Air in SMC Query

I could see how a collapsed hose would hold a brake on but not after a long period of normal brake function without the reapplication of the brakes. I sympathize re locating a good mechanic, my go to motorcycle guy is a 150 mile round trip and the MOT a 40 mile round trip, just so you can take it to someone you can trust, luckily I do most myself and luckily I don't have a SMC.
Have you a trusted trader site over there which could provide a name. I wouldn't rule out a Honda dealer, there are still some good ones out there, but not many and I appreciate you don't want to gamble on the result.
Fawlty, how much is it grabbing, are we talking you can feel a bit of drag or the wheel is almost solid. If like Larry says it could be a bent pin etc then my view would be that heat could cause an issue, are there any signs of heat build up, discolouration etc.
Good luck.
Upt'North.
 
Upt' North said:
I could see how a collapsed hose would hold a brake on but not after a long period of normal brake function without the reapplication of the brakes. I sympathize re locating a good mechanic, my go to motorcycle guy is a 150 mile round trip and the MOT a 40 mile round trip, just so you can take it to someone you can trust, luckily I do most myself and luckily I don't have a SMC.
Have you a trusted trader site over there which could provide a name. I wouldn't rule out a Honda dealer, there are still some good ones out there, but not many and I appreciate you don't want to gamble on the result.
Fawlty, how much is it grabbing, are we talking you can feel a bit of drag or the wheel is almost solid. If like Larry says it could be a bent pin etc then my view would be that heat could cause an issue, are there any signs of heat build up, discolouration etc.
Good luck.
Upt'North.
Click to expand...

No there are no trusted trader equivalents in my area unfortunately.

The wheel is fairly solidly locked. It is possible to turn it by hand, but not with ease, when i press the brake pedal it frees up no problem. I have just been out for a ride again, put it on the centre stand, rear wheel moving freely, within 15 minutes it had locked up again!

No evidence of discolouration.

I have just been out and unfastened the rearmost bleed valve, no fluid came out but the wheel immediately unlocked.
 
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I'm sure either Heathy or Larry will chime in now, I would have thought that will confirm what circuit it is, i.e either front Possible SMC related or not. Having an 11 without CBS I'm not sure I know where that bleed valve leads to, but it's got to be a good clue.
I'm surprised someone hasn't invented a Honda ST1300 SMC board game, where do the clues lead us etc.
Good luck.
Upt'North.
 
Did you check the level of the fluid in the rear reservoir? I've put new pads on my f650 BMW before and the thicker pads caused the reservoir to be overfilled. This caused my rear brake to drag until I bleed the fluid to the right level? This might explain why it only drags when it warms up (fluid expands)?
 
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I'm still standing by the bent bracket/pin, and/or air still in the system.
We don't know if the "guy who doesn't know a lot about the ST's brakes" bled them correctly, used a vacuum bleeder, tilted the SMC correctly, or took the rear caliper apart when attempting to clean/rebuild it.
We don't know if the retaining clips are bent, or if the guide rod(s) are damaged and/or bent as well. They may not LOOK bent, but that does not mean they are not bent.
Mr. Wilson and I discovered this VIA the white courtesy phone, with text pictures. You could see the piston was not square against the rotor etc.
The line in question runs UNDER the caliper, and may be pinched between the swing arm hump and the caliper.
If the pins are bent, for force of pressure against the rear pedal (it frees up the wheel) could simply be straightening the caliper out enough to free up the wheel, until it works crooked again.
What I would do at this point.
Again, find new mechanic or have a forum member who's bled brakes help you this time.
Lower the mufflers, remove the axle, and remove the STOPPER BOLT, and lift up the caliper assembly and inspect the "work that was done" looking for damage (signs that the hose was pinched between the swing arm and caliper) bent clips, damaged pins etc.
Put everything back together in the correct order, and do a complete bleed again, using a check valve and not a vacuum, or by hand to make sure no air is sucked in around the threads.
Open the handle bar master cylinder and remove the deflector spoon, and gently take a small probe, think small guitar string, and make sure the hole is clear and not blocked.
Bleed then entire system, then strap down both levers over night.
Again, make sure you pull all (3) calipers APART and clean the grease out of the guide pin boots, then LIGHTLY grease the pins, pulling them apart a few times to check for suction. (both front brake calipers, and the rear one).
Are there any forum members who service their own bikes near our friend?
 
drtyrrel said:
Did you check the level of the fluid in the rear reservoir? I've put new pads on my f650 BMW before and the thicker pads caused the reservoir to be overfilled. This caused my rear brake to drag until I bleed the fluid to the right level? This might explain why it only drags when it warms up (fluid expands)?
Click to expand...

