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iThinkergoiMac

Rear Brake Locking After Pressing Pedal

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Hey everyone, this is my first post here. I've just picked up a '98 VFR800 and I'm really excited by it. The previous owner bought it in '99 and then it has sat for a long time (after he put 40k miles on it) because he had 3 other bikes he was riding. He's done a lot of work getting the bike back up and running and it's 90% of the way there at this point, but we're getting hung up on one main thing. The rear brake caliper is locking up when you press the brake pedal, but I think it is the center piston that's locking. From my understanding of the system, this actually shouldn't be possible.

One of the things we've done is rebuild most of the brake system. We've rebuilt all the calipers with new seals and cleaned up all the pistons. We put speed bleeders in all the calipers and the PCV. We bled the system (I've never encountered such a complicated bleeding process, holy cow) fully. After that, we found that the rear caliper was locking up when you press the brake pedal, but bleeding the center valve or the PCV frees it. Pressing the lever doesn't duplicate the problem (in fact, I test rode it around the neighborhood using only the front brake and it worked fine). It doesn't matter if the bike is moving either, pressing the rear pedal engages the rear brake and it doesn't fully disengage; subsequent presses get it stuck more and more.

I haven't pulled the caliper off to determine which piston is getting stuck, but considering the center valve and the PCV release it, it has to be the center piston.

I've ordered a replacement PCV to see if maybe that fixes things. Due to other threads I've found, I initially suspected the SMC but that doesn't make any sense to me since it doesn't matter if the bike is moving or not, unless it's possible the SMC is not behaving correctly and is just allowing the brake fluid to flow through but not releasing it.

Actually, that makes me think of another possibility: the guy I bought it from isn't as methodical in disassembling things as I am, so he didn't mark any of the brake lines. This left us with 4 brake lines for the front left; he says he connected them back properly by looking at the shape of the curves in the lines; if they're connected to the SMC backwards, could it cause this issue? EDIT: Nevermind, it was doing that before they removed any lines at all.

I was up until 1 AM this morning ordering the parts I need for the bike (tires, lights for the dash, etc), so I haven't had a chance to look at the bike in person, but I'm really excited to get it on the road (I've got a couple long trips coming up that I'd much rather take this bike on, with fully Givi luggage, than my Ninja 500) as soon as I can. Thanks for all your help!

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A bad brake line can do that. I think it gets de-laminated inside and the fluid flows between the layers and expands the inner layer closed forming a check valve. Something to consider anyway.

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Ugh, I'm hoping it's not that. How would one check for that?

My initial reaction is that I would think it's not that since opening a bleeder valve releases it, but maybe that doesn't really rule it out?

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I've had a similar problem then I realized it was the pivot where pedal is turning over that was binding - a disassembly and lube fixed that - maybe not in your case but just a tip.

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I've had a similar problem then I realized it was the pivot where pedal is turning over that was binding - a disassembly and lube fixed that - maybe not in your case but just a tip.

So the pedal was essentially not returning to the fully disengaged position? I'll certainly check that, but I don't know that it would cause the center piston to engage without the bike moving.

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Isn't the centre piston connected to the front brakes? Pressing the pedal should not make the centre piston move at all.

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Isn't the centre piston connected to the front brakes? Pressing the pedal should not make the centre piston move at all.

Yeah, that's kind of my point, haha. I'm pretty mechanically inclined, but this seems to be behaving in a way that doesn't make sense.

The center piston is connected to the SMC, which goes through the PCV, all of which is fed from the rear reservoir. When bleeding the PCV and then the rear center piston, you pump the brake pedal to do so. This means they are connected, but my understanding is that it's the pressure from the SMC that engages the rear center piston. However, the pedal seems to be definitely engaging the rear center piston.

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Update: I've replaced the PCV, but to no avail. Bike still behaves exactly as before. I've ordered a rebuild kit for the SMC, but of course that won't arrive until next week. I've also ordered a full set of Galfer SS brake lines. If rebuilding the SMC and replacing the lines doesn't fix it, I'll be at a complete loss since everything else, except the front master cylinder, has been rebuilt or replaced at this point.

I'm not really concerned that the lines are a specific issue, but they're the original lines and the bike has 52k miles on it. The front lever feels a bit squishy and there's definitely no air in the system, so I might as well replace the lines while I'm at this. Getting new tires as well.

This is turning into a headache, but it's going to be great once it's done!

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Check the rear brake & front slave master cylinder fluid return holes, if you get some swarf or corrosion in the M/C to brake line area, then this can block & stop pressure relief I had that on a Honda rear brake before. Just strip & clean the M/C & ensure the return bleed hole is clear.

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The rear master cylinder has been rebuilt and I know for sure the return hole is clear. I'll look into the return hole for the SMC in the factory service manual and see how difficult it is to get to. If it's not too bad, I may look at it while I'm waiting for the rebuild kit to arrive.

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Make sure the push pin from the front break leaver to the master cylinder is the right way around.

It fits both ways, but the wrong way doesn't let the front master cylinder piston fully return, this in turn creates a slight drag in the SMC which in turn activates the rear centre piston, which will not return by itself.

