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iThinkergoiMac

Rear Brake Locking After Pressing Pedal

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24 minutes ago, iThinkergoiMac said:

This will probably be a winter project

One hours work, just do it, get some resolution and enjoy your summer :-)

 

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7 hours ago, GleninAus said:

One hours work, just do it, get some resolution and enjoy your summer :-)

It's a little more than that since you have to bleed that caliper twice and either empty the braking system or let it drip. Besides, at this point, it performs flawlessly; it just doesn't activate the rear wheel when I hit the front lever. Considering it acts just like virtually all other bikes, I'd say I'm going to enjoy my summer, haha.

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On April 25, 2016 at 7:16 AM, GleninAus said:

 The Solution.

Disconnect hoses and remove the calliper with the SMC.

Remove the 2   8 mm bolts on the cover

Remove the O ring.

Look at the green screen with all the crap in it.

Cleaning the screen from the outside is a waste of time. you actually have to remove it. Compressed air or mouth to mouth on the bottom hole of the SMC will pop out the green thing that actually turns out to be something much bigger and full of crap. 

Disclaimer, i'm sure it probably wasn't designed to be serviced so if you break it then try and find a new one or buy a whole SMC.

What you have to do is carefully get a fine flat blade screw driver and open the mesh cap, there are little tabs to work with. If you succeed, you will find a spring and ball, put them aside and now you can clean the screen. While you have the filter out make sure the 2 SMC holes are clear.

You're talking about the front left caliper with the Secondary Master Cylinder attached, right? I'm afraid I can't map what you're writing about to what I'm seeing in the manual (pp. 15-23). There, they describe a snap ring, push rod, master piston and spring. No description of an O ring, green screen, or spring and ball. Do you have any pictures, or can you help me map your description to what's in the manual?

I'm afraid I'm in the same camp: 2001 VFR, rear brake dragging, pumped the SMC about 50 times to push out the center piston on the rear caliper for cleaning and inspection (it looked fine), and now I can't push it back. Outside pistons returned fine with thumb pressure.

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Found a picture of the factory rebuild kit; is the screen you refer to part of this?

45620mbg026-piston-set-second-master-cylinder-honda-xl-1000v-varadero-.jpg

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12 hours ago, RogerRamjet said:

You're talking about the front left caliper with the Secondary Master Cylinder attached, right? I'm afraid I can't map what you're writing about to what I'm seeing in the manual (pp. 15-23). There, they describe a snap ring, push rod, master piston and spring. No description of an O ring, green screen, or spring and ball. Do you have any pictures, or can you help me map your description to what's in the manual?

I'm afraid I'm in the same camp: 2001 VFR, rear brake dragging, pumped the SMC about 50 times to push out the center piston on the rear caliper for cleaning and inspection (it looked fine), and now I can't push it back. Outside pistons returned fine with thumb pressure.

The manual has no reference to the procedure I've explained. As I said, "Disclaimer, i'm sure it probably wasn't designed to be serviced so if you break it then try and find a new one or buy a whole SMC".

First,follow the process of finding what part of the system remains under pressure, making the rear center piston not return.

If SMC is last stop, and remember the foot brake fluid reservoir feeds the SMC even though its meant to be activated as a front brake action but I think the one way valve that's clogged was where I found the problem. So you can partially bleed that system with the foot brake.  Its a complex work of  Honda engineering art but I think that if the foot brake pressure being applied is larger than the pressure being applied by the SMC then it overrides.

When you remove the hoses attached to the SMC you will see the plate held in by the 2*8mm bolts.

Sorry no pictures, I was trying not to go insane at the time trying to fix it.

 

I remember when I got the bike, I saw the brake system an remarked to my friends that I hope I never need to fix this. Looks light a nightmare .... yeah........ 2 weeks later.......ugh!!

But, now its fixed, really NICE big difference. 

 

 

 

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12 hours ago, GleninAus said:

First,follow the process of finding what part of the system remains under pressure, making the rear center piston not return.

As far as I can tell, the possible culprits are: 1) the rear caliper; 2) the PCV; 3) the SMC; 4) the rear MC. How does one go about identifying the problem component?

I assume that it's not the rear caliper because the outer pistons retract fine. I'm guessing that clears the rear MC as well, at least it's return hole.

The SMC moves freely and pushes the center piston on the rear caliper out. However, it just can't be pushed back.

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3 hours ago, RogerRamjet said:

As far as I can tell, the possible culprits are: 1) the rear caliper; 2) the PCV; 3) the SMC; 4) the rear MC. How does one go about identifying the problem component?

Pump the brake peddle to lock the rear brake and release,( unlike bleeding the brakes no pressure to be maintained to peddle as we are looking for a blockage) crack the bleed nipple, if it squirts and releases the wheel, move back along the circuit and repeat the priming procedure. Start from  ( your numbers) 1 goto 2 and on 3, identify the banjo bolt ( as there is no bleed nipple) on the brake line that runs to the SMC and crack that. That will be the final point of failure if you have a blocked screen or valve in the SMC.