We were hoping that it might be something that simple but unfortunately he has already checked and ruled that possibility out and found that the masters are not overfilled. To bad it isn't something this simple.
 
If you are certain that there is no air in the brake system than I am leaning towards Larry's idea that something is bent, out of alignment or improperly installed. I have no idea if this is a plausible possibility but here is what I am thinking. As the temperature increases the brake fluid expands and causes the rear caliper pistons to move out which pushes the caliper away from the rotor. This may simply be normal pressure build up and movement due to temperature increase that always occurs and we never notice it on a normally functioning brake system. I have no idea if temperature can cause such movement but maybe it does and we are not aware of this because normally it does not cause an issue. In your case it may be an issue because the caliper is not moving away from the rotor equally at both ends because something is amiss. It ends up cocked out of alignment and is no longer parallel to the rotor which causes it to bind. When you step on the pedal the increased hydraulic pressure forces all of the pistons out equally. The hydraulic pressure overcomes the force of whatever is binding and forces the caliper to move back in to parallel alignment with the rotor. The caliper is now straight in its mounts and can move freely again. Just a thought. I would still want to be sure that there is no air in the brake system while I am checking the mechanical items.
 
Igofar said:
I'm still standing by the bent bracket/pin, and/or air still in the system.
We don't know if the "guy who doesn't know a lot about the ST's brakes" bled them correctly, used a vacuum bleeder, tilted the SMC correctly, or took the rear caliper apart when attempting to clean/rebuild it.
We don't know if the retaining clips are bent, or if the guide rod(s) are damaged and/or bent as well. They may not LOOK bent, but that does not mean they are not bent.
Mr. Wilson and I discovered this VIA the white courtesy phone, with text pictures. You could see the piston was not square against the rotor etc.
The line in question runs UNDER the caliper, and may be pinched between the swing arm hump and the caliper.
If the pins are bent, for force of pressure against the rear pedal (it frees up the wheel) could simply be straightening the caliper out enough to free up the wheel, until it works crooked again.
What I would do at this point.
Again, find new mechanic or have a forum member who's bled brakes help you this time.
Lower the mufflers, remove the axle, and remove the STOPPER BOLT, and lift up the caliper assembly and inspect the "work that was done" looking for damage (signs that the hose was pinched between the swing arm and caliper) bent clips, damaged pins etc.
Put everything back together in the correct order, and do a complete bleed again, using a check valve and not a vacuum, or by hand to make sure no air is sucked in around the threads.
Open the handle bar master cylinder and remove the deflector spoon, and gently take a small probe, think small guitar string, and make sure the hole is clear and not blocked.
Bleed then entire system, then strap down both levers over night.
Again, make sure you pull all (3) calipers APART and clean the grease out of the guide pin boots, then LIGHTLY grease the pins, pulling them apart a few times to check for suction. (both front brake calipers, and the rear one).
Are there any forum members who service their own bikes near our friend?
Click to expand...

Larry, just wondering how the pins get bent, I'd guess:
Worn pins that allow movement to the point that they may bend under braking pressures and turning forces?
Simple wear and tear, unlikely?
Mechanic resembles a full grown silverback?
Just wondering as we do.
Glad to see things are getting sorted for you and er'indoors as well Larry.
Upt'North.
 
This doesn't make sense. Or more to the point - I don't undestand what is going on.

