GMC 4000 Series Service Manual page 112

ually as possible with the longest section installed
(fig. 6) in the area of highest loads.
There are five basic types of reinforcem ents
that may be used on truck fram es. However, it
must be pointed out that the material used for the
reinforcement must be sim ilar to that of the base
rail. Base rails of S.A.E. 1023 material could use
reinforcem ents of S.A.E. 950 material. S.A.E. 1023
rails may be reinforced with S.A.E. 1023 steel,but
under no circum stances should strength of rein­
forcement be le ss than base rail. Figures 7 and 8
illustrate the five basic reinforcem ents.
1. Upright "L" Reinforcement - Maybe placed
on either the inside or outside of the frame side
rail. It should be used where maximum str ess oc­
curs at the bottom of the lower flange and buckling
of the upper flange is not a problem. This rein­
forcem ent is quite versatile as it may be used in
full length or in a short localized reinforcement.
The configuration of the frame or spring hanger
brackets may lim it the use of the upright "L" r e ­
inforcement.
2. Inverted "L" Reinforcement - This may be
used on the inside or outside of the frame rail. It
is recommended where the maximum str ess area
is transferred to the upper flange; for example,
dump trucks with the box in the raised position.
This is also readily adapted where frame and hang­
er bracket design restricts using an upright "L"
reinforcement or where frame upper flange buckl­
ing has been noted.
3. Channel Reinforcement - This may also be
installed on the inside or outside of the frame side
rail and can be full length oralocalized reinforce­
ment. The principle disadvantage of the channel is
additional weight and hours of labor required to
make an installation. Additional difficulty may
arise when attempting to place the channel inside
or over the existing rail due to manufacturing tol­
erances, cross members or mounting brackets.
4. Strap Reinforcements - This type of rein­
forcem ent may also be used to increase the section
modulus of a frame if previous damage and repair
has resulted in a lo ss of frame strength which
would require additional modulus to return the
fram e strength to original design. These reinforce­
ments are plug welded at 6 to 8 inch intervals. Do
not weld across the end or along the flange edges.
Ends should be cut at an angle and edges of plug
welds must not be closer than 3 /4 " to the edge of
a frame flange.
5. Inverted "J" Reinforcement - This is a
rather new type of frame reinforcement that is de­
signed to increase the flange strength to prevent
flange buckling due to high torsional inputs or
shock loading during tractor hook-up operations.
The inverted "J" reinforcement is attached to the
web section only with a spaced bolt pattern. This
G M C S E R V I C E M A N U A L
reinforcement has been released in six-foot lengths
through the Factory Warehouse under GMC Part
Number 2446489.
rail may vary somewhat with m aterials. The fol­
lowing general rules apply:
ment is not generally available in most field serv­
ice outlets; therefore, the use of 300M bolts and
hardened flat washers are recommended.
Figure 7 — Frame Reinforcements
The attachment of reinforcement to the basic
1. Do not use rivets. Proper riveting equip­
2. Reinforcements, with the exception of strap
Sec. 2
Page 105
FRAME