The manual is pretty clear that the suspension parts are thrown together so that they can roll the car on a trailer for shipping purposes and that every fastener should be treated with suspicion... i.e., it might not be the correct fastener and it will likely not be torqued to the correct value.
The area which generates the most force and hence the most concern is the suspension. All most all parts require grade 8 hardware.
- MachineToolHelp.com (Socket Head Cap Screws & Hex Head)
- Torque units.. http://www.macsmotorcitygarage.com/2013/10/24/foot-pounds-and-pound-feet-whats-the-difference/
AN grips come in 1/8" increments. Since they start at 1/16" rather than 0, it's easier to think of them in 2/16" increments. The following list is useful when buying AN bolts and using a micrometer to measure the desired grip length.
Rules of Thumb and observations
- Minimum recommended thread engagement into steel is 1x nomimal thread diameter and aluminum is 2x.
- No two bolts respond exactly the same to a given torque. Dirt in a tapped hole, grease or oil on the threads damaged threads, hole misalignment, accuracy of torque measuring device, and numerous other factors can alter the torque-tension relationship. Even perfect input torque can give a variation of preload by as much as 25%.
The following table was taken from here and shows torque changes for different type of coatings:
|Oil||15% to 25%|
|Dry Film (Teflon or Moly Based)||50%|
|Dry Wax (Cetyl Alcohol)||50%|
Note, the torque reductions are not additive, i.e. for a cadmium plated bolt with dry wax film, torque should only be reduced by the greater of the twp suggested reductions, in this case 50% reduction for the dry wax, NOT 50%+25% or 75% reduction because the bolt is both cadmium plated and dry wax coated.
There's lots of talk about having a calibrated arm. I don't have one and according to guy who works at a nuclear power plant, most professionals don't either.
So let's get that straight:
- They were merely looking for even torque, not a specific torque
- Six repeat operations in optimal conditions; one after the other, same orientation, same wrench, same materials, etc.
- All experts
- According to this resource the proper torque spec is usually around 65-70% of the failure torque rate; that puts the 30% variance into perspective
Steel Fastener into Aluminum
Annealed 6061 (6061-O temper) has maximum tensile strength no more than 120 MPa (18,000 psi), and maximum yield strength no more than 55 MPa (8,000 psi). %.
T6 temper 6061 has an ultimate tensile strength of at least 290 MPa (42,000 psi) and yield strength of at least 240 MPa (35,000 psi). More typical values are 310 MPa (45 ksi) and 270 MPa (39 ksi), respectively.
Mild steel (i.e., A36/SA36 material) the tensile and yield strength are moderate. The yield is approximately 36,000 PSI, and the tensile strength varies from 58,000 PSI to 80,000 PSI. Variations in tensile strength allow for the difference in carbon, manganese, and silicon content in different thickness. Also the production method—rolling, hot or cold, or extruding—can affect tensile strength.
Types of aluminum explained.
Note for aluminum the values are the same for grade 2, 5 and 8. Further note that it appears that the aluminum value is the same as the one for grade 2 into steel. So putting grade 8 into aluminum is less than half of grade 8 into steel.
H Craft recommends Tridar over Dzus (more expensive, but better)