Check that the SMC is moving freely when rear brake is not releasing.

If it's tight it's because the front lever pin is the wrong way around.

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If it's that simple, I'm going to be pissed. When the rear brake is locked up, I can't move the SMC at all. I figured that was just because the system was pressurized. It does move without issue once I bleed the pressure out. It also doesn't seem to do anything at all when I actuate it by hand.

The thing that makes me think that it may not be that, though, is that they were having this issue before the brake system came apart. It's possible, though, that the piston was sticking, a caliper rebuild kit fixed it, but then things were installed incorrectly which recreated the problem. Also, I can drive around all day using only the front brake and it doesn't cause this problem. These factors have me thinking that the SMC isn't functioning correctly.

Lastly, I'm still very new to this system. Where, precisely, is this push pin? Is it the one that the lever depresses into the master cylinder?

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The push pin Oz is referring to is between the hand lever and the master cylinder piston.

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I keep looking at this and keep wondering. Are you sure you bled brakes correctly since you did a lot of work on components and opened system up? It is my understanding that there is an order to bleeding. Your symptoms are also exactly the same as I had on my 2002 few months ago after I let air get into system. My center piston on rear would stick like yours, I could let pressure off with PCV bleed, could drive and use front brake only etc.... This is guide I used and followed. I bled in same order as indicated in post. I know this is for newer model and I am unfamiliar with earlier models such as yours but think it may still apply. Not sure if you had seen this or if it might be of help.

http://www.vfrdiscussion.com/forum/index.php/topic/70842-bleedingfluid-replacement-on-linked-brakes-wabs-on-6th-generation-the-ultimate-guide/

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From memory, the thin end of the pin fits into the master cylinder piston, and fat end to lever.

It might be something else, but I'm betting a beer against myself to this being the problem.

60 seconds to check.

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I keep looking at this and keep wondering. Are you sure you bled brakes correctly since you did a lot of work on components and opened system up? It is my understanding that there is an order to bleeding. Your symptoms are also exactly the same as I had on my 2002 few months ago after I let air get into system. My center piston on rear would stick like yours, I could let pressure off with PCV bleed, could drive and use front brake only etc.... This is guide I used and followed. I bled in same order as indicated in post. I know this is for newer model and I am unfamiliar with earlier models such as yours but think it may still apply. Not sure if you had seen this or if it might be of help.

http://www.vfrdiscussion.com/forum/index.php/topic/70842-bleedingfluid-replacement-on-linked-brakes-wabs-on-6th-generation-the-ultimate-guide/

I have seen that guide. I'm pretty sure it's bled properly, but I can make mistakes. The VFR800FI is basically the same, it's just "missing" one of the PCVs that the 6th gen has. Additionally, this problem was present before the system came apart, so I don't think it needs to do with bleeding.

From memory, the thin end of the pin fits into the master cylinder piston, and fat end to lever.

It might be something else, but I'm betting a beer against myself to this being the problem.

60 seconds to check.

I guess I'll hold you to that?

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From memory, the thin end of the pin fits into the master cylinder piston, and fat end to lever.

It might be something else, but I'm betting a beer against myself to this being the problem.

60 seconds to check.

Just checked, it's definitely in correctly. I guess you owe yourself an unbeer?

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OK, another update. I think I've narrowed the problem to the SMC, but I just rebuilt it and the problem hasn't gone away, though it has changed slightly. If I let it sit for 20+ minutes, the pressure dissipates by itself, which I don't think it did before.

Here's what I know:

  • The caliper isn't sticking; if I actuate just the SMC, it works like it should
  • The lines from the SMC to the caliper, as well as the PCV, are fine due to the above
  • The return on the RMC is fine
  • The center piston on the left side retracts fine even if the caliper is stuck, so there is no pressure in the incoming line from the RMC
  • The pin in the front MC is in correctly
  • All calipers have been rebuilt
  • The PCV has been replaced
  • The SMC has been rebuilt
  • The RMC has been rebuilt

This tells me that it is almost certainly the return hole for the SMC, but I'm not sure how to clear it properly. There's a filter built into the port for the incoming line that makes it basically impossible to get to the hole. I tried blasting it with some compressed air and the air seems to flow fine. Any suggestions? Any corrections to my logic?

For the moment, I think I'm going to just block off the port coming out of the PCV and block off the port into the center piston on the rear and ride that way. There will be very little reduction in power and I can get riding this thing that way. My dad and I are taking an 800 mile trip in a week and a half and I'd like to have a few miles on the VFR down before we start (and I'd much prefer the VFR to my Ninja 500 for a trip like that).

I do have SS lines coming in that I will be trying to install, at which point I'll again have the whole system apart. If I have some suggestions to try with the SMC by then, I'll give them a whirl.

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Having a beer as I type.

Make sure the spring behind the SMC piston is still there.

