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When mounting the brake caliper on the front right side, I tried to turn the bolts to the proper torque (40nm). However, I soon felt that I had no grip and then one broke off.

See the picture. What you can see is that part of the bolt is thinner than the rest. Does anyone know what can have caused this? Does anyone have experience with this?

I already bought 4 new bolts. The caliper on the left side showed the same strange wear.



Greetings from the Netherlands. :wave
 

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1++++

Gorilla tightened in the past. It is not worn, it is stretched. Tightened beyond metal's yield strength. Torque wrenches are your friend!
 

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1+++++ I just wanted to outdo Dave's +'s. These guys know , they are several of the Mechanical genius's on this site.
 

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Wrencher Extraordinaire
2005 K1200LT
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The 2001 and up (BMW on the calipers) are 30 Nm with an M8 bolt. The earlier bikes were 40 Nm with an M10 bolt
 

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The 2001 and up (BMW on the calipers) are 30 Nm with an M8 bolt. The earlier bikes were 40 Nm with an M10 bolt
John,
This is a very good point and is enough to damage these bolts. I can imagine a few getting confused - either:
(1) they use wrong chapter / section in CLYMER for their bike and get wrong torque specs (ABSII -vs-Integral ABS)

(2) they get on of these "free copy" of the K1200LT shop manual floating around the web - However they do not pay attention if manual version is for ABSII models (1999-2001) or for the next generation having IABS with BMW markings on calipers.
 
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This could be from a bad torque wrench, or bad torque spec, or bad conversion of torque spec (this happens a lot!). I is not likely bad bolts as these sort of fasteners are pretty carefully controlled in Germany.

Torque wrenches are usually so long-handled and they don't give any realistic feel to the mechanic.

Torque wrenches do not prevent a shade tree mechanic from doing crappy work. Sometimes they even help them do crappy work by giving a feeling of error invincibility.
 

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Torque wrenches are usually so long-handled and they don't give any realistic feel to the mechanic.---------------------
One of the main reasons for using torque wrenches is to remove any need for "feel". You watch the gauge, or wait for the click, no "feel" necessary or needed.
 

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One of the main reasons for using torque wrenches is to remove any need for "feel". You watch the gauge, or wait for the click, no "feel" necessary or needed.
And if you miss the click (or whatever) the OP pix above is what the bolt looks like afterwards..........:)
 

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And if you miss the click (or whatever) the OP pix above is what the bolt looks like afterwards..........:)
I have three different click type torque wrenches, and anyone brain dead enough to "miss" the click should not be working on mechanical things. :histerica
 

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I have three different click type torque wrenches, and anyone brain dead enough to "miss" the click should not be working on mechanical things. :histerica
I agree, I have twice had someone else use my 1/4" drive inch pound torque wrench & break off the square drive.
 
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