In a message dated 97-10-27 09:48:21 EST, brian@uunet.ca writes:
<< Make sure that you lube the nut and bolt threads before torqueing. >>
Torque specifications are determined by the finish that a particular bolt or
nut is expected to have when manufactured. Phosphate, Phosphate and Oil, Cad
plate Zinc plate..etc: will all give different compression versus torque
readings when torqued to the same spec. Applying a lubrication to the bolt
or nut will give a false torque reading. By that I mean if it is lubricated
you can obtain a higher compression for the same torque reading due to the
lower friction between the threads. This can over stress the bolt and
potentially cause stress cracks in the bolt which ultimately might cause the
bolt to fail. As an example, you can take a bolt as manufactred and torque
it to specification without a problem. Take the same bolt, lubricate it and
then break the bolt before you reach the torque spec. I worked in the Brake
Group at Ford many years ago when the Federal Government started regulating
safety items on cars. All fasteners in the Brake system came under those
regulation. We ran extensive torque test on all the fasteners used and found
a wide range of torque versus compression between the different suppliers
depending on the finish. As a result we applied strict specifications on the
finish of fasteners used in safety related application and filed a report
with the government on our result.
Just a note of caution when it comes to lubricating bolts and nuts on your
car. especially in the suspension, steering and brake systems. DON'T!!!!
Ron
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