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Author Topic: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback  (Read 6518 times)

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Offline Heimer

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I will do a more detailed post later, as I am waiting for a report from the person this happened to.


If you look at the attached picture, you will see the rear brake caliper and the two screws that attach it.

This friend of mine fell after the rearward caliper screw on his bike came out. It loosened itself. The caliper fllipped over forward and stripped his wheel of all the spokes.

Result: The rear wheel came off at 140 and he had a serious off - Luckily he did not hit too many things and is still with us to talk about it.

Being an engineer, he saw that this is not the correct type of screw for the application (it is a full threaded screw) and with the resulting stresses on the caliper, failure is a matter of time, because the judder and stress caused by braking, is applied directly on a screw thread, causing movement and wear.

I hope I described this as accurately as I understood him. I will update this post when he emails me the full analysis and the pictures he took.

He is taking legal action presently

But in the meantime we would like to know to whom  this has happened (Vote in the poll). A brief investigation shows that quite a few people has had failure on the caliper screws.

And also people - please go check your calipers screws and see if they are OK and if the hole has been worn out

The torque setting is listed as 24Nm on the 2005 Reprom CD


« Last Edit: February 10, 2014, 03:19:57 pm by Heimer »

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Offline Heimer

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #1 on: February 10, 2014, 10:04:39 am »
I checked my and MoederYster's bikes last night and the caliper screws on both our bikes are the correct torque.

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Offline King Louis

Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #2 on: February 10, 2014, 10:34:06 am »
Interesting fred, which I will follow. I will also check what the chaps on the German GS forum have to say, or said.

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Offline BikerJan

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #3 on: February 10, 2014, 10:54:47 am »
subcribe
 

Offline TransAlpie

Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #4 on: February 10, 2014, 11:04:38 am »
.
 

Offline capeklr

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #5 on: February 10, 2014, 11:34:01 am »
Just checked them on my 07 adventure, took them out no wear in the holes or on the bolts.
Is this only the rear caliper where this happens?
 

Offline Heimer

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #6 on: February 10, 2014, 11:56:57 am »
Just checked them on my 07 adventure, took them out no wear in the holes or on the bolts.
Is this only the rear caliper where this happens?


Yep  , the rear caliper

I will certainly check mine frequently,  knowing of this

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Offline lecap

Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #7 on: February 10, 2014, 12:48:31 pm »
Some stuff:

Firstly please go and put into the header of the referring thread that this is about the OILHEAD R1200GS NOT the new water cooled one. Else I might have some LC boys climbing onto my back again because I don't own one of their beloved bikes :lol8:

The engineering side:
I don't see any good reason why they should not use a full thread screw. There is no movement between the caliper and the mounting bracket. The bolts are ONLY loaded in tension, not bending or shear which makes it irrelevant if it's a full thread bolt or not.

The problem:
If your bike and its brake caliper gets a bit older you very often have floater pins getting stuck. If you apply brakes the pistons push against the caliper but instead of the caliper responding by floating and applying an equal, opposing force to the other side of the brake disc the caliper does not float but rather bends the disc and the caliper mount.
This bending movement adds additional tension to the bolts which might get stressed beyond their capabilities and either come loose or shear.

The fix:
Nothing simpler than tightening the caliper mounting bracket bolts to the prescribed torque and checking the brakes for proper function on a regular basis.

As an added safety measure you can fit bolts with a higher tensile strength and yield strength. The OEM bolts are most likely grade 10.9 You can get 12.9 which has 20% more tensional and yield strength.
The reason behind this: It is very unlikely for this connection coming loose from vibrational loads or thermal cycling alone.
Overloading the bolt in tension beyond its yield strength will stretch the bolt and loosen the connection. Sooner or later the bolt will fall out.

Do NOT tighten the bolts to a higher than standard torque since this only aggravates the problem.
« Last Edit: February 10, 2014, 12:50:58 pm by lecap »
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Offline Jughead

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #8 on: February 10, 2014, 01:28:56 pm »
Have a 2010 in my shop with exactly the same issue.  Fortunately didn't take out the entire wheel but buggered up a number of spokes.  Rear wheel locked up, fortunately not at high speed.
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Offline Uncle Et

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #9 on: February 10, 2014, 01:35:53 pm »
My bike, 2006 model, at the second brake pad change ( i think it was around 28000km) when I was undoing the rear bolt it sheared off, I was lucky to get it out without much trouble. Fitted a new one from the agents and has not had any issues.  Bike now at 97000km's.

