An interesting non-breakdown breakdown today, TWICE!

irunamok

irunamok

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Joined
May 26, 2024
Messages
97
Location
Houston soon
Bike
‘01 ST1100
TLDR: Rear brake is binding all of a sudden

I'll spare you the long story, kind of funny, but to summarize: my rear brake overheated and stopped the bike. I was close to my son's home and after it cooled off and the wheel would turn, l limped it home, about 10 miles, and halfway home it did it again. I never touched the brake today and that second stop I checked the disk and it was smokin' hot. It's on the center stand now in his garage and as it is cool again I can spin the wheel and I can hear it rubbing, kind of a "sshhhh" sound.

I'm no mechanic and I wonder why a rarely used rear brake would suddenly rub. I'm overjoyed that it's not the drive shaft, my first guess since the bike would not roll even an inch, literally. We have no special tools here but are lucky to have his neighbor who is a dirt track (car) racer we could borrow from. I'm about the head to YouTube look for a rear brake video but thought I'd post my experience here for future reference if another rider has the same surprise,.
 
Sometimes it's the the tiny return hole in the rear master cylinder get's plugged up and traps the brake fluid in the caliper. However, you said that you did not touch the brake and it happened.... so maybe this is not the issue in your case. Try putting it on the center stand and apply the rear brake, if it locks up, crack the bleeder valve and see if it releases.

Does your bike have linked brakes?
 
Mike M. said:
Sometimes it's the the tiny return hole in the rear master cylinder get's plugged up and traps the brake fluid in the caliper. However, you said that you did not touch the brake and it happened.... so maybe this is not the issue in your case. Try putting it on the center stand and apply the rear brake, if it locks up, crack the bleeder valve and see if it releases.

Does your bike have linked brakes?
Click to expand...
No linked brakes. No ABS. I'll try that.
 
Hmmm..... perhaps the next time you take it for a ride take along a 8mm box end and if the wheel locks up again - try slightly opening the bleeder valve and see if it releases the wheel. Cover the top of the bleeder with a rag so you don't get any brake fluid on paint or brake pads.

How does the fluid look in the rear master cylinder?

I might be a good time to flush the fluid if it's been awhile.

It could also be that the pistons in the calipers are sticking, but that's a little more rare. I'll be interested to see what the cure turns out to be.
 
The rear brake fluid heats up as you are riding. it is behind a hot engine and next to hot exhaust pipes. It expands and needs an escape route for the fluid back to the reservoir. That is via a very tiny compensation port which sits inside the master cylinder just in front of the piston seal. As soon as you apply the brakes, the seal moves past that hole and the escape route is blocked. As soon as you release the pedal, the piston moves back and the tiny hole - the compensation port - is exposed again to allow pressure / fluid back to the reservoir.

That is what should happen. There are a number of reasons why it may not.

1. The brake lever has spring has become ineffective
2. The brake lever is unable to return because the pivot is clogged with corrosion / muck.
3. You are wearing large boots and are pressing on the pedal without realising.
4. The filter in the union where the hose from the reservoir joins the master cylinder is full of crud. (I am assuming that it has such a filter - I never looked when I had my 1100s)
5. The compensation port is blocked.
6. Seals / caliper piston bores are clogged preventing proper movement.
7. The rear reservoir is filled beyond the max line.
8. The slider pins are rusted, clogged.
9. The chrome pad retainer clip is not seated properly.

You might get an idea about what is going on by removing the pads and caliper and trying to push in the pistons. They should push in fairly easily with thumb pressure. Note that one piston will push out when you push the other in. If that doesn’t happen, then you have an issue with pistons/seals/cylinder bores.
But you need to push in both pistons at the same time - or at least stop the other from being pushed out. If the pistons will not move, then you have an issue with the master cylinder.

Note that pistons must be cleaned before pushing them in.

Do not undo the slider pins to get the caliper off. You have to remove the pads, remove the bracket - stopper bolt and axle bolt, and manoeuvre the bracket and caliper from the brake disc. The caliper should slide off the bracket easily.

