[Efthreeoh]

Originally Posted by BenitoBlanco

I'm not a physicist or forensic scientist but I don't think it's as impossible as you claim. Unlikely, of course, it's pretty much the definition of a "freak accident", but the size of the rotor, wheel and caliper would factor in, along with the strength of the brake line and any supporting grommets and other hardware (based on age and maybe bad maintenance practices like letting the caliper dangle by the brake line).

So picture a caliper finally sliding off the rotor, these cars are going at interstate speeds. While falling in whichever order of operations, the brake line ruptures and the caliper hits the barrel of the wheel and spits out under the car.

Obviously kinetic energy is not taking it half a mile down the road but if the car was maybe 1-5 lengths behind, could definitely happen. I have seen dashcam videos of less probable things happening at interstate speeds.

Lots of claims of this coming off some type of load but no actual indication of that being the case from any news reports I have seen.

I have a minor in Physics, an engineering degree in industrial engineering, and I've been working on cars for 45 years. So to believe a caliper came loose off a wheel brake it has to have both caliper mounting cage bolts unscrew and fall out exactly the same time. Then the caliper has to rotate down with the help of gravity to the bottom of the rotor. Release itself from the rotor, knowing that any wear on the rotor will leave a lip that the pads have to slip over. THEN, somehow, the brake hose has to separate from the brake pipe connected to the chassis. IF the disk brake uses an electric motor or cable to actuate the parking brake (not an integral drum brake like BMWs use), that cable or electric harness also had to disconnect from the caliper. Then the caliper drops to the wheel barrel, slides in towards the center of the car, then onto the road, clears the donating car's underbody, then catches the pavement and starts flipping around, jumping up high enough to hit the following car's windshield.

Now looking at the hole in the windshield, to me it looks like the caliper dropped straight down from some significant height. The rim of hole in the glass points downward, not rearward. Additionally the caliper would be traveling in the same forward motion as the Hyundai and at nearly the same speed, so the force on the windshield would be only 10, maybe 15, miles per hour less than the assumed highway speed. All motion is broken into X, Y, and Z axis (vectors).

I just can't see anyway that caliper ripped from a truck in front of the Hyundai and went through the windshield.

[M5Rick]

When I get the right moment (recovering from illness) to change my rear pads I'll make sure I'll use the calliper bolts supplied with the new pads with the fresh loctite bands on them and not to re-use the old ones.

[///MPhatic]

Originally Posted by BenitoBlanco

What part of the article you linked confirms that it was "definitely an unsecured load" that "came off the back of a truck"? The article mentions the penalty for driving with an unsecured load. There is no mention of it coming off a truck.

It's in the beginning of the video.

[TheMidnightNarwhal]

Originally Posted by forza1976

It wasn't originally....

Ahh copy that, I understand now. Got moved eh

[BenitoBlanco]

Originally Posted by M5Rick

When I get the right moment (recovering from illness) to change my rear pads I'll make sure I'll use the calliper bolts supplied with the new pads with the fresh loctite bands on them and not to re-use the old ones.

My point, loctite or not, was moreso just to torque to spec. It's crazy to me how many people insist they don't need to.

[BenitoBlanco]

Originally Posted by ///MPhatic

It's in the beginning of the video.

Ah, got it, thanks. I never watch videos on those news sites because I'd rather read than sit through 2-3 ads as most of them have.

Either way, I stand by my statement: torque your calipers to spec.

[BlkGS]

I'm gonna disagree. Don't torque to spec on caliper bolts. Torque over spec. Not by a hundred extra ft lbs, but by a little bit. Why? Because what we are really after with torque is clamping via bolt tension. A bolt that's 35 years old and has been on and off 100 times is going to lamp less via bolt tension than a brand new bolt.

I once lost a front caliper bolt that was torqued to spec. The caliper rotated on the other bolt, and smashed into the wheel, scraping against the wheel barrel (which was a VERY effective brake btw). I don't recommend having that happen to you. A little extra torque, and a new bolt when your old one feels "sloppy" makes life a whole lot better.

[Efthreeoh]

Originally Posted by BlkGS

I'm gonna disagree. Don't torque to spec on caliper bolts. Torque over spec. Not by a hundred extra ft lbs, but by a little bit. Why? Because what we are really after with torque is clamping via bolt tension. A bolt that's 35 years old and has been on and off 100 times is going to clamp less via bolt tension than a brand new bolt.

I once lost a front caliper bolt that was torqued to spec. The caliper rotated on the other bolt, and smashed into the wheel, scraping against the wheel barrel (which was a VERY effective brake btw). I don't recommend having that happen to you. A little extra torque, and a new bolt when your old one feels "sloppy" makes life a whole lot better.