I've been watching Jesse Stone - "If you don't like the answers you are getting, check your premises". (assumptions)

The problem started with a squishy pedal.
You bought a brand new SMC from partzilla.
Someone else fitted it.
Is the part that is now fitted to the bike, the new part that you supplied ?
Has the pushrod adjustment been tampered with ?
Is the part that you were shown the same part that came off your bike ?​

Recently:

Your front wheel brakes do not bind.
Your rear brake was locked
You opened the rearmost bleed valve.
No fluid came out.
The brakes unlocked.
The rear most bleed valve opens up the fluid in the outer pistons.
Opening this valve to release the brakes suggests that the fluid in the line is under pressure.
No fluid coming out suggests that it is not under pressure.
These last two statements seem to contradict each other.​

But what if the binding brakes is caused by something else? Why would opening the valve cure the locked brake. Well maybe the action of the spanner/wrench on the bleed valve is what does that. You could test that idea by seeing if grabbing hold of the caliper and moving trying (not to hard) to twist it in the same way that the spanner would.

So possible sources of brake binding:

Take a look at this little animation of how the brakes move.

[video=youtube_share;Kq5GbW-tVKM]https://youtu.be/Kq5GbW-tVKM[/video]

Notice the caliper being pulled across as the brakes are applied.
Notice the contact with the pad springs at the top.
Notice the light blue guide pins moving freely

As I write this, I see Andrew has just posted some suggestions along the same lines.

The suction / pressure theory - from too much grease in the rubber boot / slider pin is one I have described earlier. Brake disc rotor was blue tinge hot.

The caliper springs are designed to cause problems with the pads.
Click the pics to enlarge them.​

P1020411.jpg P1020413.jpg


First the pad spring - this is the rear caliper on an ST1300. Notice two things:

The wide part of the spring is closest to the pistons. This is absolutely essential.
The circled tags on the narrow part of the spring are there to keep the pad on the inside firmly in place against that side of the caliper. The tags may be bent due to incorrect location of brake pads. If the spring is inserted the wrong way round with the tags closest to the pistons, the pistons will push the pads, the tags will stop the pads. The spring will bend a bit and push back later - if it doesn't break. The second photo shows that inside pad located in a caliper which I have taken apart.

Next the slider pins. I've circled the retaining clip because the photo was used for something else. The slider pin is the obvious shaft sticking out to the left just below the white circle. The other is on the caliper itself.

P1020427.jpg

A smear of silicon / rubber grease. Not a butter tub. It WILL create enough pressure or suction to shift the caliper and it WILL cause brakes to generate enough heat for them to lock on.

P1020440.jpg

The slider pin needs to be smooth, clean and greased to allow the outer (left on the photo) pad to slide as the pads wear down.

P1020443.jpg

And here is a sign of a problem. The outer pad is worn. The inner pad, much less so. If the pads are properly seated and the calipers are moving as they should, the wear will be the same.

Larry's suggestion of bent slider pins also need to be considered. I don't have any photos of that though.

There shouldn't be air in the system, but how it can cause the brakes to is completely unclear to me.

If Fawlty has the necessary tools, it would be useful to be able to have some clear photos of the back end - and the hoses that Larry mentioned. It may mean partly removing the axle (and swinging the exhausts out of the way) and taking the caliper bracket of the axle to allow the caliper to be lifted and inspected.

But hang fire, Fawlty, wait to see what other suggestions are out there.

Ps - I have the measurement for a properly adjusted (brand new) SMC push rod/bracket if my earlier point is being considered.






​
 
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Interesting point Mr.Heath re the movement the spanner would create in the caliper and pads. I know when mine have dragged on the 11 it doesn't usually take much of a raffle to free things up and it would explain why no fluid came out. Unless of course it's all air and no fluid. Although I appreciate this as already been ruled out.
Upt'North.
 
Many thanks again John. I have answered your questions in bold below and have one question about the location of the rubber boot. I really appreciate the time and effort that you and everyone else are putting into this problem. I am confident that with your help and advice it will be resolved. Very frustrating but I'm not giving up!



jfheath said:
This doesn't make sense. Or more to the point - I don't undestand what is going on.

