Guess what i've been up to this afternoon.....

[TownsendsFJR1300]

Nope, no vice. I did all the work on my bench while it was loose. No clamps or anything.

It doesn't bolt to anything. Its for the slider pins.

Well, if everything else is on the money, I guess I'd have to look at the accuracy of that torque wrench..

Do you have another wrench you can compare it to?

Torquing down say a cage wheel stud to 40NM with another, known good wrench, then put THIS WRENCH on it and so if it goes further...

Be nice to know so if it is the issue, you don't break any other fasteners...

 

[AdamFZ]

The other brake caliper didn't break with the same torque wrench

 

[FinalImpact]

I'll play my Mechanical Engineering degree card here...
Looks like there is copper anti-seize on the threads, is that right? Bolt torques are specified based on a certain thread lubrication to get the appropriate loads on the bolts and the threads. The manual specifies 40Nm DRY. So if you use a lubricant such as anti-seize or loctite, that same 40Nm is actually putting a higher stress on the bolts and the threads than if it was dry. To get the same bolt load and stress, you would need to decrease the torque if you're using a lubricant.

Well said ^^ - ironically the same reason oil pan drain bolts end up cracking pans!
FSM specifies DRY and NEW CRUSH Washer. Used and oiled = broken pan!

It appears the caliper was cracked for some time and one side was hanging on by a tiny patch.

 

[FinalImpact]

Well said ^^ - ironically the same reason oil pan drain bolts end up cracking pans!
FSM specifies DRY and NEW CRUSH Washer. Used and oiled = broken pan!

It appears the caliper was cracked for some time and one side was hanging on by a tiny patch.

If I'm not mistaken there was a carrier with six studs that also failed. Is it time to check your torque wrench of remove the grease?? Not sure...

 

[TownsendsFJR1300]

If I'm not mistaken there was a carrier with six studs that also failed. Is it time to check your torque wrench of remove the grease?? Not sure...

The Op posted the threads were dry, NOT true?? There's no washers to replace with new ones either, ??..

72 ft lbs vs 20 (or 30) is a big difference.

Agreed, it was probably stress cracked before this from over previous over tightening. It just let loose this time..


Apples and oranges.., Round but not the same..

 

[FIZZER6]

I'll play my Mechanical Engineering degree card here...
Looks like there is copper anti-seize on the threads, is that right? Bolt torques are specified based on a certain thread lubrication to get the appropriate loads on the bolts and the threads. The manual specifies 40Nm DRY. So if you use a lubricant such as anti-seize or loctite, that same 40Nm is actually putting a higher stress on the bolts and the threads than if it was dry. To get the same bolt load and stress, you would need to decrease the torque if you're using a lubricant.

While you're correct. 40Nm with anti-seize in no way is enough clamping force to snap iron like that. It was already weak. Probably best that it broke because that could just as easily happened the first time you did a power stop!

 

[AdamFZ]

While you're correct. 40Nm with anti-seize in no way is enough clamping force to snap iron like that. It was already weak. Probably best that it broke because that could just as easily happened the first time you did a power stop!

The brake calipers aren't iron, they're aluminium. The slider pins are steel.

 

[FIZZER6]

The brake calipers aren't iron, they're aluminium. The slider pins are steel.

Interesting. Every car caliper I've rebuilt has been iron. Makes sense though. We don't need a caliper to be as strong as one on a 4,000 lb cage.

 

[TownsendsFJR1300]

The aluminum dissapates the heat MUCH better too..