This article was written for a model with linked brakes and abs - the 3 piston version. The detail may not apply to your model, but the logic is still sound.
https://www.st-owners.com/forums/threads/st1300-brake-maintenance-avoiding-the-pitfalls.135125/

Also - this explanation of how the master cylinder operates - drawn and described for the front master cylinder (brake lever). The rear master cylinder operates in the same way except the plunger end is pointing downwards, and the reservoir is attached by a hose.

https://www.st-owners.com/forums/threads/brakes-operation-of-the-master-cylinder.159167/

This next bit may or may not be relevant. I suspect that it is, but I really don't know.

I know your model does not have an SMC. But these are the only photos that I have that show the filter that I was talking about.

I have never looked seriously at the 1100 rear master cylinder port where the fluid enters from the reservoir, but looking at photos it seems to be similar to this - and the casting of the ST1100 master cylinder appears to have room for such a filter.
The left photo shows the bottom the filter from the ST1300s SMC. All you see from the other side is a white gauze. Inside that nylon filter is a very tiny compensation port, which can also become clogged.

I suspect that it is there, but I could be wrong. The part never appears on the microfiches - so that doesn't help. @Uncle Phil may be able to say one way or the other.

Note that in the right hand photo, you can see the compensation port deep inside the recess. Just past 12 o'clock position. It is a dimple with a very tiny - smaller than a pin prick - hole. That hole will definitley be there. If either are clogged, your brakes will drag.

They become clogged by failing to replace the brake fluid every 18-24 months. The fluid absorbs moisture over time and starts to go gooey and then starts to form crystals.
To get fresh fluid through these holes, you need to push the pistons back in a tad, once the new fluid is in the system - just to get the fluid going back to the reservoir.

1770023201623.png 1770023224127.png
 
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jfheath said:
The rear brake fluid heats up as you are riding. it is behind a hot engine and next to hot exhaust pipes. It expands and needs an escape route for the fluid back to the reservoir. That is via a very tiny compensation port which sits inside the master cylinder just in front of the piston seal. As soon as you apply the brakes, the seal moves past that hole and the escape route is blocked. As soon as you release the pedal, the piston moves back and the tiny hole - the compensation port - is exposed again to allow pressure / fluid back to the reservoir.

That is what should happen. There are a number of reasons why it may not.

1. The brake lever has spring has become ineffective
2. The brake lever is unable to return because the pivot is clogged with corrosion / muck.
3. You are wearing large boots and are pressing on the pedal without realising.
4. The filter in the union where the hose from the reservoir joins the master cylinder is full of crud. (I am assuming that it has such a filter - I never looked when I had my 1100s)
5. The compensation port is blocked.
6. Seals / caliper piston bores are clogged preventing proper movement.
7. The rear reservoir is filled beyond the max line.
8. The slider pins are rusted, clogged.
9. The chrome pad retainer clip is not seated properly.

You might get an idea about what is going on by removing the pads and caliper and trying to push in the pistons. They should push in fairly easily with thumb pressure. Note that one piston will push out when you push the other in. If that doesn’t happen, then you have an issue with pistons/seals/cylinder bores.
But you need to push in both pistons at the same time - or at least stop the other from being pushed out. If the pistons will not move, then you have an issue with the master cylinder.

Note that pistons must be cleaned before pushing them in.

Do not undo the slider pins to get the caliper off. You have to remove the pads, remove the bracket - stopper bolt and axle bolt, and manoeuvre the bracket and caliper from the brake disc. The caliper should slide off the bracket easily.

This article was written for a model with linked brakes and abs - the 3 piston version. The detail may not apply to your model, but the logic is still sound.
https://www.st-owners.com/forums/threads/st1300-brake-maintenance-avoiding-the-pitfalls.135125/

Also - this explanation of how the master cylinder operates - drawn and described for the front master cylinder (brake lever). The rear master cylinder operates in the same way except the plunger end is pointing downwards, and the reservoir is attached by a hose.

https://www.st-owners.com/forums/threads/brakes-operation-of-the-master-cylinder.159167/

This next bit may or may not be relevant. I suspect that it is, but I really don't know.

I know your model does not have an SMC. But these are the only photos that I have that show the filter that I was talking about.

