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Hi all, to those asking it is a 6th Gen VTEC, my friend is picking up the bike today and we'll see what the garage has done... I'm pretty sure I would have noticed the brake line holder piece missing but this is a very good point! I'll post an update when she has the bike back and if the chain becomes loose... it was checked by another garage already and the chain they stated was in good condition.

I'm afraid of stripping threads so I go by manual for most torques, 74nm. I'll update here if I hear anything.

My friend's VFR chain keeps becoming loose, literally after a few miles of riding. Adjusted the sag, torqued the eccentric hub(?) pinch bolt correctly. I have worked on my VFR and know how to do this. The chain is in good condition, I can't fathom anything else causing the chain to become very loose that soon. Has anyone else had this issue? Could grease on the hub cause it to slip like that? I've only had experience of mine and I've never removed it or touched it, and it adjusts and pinchs just fine. Currently they took it to a mechanic because I wasn't around for a while to check it and they aren't mechanically minded. Just wondering what the cause/price to fix could be.

Sorry to hijack post, but I'm putting a relay from my rear lights, now can I run my heated grips and a USB /voltmeter thing from the same relay or would I need two?

So after a test ride, the rear brake was getting stuck still. Rather than deal with brake line companies over a few mm short hose I drilled the hanger that attaches above and this gives enough slack for the SMC to be fully released. 2nd test ride, front brakes weak, either pads contaminated or need to bleed. Have pads and will bleed this weekend. Rear brake strong, stops, doesn't lock up. Did the linked brake test, riding and coming to halt with no brakes, can touch both discs with bare hands. Using only front brake: Front discs warm, rear disc v.hot. Using Rear brake: Front disc warm, rear disc v.hot again, but not locking up and is free. Spinning the rear wheel by hand gives 3/4 turn, front wheel the same. Seems normal. So what I have learnt: DO NOT upgrade your hoses using Frentubo, or (Galfer too from what I've read). Unless your hoses are leaking or obviously bulging it's not worth any of the hassle. Preventative maintenance on SMC, reapply (correct) grease and check under the rubber cover for rust, even slight build up over time can cause issues. Look after your pistons, during this I found corrosion on them which I replaced them all, now I'll apply ACF grease around the outer area of the pistons (not in contact with brake fluid). Grease the caliper slide pins. Bleeding a dry system or after unbolting a line requires a lot of fluid. I bought 4L of DOT4 and used a lot of it during this, I bled it 3 times over 2 days to make sure any air moves through the line. If you still have problems with the SMC after a rebuild with return flow, remove the ball bearing from the green cartridge and re-insert (retain the filter mesh and base, as it needs to seal against the o-ring when you reassemble. I have some cool diagrams from blackbird and ST1300 forums for reference:

Second to last update. I rebuilt the SMC although it didn't need it IMO. The fault is the green cartridge inside. Basically I took this out, removed the one way ball bearing and so it has free fluid movement. I am very sure this is just to assist bleeding, when putting the rebuild kit in and priming it before connecting, the amount of air bubbles being generated in the unit would probably end up pushing back down the line to the front brakes. This almost one way valve would stop this problem. This would only be a problem when doing an initial bleed on the bike, so probably helps honda mechanics do the job quicker. I left the gauze in place so it would trap any dirt from entering the SMC. Before removing the SMC again I extended the rear centre piston, undid the bleed valve on the Front Left bleed nipple, and it would not push fluid through. I then undid the bolt on the SMC out, which released fluid, ruling out the PCV unit at fault. After I removed the one way piece (I still had to insert the green cartridge as a seal), I could easily move the rear centre piston in and out. I bled the bike and will test ride tomorrow to see if the rear locks up again under braking/heat. Now that the SMC definitely allows the fluid to expand back to the Rear MC it should be fine. Only problem is that these awful 'upgraded' lines are slightly short (picture) and I feel it might be slightly activating the SMC. If so I will just use my old rubber honda one if there is any trouble tomorrow. Will report back in 24 hours with the result of the test ride. If all is well then I at least will not shy away from owning other Honda linked bikes (blackbird, varadero, ST1300). These linked brakes seem to cause problems across all models. I would definitely recommend people focus on this area for rust prevention as well as taking the brake fluid changes extremely seriously as over a long time it will cause problems.

Good videos. I wish my bike were in such a clean condition... although I'm sure I'd still have these troubles, 59,000 miles on the clocks. I note there's aftermarket hoses, I'm going to reposition mine as I also thought the way mine are could be activating the SMC inadvertently. Something for people to be aware of when fitting aftermarket hoses (can't remember if I mentioned that). Useful that you mentioned undoing the front bleed valve and checkign the rear piston returns, I will do that, then crank the hose that goes to PCV to check that. Also from looking at your picture it looks like you have more pushrod exposed than on mine, although as you can see in the picture I wedged the SMC far back and that's as much as I can see.

I'm in the UK so the parts are not in stock, $135 is quite reasonable though, better than PCV which I think is quoted £500!!! Ebay is very hit and miss here. The fact that on 5th (and 6th?) Gen you bleed the rear brake caliper using the rear MC and Rear foot pedal shows that the piston should activate by the rear pedal, but only when stationary. The force of fluid from the pedal should collapse the SMC seal and force fluid past it. The fluid should then return through the tiny hole which maybe mine is blocked or what. When the bike moves the rear pedal shouldn't over ride the SMC for centre piston, because that much force would likely trigger the PCV. I've also just joined a CB1100xx forum that has some cool diagrams and charts for the pressures in the hydraulic system. Definitely more posts on VFR forums and ST forums than the CB and Varadero, from my minimal internet searching at least.