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Okay, back to the project. I'll describe as best I can the steps I think I need to go through. Please help me fill in the blanks.

 

Current state: Rear caliper off wheel, center piston extended and can't be pushed back (pictured). Pressing rear brake pedal extends two smaller pistons, which can easily be retracted with thumb pressure. Pumping Secondary Master Cylinder (SMC) on left fork leg extends center piston (took about 50 cycles to extend it as shown).

 

1. Open the center bleed nipple on the rear caliper (the one without the rubber boot in the picture). Fluid should squirt out due to pressure in system. Should be able to return the center piston with the nipple open. If not, rebuild the rear caliper.

2. Close the bleed nipple and add fluid to the rear master cylinder if needed.

3. Reinstall the pads & insert a block of wood between them or reinstall the caliper on the rotor (need to provide something for the piston to push against).

4. Pump the rear brake pedal and release. Pressure should be present against rotor/block of wood.

5. Open the bleed nipple on the PCV. If fluid squirts out, then <what?>, else <what?> 

 

I suppose that if the PCV bleeder is upstream of the actual valve and it squirts, that points to problems further upstream. On the other hand, if the PCV bleeder is downstream of the actual valve, it should squirt whether the PCV is the culprit or not, right? I'd really have to crack the inlet & outlet hoses to know for sure.

 

I just read Section 21 of the 5th gen manual, which goes into more detail of the LBS, but haven't quite decoded how to fully diagnose the issue. I do see how the PCV internals could cause this behavior if they're not working right, though.

IMG_3194.jpg

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I've narrowed it down to the SMC; it can't possibly be anything else.

  • The caliper has been rebuilt
  • The PCV has been replaced
  • The RMC has been rebuilt and the return hole ensured clear
  • The SMC has been rebuilt

Another poster nailed it on the head a few posts back. It's almost certainly the screen in the SMC causing problems. Everything else apart from the lines themselves has been rebuilt or replaced.

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4 minutes ago, iThinkergoiMac said:

I've narrowed it down to the SMC; it can't possibly be anything else.

  • The caliper has been rebuilt
  • The PCV has been replaced
  • The RMC has been rebuilt and the return hole ensured clear
  • The SMC has been rebuilt

Another poster nailed it on the head a few posts back. It's almost certainly the screen in the SMC causing problems. Everything else apart from the lines themselves has been rebuilt or replaced.

 

IThinkergoiMac, that's for your bike, right? I haven't rebuilt or replaced anything at this point on mine, and my components seem pretty clean and corrosion-free, at least from external inspection.

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6 minutes ago, RogerRamjet said:

 

IThinkergoiMac, that's for your bike, right? I haven't rebuilt or replaced anything at this point on mine, and my components seem pretty clean and corrosion-free, at least from external inspection.

 

Right, sorry, misread your post.

 

With the way the system works, you can pretty quickly narrow down the problem.

  • If loosening the bleeder on the caliper allows you to return the piston with thumb pressure, the caliper should be fine. If not, the piston is sticking in the caliper.
  • If loosening the PCV allows you to return the piston, the line itself doesn't have a problem. The bleeder is after the PCV mechanism.
  • If the outside pistons retract, the return to the RMC is clear.
  • This leaves the SMC; if all the other steps clear, the SMC must be the problem.
  • Either the SMC needs rebuilding or the screen is an issue like on mine.

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8 minutes ago, iThinkergoiMac said:

If loosening the PCV allows you to return the piston, the line itself doesn't have a problem. The bleeder is after the PCV mechanism

 

Loosening the PCV bleeder, not the banjo bolts, right?

If the bleeder's downstream from the PCV, and loosening it allows me to return the piston, that doesn't eliminate the PCV as a possible cause, does it, because the PCV could still be holding pressure upstream? It seems that the PCV and SMC are still both possible culprits, and I can only know it's the PCV if cracking the banjo bolt at either end of the SMC-PCV hose doesn't allow me to return the piston. That would mean the PCV is holding line pressure even when the upstream pressure is removed.

 

It's a fascinating system, but troubleshooting's a pain, as you can certainly attest!

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If you want to eliminate the PCV as a possibility, loosen the banjo bolt that goes from the SMC to the PCV and then depress the center piston on the rear caliper. If it flows, the PCV is not keeping it stuck, as you said.

 

It's complicated, but once you get a grip on it it's really not too bad, if a bit over-engineered.

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Well, opened the center nipple on the rear caliper and the center piston still would not budge. Pumped the SMC and fluid flowed. Looks like the center piston has an issue, so I removed the caliper and plan to do a rebuild. The fluid is clear (no water, dirt, or corrosion) but I'm seeing what looks like little black bits of rubber. Time to order a caliper rebuild kit.

