A few weeks ago, I allowed Les Schwab in Richland WA remove two rear wheels from my vehicle and balance them. I watched their mechanic improperly use a torque wrench to install the wheel lug nuts, resulting in the nuts being grossly overtightened and unevenly tightened.
Not by a couple pounds, but by 83%. I detorqued two lug nuts on the same wheel, one at 140 ft/lbs and another at 160 ft/lbs the mechanic tightened the nuts in a circular pattern, and not the required cross tightening pattern.
I confronted them with this and to their credit, they did not attempt to cover it up. After showing them some impressive 'mechanical credentials' I went with a mechanic and manager to the vehicle and used my expensive torque wrench to prove to them the nuts were grossly overtightened.
The mechanic that worked on the wheels the second time was going to:
1.) use an AIR IMPACT GUN to install the lug nuts-
and in the process, overtighten them AGAIN and possibly warp the rim.
Impact guns are NOT calibrated and depend on air line pressure and oil inside them (for sealing) for torque and tighten each nut to full torque, in turn, which may easily warp the rim.
2.) pound a damaged wheel stud out with a 2 pound steel HAMMER-
and possibly destroy an axle bearing, there are PROPER TOOLS for doing such work.
I had to stand over their mechanic and show him how to properly install a wheel and lug nuts.
Overtightened lug nuts were reported recently in a UK paper as causing a multiple - fatality accident when a med student overtightened wheels on a car.
Http://www.dailymail.co.uk/news/article-1092207/Woman-medical-student-died-crash-driver-bolted-wheel-nuts-tightly.html
See your vehicles Owner or Shop Manual for proper wheel lug nut torquing procedures and specs or here is how I do it, which exceeds most manufacturers requirements:
1.) ensure clean and undamaged threads on nuts and studs. All nuts must thread completely on by hand with no binding else threads are dirty or damaged. Dirty threads cannot be accurately torqued. Damaged studs AND their nuts should be replaced as mechanics and most vehicle owners are not sufficiently trained to determine whether a damaged stud is repairable.
2.) clean mating surfaces of wheel and hub.
3.) install wheel and HAND TIGHTEN all lug nuts to seat the rim on the hub. Start with a nut at the top of the wheel.
4.) tighten each lug nut in turn in a cross-tightening pattern to an initial torque which is a fraction of final torque. I go by 10-20 ft/lb increments. This prevents the wheel from being warped as happens when one lug nut is tightened fully.
"Cross tightening" depends on teh number and arrangement of the nuts, but is often tightening nuts which oppose each other in pairs at 180 degrees.
5.) repeat 4.) at 10-20 ft/lb increments to final torque. Do not exceed final torque.
6.) test drive a few miles at low speeds and recheck final torque.
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