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Another update: Well, I've sidestepped the issue. I took one of my old banjo bolts from my EX500 and had a friend plug weld it. I replaced the bolt with the modified one on the incoming banjo. This allows the fluid to continue to the center piston of the front but prevents it from entering the SMC. By relieving the pressure and retracting the center piston of the rear caliper all the way, I've effectively made that part of the system inert. This does leave the fluid in the system, so hopefully that means it won't corrode like it might if it were emptied.

This "fixes" the issue until I can figure out why the return on the SMC isn't functioning.

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 Hi.  Just went through this problem and hope my solution is yours.

 

Symptoms.

On my 2000 VFR 800 I replaced all brake pads and bled the system and got a locked up rear wheel for my effort that was traced to the center brake piston not releasing.

While locked up, if you open the bleed nipple on center piston, fluid under pressure escapes and the wheel spins.

Going back through the brake circuit and pumping the brake to charge the hydraulics and testing each point for pressure release it led me to the SMC.

 

The Cause

The rear brake fluid reservoir supplies fluid the the rear brakes and the rear brake controlled front brakes, and everything else that's something to do with brakes other than 4 pistons of the front callipers. For some wonderful reason known to Honda they decided to insert another screen filter into a locked system and the process of bleeding all those metres of piping with fresh fluid puts all the years of crap into it and blocks it. Instant one way hydraulic lock-up. And I put it to everyone that if you clean it, and I'm comparing before and after my initial fluid change, the braking system comes back to how it was new.

 

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.

Put it all back together  and bleed the system, front, middle and rear points to a reasonable level and have fun spinning the back wheel by hand. You may notice that the wheel locks for up to 10 secs and frees. This is because you can't actually prime the SMC easily and there's a bit of an air lock going on and only riding does the correct action. You'll also hear a squishing sound from the SMC. No prob, the front brakes will save you while they pump the system and you do a few more bleed cycles.  obtw, the manual says to bleed the rear middle calliper, remove it. If your patient and don't mind a bit of fluid mess, an 8 mm ring spanner will fit while its on the bike.

End result and test

After the repair, I've noticed now is that on rear brake application at steady foot pressure, a moment later i hear the hiss from my sintered pads on the front disks followed by i think more stop on the rear. 3 sections working together.  

I won't be one that considers the system as rubbish. This is a mechanical system that after 16 years had a problem that could  be fixed with just a hell of a lot of patience and perseverance. I don't believe current electronically controlled ABS systems in 16 years would be so kind.  

You are on the right track, just get that filter out.

Cheers

Glen

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Just a thought here but do you all ever look at the factory shop manual? It got all the routing info for cables and hoses. Also shows how to rebuild every component on the bike and is downloadable on this site. 

Most of the brake problems I've run in to are the result of not changing the brake fluid. I did find a de-laminated brake hose on 40 year old CB400/4 as well as a stuck caliper piston. Make sure the return orifice in the mastercylinder isn't plugged. You can use. .009 guitar string to clear it... carefully! 

I just had my front end apart on my second 98 VFR in order to service/rebuild the forks, clean the brake calipers and was thinking of finally installing new brake lines. I've never, ever had a problem with either bike, both 15 yrs. old. While cleaning the calipers I was surprise how clean the pistons were but also how much brake dust was in all the nooks and crannies. All six of the pistons easily pushed back into the calipers with only finger pressure. The oem pads had plenty of life left so they got reinstalled. I think you can do an easy job of cleaning the calipers up using either HondaBrite (actually S100) or aluminum wheel cleaner and a good stiff brush. 

By the way, the notchy feeling from the steering head bearings turned out to be the 15 year old hardened grease on the bearing races. Cleaned and retorqued (good idea to use the special socket from Honda for that- don't know how you'd ever get it correct without it), it feels like a new bike.

Also, installed Jamie Daugherty's damper kit. For the money, one of the best kits out there.

Mac Morgan

 

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On April 25, 2016 at 10:16 AM, GleninAus said:

 For some wonderful reason known to Honda they decided to insert another screen filter into a locked system and the process of bleeding all those metres of piping with fresh fluid puts all the years of crap into it and blocks it. Instant one way hydraulic lock-up. And I put it to everyone that if you clean it, and I'm comparing before and after my initial fluid change, the braking system comes back to how it was new.

This, this right here. It's what I believe the issue is as well.

This will probably be a winter project, since I've worked around it and gotten the bike safe to ride, just without actually actuating the rear system from the front. I had a friend weld shut a banjo bolt I had lying around that's the same size as what the VFR uses. I put that in to prevent any brake fluid from entering the SMC, which did the trick. I'll pull it apart later and try to get that screen out.

10 hours ago, Mac Morgan said:

Just a thought here but do you all ever look at the factory shop manual? It got all the routing info for cables and hoses. Also shows how to rebuild every component on the bike and is downloadable on this site.

I have a FSM, both the physical one and the digital one from this site. GleninAus hit the nail on the head with his analysis. Everything, including the SMC, has been rebuilt. Many of the lines are still old, but I've confirmed they flow fluid in both directions and I have a full replacement set; just have only put on the front lines and the clutch line.

Can you link to that dampener? I'm assuming it's a steering dampener. I looked on the website and couldn't find anything.

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