Torque on shackle

[krafty33]

What do you guys torque your front and rear shackles to? Also what do you torque the other spring mounts to?

[VileZambonie]

If you're talking about the spring bushing bolts Don't torque them. That's right you heard that from me! lol If you follow the recommended torque specs you wil usually destroy the bushings. Use a self locking nut instead and use your German spec's Goodntight. Here are the torque values but if you see the bushings starting to squish stop!

Torque leaf spring-to-frame attaching nut to 92 ft. lbs.
Torque leaf spring-to-axle attaching nuts in a diagonal sequence first to 18 ft. lbs. then to 80 ft. lbs.
Tighten stabilizer link-to-axle attaching nut until distance between each retainer is .82 inch.
Torque stabilizer bar-to-link attaching nut to 50 ft. lbs.
Torque lower shock absorber attaching nut to 37 ft. lbs

[SUX2BU99]

I wonder how and who determines torque values? Like the values of 92 and 37 ft-lbs. Is 2 lbs more than 90 or 35 ft-lbs THAT much different? Interesting.

[VileZambonie]

http://www.zerofast.com/torque.htm

[SUX2BU99]

Very interesting. Thank you for that. Torque values are more about the kind of bolt being used for the application rather than the application itself. That leads to the next question: who and what determines what kind, size and type of bolt is used for a particular application. I have a feeling it's much less about engineering than it is about cost, availability, personal preference and maybe even guesswork.

[VileZambonie]

Engineer's are responsible for calculating proper clamping force based on metal hardness, type of connection, etc. It is critical and especially with different composites. Here read this:

FASTENERS
Fasteners are those things used to secure or hold parts of
something together. Many types and sizes of fasteners are
used by the automotive industry. Each fastener is designed
for a specific purpose and condition. One type of fastener
most commonly used is the threaded fastener. Threaded
fasteners include bolts, nuts, screws, and similar items
that allow a technician to install or remove parts easily

Threaded fasteners are available in many sizes, designs,
and threads. The threads can be either cut or rolled
into the fastener. Rolled threads are 30% stronger than
cut threads. They also offer better fatigue resistance because
there are no sharp notches to create stress points.

Fasteners are made to Imperial or metric measurements.
There are four classifications for the threads of Imperial
fasteners: Unified National Coarse (UNC), Unified National
Fine (UNF), Unified National Extrafine (UNEF),
and Unified National Pipe Thread (UNPT or NPT). Metric
fasteners are also available in fine and coarse threads.
Coarse threads are used for general-purpose work, especially
where rapid assembly and disassembly is required.
Fine-threaded fasteners are used where greater
holding force is necessary. They are also used where
greater resistance to vibration is desired.
Bolts have a head on one end and threads on the other.
Bolts are identified by defining the head size, shank diameter,
thread pitch, length and its grade.
Bolts have a shoulder below the head and the threads do
not travel all the way from the head to the end of the bolt.
Cap screws are similar to bolts; however, cap screws
have no shoulder. The threads travel from the head to the
end of the bolt. It is important that you never use a cap
screw in place of a bolt.

Studs are rods with threads on both ends. Most often,
the threads on one end are coarse while the other end has
fine threads. One end of the stud is screwed into a
threaded bore. A hole in the part to be secured is fitted
over the stud and held in place with a nut that is screwed
over the stud. Studs are used when the clamping pressures
of a fine thread are needed and a bolt will not work.
If the material the stud is being screwed into is soft (such
as aluminum) or granular (such as cast iron), fine threads
will not withstand a great amount of pulling force on the
stud. Therefore, a coarse thread is used to secure the stud
in the work piece and a fine-threaded nut is used to secure
the other part to it. Doing this results in having the
clamping force of fine threads and the holding power of
coarse threads.
Nuts are used with other threaded fasteners when the
fastener is not threaded into a piece of work. Nuts of
many different designs are found on today’s cars.
The most common one is the hex nut, which is used
with studs and bolts and is tightened with a wrench.
Setscrews are used to prevent rotary motion between
two parts, such as a pulley and shaft. Setscrews are either
headless or have a square head. Headless setscrews require
an Allen wrench or screwdriver to loosen and
tighten them.
Machine screws are similar to cap screws but have a
flat point. Machine screws can have a round, flat, Torx®,
oval, or fillister head.
Self-tapping screws are used to fasten sheet-metal
parts or to join light metal, wood, or plastic parts together.
These screws form their own threads in the material they
are screwed into.
Bolt Identification
The bolt head is used to loosen and tighten the bolt. A
socket or wrench fits over the head and is used to screw
the bolt in or out. The size of the bolt head varies with the
diameter of the bolt and is available in Imperial and
metric wrench sizes. Many confuse the size of the head
with the size of the bolt. The size of a bolt is determined
by the diameter of its shank. The size of the bolt head determines
what size wrench is required to screw it. Table
5–1 lists the most common bolt head sizes. Notice that
the sizes are listed as fractions of an inch or as millimeters.
Bolt diameter is the measurement across the major diameter
of the threaded area or across the bolt shank. The
length of a bolt is measured from the bottom surface of
the head to the end of the threads.
The thread pitch of a bolt in the Imperial system is determined
by the number of threads that are in one inch
of the threaded bolt length and is expressed in number of
threads per inch. A UNF bolt with a 3⁄8-inch (9.54 mm)
diameter would be a 3⁄8 × 24 bolt. It would have 24
threads per inch. Likewise a 3⁄8-inch (9.54 mm) UNC bolt
would be called a 3⁄8 × 16.
The distance, in millimeters, between two adjacent
threads determines the thread pitch in the metric system.
This distance will vary between 1.0 and 2.0, and depends
on the diameter of the bolt. The lower the number, the
closer the threads are placed and the finer the threads are.
The bolt’s tensile strength, or grade, is the amount of
stress or stretch it is able to withstand before it breaks.
The type of material the bolt is made of and the diameter
of the bolt determines its grade. In the Imperial system,
the tensile strength of a bolt is identified by the
number of radial lines (grade marks) on the bolt’s head.
More lines mean higher tensile strength.
Count the number of lines and add two to determine the
grade of a bolt.
A property class number on the bolt head identifies
the grade of metric bolts. This numerical identification is
comprised of two numbers. The first number represents
the tensile strength of the bolt. The higher the number,
the greater the tensile strength. The second number rep-
resents the yield strength of the bolt. This number represents
how much stress the bolt can take before it is unable
to return to its original shape without damage. The
second number represents a percentage rating. For example,
a 10.9 bolt has a tensile strength of 1,000 MPa
(145,000 psi) and a yield strength of 900 MPa (90% of
1,000). A 10.9 metric bolt is similar in strength to an SAE
grade 8 bolt.
Nuts are graded to match their respective bolts (Table
5–2). For example, a grade 8 nut must be used with a
grade 8 bolt. If a grade 5 nut were used, a grade 5 connection
would result. Grade 8 and critical applications require
the use of fully hardened flat washers. These will
not dish out when torqued, as soft washers will.

