GMC 4000 Series Service Manual page 110

Improper reinforcement or attachment of r e ­
inforcement may cause more difficulty than the
original problem as the creation of localized stress
concentrations may reduce the frame load carry­
ing capacity below the original frame before add­
ing reinforcements. The use of rivets for attaching
reinforcement duringfield modification is generally
not recommended due to the lack of proper rivet­
ing equipment in most service locations. For this
reason it is recommended that most reinforce­
ments be attached with 300-M bolts and that hard­
ened washers be placed on both ends of the bolt to
provide a good torquing surface and to maintain
tight bolts.
GENERAL WELDING INSTRUCTIONS
Good welding is a very favorable method of
attachment or repair; however, improper welding
or welding procedure may result in further frame
damage. Additives of reinforcements may be nec­
essary in the repair area to prevent reoccurrence.
WARNING: Before welding, disconnect one or
both battery cables.
WELDING EQUIPMENT
CAUTION
NEVER USE OXYACETYLENE
FOR WELDING FRAME RAILS!!
There are several types of welding machines
that are used for welding on frame rails. Listed
below are the three most commonly used machines
and their advantages:
1. DC (Rectifier Type) - This machine re­
quires very little service as there are no moving
parts, also reduces chance of arc blows.
2. DC (Motor-Generator Type) - Theprinciple
advantage is the power supply may be self-con -
tained; thereby, this machine is readily portable
and has very good voltage variation control and
versatility with all types of electrodes.
3. AC - This is the least expensive and re­
duces possibility of arc blows; however, some
difficulty may be encountered in striking an arc
when using sm all diameter electrodes.
It is recommended that for all-purpose weld­
ing, the minimum capacity of any machine should
be 350 amperes. There are four basic types of
welding used in the repair or reinforcing of frame
rails. All of these can be used with any type of
material except heat-treated material which re­
quires electrodes E12016 or E11018. Following
are the descriptions of the types of welds;
G M C S E R V I C E M A N U A L
weld a continuous bead along a reinforcement plac­
ed on the web section of the frame rail or for add­
ing gussets or plates to crossm em bers. Continuous
fillet welds should never be made across frame
flanges or along inside edges of frame flanges.
When welding in the flat position use high range of
electrode current and voltage chart. When welding
overhead or in difficult areas, use low range of the
electrode chart.
weld which is applied after the surface has been
vee ground for good penetration. Particular care
should be taken when welding cracks which cross
either the upper or lower flanges. Weld completely
then grind off the excess weld to eliminate the p os­
sibility of notches or weld build-ups on the flange
edge. Use medium range of electrode chart.
taching reinforcements as it eliminates the p o ssi­
bility of loose fitting bolts; however, care must be
exercised in locating plug welds in different types
of reinforcements. E-6011 electrode is highly rec­
ommended for plug welding because of its good
penetration and light coating. Use high range of
electrode chart for flat or vertical plug welds.
Overhead plug welding is very difficult and should
not be used unless other approaches are not prac­
tical, then use high range for first pass and com ­
plete plug at medium range. Refer to plug weld
table for size of hole to use for variations of ma­
terial thickness.
type is not generally used on frames as continuous
fillet welding provides better attachment; however,
where warpage and heat control is critical, use
stitch welding at medium range of electrode chart.
ing include:
close to working area as possible.
trode and make several passes rather than large
diameter electrode and single pass.
applied, as inadequate repairs will create addi­
tional localized stress concentration which may
result in repeat failures. There are two basic
types of cracks which may be encountered in frame
difficulties (fig. 5). The straight crack or the mul­
tiple sunburst cracks which will radiate from a
hole in the web section.
a. Continuous Fillet Weld - This is used to
b. Groove Welding - This is a basic repair
c. Plug Welding - This is a good method of at­
d. Stitch (Intermittant Fillet) Welding - This
Other recommendations for all types of weld­
1. Connect welding machine ground cables as
2. Where possible, use sm aller diameter e lec­
FRAME RAIL REPAIR
It is very important that repairs be correctly
Sec. 2
Page 103
FRAME