I think most caliper failures are from over torqued mounting bolts. Look at the specs for, say a BMW 3-Series, the cage-to-hub spec is 45 pd-ft or so, and caliper guide pins are 25 pound-foot or less. Most novice think brake system requires gorilla-torque. Grade 10.9, 12MM or 14MM bolts are not stretching at 45 pd-foot. Blue locktite is good enough for an added margin of safety. Over torquing guide pins just bends them and you end up with sticking calipers.

[///MPhatic]

Originally Posted by BlkGS

I once lost a front caliper bolt that was torqued to spec. The caliper rotated on the other bolt, and smashed into the wheel, scraping against the wheel barrel (which was a VERY effective brake btw). I don't recommend having that happen to you.

Holy hell! I can't even imagine how this would happen.

[Efthreeoh]

Originally Posted by ///MPhatic

Holy hell! I can't even imagine how this would happen.

That's what I'm saying, a caliper removing itself from the brake system will not go unnoticed.

[BlkGS]

Originally Posted by Efthreeoh

I think most caliper failures are from over torqued mounting bolts. Look at the specs for, say a BMW 3-Series, the cage-to-hub spec is 45 pd-ft or so, and caliper guide pins are 25 pound-foot or less. Most novice think brake system requires gorrilla-torque. Grade 10.3, 12MM or 14MM bolts are not stretching at 45 pd-foot. Blue locktite is good enough for an added margine of safety. Over torquing guide pins just bends them and you end up with sticking calipers.

Yes, don't overtorque guide pins. But the caliper bracket bolts are monsters, torqued to like 110 lb ft. If you hit 130, it won't hurt a thing.

[BlkGS]

Originally Posted by ///MPhatic

Holy hell! I can't even imagine how this would happen.

What do you mean? The top bolt came out, and the caliper (and bracket) rotated around the (still bolted) lower bolt when I applied the brakes. It almost immediately locked up that wheel (because the caliper was quite literally jammed against the wheel).

There was no way someone would "not notice" it. It locked up a front wheel and dragged the car to the side abruptly. I was able to drive it a few hundred feet with the steering wheel pointed the other way to get out of the road. We used a large hammer to knock the caliper back into place.

It was super sketchy, and the car gods were smiling on me that day. We had just got back down from some spirited mountain driving. We were a couple hundred feet from my buddy's parents house that had enough tools to effect some basic investigation and repair. It was 15 minutes away from disaster with me going over the edge of a mountain.

[TheMidnightNarwhal]

Originally Posted by BlkGS

Yes, don't overtorque guide pins. But the caliper bracket bolts are monsters, torqued to like 110 lb ft. If you hit 130, it won't hurt a thing.

Depends on the car/bolt, on my E92 the caliper brackets bolts torque specs are 48ft lbs on the rear and 81ft lbs front.

But for sure, guide pins torque are usually much lower. I remember my noob mistake once on my first car, I thought the torque spec I had was for the caliper bracket bolts but I was tightening the guide pins... ehehe *snap*. Thankfully the way those guides pins were designed was like a screw into the pin type of design compared to how it is on BMW, so was easy to swap and got part at local store since it was just a generic Hyundai.

[BlkGS]

Originally Posted by TheMidnightNarwhal

Depends on the car/bolt, on my E92 the caliper brackets bolts torque specs are 48ft lbs on the rear and 81ft lbs front.

But for sure, guide pins torque are usually much lower. I remember my noob mistake once on my first car, I thought the torque spec I had was for the caliper bracket bolts but I was tightening the guide pins... ehehe *snap*. Thankfully the way those guides pins were designed was like a screw into the pin type of design compared to how it is on BMW, so was easy to swap and got part at local store since it was just a generic Hyundai.

That's something I haven't (and likely won't ever) get used to coming from domestics. Like the performance you get out of a Corvette is beyond insane, and you can just get parts for them literally anywhere. Meanwhile a low performance BMW 3 series you have to get parts at the dealer and they order them from Germany like they're some special super high performance part.

But yes, that's fair. Domestics like to use a hell of a lot of torque.

[Efthreeoh]

Originally Posted by BlkGS

Yes, don't overtorque guide pins. But the caliper bracket bolts are monsters, torqued to like 110 lb ft. If you hit 130, it won't hurt a thing.

The torque spec on a bolt depends on numerous factors, but the purpose is to set the tension of surface friction between the male and female threads based on the desired clamping force. For critical fasteners it's best to follow the spec to uphold the intent of the engineered design. Over torquing does not add value to the assembly.

I'm not saying you specifically, but most people don't understand how fasteners work and how threads work.

[carseatsm5]

That is a very, very sad story. Boy that’s tough.

[BlkGS]

Just for funsies, gonna throw out the concept of running torque, and how I've never seen an automaker specify a value over running torque. One would think in automotive applications where you've got variation due to corrosion, penetrating fluids, loctite, etc it would be the ideal place to have a spec for value over running torque...

