[M3 GUSTA.G80]

Originally Posted by Efthreeoh

Seriously, do I need do go get my Bentley manual or look up the bolt sizes on realoem when I write a fucking post. Who gives a shit if the rear caliper mounting bolts are M10 or M12 or even M14? The point I was making is (a) most noob DIY'ers way over-torque brake hardware because they think tighter is better, and (b) I was indicating the torque values are far less than noobs think they are.

But all of this arguing is pointless because the caliper that killed the poor young woman didn't come from the wheel of the truck after breaking away from the hub, it reportedly fell out of the bed as part of an unsecured load. No one has thought of the possibility the truck didn't have a tailgate and the dumbass driving the truck didn't think his unsecured caliper could fall off the back of his truck and kill some one.

Sheesh, somebody a little upset? 😬

[Efthreeoh]

Originally Posted by GuidoK

But the rear calipersbrackets afaik aren't fit with M12 or M14 bolts, but M10 bolts.
These have indeed lower torque rating (indeed roughly 47lbs-ft)

The guide pins indeed need far less torque. but there is a difference in function between the guide pins and the bracket bolts.
The guide pins don't get to endure the rotational braking force. Neither does the caliper.
The brake pads (who get the rotational braking force) transfer that force to the caliper brackets and then into the hub.
(For a floating caliper that is)
But for a rear caliperbracket I can imagine it's of far less importance that it's torqued to a very high value. Braking forces on the rear are almost negligible compared to the front (if I had to make an estimate...maybe 25% tops of the front braking force?).
I'm always amaized for example after driving an alpine pass how hot the front brakes get and how cool the rear brakes stay. (and I even run slightly more rear brake bias than stock)

So I guessed 45 pd-ft ("45 pd-ft or so" vs. 47 pounds actual), and you guys are giving me shit, like I'm way the fuck off the number. And oohhh, its an M10 instead of an M12, a whole wopping 2MM. Its not like I replace brakes on my BMWs every other week and I have the numbers and sizes memorized.

[Efthreeoh]

Originally Posted by BenitoBlanco

Sheesh, somebody a little upset? ��

No, but read the following post. ^

[GuidoK]

Originally Posted by Efthreeoh

So I guessed 45 pd-ft ("45 pd-ft or so" vs. 47 pounds actual, and you guys are giving me shit, like I'm way the fuck off the number. And oohhh, its an M10 instead of an M12, a whole wopping 2MM. Its not like I replace brakes on my BMWs every other week and I have the numbers and sizes memorized.

Do you think that when you start boasting about your degrees and start saying things like "most people don't understand how fasteners work and how threads work", referring to 'noobs', people gonna cut you some slack?

In most standard torque charts, the difference in tightening torque between an M10 and M12 bolt is roughly 80% (when threaded in steel)
And given that the expected accuracy of a torque wrench is 3-4%, I'd say yes, that 'whole wopping 2mm' makes quite the difference.
And it's not that you don't remember that the bolt isn't M12 but M10, it's that you don't recognize that 45lbs-ft (61Nm) is a very low value for a M12 bolt (let alone a M14 bolt to quote you further).
You don't need 45 years of experience working on cars to get that gut feeling.
And naming them grade 10.3 ...what's that? A bolt with 300N/mm² yield strength while having 1000N/mm² tensile strength?

[M5Rick]

Nothing stopping anyone from time to time removing wheels and re checking the torque/tightness of those bolts than just praying they're alright, just use fresh bolts to be sure.

[Efthreeoh]

Originally Posted by GuidoK

Do you think that when you start boasting about your degrees and start saying things like "most people don't understand how fasteners work and how threads work", referring to 'noobs', people gonna cut you some slack?

In most standard torque charts, the difference in tightening torque between an M10 and M12 bolt is roughly 80% (when threaded in steel)
And given that the expected accuracy of a torque wrench is 3-4%, I'd say yes, that 'whole wopping 2mm' makes quite the difference.
And it's not that you don't remember that the bolt isn't M12 but M10, it's that you don't recognize that 45lbs-ft (61Nm) is a very low value for a M12 bolt (let alone a M14 bolt to quote you further).
You don't need 45 years of experience working on cars to get that gut feeling.
And naming them grade 10.3 ...what's that? A bolt with 300N/mm² yield strength while having 1000N/mm² tensile strength?

Apologies, 10.9. Typo.

An M10 brake caliper mounting bolt (over) torqued to 94 pound-foot is more likely to fail (break) than an M12 (under) torqued to 44 pound-foot will fail (by backing out of its thread). Noobs have a tendency to over-torque bolts, which break at the time of assembly, or worse the bolts eventually fail due to over-tension. That was and is my point.

I didn't see the need to delve into an in-depth engineering discussion to make the point.

Regarding torque wrenches, I can point to at least 20 posts of mine over the years trying to explain (to noobs) why the use of click-type 3/8-drive torque wrenches when setting spark plug torque in a cylinderhead is bad practice. But that's a different discussion for a different day...