I have never looked seriously at the 1100 rear master cylinder port where the fluid enters from the reservoir, but looking at photos it seems to be similar to this - and the casting of the ST1100 master cylinder appears to have room for such a filter.
The left photo shows the bottom the filter from the ST1300s SMC. All you see from the other side is a white gauze. Inside that nylon filter is a very tiny compensation port, which can also become clogged.

I suspect that it is there, but I could be wrong. The part never appears on the microfiches - so that doesn't help. @Uncle Phil may be able to say one way or the other.

Note that in the right hand photo, you can see the compensation port deep inside the recess. Just past 12 o'clock position. It is a dimple with a very tiny - smaller than a pin prick - hole. That hole will definitley be there. If either are clogged, your brakes will drag.

They become clogged by failing to replace the brake fluid every 18-24 months. The fluid absorbs moisture over time and starts to go gooey and then starts to form crystals.
To get fresh fluid through these holes, you need to push the pistons back in a tad, once the new fluid is in the system - just to get the fluid going back to the reservoir.

1770023201623.png 1770023224127.png
Click to expand...
Enormously helpful, thank you.
 
Im feeling like an idiot but might as well keep going. I removed the pads and the piston was as seen in previous picture. Obviously with the back frozen there was no play in the pedal. I could not push them in with my fingers nor with a lever (screwdriver). I pushed on the pedal and of course there was play in the pedal and a couple pushes pushed out the piston as you see in this picture. I can’t push them in now from the more extended position. Which means that I also can’t get the replacement pads in. Ive obviously never worked on brakes before so I’m clueless.
 

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irunamok said:
Im feeling like an idiot but might as well keep going. I removed the pads and the piston was as seen in previous picture. Obviously with the back frozen there was no play in the pedal. I could not push them in with my fingers nor with a lever (screwdriver). I pushed on the pedal and of course there was play in the pedal and a couple pushes pushed out the piston as you see in this picture. I can’t push them in now from the more extended position. Which means that I also can’t get the replacement pads in. Ive obviously never worked on brakes before so I’m clueless.
Click to expand...
Those pistons look a bit rough. If it were me I would rebuild the caliper with new pistons and seals and rebuild the master cylinder. Then again I would also do the fronts while I was at it. Then I would not worry about it for 2 years. I might even replace the brake lines it they look at all suspect.
 
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irunamok said:
Im feeling like an idiot but might as well keep going. I removed the pads and the piston was as seen in previous picture. Obviously with the back frozen there was no play in the pedal. I could not push them in with my fingers nor with a lever (screwdriver). I pushed on the pedal and of course there was play in the pedal and a couple pushes pushed out the piston as you see in this picture. I can’t push them in now from the more extended position. Which means that I also can’t get the replacement pads in. Ive obviously never worked on brakes before so I’m clueless.
Click to expand...

There are folks & how-to's here that can help you, but if you feel you're in over your head there's no shame in getting a professional to help (other than is costing you some $$) or even a knowledgeable friend. Brakes are one of those things you don't really want to mess around with. Having them work when you want, and not work when you don't, is important!
 
Things that I can see here.

1. The piston is a long way out - but that left hand pad seems to have quite a lot of friction material left - I think some of that 'thickness' is the refelction in the disk surface. The right hand backing plate - I can only see the top of it in this photo - seems to have hardly any judging by how close the backing plate seems to be to the disk surface.

1770060800765.png


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2. This is with the pads removed, and the aliper is pulled over as far to the right as it will go. The part of the piston that has been exposed to the elements looks shabby. It may be just surface grime, but I doubt it. You will know when you try to clean it up. Perhaps more significant are the longitudinal streaks on the shiny bit. Might sugegst that much and grit have got past the seals.

Lower down the slider pin is exposed. Normally, the rubber boot that it is slifing in will concertina so that you never get to see the shiny bit. It is nicely sealed in its own little environment. But the calipe ris pulled over a long way.
The slider looks clean, but it ought to be lightly greased. Silicone grease or red rubber grease. Just a smear, not a splodge. A splodge will fill the rubber boot with grease and take up all of the air space. That results in a pressure or vaccum build up and it sucks/blows the caliper backk against the disk. That slider is attached tot he caliper bracket. Do not undo that nut - it is a very tempting hex nut in a handy position crying out for a spanner to be taken to it. Don't be conned. Leave it where it is. That slider pin will clean up nicely.

