Headache with Brakes, any help appreciated

Gungurdin

Joined
Nov 3, 2025
Messages
2
Age
60
Location
Shropshire
Bike
ST1300
Hi All,
I have a 2007 ST1300A and recently had a problem where the front left hand caliper detached from the bike (dont ask) resulting in me having no breaks but having to use what i did have until they failed completely.... The result, rebuilt the SMC with new parts, the screen filter is clean and the port free of blockages, rebuilt the master brake cylinder fitted new pads and have bled the system according to the Honda process steps. The calipers were all serviced in December of 25 and were working perfectly prior to the event. When i was fitting the new pads i noticed that as i pushed a piston in (centre) the two outers on the rear caliper would come out and vice versa. Fitted the pads all round and both the lever and the pedal felt good. However, after depressing the rear brake pedal the rear wheel is solid and does not rotate, if i crack the outer bleed nipple the wheel will turn. the fronts wheel is also binding slightly. I have never experienced this with a bike before but have with a car where the flexible brake hose had failed and would allow fluid to go one way but not return creating the same issue. Any advice on how to identify which pipe could be causing this as im guessing it could be any given the interlinked nature of the system would be appreciated. Another thing to note is that when the brakes failed the front brake leaver went solid and the rear pedal just traveled to the lower point. I have throughly bled the brakes and am sure that there is no air in the lines.
Thanks in advance
Stuart
 
If a locked rear wheel can be released by opening the bleed nipple it is almost guaranteed that the itty bitty tiny port in the SMC is blocked. As @Sadlsor said, there have been very very few successful SMC rebuilds, and I remember at least one of these was reported to fail roughly 6 months after the rebuild. (That thread is long since gone in the big evaporation.)

Just one question, did you perform the 7 step brake bleeding procedure outlined in the Honda Service Manual?

You are not a likely candidate to get Larry's help via phone since you are across the pond, however, I suggest you go to Articles>ST1300 and search for @jfheath's dissertation on the 1300's brakes.
 
Google Meet is free, with the advantage of love video.
Apples Face Time may be an option, or even Zoom.
"We can rebuild it / him.
We have the technology."
Not referring to the SMC rebuild kit, but rather the 1970s TV show "The 6 Million Dollar Man."
 
SMSW said:
If a locked rear wheel can be released by opening the bleed nipple it is almost guaranteed that the itty bitty tiny port in the SMC is blocked. As @Sadlsor said, there have been very very few successful SMC rebuilds, and I remember at least one of these was reported to fail roughly 6 months after the rebuild. (That thread is long since gone in the big evaporation.)

Just one question, did you perform the 7 step brake bleeding procedure outlined in the Honda Service Manual?

You are not a likely candidate to get Larry's help via phone since you are across the pond, however, I suggest you go to Articles>ST1300 and search for @jfheath's dissertation on the 1300's brakes.
Click to expand...
Hi, thanks for the reply, i am sure as i can be that the SMC rebuild is good and that the port is clear. I have concluded from yesterdays efforts that i will go back through the calipers and ensure all is good with them and not assume that they are given the December work. I will be on that this evening.
I did follow the bleeding process to the letter. :)
 
It is an old machine with the old style of SMC. This has a drain hole near the uphill end of the plunger - the idea being to drain away the water.
This was not often kept clear so the water that gatered around the rubber boot was prone to eventually seeping into the chamber.

Some people attampted to fix that based on ill-advised information about peeling the rubber boot back and packing it with silicone grease. If they had mentioned that they put the rubber boot back without saying how, then it is (in my opinion) almost certain that it wasn't put back properly. The reason that I say that is that when I took my old one apart, I found out how to do it properly. It requires a hefty push on the brim of the seal (deep down inside) and there is a VERY definite click as the spring in the brim is forced to compress and the brim slots into position with a clunk. Anyone that has doen this would surely have mentioned it.​
​
I cannot get that brim back in without removeing the bracket on the end (Which you are not supposed to do - because the measurement is absolutely critical. I measured it with a vernier caliper and when I put if back it wasn't the same. So I guessed that a bit of grit had got on the surface, cleaned it up and tried again. That did the trick.​

So there are two issues both of which cause problems in the SMC. Both are to do with water. One caused by incorrect seating of the rubber boot, one caused by lack of proper servicing.