I've been watching Jesse Stone - "If you don't like the answers you are getting, check your premises". (assumptions)

The problem started with a squishy pedal.
You bought a brand new SMC from partzilla.
Someone else fitted it.
Is the part that is now fitted to the bike, the new part that you supplied ?
Yes, Definitley
Has the pushrod adjustment been tampered with ? No
Is the part that you were shown the same part that came off your bike ? No doubt, I was present when it was fitted and when the system was bled
​

Recently:

Your front wheel brakes do not bind. Correct. Both when the rear wheel was moving freely and when binding
Your rear brake was locked Correct
You opened the rearmost bleed valve. Correct
No fluid came out. Correct
The brakes unlocked. Correct
The rear most bleed valve opens up the fluid in the outer pistons.
Opening this valve to release the brakes suggests that the fluid in the line is under pressure.
No fluid coming out suggests that it is not under pressure.
These last two statements seem to contradict each other.​

But what if the binding brakes is caused by something else? Why would opening the valve cure the locked brake. Well maybe the action of the spanner/wrench on the bleed valve is what does that. You could test that idea by seeing if grabbing hold of the caliper and moving trying (not to hard) to twist it in the same way that the spanner would.

So possible sources of brake binding:

Take a look at this little animation of how the brakes move.

[video=youtube_share;Kq5GbW-tVKM]https://youtu.be/Kq5GbW-tVKM[/video]

Notice the caliper being pulled across as the brakes are applied.
Notice the contact with the pad springs at the top.
Notice the light blue guide pins moving freely
Interesting video. Very informative for me as a brake novice!
As I write this, I see Andrew has just posted some suggestions along the same lines.

The suction / pressure theory - from too much grease in the rubber boot / slider pin is one I have described earlier. Brake disc rotor was blue tinge hot.

The caliper springs are designed to cause problems with the pads.
Click the pics to enlarge them.​

P1020411.jpg P1020413.jpg


First the pad spring - this is the rear caliper on an ST1300. Notice two things:

The wide part of the spring is closest to the pistons. This is absolutely essential.
The circled tags on the narrow part of the spring are there to keep the pad on the inside firmly in place against that side of the caliper. The tags may be bent due to incorrect location of brake pads. If the spring is inserted the wrong way round with the tags closest to the pistons, the pistons will push the pads, the tags will stop the pads. The spring will bend a bit and push back later - if it doesn't break. The second photo shows that inside pad located in a caliper which I have taken apart. Understood and noted

Next the slider pins. I've circled the retaining clip because the photo was used for something else. The slider pin is the obvious shaft sticking out to the left just below the white circle. The other is on the caliper itself.

P1020427.jpg

A smear of silicon / rubber grease. Not a butter tub. It WILL create enough pressure or suction to shift the caliper and it WILL cause brakes to generate enough heat for them to lock on.

P1020440.jpg

The slider pin needs to be smooth, clean and greased to allow the outer (left on the photo) pad to slide as the pads wear down. Too much grease could cause locking. Where is the rubber boot situated?

P1020443.jpg

And here is a sign of a problem. The outer pad is worn. The inner pad, much less so. If the pads are properly seated and the calipers are moving as they should, the wear will be the same.

Larry's suggestion of bent slider pins also need to be considered. I don't have any photos of that though.

There shouldn't be air in the system, but how it can cause the brakes to is completely unclear to me.

If Fawlty has the necessary tools, it would be useful to be able to have some clear photos of the back end - and the hoses that Larry mentioned. It may mean partly removing the axle (and swinging the exhausts out of the way) and taking the caliper bracket of the axle to allow the caliper to be lifted and inspected. Not able to do this at the present time, but when I find a mechanic I want to be present when he works on it and I shall be taking photos.

But hang fire, Fawlty, wait to see what other suggestions are out there. Hanging fire!

Ps - I have the measurement for a properly adjusted (brand new) SMC push rod/bracket if my earlier point is being considered. Thanks, but I am confident the SMC has not been tampered with






​
Click to expand...
 
Good answers thank you.

The caliper bracket is fixed firmly to the axle and is stopped from rotating when you brake by the heavy duty stopper bolt - which you can just about through the gap above the exhaust pipe. The bracket does not move.

The caliper body (in which the brake pads are mounted, and which has the 2 bleed valves) is mounted very loosely - quite alarming when you think about it. There are two slider pins - one on the caliper which mates with the corresponding hole in the caliper bracket. The other slider pin is mounted on the caliper bracket and this mates with the a corresponding hole in the caliper body. These pins need to be lubricated with a 'rubber' silicone grease - sutiable for use in hydraulic seals. A visible smear is enough. Too much and you create an airlock.

