Strange front brake issue today - 2004 CB600F | GTAMotorcycle.com

Strange front brake issue today - 2004 CB600F

Kuro

Well-known member
Site Supporter
So I was riding home today for a quick stop before heading out again. I stopped by at home to grab my backpack and roughly 3 minutes later I came back to the bike, started her up and began to back pedal out of the parking spot I forwarded into.

I noticed it was strangely difficult to back out and there was no incline. I got off the bike and tried pushing in neutral and same deal, I encountered significant resistance. I squeezed the brake lever and it felt tight as though it was already half depressed.

I tried squeezing it a few times hard to see if I could relieve any pressure but no luck. I sat down and googled online to see if there were any fixes to my issue. I do have aftermarket levers but never encountered this issue before until now.

After about 10 minutes I fiddled around some more and discovered that my brake lights were disconnected (probably due to vibration, plugs aren't that tight). I plugged the brake lights back in and tested them by using the lever. At that point I noticed the brakes had released and the bike was back to normal.

How could this possibly happen?

Notes:
- My master cylinder is slightly tilted due to my handlebar set up
- it was slightly warmer today and the bike sank into the asphalt a little bit which titled the bike, and added even more tilt to the master cylinder (though there is enough brake fluid to cover the hose the entire time)
- I did not do any hard braking
- I have not done any recent brake maintenance recently
 

kellen

Well-known member
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My guess would be calipers sticking. Take the brake pads out, take a look at the pistons. Are they all gunked up?
 

Kuro

Well-known member
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ok thanks, I'll take it apart and check. I did service the forks about 2 months back and I didn't notice any build up or anything when holding the calipers. Maybe something seized it momentarily... anyway I'll take it apart regardless.
 

frekeyguy

Well-known member
What bike is it ? what master cylinder is it using?

show us a picture of the master w/ lever setup. My hunch - the lever is leaving the plunger depressed after you release the lever.
 

Kuro

Well-known member
Site Supporter
Hey fiaz
its a 2004 cb600f
i believe they are stock brakes, I'll have to check what brand but looks to be same as any other super sport, dual caliper twin piston setup. I don't think they're nissin, but I'll check

ok so I haven't had a chance to remove the calipers yet but I rode it again and the issue happened again, except in traffic this time. Strange thing is, it wasn't due to a sticky lever or piston because the brake seemed to begin tightening when stopped. When I accelerated, it started to tighten more and more (without me squeezing the brake lever) until I basically couldn't move anymore. I barely made it to pull into a random driveway.

Again like last time I tinkered around with the brake lever, hitting the perch with my hand maybe to unstick whatever might be stuck. I also undid the master cylinder cap. My reasoning was that maybe the heat from the air caused the liquid and air to expand and become more pressurized thus applying braking without my input. Opening the cap might release pressure? It's never been this hot before since my ownership of this bike which would explain why this has never happened to me in the past. Shortly after I did this, the brakes released its grip.

i do have the ss braided lines if that makes a difference.
maybe the fluid is overfilled not leaving enough space for minor expansion of liquid and air due to temperature variations?

i couldn't quite tell from the reservoir because the master cylinder is quite slanted.
 
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frekeyguy

Well-known member
Hey fiaz
its a 2004 cb600f
i believe they are stock brakes, I'll have to check what brand but looks to be same as any other super sport, dual caliper twin piston setup. I don't think they're nissin, but I'll check

ok so I haven't had a chance to remove the calipers yet but I rode it again and the issue happened again, except in traffic this time. Strange thing is, it wasn't due to a sticky lever or piston because the brake seemed to begin tightening when stopped. When I accelerated, it started to tighten more and more (without me squeezing the brake lever) until I basically couldn't move anymore. I barely made it to pull into a random driveway.

Again like last time I tinkered around with the brake lever, hitting the perch with my hand maybe to unstick whatever might be stuck. I also undid the master cylinder cap. My reasoning was that maybe the heat from the air caused the liquid and air to expand and become more pressurized thus applying braking without my input. Opening the cap might release pressure? It's never been this hot before since my ownership of this bike which would explain why this has never happened to me in the past. Shortly after I did this, the brakes released its grip.

i do have the ss braided lines if that makes a difference.
maybe the fluid is overfilled not leaving enough space for minor expansion of liquid and air due to temperature variations?



i couldn't quite tell from the reservoir because the master cylinder is quite slanted.

Pop by , haven't seen you for a while . We can figure it out, it's a simple system.

I'd take a look at the lever and the plunger first.

Air trapped in the line will cause mushey brakes..
 

TwistedKestrel

King of GTAM
Site Supporter
Your theory about the system being overfilled is not unreasonable, but it would be pretty obvious once you took the reservoir cap off - there would pretty much be brake fluid spilling out immediately.
 

crazy_stunter_6

Well-known member
Rebleed your brake system. It should make the problem go away. Your master may have gotten stuck since it got air into your brake system.
 

Kuro

Well-known member
Site Supporter
Pop by , haven't seen you for a while . We can figure it out, it's a simple system.

I'd take a look at the lever and the plunger first.

Air trapped in the line will cause mushey brakes..

Hey frekey,
I can't ride it until I know it is safe. I don't want to risk another incident like what happened that day.
If I was something else, I would drop by.

Your theory about the system being overfilled is not unreasonable, but it would be pretty obvious once you took the reservoir cap off - there would pretty much be brake fluid spilling out immediately.

I'm assuming the air and liquid both would expand so it might not have to spill over to be too pressurized. There was no spillage, and the liquid wasn't at the top.


Rebleed your brake system. It should make the problem go away. Your master may have gotten stuck since it got air into your brake system.

I thought air in the system would have the opposite effect.

