Lug bolts for brake carrier, Audi A4 8K

Hi,
For the brake carrier on the front, M14x1.5 ribbed screws are used, while on the rear, M12x1.5 ribbed screws are used, both additionally with ribbed washers. Both have a strength class of 10.9, and the non-threaded shaft is 3mm/5mm long.
Based on the bolt diameter, I would have expected different tightening torques in proportion to the bolt cross-sections, for example, a ratio of 200:150.

For the front M14 bolt, Mr. Audi would like 190 Nm of torque, and accordingly, I would expect around 140 Nm for the rear M12 bolt. Actually, it should be 100 Nm + 90 degrees.
With a 90-degree turn beyond the 100 Nm mark, I achieved a tightening torque of around 200 Nm, possibly even more. In fact, I had to really force the screws to only turn them another 60 degrees after reaching 100 Nm. In the process, it even broke a nut (from the Rahsol nut box that I received from my old master 40 years ago).
For comparison, I then checked the torque on the front screws. While the specified torque is 100 Nm, I tightened them another 60 degrees.
The specified torque of 100 Nm plus 90 degrees for the M12 screw seems very unusual to me. I tend to tighten to 150 Nm, and that's good enough.
Please provide comments.
hg
Herbert.

Hello Herbert,

Does that come from Elsa or a repair manual? Unfortunately, if that's the case, I can't think of anything else to do other than consulting the repair manual.
"Around 200 Nm seems a bit too high for an M12 thread, in my opinion."


Edit: Could it be that you accidentally used a screw that is too rigid and not a stretch bolt? After "fest", it's not "dehn" that comes next, but "ab". http://www.schrauben-normen.de/anziehmomente.html

Best regards, Rainer.

Hello Rainer,
"Mr. Audi wants" = RLF. The screws are, of course, OE parts from .

The torque value of 190 Nm for M14x1.5 screws is similarly found in tables for 10.9 grade screws and for 100-ribbed screws.

For M12x1.5 threads, a torque of 120-130 Nm is typically used.

hg
Herbert.

Hello!

Based on my experience, you tend to make more progress when you rely on your long-standing experience and common sense.

Bolts/nuts for the wheel hub and the cylinder head are a different matter.

Many years ago, I also had the idea to use torque wrenches for everything to improve the quality of my work.
This then resulted in several disasters, such as screws being stripped, studs breaking off, etc.
Normally, something like this wouldn't happen to me, considering my feelings and common sense. And nothing has ever been resolved.

Steffen,
How would you tighten a M12 bolt for which the manufacturer specifies 100 Nm plus 90 degrees?
hg
Herbert.

If it were my car, I would look up the

Quote:

recommended torque values for DIN 912 screws with fine threads, strength class 10.9, M12x1.5

based on the application, and either stop the process at 90° or when 130Nm is reached (table value 127.54 Nm).

Do you still have the old screws? And were they really 10.9 grade? Do they look the same as the new screws (in terms of the head shape, etc.)?

Best regards, Rainer.

The old screws are 10.9 grade, just like the new ones, and they have the same geometry (as also described earlier).
A torque of 130 Nm corresponds to 100 Nm plus approximately 30 degrees (which can be easily observed on the marked 6-point screw if you first tighten it to 100 Nm).
As I mentioned, the manufacturer's specification is very unusual, especially when compared to the specifications for M14 screws with otherwise similar designs.
Screw manufacturers specify tightening torques of 115-130 Nm for ribbed screws M12, depending on the material being fastened.
hg
Herbert.