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GROUP
13 - 1
FRAME STRUCTURES
C O N T E N T S
Page
INSPECTION PROCEDURES
6
SERVICE PROCEDURES
11
GENERAL INFORMATION
The m a i n function o f the t r u c k frame is t o provide
support for a l l chassis components, body m o u n t i n g
and t o carry the payload w h i l e keeping deflections a t
a tolerable level.
The
frame
is a complex
s t r u c t u r a l
mechanism
w h i c h reacts to applied loads a n d road inputs b y
bending a n d t w i s t i n g . T h e m a i n bending members
are t h e siderails. Resistance t o frame t w i s t is pro-
vided b y crossmembers w h i c h are r i g i d l y attached to
t h e siderails w i t h either r i v e t s or bolts t o f o r m t h e
so-called "ladder t y p e " frame (Figs. 1 t h r u 4).
FRAME SIDERAIL
MATERIAL
Carbon steel w i t h a m i n i m u m y i e l d s t r e n g t h o f
32000 psi is used to fabricate t h e l i g h t a n d t h e me-
d i u m d u t y t r u c k frame siderails.
Since the y i e l d s t r e n g t h for t h e same steel can vary
considerably i t has been Dodge's practice t o specify
t h e m i n i m u m y i e l d s t r e n g t h . T h u s t h e 32000 psi
m i n i m u m frame has i n r e a l i t y a range o f 32000 to
44000 psi w i t h a t y p i c a l average value o f 38000 psi.
For severe applications, h i g h s t r e n g t h steel frame
siderail reinforcements o f the same steel are used.
FRAME LOAD-CARRYING
CAPACITY
Since by f a r the most i m p o r t a n t factor o f frame ac-
t i o n is i t s flexing, i t is customary t o compare t h e
frames
b y t h e i r
"Resisting
B e n d i n g
M o m e n t "
(R.R.M.), t e r m denoting t h e m a x i m u m bending t h e
siderails can safely w i t h s t a n d .
Page
SPECIFICATIONS
12
TIGHTENING REFERENCE . . . . . . . . . . . . . . . . 12
The resisting bending moment can be used for
quick comparison o f frames h a v i n g different r a i l con-
figuration
and materials.
The Resisting B e n d i n g Moment consists of t w o
terms: Section Modulus and M a t e r i a l Y i e l d Strength.
(Section Modulus x Y i e l d Strength = R.B.M.)
The greater the section modulus and the higher the
yield strength, t h e stronger t h e siderails.
The t e r m Section Modulus pertains to the cross-sec-
tion of the siderail a n d is determined b y r a i l depth,
flange w i d t h , and m a t e r i a l thickness.
Y i e l d s t r e n g t h is a measurement i n psi o f stress a t
which a m a t e r i a l exhibits a specified permanent de-
formation.
FRAME
TYPE
L i g h t D u t y T r u c k a n d Sport U t i l i t y frames are o f a
ladder type w i t h drop center section channel siderail
and crossmembers.
Crossmembers
are riveted or
bolted to t h e frame. Body support a n d suspension
m o u n t i n g brackets are riveted to siderails. (See Figs.
6, 7, and 8 for i n c h dimensions.)
A D 1 - A D 4 frames are designed to accommodate i n -
dependent
f r o n t suspension
w i t h
t h e suspension
crossmember as a p a r t o f the frame assembly as are
engine front m o u n t i n g brackets w h i c h are welded to
the
suspension
crossmember
a n d riveted to t h e
siderail.
AD5-AD8
(four-wheel-drive
vehicles) frames are
basically t h e same, except front suspension cross-
member is replaced w i t h a smaller engine support
crossmember.
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