The boots are there to keep water and grit out of the holes, so that the caliper body can slide in and out towards the caliper bracket. They allow the movement that is necessary and which is exaggerated on that video I attached. You can test this by removing the brake pads and grabbing hold of the caliper and moving it in and out (right and left in the photo). Note the photo shows the pads in place. You should be able to move it and it should stay where you put it. If it move by itself, then run away - your workbench is toppling over. Or - you have too much grease in there.

attachment.php


You can see one of the slider pins in the photo with the white circle that I sent post #94. The other slider looks similar.

The boots look like this:

attachment.php


The left hand one is longer and it fits into and through the hole in the caliper body - it is located under the smaller centre piston, between the two outer pistons.

Here is an image of the lower boot in place. It is taken from between the exhaust and the number plate with the pannier removed, from low down. The yellow lines show the same boot protruding at each end. The slider pin is fully inserted, but you can see the hexagon nut which is used to tighten the slider pin into the caliper bracket. The red stuff is the hydraulic 'rubber' grease that has squished off the slider pin when I inserted it into the boot. The yellow lines point to the exposed rubber parts.

attachment.php



The smaller boot fits into the hole in the caliper bracket. The little lip fits under a corresponding lip in the caliper bracket. If you use 'normal' grease to lubricate the pins, this rubber boot will absorb the oils and it will expand considerably. It will then stop sealing, and if you take the seal out of its hole, you will have far too much seal to seat in the caliper braket hole when you come to put it back. The photo below is taken from above the rear caliper looking down towards the front of the bike slightly. The yellow line is touching the rubber of the boot.
You can just make out the hexagon head of the slider pin on the left of the caliper, part hidden by the hydralic 'banjo' coupling.

attachment.php


This is an ST1300A9 model, but the rear caliper on the ST1300 has not changed. The observant will notice that this is not the standard pad pin. Neither have I simply substituted one of the front pins. There have been some subtle modifications, as the front pad pin does not fit the rear caliper - it seems to, but it will not be secure without modification. Copy this idea at your own risk.
 
These are great photos John and makes it a lot easier to understand, Many thanks.
 
Fawlty said:
I have just been out and unfastened the rearmost bleed valve, no fluid came out but the wheel immediately unlocked.
Click to expand...

There is of course no certainty on what exactly could have happened when unfastening, could be wiggling was good enough to loosen up mechanical binding or hydraulic blockage.

But assuming your theory of pressure build up, the good news is that you have no or very little air in the line, otherwise chances are you'd seen oil out.

And no oil dripping out doesn't necessarily mean there was no pressure in the line.

With the bike stationary, there is really nothing pushing the pistons back, so no oil flow. All is needed to unbind is relieve whatever little compression there might have been on the fluid when starting to bind, which is not much volume expansion that might have been accommodated just by backing off the valve.
 
Upt' North said:
Larry, just wondering how the pins get bent, I'd guess:
Worn pins that allow movement to the point that they may bend under braking pressures and turning forces?
Simple wear and tear, unlikely?
Mechanic resembles a full grown silverback?
Just wondering as we do.
Glad to see things are getting sorted for you and er'indoors as well Larry.
Upt'North.
Click to expand...

I've replaced more than a few bent guide pins that were damaged by folks trying to remove pads by reaching through the right side of the wheel, and removing the 3 bolts, and splitting the caliper in half, then bending the clips/tabs trying to put them back together, or by removing the guide pin from the bracket, then forcing the caliper up and away from the rotor etc.
I've had to replace brackets/calipers and cross threaded bolts.
I've seen bikes back from dealerships that had PRY marks on the swing arm where the mechanic tried to get a little more room... and even bent rear rotors etc.
I swear some folks just have a ball peen hammer, a pair of vice grips, a can of WD40, and a roll of duct tape and safety wire instead of the correct tools! And don't even get me started on Impact tools :rofl1:
 
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Igofar said:
And don't even get me started on Impact tools
Click to expand...
I don't see that there is anything wrong with impact tools. The problem is the person using the impact tools. I view them the same way that I see a hammer or an acetylene torch. They can easily be your best friend and they can just as easily be your worst enemy- it all depends on how you use them. The same applies to any tool.
 
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