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Just a major Oh Wow.. and just another reason these linked brakes are going By By.  thanks for a great read,  makes me know for a fact I'm doing the right thing.  Good luck guys. 

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I'm reviving this thread to see what the resolution to this was. Anyone know? The beauty of the great interweb, problems get posted, solutions don't always make it into print.

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I'm also thinking a de-link would be a great solution...

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people insist on creating these DIY’s without photos and it drives me NUTS!

 

this is the “green screen” they are taking about. It’s under a banjo bolt in the secondary MC. 

 

I removed the brake calipers because they were covered in brake fluid and grime. I wanted to clean them. 

 

While they were out I replaced the seals with K&L seals (MISTAKE!!!!!!) and rebuilt the master with All Balls rebuild kits. The clutch MC worked fine, but the brake MC was not sized correctly. I cleaned out the green screen, but mine wasn’t dirty really. I thought putting it back a certain way mattered, but it actually doesn’t (it can be put back any one of 360*).  

 

I bled and bled and bled and couldn’t get it to work, so I sent it off to Honda for work and winter storage here in Ohio. 

 

My dealer replaced all 12 seals on the calipers, and rebuilt the brake master cylinder with OEM seals. Then they bled the shot out of it and the problem went away. It’s air in the secondary MC line. That’s what my dealer came to the conclusion of. I’m a happy camper and now I’ll probably get increased MPG’s! Wooooooo! Only cost me $269 for the dealer to diagnose, replace parts, and bleed new fluid!

 

B809A55F-B863-4187-8A74-57CC395FB0D2.jpeg

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Nice write up Urban. Having the pics do help. I'm going to be faced with bleeding my whole system and have the front calipers on the workbench now waiting to be rebuilt. Now I know where the famous green screen is. 

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Just giving this a 2018 bump as I've just come across the stuck center rear piston and have traced it back to the SMC.

Never knew about the green screen, so many thanks to GleninAus for his comprehensive troubleshoot. And Urbanengineer for what it is I'm looking for.

Here's hoping it fixes the problem... as it almost destroyed my rear disc and wore down new pads in under a year.

 

Looks like I'm gonna get my hands dirty again tomorrow morning. :comp13:

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Not sure what happened to my post... but

I read this article not long ago - https://www.sportrider.com/sportbike-for-sport-coat-crowd?con=TrueAnthem&dom=fb&lnk=TA&src=SOC&utm_campaign&utm_content&utm_medium&utm_source#page-9

 

"When the foot lever is actuated, the secondary master located on the front left caliper is back-pressurized so that the braking of the front wheel does not cause additional braking at the rear. In short, using the linked foot lever for braking delinks the other system."

 

Maybe this is what this valve is for... dunno, took some pictures while I had it apart, clean and the brakes work fine.

 

 

valve1.jpg

valve2.jpg

valve3.jpg

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On 2/26/2018 at 12:03 AM, Vee-Ef-Ar said:

Not sure what happened to my post... but

I read this article not long ago - https://www.sportrider.com/sportbike-for-sport-coat-crowd?con=TrueAnthem&dom=fb&lnk=TA&src=SOC&utm_campaign&utm_content&utm_medium&utm_source#page-9

 

"When the foot lever is actuated, the secondary master located on the front left caliper is back-pressurized so that the braking of the front wheel does not cause additional braking at the rear. In short, using the linked foot lever for braking delinks the other system."

 

Maybe this is what this valve is for... dunno, took some pictures while I had it apart, clean and the brakes work fine.

 

 

valve1.jpg

valve2.jpg

valve3.jpg

Good man! Thank you for coming back and bumping this. There isn't enough info on this guy.

 

I think it mainly comes down to the usual suspect problem of people not changing brake fluid on time. Oh bother, now both our bikes work :). 

 

Too bad I can't ride mine right now though, snow is falling! (pic added below to immortalize it on VFRD)

SMC green thing.jpg

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I have a very similar problem. In the Honda Gen Workshop manual they list a probable cause as an incorrect Length of the secondary master cylinder pushrod.

The manual does not give you the correct length. Honda Australia seem unwilling to help, all my local deadlers have no idea. There fore does any one actually know what the length should be. I note the rear master cylinder lengths are in the manual.

I am very close to throwing the towel and de linking the Brakes.

Has any one just tossed the screen out or does the one way valve / check valve have a real function ?

 

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For the life of me I can't see how the secondary master push rod length could have anything to do with it, or how they could be different from one bike to the other.

The check valve in the other hand, is needed.

Most linked brake problems are due to wear and/or bad history of cleaning.

There is too many places to clog up with sludge, and its hard to clean without complete dismantling.

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