For some reason, the first set of brake pads only lasted 8000km's and I did not 'ride' the lever with my foot, the disk was not blue to indicate overheating and the inside pad was metal to metal.
The set of pads on the bike now is my fourth set.
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Online BiG DoM

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #10 on: February 10, 2014, 01:36:14 pm »
Mine are fully threaded and never had an issue in almost ten years on two 1200's. I consider this thread unnecessarily alarmist claiming failure of the screws!
« Last Edit: February 10, 2014, 01:38:33 pm by BiG DoM »
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Offline alwyn_gs

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #11 on: February 10, 2014, 01:50:52 pm »
Also no problems... yet, but this is one more reason why I wash my own bike! You pick up loose screws, and then those who already gone  :o... maar moet confess... het amper in my broek gebollie net om the thread te lees... sal bietjie meer attend wees om voor en agter brake calipers na te gaan...
« Last Edit: February 10, 2014, 01:57:47 pm by alwyn_gs »
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Offline lecap

Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #12 on: February 10, 2014, 01:58:37 pm »
My bike, 2006 model, at the second brake pad change ( i think it was around 28000km) when I was undoing the rear bolt it sheared off, I was lucky to get it out without much trouble. Fitted a new one from the agents and has not had any issues.  Bike now at 97000km's.

For some reason, the first set of brake pads only lasted 8000km's and I did not 'ride' the lever with my foot, the disk was not blue to indicate overheating and the inside pad was metal to metal.
The set of pads on the bike now is my fourth set.
regards


The one (inside) pad having worn before the outside one clearly shows that there was a problem with the calipers floater pins.

There is a very good chance that this overstressed the bolt which snapped at the second brake pad change. A bolt which snaps when you try to loosen it without giving you problems when you extract the rest of it from the threaded hole is a clear indication of a bolt which was overstressed before you attempted to loosen it.

Can some one maybe shed some light onto what class the OEM bolts are? They should have something stamped into the head.

I consider this thread an important lesson to maintain your bike professionally. A "small" issue might have catastrophic consequences to seemingly unrelated parts of the bike.
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Offline CandyMan_ZA

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #13 on: February 10, 2014, 02:16:58 pm »
My calliper came off and got lodged in the rear wheel. I suspect it was as a result of recent work done or at least that the mechanic did not notice it was already loose  :deal:
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Offline capeklr

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #14 on: February 10, 2014, 02:35:46 pm »

Can some one maybe shed some light onto what class the OEM bolts are? They should have something stamped into the head.


M8x1.25x25
Tensile strength 8.8
« Last Edit: February 10, 2014, 02:38:00 pm by capeklr »
 

Offline capeklr

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #15 on: February 10, 2014, 02:42:32 pm »

If your bike and its brake caliper gets a bit older you very often have floater pins getting stuck. If you apply brakes the pistons push against the caliper but instead of the caliper responding by floating and applying an equal, opposing force to the other side of the brake disc the caliper does not float but rather bends the disc and the caliper mount.
This bending movement adds additional tension to the bolts which might get stressed beyond their capabilities and either come loose or shear.


This is what I also suspect to be the reason.
I know of one GSA where the bracket where the bolts go through to hold the caliper broke off! This is a casting and part of the final drive.
 

Offline Heimer

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #16 on: February 10, 2014, 03:04:19 pm »
Mine are fully threaded and never had an issue in almost ten years on two 1200's. I consider this thread unnecessarily alarmist claiming failure of the screws!

Dom - the screws don't fail - they loosen, pointing to a design issue

Le-Cap - thanks for your analysis. Thorough as usual

Presently I am guaging with whom else this has happened. I believe many people just kind od 'take it' as something they overlooked, or as normal wear.

I might be that work that was done, involving the removal of the calipers, led to incorrect torquing.