Bolt heads can pop off because of fillet damage. The
fillet is the smooth curve where the shank flows into the
bolt head (Figure 5–6). Scratches in this area introduce
stress to the bolt head, causing failure. Removing any
burrs around the edges of holes can protect the bolt head.
It is also a good practice to place flat washers with their
rounded, punched side against the bolt head and their
sharp side to the work surface.
Fatigue breaks are the most common type of bolt failure.
A bolt becomes fatigued from working back and
forth when it is too loose. Undertightening the bolt causes
this problem. Bolts can also be broken or damaged by
overtightening, being forced into a nonmatching thread,
or bottoming out, which happens when the bolt is too
long.
Tightening Bolts
Any fastener is near worthless if it is not as tight as it
should be. When a bolt is properly tightened, it will be
“spring loaded” against the part it is holding. This spring
effect is caused by the stretch of the bolt when it is tightened.
Normally a properly tightened bolt is stretched to
70% of its elastic limit. The elastic limit of a bolt is that
point of stretch from which the bolt will not return to its
original shape when it is loosened. Not only will an overtightened
or stretched bolt not have sufficient clamping
force, it will also have distorted threads. The stretched
threads will make it more difficult to screw and unscrew
the bolt or a nut on the bolt.
Washers
Many different types of washers are used with fasteners.
The type of washer it is defines the purpose of the washer.
Flat washers are used to spread out the load of tightening
a nut or bolt. This stops the bolt head or nut from digging
into the surface as it is tightened. Soft, flat washers,
sometimes called compression washers, are also used to
spread the load of tightening and help seal one compo-
nent to another. Copper washers are often used with oil
pan bolts to help seal the pan to the engine block.
Lock washers are used to lock the head of a bolt or
nut to the work piece to keep it from coming loose and
to prevent damage to softer metal parts.
Thread Lubricants and Sealants
Often manufacturers recommend that the threads of a
bolt or stud be coated with a sealant or lubricant. The
most commonly used lubricant is antiseize compound.
Antiseize compound is used where a bolt might become
difficult to remove after a period of time, for example in
an aluminum engine block. Thread lubricants introduce
the possibility of a hydrostatic lock, where oil is trapped
in a blind hole. When the bolt contacts the oil, it cannot
compress it; therefore the bolt cannot be properly tightened
and a cracked part may result.
Thread sealants are used on bolts that are tightened
into an oil cavity or coolant passage. The sealant prevents
the liquid from seeping past the threads. Another commonly
used thread chemical, called threadlocker,
prevents a bolt from working loose as the engine or
another part vibrates.

[SUX2BU99]

That's a good read. I like to sometimes think of where things originate from. I think the reason something originates from or evolves from is due to a combination of design, previous failure in the field (necessitating an upgrade) and some guesswork. I work in the engineering field as a designer. Mechanical in fact, although not machine or automotive related. And while designs stem from a lot of knowledge and previous research, there is a lot of "hmmm, the calculation says this but we'll step it up by x amount just to be sure".  Sometimes it's enough, sometimes it isn't and you learn for the next go-round. Anyway, I'm probably digressing.

[78 Chevyrado]

Dang, Vile's got it on TAP like that!  good read man!

[VileZambonie]

It's amazing how much people don't really know about nuts and bolts, thread pitch, rolled vs cut threads, grade markings and torque values. Lot's of good stuff to know! Glad to help