RE: What a saga, binding rear brake - 2

Because the brakes are linked it might be worth trying it without using the back brake. Make sure it’s not binding to start with by slackening off the bleeder and tightening again or push the piston back. Operate the front brake to make sure it’s ok.

Then go out and test it without using the back brake, if it sticks again it’s unlikely to be the rear master cylinder.

When you pushed the piston back the first time did you push it back through the system. With ABS systems I usually open the bleeder when pushing it back so it doesn’t affect anything else in the system. And then top it up after.

Don’t know exactly how bike systems work but pushing fluid back through the system might have affected it somehow.

Just clutching at straws here

Following on from my earlier thoughts, if I push the calliper towards the wheel the wheel frees and the scraping sound stops. It can only be the fixed pads that are binding so nothing to do with the pistons, seals, brake lines or master cylinder.

If I push the calliper right over and then use the brake foot lever to just move it back a fraction and set the pistons against their pad, it’s still free. So those pistons are drawing back fine.

I’m trying to work out what mechanism draws the fixed pad away from the disc. I’ve tried clearing away some of the copper grease on the calliper pins.

Usually the moving pad wears more because it’s the first to contact the disc. On my old pads the fixed is the one nearer it’s limits.

Still not sorted though.

Zitat von Sanemancured im Beitrag #17

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Following on from my earlier thoughts, if I push the calliper towards the wheel the wheel frees and the scraping sound stops. It can only be the fixed pads that are binding so nothing to do with the pistons, seals, brake lines or master cylinder.

If I push the calliper right over and then use the brake foot lever to just move it back a fraction and set the pistons against their pad, it’s still free. So those pistons are drawing back fine.

I’m trying to work out what mechanism draws the fixed pad away from the disc. I’ve tried clearing away some of the copper grease on the calliper pins.

Usually the moving pad wears more because it’s the first to contact the disc. On my old pads the fixed is the one nearer it’s limits.

Still not sorted though.

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As I said, I firmly now believe my issue is the fixed pad binding not the hydraulic side. I could of course be wrong. Are you certain that there is an electric pump involved in the braking system?

I wasn’t aware. I thoughts servo brakes died in 06.

I’d love to know how the linked brakes work.

What would it tell you, I wonder, and just thought of this, if you took a measuring caliper to your calipers?

1) Put bike up on center stand
2) If things are "zeroed and reset" and not binding, after spinning the wheels, remove both front and rear calipers and measure the space between the pads where the rotor would occupy with a caliper and record it. Remount the calipers
2) Put in gear and "drive", spin the rear wheel in 1st gear some rpms. Actuate brakes together. Check for binding. Still proceed if none. You might want to simulate some load on the front forks. You could put a board underneath front tire, even jack it a little possibly. Bounce the front while "braking" on the center stand. "Hard brake". Do you trust your center stand with you on the bike and accelerating with a jacked rear wheel? You could devise fail-safe supports to dissuade the rear tire suddenly falling and grabbing a patch.
3) Pull both calipers and measure with a caliper again. Do they return to the same opening size? Does the rear get steadily narrower?
4) Keep repeating until you notice binding in the rear. Take off the caliper and measure. What's going on with the distance between the pads in front caliper versus rear? Again, does the rear get steadily narrower. Is it not returning like the front?
5) If you do try this, I wonder especially if front caliper space readings stay consistently spaced vs. the rear.

Just some ideas. Something unusual might reveal itself. Maybe some abnormal interaction during "simulated" ride test is causing the rear to steadily close and not backoff.
What value such an exercise? Might be just another perspective that proves that after a certain amount of time, rear caliper/braking/piston-compress-release is abnormal.

Zitat von Sanemancured im Beitrag #19

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As I said, I firmly now believe my issue is the fixed pad binding not the hydraulic side. I could of course be wrong. Are you certain that there is an electric pump involved in the braking system?

I wasn’t aware. I thoughts servo brakes died in 06.

I’d love to know how the linked brakes work.

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Zitat von TriangleRider im Beitrag #21

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Zitat von Sanemancured im Beitrag #19

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As I said, I firmly now believe my issue is the fixed pad binding not the hydraulic side. I could of course be wrong. Are you certain that there is an electric pump involved in the braking system?

I wasn’t aware. I thoughts servo brakes died in 06.

I’d love to know how the linked brakes work.

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Here you go! :) No servo brakes. Front brakes are hydraulic only. The rear is "linked" using a pump.

www.webbikeworld.com/bmw-abs-and-automat...bility-control/

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Zitat von basskleff im Beitrag #20

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What would it tell you, I wonder, and just thought of this, if you took a measuring caliper to your calipers?

1) Put bike up on center stand
2) If things are "zeroed and reset" and not binding, after spinning the wheels, remove both front and rear calipers and measure the space between the pads where the rotor would occupy with a caliper and record it. Remount the calipers
2) Put in gear and "drive", spin the rear wheel in 1st gear some rpms. Actuate brakes together. Check for binding. Still proceed if none. You might want to simulate some load on the front forks. You could put a board underneath front tire, even jack it a little possibly. Bounce the front while "braking" on the center stand. "Hard brake". Do you trust your center stand with you on the bike and accelerating with a jacked rear wheel? You could devise fail-safe supports to dissuade the rear tire suddenly falling and grabbing a patch.
3) Pull both calipers and measure with a caliper again. Do they return to the same opening size? Does the rear get steadily narrower?
4) Keep repeating until you notice binding in the rear. Take off the caliper and measure. What's going on with the distance between the pads in front caliper versus rear? Again, does the rear get steadily narrower. Is it not returning like the front?
5) If you do try this, I wonder especially if front caliper space readings stay consistently spaced vs. the rear.