I will leave that part of the discussion for the gentleman (Dave Coetzee) when he provides his input, which I am waiting for by email. He had not done any work on his bike - it was done by dealers



« Last Edit: February 10, 2014, 03:05:57 pm by Heimer »

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #17 on: February 10, 2014, 03:13:44 pm »
Mine are fully threaded and never had an issue in almost ten years on two 1200's. I consider this thread unnecessarily alarmist claiming failure of the screws!

Dom - the screws don't fail - they loosen, pointing to a design issue

Le-Cap - thanks for your analysis. Thorough as usual

Presently I am guaging with whom else this has happened. I believe many people just kind od 'take it' as something they overlooked, or as normal wear.

I might be that work that was done, involving the removal of the calipers, led to incorrect torquing.

I will leave that part of the discussion for the gentleman (Dave Coetzee) when he provides his input, which I am waiting for by email. He had not done any work on his bike - it was done by dealers



My point exactly - YOU used the words "Caliper screws failure" in your subject heading! ... suggesting that it is the screws that are failing. I believe you should edit the title to at least have a question mark rather than it being a statement.

The screws will not loosen because they are threaded  - they will loosen due to HUMAN ERROR of not tightening to correct torque or over tightening compromising their tensile strength and stretching the thread. The "DESIGN ISSUE" is that of humans being fallible (ie often dof).
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Offline Heimer

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #18 on: February 10, 2014, 03:20:57 pm »
Mine are fully threaded and never had an issue in almost ten years on two 1200's. I consider this thread unnecessarily alarmist claiming failure of the screws!

Dom - the screws don't fail - they loosen, pointing to a design issue

Le-Cap - thanks for your analysis. Thorough as usual

Presently I am guaging with whom else this has happened. I believe many people just kind od 'take it' as something they overlooked, or as normal wear.

I might be that work that was done, involving the removal of the calipers, led to incorrect torquing.

I will leave that part of the discussion for the gentleman (Dave Coetzee) when he provides his input, which I am waiting for by email. He had not done any work on his bike - it was done by dealers



My point exactly - YOU used the words "Caliper screws failure" in your subject heading! ... suggesting that it is the screws that are failing. I believe you should edit the title to at least have a question mark rather than it being a statement.

The screws will not loosen because they are threaded  - they will loosen due to HUMAN ERROR of not tightening to correct torque or over tightening compromising their tensile strength and stretching the thread. The "DESIGN ISSUE" is that of humans being fallible (ie often dof).

Yes professor, I did as you asked. Thanks for telling me. Do not lose hope with me yet.  8)

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Re: BMW R1200 GS rear brake Caliper screws failure. Warning & feedback
« Reply #19 on: February 10, 2014, 05:34:24 pm »
Mine are fully threaded and never had an issue in almost ten years on two 1200's. I consider this thread unnecessarily alarmist claiming failure of the screws!

Dom - the screws don't fail - they loosen, pointing to a design issue

Le-Cap - thanks for your analysis. Thorough as usual

Presently I am guaging with whom else this has happened. I believe many people just kind od 'take it' as something they overlooked, or as normal wear.

I might be that work that was done, involving the removal of the calipers, led to incorrect torquing.

I will leave that part of the discussion for the gentleman (Dave Coetzee) when he provides his input, which I am waiting for by email. He had not done any work on his bike - it was done by dealers



My point exactly - YOU used the words "Caliper screws failure" in your subject heading! ... suggesting that it is the screws that are failing. I believe you should edit the title to at least have a question mark rather than it being a statement.

The screws will not loosen because they are threaded  - they will loosen due to HUMAN ERROR of not tightening to correct torque or over tightening compromising their tensile strength and stretching the thread. The "DESIGN ISSUE" is that of humans being fallible (ie often dof).

Yes professor, I did as you asked. Thanks for telling me. Do not lose hope with me yet.  8)

No hopeless cases only hopeless causes  :biggrin:  I still think the subject title should have a question mark after failure... it is a moot point at this stage ... a questions is being asked ... is there a design fault?
« Last Edit: February 10, 2014, 05:37:05 pm by BiG DoM »
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