There is another slider pin that it attached to the caliper that slides into a boot in the caliper bracket. It is tucked out of sight underneath the caliper.

1770061209098.png

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3. This is the left side rear brake pad. It seems to have plenty of tread left on it. Honda pads normally come with a chrome anti-squeal plate attached to the back of the metal backing plate.
The rear pads also normally have a thin white insulation pad which sits between the antisqueal plate and the backing plate. I cannot remember whether or not the ST1100 had this white insulation layer. I assume so, but I cannot find pictures that verify this.


1770061759183.png

I'd like to see the left hand side pad. If that is worn down much more than this, then I think that you may have a problem with the caliper not sliding properly on it slider pins. Which may explain your drag.

Let me try to explain. When you press the brake pedal, the pistons move out of the caliper to press the left hand pad against the surface of the disc. But the caliper isn't fixed, so it cannot press. Instead of pushing hard against the disc surface, it pushes itself backwards - to the left viewing from your photo - bringing the right hand side of the caliper and the right pad against the right hand side of the disc. When the pushing pistons out and pulling the caliper back/left both pads meet the disc surface, the caliper and pads can squeeze the disc equally from both sides and slow the bike.

When you release the brakes the seals lend a hand in pulling the pistons back in - but essentially the disc spinning through a very tight gap helps to nudge the pistons back in and the right hand side of the caliper back. As soon as no part of the pads are touching they cannot be nudged any further.

That is only possible because the caliper and the caliper bracket can slide away from each other on those sliders. So while you have got your pads out - see how smoothly it slides. Grap a handful of caliper and pull it to the outside of the bike. Let go. Then push it back as far as it will go. How does it feel ? Smooth ? or hard to push ? When you let go does it stay where it is or does it move back all by itself ?

Put your right hand pad back into the caliper and hold it in palce with the pad pin. Take a photo from the right hand side through the wheel spokes.
 
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You are very kind to be so helpful. The other pad is exactly the same. Since I was foolish enough to pump the rear brake enough to see if the piston would retract, I managed to jam it against the disk--since it won't retract I can't get the right hand pad (or left!) into place. I was low on fluid and I refilled it with the hope it might make a difference. It didn't. The buried lede in a nutshell: I MUST be in Houston on Thursday at the latest and if I can't get the bike on the road, it's an exorbitant plane ticket in my future. SO...I found a mobile mechanic with 4.8 stars who can come to the house. I ordered the rebuild kit which FedEx brings on Wednesday. Good news for me but now I feel like a heel that there has been such helpful instruction that I can't use because of the timing issue. I'm sorry about that. It was very clear instructional information in this thread, to me, and to the next unfortunate soul who has the same problem. Maybe there will be one.
 
Just glad that you will be able to get it working in time. It actually isn't difficult - but I have to admit that opening up the hydraulics is rather daunting the very first time that you do it - and when you think about how serious it is if you get it wrong .....

Stuff that we post on here is never not worth it. If you watch the guy working on it - just watch quietly if he doesn't mind - you will see things that you have read about and you will mutter to yourself - 'Ah, thats what John was on about' , or 'so what the hell was John on about then ?' Either way that is the way to learn. Second time through, things fall in to place in your head.

You will see him open up the brake lines. Push the pistons back in and eject fluid, remove caliper and bracket, new seals and piston if appropriate, fit new banjo bolt washers, refit caliper.

Hopefully you won't see him removing the stopper bolt and pushing the rear axle back to remove the caliper and bracket rather than removing the slider pins. He'll probably remove the brake hose so that the caliper is in his hand in ordert o fit the seals / pistons etc. And you'll see him put it all back into place.
Hopefully he will tighten the stopper bolt BEFORE he tightens the rear axle. And you'll see him re-attach the banjo bolt with two new washers, fill it with fresh brake fluid and bleed it.
 
I hope all goes well with the mobile mechanic, keep us posted.

Did you ever try opening the bleeder to see if that would release the pistons to retract? ( I'm just curious )
 
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