Just some ideas. Something unusual might reveal itself. Maybe some abnormal interaction during "simulated" ride test is causing the rear to steadily close and not backoff.
What value such an exercise? Might be just another perspective that proves that after a certain amount of time, rear caliper/braking/piston-compress-release is abnormal.

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I've just been out to get a friend to reset my service interval for me. He is a mechanic who has his own YouTube channel featuring riding, maintenance tips and general bike stuff. We had a long chat, put the world to rights and we both feel that the issue is with the calliper itself not moving sufficiently on the release of pressure to give the correct clearance for the fixed pad. His GS also had excessive wear on its fixed pad. Traditionally the moving pad wears more because it is the 1st to make contact. From tales on the internet this design of calliper seems to break that rule.

I've been a motor mechanic for a few years in my youth, maintaining a wide variety of vehicles. I've worked on my own motorcycles for over 50 years. I've also worked on ships and submarines over many years fixing stuff.

A golden rule, easily broken. If you've done something and then something doesn't work correctly look to the obvious, something related to what has changed, first. Don't go into realms of relative fantasy, at least not until everything basic has been triple checked.

1. I fitted new, thicker pads. The old pads were worn on the fixed inboard side the most. The thicker pad changes the resting position of the calliper.

2. I cleaned around the pistons before reassembly.

3. The rear brake started binding.

My initial thoughts were, that in cleaning around the pistons I'd introduced a fine bit of grit into the clearance that caused them to bind slightly and not retract on brake pressure release. That has more or less been ticked off as a no after cleaning the pistons and seals and checking for damage. The only thing further would be to install the new seals. It's good practice and I will today.

My experiments with moving the calliper inboard by force lead me to believe that the problem is the fixed pad. Being thicker than the old pad it is settling the calliper itself to a new position. Here in I feel lies the problem. I have a question around what forces the calliper body and therefore this pad away from the disc. I can't find the answer online. The floating calliper pins are well lubricated and free. The only thing that I could see that would move the calliper away the microns required for clearance are the rubber boots on the pins.

I'll maybe try new ones as they are aged and may have been contaminated and lost their resilience.

I'll see if I can email Brembo UK and ask them about the function of this calliper.

Peter

I fitted the new seals to the calliper and thought, what the hell I might as well fit the new pistons too. The seals snapped into place easily and after bleeding I had a serious leak. I didn’t have any new copper washers for the banjo bolt and they cried enough. Luckily I found some locally although annealing the old ones was an option.

A theory I came up with this morning was that new seals might translate to extra piston clearance and that would affect both sides. I’ve some bike training on tomorrow and that’ll be the test. The rubber boots on the pins actually have the effect of moving the fixed pad toward the disc, not away.

Your "thicker" pads- does that just mean new OEM/genuine Motorrad models with "newness meat and material" on them? Are they exactly what a dealer would install? They're not otherwise thicker than normal?
I just wondered with this sophisticated, semi-linked system and integral with ASC and all that, could the central control somehow have "learned" the thickness of the prior worn pads and modulated the pistons' extension to align with that?
And for some reason the pistons have not been allowed to be backed up and off for replacement/service activity and a new set of pads? Seems lucky in a way that you were able to slide them and the caliper on the disc, but also taunting in a way, because it allowed it to appear normal and installed, and then your woes set in. I wonder if there's a ODB-scanner-control-service-module that collapses the pistons to zero, and then they can be then extended and allowed to learn the new pads.
Tricky.

The system really is no where near that sophisticated. The new pads are Ferodo sintered pads. Thickness wise they are thinner than new OEM Brembo pads.

Basically from my understanding the rear circuit is conventional with the added feature of an electrically powered and activated pump that combines ABS and linked brake functions. There is no hydraulic connection front to rear.

I don’t think that the rear calliper is a brilliant design. The fixed pad generally wears prematurely and is prone to binding issues. A search of the internet brings up other cases across the 1200LC spectrum.

I found the answer to be making sure the calliper pins are clean and well lubricated, bleed the system well and then some more and finally, in my case install new calliper seals.

Mine is still dragging ever so slightly and getting warm but it’s acceptable. I suspect that as the pad wears it’ll get slightly freer.

Yes the rear circuit itself is basic stuff.

Zitat von Sanemancured im Beitrag #28

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The new pads are Ferodo sintered pads. Thickness wise they are thinner than new OEM Brembo pads.

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Zitat von Lee im Beitrag #29

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Zitat von Sanemancured im Beitrag #28

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The new pads are Ferodo sintered pads. Thickness wise they are thinner than new OEM Brembo pads.

.

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Total thickness is less? Pad and backing plate?
Awhile back I read where someone had problems with a aftermarket pad being too thick.
It was not Carbon Lorraine.

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