I think what I'll do is like Kellen said, make sure the pistons aren't seizing or cruddy. Then I'll remove the lever and make sure the activator push rod isn't sticky either. I'm deciding if I should either remove some liquid or replace it completely. Replacing it completely would have me bleeding the brakes too, which is a pain as I dont have a bleeder kit, I'll have to get someone to squeeze my lever as I open the bleed screw.

Thanks for the replies.
 

GateKeeper

Well-known member
even without a bleeder kit, you should be able to bleed your front brakes, yes on your own....

you have crud in the mater cylinder or in the calipers and this is not allowing the pistons to retract quick enough, but slowly over time, either bleed the entire system and ensure you have more or less replaced all the existing fluid or take apart the master cylinder and clean it, same with the calipers, if your pads ride on pins make sure they are clean as well and not crusty with rust or something else...

small glass jar with lid and some tubing, make a great bleeder kit
 

49over

Well-known member
Site Supporter
So I was riding home today for a quick stop before heading out again. I stopped by at home to grab my backpack and roughly 3 minutes later I came back to the bike, started her up and began to back pedal out of the parking spot I forwarded into.

I noticed it was strangely difficult to back out and there was no incline. I got off the bike and tried pushing in neutral and same deal, I encountered significant resistance. I squeezed the brake lever and it felt tight as though it was already half depressed.

I tried squeezing it a few times hard to see if I could relieve any pressure but no luck. I sat down and googled online to see if there were any fixes to my issue. I do have aftermarket levers but never encountered this issue before until now.

After about 10 minutes I fiddled around some more and discovered that my brake lights were disconnected (probably due to vibration, plugs aren't that tight). I plugged the brake lights back in and tested them by using the lever. At that point I noticed the brakes had released and the bike was back to normal.

How could this possibly happen?

Notes:
- My master cylinder is slightly tilted due to my handlebar set up
- it was slightly warmer today and the bike sank into the asphalt a little bit which titled the bike, and added even more tilt to the master cylinder (though there is enough brake fluid to cover the hose the entire time)
- I did not do any hard braking
- I have not done any recent brake maintenance recently

So far..... Every Honda I've owned, the piston in the calipers are aluminum and the get pitted. My 2012 has same problem, I can't spin the tire because of brake drag.
Remedy; take Pistons out replace them and the seals, clean throughly where the seals seat,
OR do plan "B" if Pistons aren't pitted get a spring and put it on the slider pin between the pads and it will help relieve the pressure. DONT put too strong of a spring on or you can push pads off the rotor and have no brakes.
I bought 4 springs from crappy tire in the hinge isle and it worked perfect.



Thank you ; Mikey Moto, Blue Streak Racing, JT Sprockets, HiFlo Filters, Cycle Pro, Dyno-Jet. For your help and support.
www.cementheadracing.ca
 

Kuro

Well-known member
Site Supporter
ok update.

I took the lever off and disassembled the caliper.

The brake pads are wearing evenly.



The pistons had a small bit of crud on them, looked like pitting but I was able to remove 90% of it. That part of the piston protrudes out of the caliper because the pads had worn down and that part of the piston is exposed. If I had brand new pads, it might've been an issue.




As I was refilling the brake fluid, I noticed that no liquid would enter the brake lines from the fluid reservoir. I opened the nipple on one of the calipers and pumped the hell out of the brakes but no liquid movement. I'm going to disassemble the master cylinder and report back.
 

Gryphon

Well-known member
Coupla points here...
This is typical behavior! Most brakes are like this, but ya don't notice until it gets severe.

Fluid pressure clamps the brakes. Upon the release of the pressure, only the elasticity of the rubber seal retracts the pads back away from the disc.
If there is any pitting, mung, stiction or the rubber seals are deteriorated and flaccid, that brake will 'drag'.
Many are unaware until, say you roll to a stop and climb off. You check the twin front discs.
One might be cool to the touch but the other smokin' hot! One caliper is dragging...
Regular inspection and constant 'being in tune with your bike' are required, ie. you're sensitive to any changes or weirdness.
Good thing you perceived this through pushing bike in garage, Kuro.

A quick kudo for Frekeyguy! Never met him but he's a legend in the community.
GTAM is fortunate indeed to have your attention regarding peoples' issues, sir. So thanks.
Regards
 
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kellen

Well-known member
Site Supporter
ok update.

I took the lever off and disassembled the caliper.

The brake pads are wearing evenly.



The pistons had a small bit of crud on them, looked like pitting but I was able to remove 90% of it. That part of the piston protrudes out of the caliper because the pads had worn down and that part of the piston is exposed. If I had brand new pads, it might've been an issue.




As I was refilling the brake fluid, I noticed that no liquid would enter the brake lines from the fluid reservoir. I opened the nipple on one of the calipers and pumped the hell out of the brakes but no liquid movement. I'm going to disassemble the master cylinder and report back.
Fwiw when you change calipers or master or lines or whatever and have the system out of fluid sometimes you have to pump/open/close literally hundreds of times sometimes before it starts to move significant amount of fluid
 

Kuro

Well-known member
Site Supporter
still weird behaviour

I took it apart



Piston wasn't too gunky or anything but I cleaned everything again anyway.
Seal on the piston looked fine visually.




I made sure the paths were clear. I added liquid to the reservoir and liquid drained right through (without the piston)

I reassembled everything and did a quick test to make sure the lever was still able to pump liquid and it didn't!! WTF

I even tried with air.




Nothing came out the other side, with or without pressing the lever.

Could it be that my piston is somehow blocking the fluid path?
It must be that because fluid could pass through without it.... not quite sure how that's possible though.
 

dricked

Well-known member
Site Supporter
Get an oem lever and continue from there. That should have been the first step. Then replace the master if that doesn't help. I had this happen with a repaired (incorrectly) brembo. Crashing sucks.
 

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