Fasteners

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.

Torque Settings:

AN (Army/Navy)

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.

DecimalFraction
0.0625 1/16
0.1875 3/16
0.3125 5/16
0.4375 7/16
0.5625 9/16
0.6875 11/16
0.8125 13/16
0.9375 15/16

 

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:

ScenarioTorque Reduction
Dry None
Oil 15% to 25%
Dry Film (Teflon or Moly Based) 50%
Dry Wax (Cetyl Alcohol) 50%
Chrome Plating None
Cadmium Plating 25%
Zinc Plating 15%

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.

Calibrated Arm

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.

I also work in the nuclear industry (power generation ) and where I work absolutely everything gets torqued. Not only that but before and after every job the (Snap ON no less) wrenches get checked on a load cell. Also the serial numbers are recorded...on every job. This may be going a little overboard but consider the consequences.

In my training there I have learned that the feel method is inconsistant at best. They had a special rig set up just to prove this fact. It was a 6 bolt pipe flange with load cells at every bolt. We couldn’t see the results at the time and were asked to tighten it evenly by hand. Nobody in the course got less than about 30% variation, and we were all Industrial Millwrights with years of experience.

At home, when it’s my money, If some procedure says torque it to X, then I torque it to X

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

6061
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). %.

6061-T6
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.

http://smallengineinformation.com/?page_id=508

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.

another table

Dzus Fasteners

Other

H Craft recommends Tridar over Dzus (more expensive, but better)