you might better bring it down to a mechanic.

[tiku]

Just went to check.. the oil level is below low level.. was shocked.. don know wth the mexh doing.. cui

[crazydj]

Just went to check.. the oil level is below low level.. was shocked.. don know wth the mexh doing.. cui

 

Are you sure the bike is fully upright and not on the sidestand when you measure the oil level?

[tiku]

Yup upright

[kaiq]

Not sure why low level at the reservoir can affect... I tot low level means harder to apply brake due to sponginess caused by air (meaning you press hard but still won't brake).

 

Unless you tell me the fluid is also used to suck the piston back when lever is released, haha...

 

Or got such thing as using a wrong brake pad that is too fat?

[tiku]

Just went to see Dr Chong. . He said low lv is ok no prob. .. he also said my prob is hi chances caliper misaligned liao.. nothing he can do.. he give me a free top up of brake oil too.. so he say u ok can live wif it, no point spending money on this.. he commented this is same wif phantom ... llst

[Tachnicolour]

Just went to see Dr Chong. . He said low lv is ok no prob. .. he also said my prob is hi chances caliper misaligned liao.. nothing he can do.. he give me a free top up of brake oil too.. so he say u ok can live wif it, no point spending money on this.. he commented this is same wif phantom ... llst

 

for the doctor. unfortunate that it can't be fixed easily. yeh, guess try to live with it. ask for your old brake pump back from the mech! heh heh.