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Weak rear brake


silverbird1100

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2 minutes ago, superhawk996 said:

Hear it how?

I can hear the pads bite down on the rotors. Or at least that's what it sounds like.  Sounds like something moving, just like it should.  I do have to apply more force that I should though

Edited by silverbird1100
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I didn’t see it, but have you FLUSHED the system with fresh fluid?  Front and rear lines?  That would be my first diagnostic step as you at least know it’s fresh and clean fluid.

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On 4/30/2020 at 9:39 PM, silverbird1100 said:

If I really stomp on it I think it slows the bike as it should. It just takes way more pressure that it should.

Re-reading from the start to remember things.  Mine takes a lot of pressure to lock the rear tire, way more than any normal (unlinked) bike.  When I bear down on it hard it slows way better than an unlinked bike since part of the pressure is actuating the front.  There may be nothing wrong with it.

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13 minutes ago, Zero Knievel said:

I didn’t see it, but have you FLUSHED the system with fresh fluid?  Front and rear lines?  That would be my first diagnostic step as you at least know it’s fresh and clean fluid.

I'm going to do that in the morning but I have a few questions about this link    https://www.cbrxx.com/threads/bleeding-bird.10490/#post-641097

 

There's no mention of raising the SMC on the left side to help get air out. Since I'm just flushing do I need to do anything with that master?

 

Also, from that link, the left and right OUTER nipples are bled from the handlebar lever. The remaining 4 are done from the brake pedal, correct? 

Edited by silverbird1100
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21 minutes ago, superhawk996 said:

Did this start suddenly while the bike was being used or something that happened after being stored a while?

I bought it from the original owner last fall with 5600 miles. He said he kept it indoors and rode it regularily.  After owning it ot for 8 months I have no reason not to believe him.  Judging from it's condition he babied the shit out of it,  the brakes are only thing on the bike that don't feel less than a year old, but yes it's been weak since I bought it. 

Edited by silverbird1100
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1 hour ago, silverbird1100 said:

I bought it from the original owner last fall with 5600 miles. He said he kept it indoors and rode it regularily.

That does not compute

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Yes, you should be hearing some "creak" or a clamping force of the pads against the rotors.  As the rotors turn, they "bump" the pads out so they're not constantly under friction against the rotor.  So the pad moving back and forth on the slide pins or slots will cause a tiny bit of noise.  If you're not hearing that from the rear, and the fluid has never been changed, then it's quite possible that the rear brakes boiled the fluid the first time it was braked on with sufficient force.  Brake fluid is hygroscopic, meaning it will pull in moisture from the atmosphere.  Moisture in brake fluid means boiling, and the more there is, the worse it is.  20 year old brake fluid with very little use means the water hasn't had many chances to boil off so you've got to start with a flush first.

Make life easy and get a vacuum bleeder from Harbor Freight.  Center stand, open handlebar and rear master cylinders, start at one bleeder cracked open and start vacuuming out fluid, one by one, until you're pretty sure all the old stuff is gone.  You still have to finish up with a pressure bleed as the last step, where you have to pump it up with the levers and bleed off the excess, but at least you're not doing that to get all the fluid out also.

If you're not comfortable with this, take it to a shop and have them do it.  Have them do the clutch fluid too because the same thing applies to it.  Nearly impossible to boil that fluid but the water can still cause issues on that system.

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Here's my flushing method: Suck the old fluid out of the reservoir and refill, not necessary, but it speeds things up rather than waiting for the old fluid to go though the bleeders.  It also lets you suck up the sludge that tends to accumulate on the bottom of the reservoir.  Open bleeder(s) and add fluid to the reservoir as needed while it drains.  Letting gravity do the bleeding makes it easier and more foolproof than pumping.  Once clean fluid is flowing from the bleeders you're done.  Optional; put a small piece of hose on the bleed nipples to guide the fluid into a container and reduce the mess all over the caliper.  After closing the bleeder gently bend/pry the hose off the nipple and it won't make a mess.  Beer is technically optional, but it gives you something to do while watching the fluid flow.