Just to update, still experiencing rear brake lock up when riding. After the brake cooled (after about an hour) the brake would loosen up. To me this shows that the fluid heats up and expands and the return port on a master cylinder is blocked (I did also check that I didn't over-fill the brakes which is not the case). Front brakes aren't dragging. I can return rear outer pistons so the rear MC is not blocked, nor is the front brake lever MC as the return port is free. This leaves the SMC, I've ordered a rebuild kit, waiting for that to arrive. I have a spare SMC bracket from ebay which is in good condition so will use that one. Might remove the one way valve on the green cartridge after. Not sure if it's worth installing 'correctly' going through 2 litres of fluid to bleed the system then having to pull it out due to a blockage still. The green valve has a one way large hole and a 0.25mm hole going both directions. The small hole should allow for fluid expansion during heat once the SMC is not actuated however there is also a small hole in the SMC itself like with all master cylinders. My opinion is that this valve works to assist the bleeding process, allowing essentially one way movement of fluid/air. Without this during the Front left (rear circuit) bleed procedure air could continually be sucked through the rest of the rear line. The cartridge in the ST1300 Linked brakes is clear plastic, and instead of ball bearing and spring, has a rubber stopper and spring, again not documented in manual and cannot order as a spare part. The ST linked brakes uses a larger bore SMC so it is not really compatible with VFR, although cheaper and still able to be ordered, I might resort to one as it would only apply a bit more brake to the rear centre piston, and there is a PCV in the middle to stop the rear brake being over activated during heavy braking anyway. One more check I did was to wedge a piece of wood to push back the SMC to ensure it wasn't being activated by an incorrect pushrod length, still rear piston not returning. Going to get circlip pliers out and remove the pushrod on SMC to see if there is anything in the piston that's causing a blockage (maybe rust or corrosion inside). After I do that it will narrow down to the green valve being the culprit. Also ordered a used PCV valve in case that's at fault (will loosen the banjo bolt at front to check this. Will report back with any solutions to help future users.

So after I reassembled (not rebuilt yet) the secondary master cylinder, I can no longer draw fluid through the PCV by vacuum pump... However if I pump the rear brake pedal then fluid will flow through the PCV valve, looking at the tube I attached, the fluid does NOT back flow even if I do not tighten the PCV bleed valve. It seems my secondary master cylinder has a one way flow, and a stiff one at that. Has anyone had a similar experience? I did take out the green cartridge in the SMC and cleaned it and replaced it back in the correct orientation. Very confused about this, not sure if this is meant to be a design feature to aid bleeding... or if I've broken something. Fluid can still force through the SMC to the rear bleed points via foot brake, just not via vacuum pump. Front centre bleed valves are both normal and can draw fluid. I did wrap the bleed nipple in PTFE tape to stop air bubbles sucked in ... so before when I was sucking air perhaps it was only coming from around the nipple thread. Currently I'm stuck with a locking rear, due to brake overheating and fluid expansion. Wheel releases when cooled down. Trying to trace if it's the SMC or rear MC. Might just rebuild both for the fun of it.

I stand corrected. the inlet port cartridge (the green piece inside SMC) does have a relief hole next to the spring one way valve. It's the size of the tiniest guitar wire... I had to force the wire through and I pierced the mesh. Still don't think this is enough to allow fluid to freely release the piston from the caliper though, or maybe it was blocked or the relief port was blocked underneath in the SMC body. I can only assume this cartridge is to assist in bleeding, to stop air bubbles being sucked back (as this hole would be too small for a bubble to pass through, and the mesh would make bubbles smaller too. Otherwise not sure of the purpose since it is NOT one way... it just heavily restricts back flow.... which only would occur if you need to push the piston into the brake caliper or to relieve pressure of the system if it were expanding.

I've wandered on to ST owners forum as one guy has written a lot about the SMC and I'm assuming it's the same design so I hope to have some more answers from there. What you say I'm not sure about. When the SMC piston is pushed then it will block both ports into the "mc" area so that doesn't need a one way piece. Unless the green valve is to aid in bleeding the system as that's essentially what speed bleeders are. The ST forum says to release the rear piston all the way in the caliper you must undo the bleed nipple otherwise they do not go in. This is similar to my experience. I'm guessing under the green valve in the video that chamber is enough for any heat expansion of fluid. And I'm thinking that to force and activate the centre piston using the foot pedal will 'break' the system as the system is design for the SMC to only activate that piston. Now I think when I rode after assembled everything that the SMC was not pressing during breaking and this causes a problem. Or there was air that expanded under heating. The brake did release slightly after it cooled. Going to look at the spare SMC I have and see if it's better condition and also going to check the needle bearing on the Lower fork leg today.

I've just seen a diagram from ST1300 forum of the SMC. Showing the small return port in SMC can be blocked, but as I was able to use my compressor to push the green thing out, I do not believe the piston is rusted and causing that hole to be blocked. Might have to ask on that forum too as they have a similar design. Video of the SMC green part and trying to explain..

The rebuild kit is just for the piston component which isn't leaking and is working correctly. The green screen is inside the SMC. There may be another in the PCV I haven't taken it apart or seen a break down of that component. The PCV I refer to is the one under the fuel tank. There's a proportional valve on the Right leg of the bike which I don't know the specifics of either. I'll put a video underneath to show the green valve out and what I'm trying to say. I also attach a diagram I made to try and get my head around the components as the service manual doesn't explain it enough for me.

I have referred to this and have carried out the process but it does not mention the specific question about the SMC and the PCV aren't serviceable. That's why I'm looking for help troubleshooting before resorting to used ebay parts.