Here is what an old 2004 model (same as your 2006) SMC looks like two years after fitting a new service kit.

SMC-ST1300A4-05.jpg SMC-ST1300A4-08.jpg SMC-ST1300A4-09.jpg SMC-ST1300A4-10.jpg SMC-ST1300A4-11.jpgSMC-ST1300A4-12.jpg SMC-ST1300A4-14.jpg

Note the first image - which is what it looked like before I started to take it to bits. The rubber boot looks to be OK, although it is not seated properly.

Sawn-in-half.JPG

The above photo is what the same SMC looked like after I had sawn it lengthways and cleaned it up. Note the dark bit near the open end. That is corrosion on the inside of the bore caused by ingress of water. Once water gets past that rubber boot, there is nothing to stop it getting into the area before the secondary seal (the primary seal is the one that applies the pressure on the fluid to activate the rear outer pistons.)

That starts to become a problem because the spring does not have enough oomph to push the secondary seal past the corrosion and th ebuild up of grunge that can be seen in the earlier photos.
It doesn't matter how clear the compensation port is, if the piston cannot move back far enough for the primary seal to clear the compensation port - the rear brakes cannot release their pressure.

End of lesson.

There are two things that you can do to check whether the problem might be.
1. Check that pressure is releasing. Put a bleed tube on the front left lower bleed valve (this is the centre piston). Part fill it with fluid and hold the open end upright. Keep the bleed valve closed. Press on the rear brake pedal hard. Like an emergency stop, and release the pedal. Remove the rear pads and get the rear caliper of the bike so that you can get at the pistons. Undo the front left lower bleed valve and let the bubble of air from the bleed valve float up - if it will. You should be able to push in the two outer pistons easily - you need a thumb on both the forward and rearmost piston and press them both ata the same time. Or alternate the pressure (but keeping a thumb on each piston). As you push one in, the other will want to come out. Don't let it. If the SMC is clear, then the fluid will push up the fluid in the bleed tube. Seal the front left lower bleed valve. Then back to the rear caliper and push in the forward piston - to check whether the rearward piston moves out. Then press on the rearward piston to make sure that the forward one moves out.
You have an answer as to whether or not the pistons are moving OK, and whether the SMC port is working properly.

2. You can also check whether the SMC is working as it should. Lie down next to the bike. Rotate the rear wheel with your foot and push forward on the back of the top of the SMC - pushing towards the bracket on the end of the SMC. You should feel the wheel lock solid. (I can get the heel of my hand on the SMC and my fingers arounf the fork leg and gently squeeze a bit like operating a brake lever. It doesn't take a great deal of effort. You shouldn't need a tool to do it.
Crucially, when you let go, the wheel should free up.
nb - comment on the last photo. It looks as though the bore is getting narrower towards the left hand end. That is becasue I couldn't saw parallel to the axis of the bore, so the cut is at a slight angle.

-------------------------

Finally - that boot fitting.

1776863868776.png

See the part labelled 'angled step'. See where the brim of the top hat it. It has been pushed past that angled step. But it won't go there by itself. It needs a very firm push which squeezes the key ring spring inside the brim and it suddenly pops past it. But in order to do it, I had to remove the bracket from the end and find a socket from my wrench set that just fits inside the bore and which fits over the top hat to press onto the brim. Then put th ebracket back on, comparing the measurement taken before and after.

If all of this works out OK, then we have to look at other things that might be causing the issue. If you get to that stage and you have familiarised yourself with "avoiding the pitfalls". Then it might be worth a phone call. I'm up north in Yorkshire.
 
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