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30 minutes ago, superhawk996 said:

Here's my flushing method: Suck the old fluid out of the reservoir and refill, not necessary, but it speeds things up rather than waiting for the old fluid to go though the bleeders.  It also lets you suck up the sludge that tends to accumulate on the bottom of the reservoir.  Open bleeder(s) and add fluid to the reservoir as needed while it drains.  Letting gravity do the bleeding makes it easier and more foolproof than pumping.  Once clean fluid is flowing from the bleeders you're done.  Optional; put a small piece of hose on the bleed nipples to guide the fluid into a container and reduce the mess all over the caliper.  After closing the bleeder gently bend/pry the hose off the nipple and it won't make a mess.  Beer is technically optional, but it gives you something to do while watching the fluid flow.

Like the gravity idea, would that work from the rear master to the front caliper though?

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2 hours ago, superhawk996 said:

Here's my flushing method: Suck the old fluid out of the reservoir and refill, not necessary, but it speeds things up rather than waiting for the old fluid to go though the bleeders.  It also lets you suck up the sludge that tends to accumulate on the bottom of the reservoir.  Open bleeder(s) and add fluid to the reservoir as needed while it drains.  Letting gravity do the bleeding makes it easier and more foolproof than pumping.  Once clean fluid is flowing from the bleeders you're done.  Optional; put a small piece of hose on the bleed nipples to guide the fluid into a container and reduce the mess all over the caliper.  After closing the bleeder gently bend/pry the hose off the nipple and it won't make a mess.  Beer is technically optional, but it gives you something to do while watching the fluid flow.

+1

I was trying to say that above, much better explanation. Definitely go tubes, brake fluid eats paint. And you can see the colour of the fluid easier. For the clutch have to put a board under left side of centre stand to get resevour level with bars full lock to the right.

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3 hours ago, silverbird1100 said:

Like the gravity idea, would that work from the rear master to the front caliper though?

If the front caliper is below the rear reservoir, I'm almost positive it is, it'll work.  It's not as far below as the front calipers to front reservoir so it'll be slower, but will still work.

 

Some will say that gravity bleeding doesn't work and that you need pressure or vacuum, but I've been solo bleeding systems using only gravity for a couple decades.

 

Another trick that's handy (especially with LBS and ABS where you REALLY don't want to deal with air intrusion) if you need to remove a hose or caliper, depress the master cylinder piston a little bit and it'll keep the rest of the system from going dry.  On a car that means using a bar or something to hold the pedal down a bit.  On a bike I use a zip tie to hold the front and a screwdriver or other slim thing to hold the rear pedal down, slip it between the pedal and stop screw or whatever limits the up-travel of the pedal.  You don't need to depress the piston enough to make pressure, but if you do it's no biggie, when you first crack the bleeder you'll get a tiny spurt then nothing.  In most masters the piston only has to move about 1/8" to block the port, but the lever/pedal travel will be much more than that since they all have a leverage advantage.  I usually move it enough to feel a little pressure and that's a guarantee that the port is blocked.  I've left systems open for days using this trick and the master was still full.  Once the repair is done open the bleed nipple, a beer, then release the caliper piston.  Pour fluids as needed, just know that beer isn't good for brakes and DOT4 might fuck with your taste buds so try to not mix them up.

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48 minutes ago, silverbird1100 said:

Flush went well, there was a lot foam in the rear center. Rear brake works better too.

 

Appreciate it 👍

 

First step of troubleshooting...make sure the maintenance schedule is current.

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14 hours ago, silverbird1100 said:

Flush went well, there was a lot foam in the rear center. Rear brake works better too.

 

Appreciate it 👍

Sweet!  kinda odd that it had air in it, maybe a botched bleeding some time in the past.

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There was a factory recall on a possible seal leak on the LBS proportioning control valve.  If fluid could get out, air might get in.

 

The following are the results of a recall search for recalls on the NHTSA Office of Defects Investigation web site.

Make / Models : Model/Build Years:

HONDA / CBR1100XX 2002-2003

HONDA / ST1300 2003-2004

HONDA / ST1300A 2003-2004

HONDA / VFR800 2002-2004

HONDA / VFR800A 2003-2004

Manufacturer : AMERICAN HONDA MOTOR CO.