[GuidoK]

Originally Posted by Efthreeoh

Look at the specs for, say a BMW 3-Series, the cage-to-hub spec is 45 pd-ft or so,
..
Grade 10.3, 12MM or 14MM bolts are not stretching at 45 pd-foot.

I don't know which specific 3 series you're referring to, but a value like 110Nm (81lbs-ft) is a more normal value (for a 12x1,5mm bolt).
45lbs-ft for a 12mm or 14mm bolt is an extremely low value.
But the caliper bolts aren't stretch bolts, like the ones used mostly on the subframes and underside tension bars and plates. They are allowed to be used again.

Originally Posted by BlkGS

What do you mean? The top bolt came out, and the caliper (and bracket) rotated around the (still bolted) lower bolt when I applied the brakes. It almost immediately locked up that wheel (because the caliper was quite literally jammed against the wheel).

I've had that exact same thing happen too on a front caliper on my Z4.
However, the caliper didnt jam against the rim. With normal driving, it was pulled into the normal position. (this is called a skating force)
Before the bolt came out (so when it was loose) I occasionally heard a small rattle. I inspected the car at the side of the road (I was abroad) and thought it migth be something with the ARB (like an ARB link that got some play or so), but couldn't find anything.

When the bolt came out I could hear the occasionaly louder clunk (and then knew something was really wrong, but no lockups or so like you describe. I had to ask other people on the roadside to look at my front wheel to see what was happening when I drove the car forewards and in reverse. They immedately saw the caliper move as soon as I changed direction.
I had no idea it was the caliper, at the time I was more thinking something wrong with the suspension arms or so.
I temporarely fixed it on the roadside by putting a wheel bolt in it (that has the same threadsize)
So I can imagine people just driving along with this.

The bolt was torqued to spec btw. I mark all bolts with a paintmarker after torquing. The lower one still had the marker (the upper one obviously was gone, but I assume it was marked also )
When replacing the bolts afterwards, I also checked the bolts on the other side and measured the torque to loosen. That was all OK.

I guess this stuff just sometimes happen.

[Efthreeoh]

Originally Posted by GuidoK

I don't know which specific 3 series you're referring to, but a value like 110Nm (81lbs-ft) is a more normal value (for a 12x1,5mm bolt).
45lbs-ft for a 12mm or 14mm bolt is an extremely low value.
But the caliper bolts aren't stretch bolts, like the ones used mostly on the subframes and underside tension bars and plates. They are allowed to be used again.


I've had that exact same thing happen too on a front caliper on my Z4.
However, the caliper didnt jam against the rim. With normal driving, it was pulled into the normal position. (this is called a skating force)
Before the bolt came out (so when it was loose) I occasionally heard a small rattle. I inspected the car at the side of the road (I was abroad) and thought it migth be something with the ARB (like an ARB link that got some play or so), but couldn't find anything.

When the bolt came out I could hear the occasionaly louder clunk (and then knew something was really wrong, but no lockups or so like you describe. I had to ask other people on the roadside to look at my front wheel to see what was happening when I drove the car forewards and in reverse. They immedately saw the caliper move as soon as I changed direction.
I had no idea it was the caliper, at the time I was more thinking something wrong with the suspension arms or so.
I temporarely fixed it on the roadside by putting a wheel bolt in it (that has the same threadsize)
So I can imagine people just driving along with this.

The bolt was torqued to spec btw. I mark all bolts with a paintmarker after torquing. The lower one still had the marker (the upper one obviously was gone, but I assume it was marked also )
When replacing the bolts afterwards, I also checked the bolts on the other side and measured the torque to loosen. That was all OK.

I guess this stuff just sometimes happen.

I was going from memory for the rear brakes. But my point really is, the brake hardware takes far less torque than most noobs think is required, because you know, it's the brakes and way tighter is better (but not really). Especially the guide pins. The guide pins offer zero clamping force, they only locate the caliper on the wheel hub.

[TheMidnightNarwhal]

Originally Posted by GuidoK

I don't know which specific 3 series you're referring to, but a value like 110Nm (81lbs-ft) is a more normal value (for a 12x1,5mm bolt).
45lbs-ft for a 12mm or 14mm bolt is an extremely low value.
But the caliper bolts aren't stretch bolts, like the ones used mostly on the subframes and underside tension bars and plates. They are allowed to be used again.

I know a bit arguing non important point but I can confirm the torque spec is correct, I have ISTA. I'm on an E92 335is but on the 328 pretty sure the rear calipers are the same.

But yeah that's the thing, you are right on the money, the bolt size is M10. On the E9X M3 for example it's a M12 bolt which that one spec rating is 81ft lbs.

[GuidoK]

Originally Posted by Efthreeoh

I was going from memory for the rear brakes. But my point really is, the brake hardware takes far less torque than most noobs think is required, because you know, it the brakes and way tighter is better (but not really). Especially the guide pins. The guide pins offer zero clamping force, they only locate the caliper on the wheel hub.

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)

[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.