NHTSA CAMPAIGN ID Number : 05V010000 Recall Date : JAN 18, 2005

Component: SERVICE BRAKES, HYDRAULIC

Potential Number Of Units Affected : 36046

Summary:

CERTAIN MOTORCYCLES EQUIPPED WITH COMBINED-BRAKE SYSTEMS HAVE A PROPORTIONING CONTROL VALVE (PCV) THAT MECHANICALLY PROPORTIONS BRAKE FORCE WHEN THE REAR BRAKE IS APPLIED. A SEAL IN SOME PCVS IS IMPROPERLY SHAPED, AND BRAKE FLUID LEAKAGE MAY OCCUR.

Consequence:

IF THE MOTORCYCLE CONTINUES TO BE USED AFTER A LEAK OCCURS, THE REAR BRAKE WOULD EVENTUALLY BECOME INOPERATIVE. A LOSS OF REAR BRAKE FORCE COULD INCREASE THE RISK OF A CRASH.

Remedy:

DEALERS WILL INSPECT THE REAR BRAKE FORLEAKAGE. IF LEAKAGE IS CONFIRMED, THE DEALER WILL REPLACE THE PCV. THE RECALL IS EXPECTED TO BEGIN ON FEBRUARY 3, 2005. OWNERS SHOULD CONTACT HONDA AT 866-784-1870.

Notes:

HONDA RECALL NO. P65. CUSTOMERS CAN ALSO CONTACT THE NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION’S AUTO SAFETY HOTLINE AT 1-888-DASH-2-DOT (1-888-327-4236).

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3 hours ago, superhawk996 said:

Sweet!  kinda odd that it had air in it, maybe a botched bleeding some time in the past.


Easy to do.  I’ve always done a manual flush.  One time, I was wondering why my rear brake was useless, so I flushed it again.  After much pumping (several reservoirs worth) some bubbles finally came out.  The circuit that loops to the front actuator takes time to get all the fluid.  The front are usually good once you have clean fluid coming out because it’s a short line to each nipple.  That long run from the rear looping through the actuator takes more fluid than you’d think.

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14 hours ago, FiXXation said:

There was a factory recall on a possible seal leak on the LBS proportioning control valve.  If fluid could get out, air might get in.

 

The following are the results of a recall search for recalls on the NHTSA Office of Defects Investigation web site.

Make / Models : Model/Build Years:

HONDA / CBR1100XX 2002-2003

HONDA / ST1300 2003-2004

HONDA / ST1300A 2003-2004

HONDA / VFR800 2002-2004

HONDA / VFR800A 2003-2004

Manufacturer : AMERICAN HONDA MOTOR CO.

NHTSA CAMPAIGN ID Number : 05V010000 Recall Date : JAN 18, 2005

Component: SERVICE BRAKES, HYDRAULIC

Potential Number Of Units Affected : 36046

Summary:

CERTAIN MOTORCYCLES EQUIPPED WITH COMBINED-BRAKE SYSTEMS HAVE A PROPORTIONING CONTROL VALVE (PCV) THAT MECHANICALLY PROPORTIONS BRAKE FORCE WHEN THE REAR BRAKE IS APPLIED. A SEAL IN SOME PCVS IS IMPROPERLY SHAPED, AND BRAKE FLUID LEAKAGE MAY OCCUR.

Consequence:

IF THE MOTORCYCLE CONTINUES TO BE USED AFTER A LEAK OCCURS, THE REAR BRAKE WOULD EVENTUALLY BECOME INOPERATIVE. A LOSS OF REAR BRAKE FORCE COULD INCREASE THE RISK OF A CRASH.

Remedy:

DEALERS WILL INSPECT THE REAR BRAKE FORLEAKAGE. IF LEAKAGE IS CONFIRMED, THE DEALER WILL REPLACE THE PCV. THE RECALL IS EXPECTED TO BEGIN ON FEBRUARY 3, 2005. OWNERS SHOULD CONTACT HONDA AT 866-784-1870.

Notes:

HONDA RECALL NO. P65. CUSTOMERS CAN ALSO CONTACT THE NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION’S AUTO SAFETY HOTLINE AT 1-888-DASH-2-DOT (1-888-327-4236).


I didn’t know about that thanks.  I should have mentioned the only air came out of the rear center nipple. But it was very foamy, not like typical bubbles. Every other bleed went perfectly.

Edited by silverbird1100
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7 hours ago, silverbird1100 said:

But it was very foamy, not like typical bubbles.

Were you pumping or just gravity?  Was it a fairly short spurt of foam or a long stream?

Edited by superhawk996
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