GMC 4000 Series Service Manual page 26

To determine the exact location of leak at
flooring or cowl, remove floor mat and dash panel
pad. Water which shows up at a certain place in­
side cab may actually be entering at a point other
than where water is found. Back-track path of
water to point of entry. Apply body sealing com­
pound over all leak points.
If leakage occurs at door opening, check wea­
therstrip. Seal with rubber cement or replace if
necessary. If door does not firmly contact weather­
strip, align door as described in applicable cab
section.
CAB ALIGNMENT
Since cab is an integrally welded structure,
repair should be attempted only by competent
craftsman using proper tools and equipment. For
best results, only genuine factory parts should be
used for replacement. As work progresses, cro ss­
checking with an adjustable tram bar is recom­
mended for obtaining proper alignment.
STRAIGHTENING
Before attempting repair of a damaged cab,
the chassis frame must be checked and aligned as
described in FRAME (SEC. 2). To straighten frame,
it may be necessary to remove cab.
Never attempt to straighten cab unless cab is
firm ly attached to chassis. The inner paneling of
cab should be straightened first. Use of a push-
pull hydraulic jack, together with extension and
adapters is recommended for this type of repair.
After straightening, it is important that strains
set up in cab framing be relieved or "normalized."
Normalizing consists of heating areas of greatest
str ess with a torch. Holding torch nozzle about
2 inches from metal, move torch over an area of
3 to 4 inches until the metal barely begins to turn
red. Cooling must be slow to avoid changing char­
acteristics of the metal. Apply slight heat with
torch, if necessary, to retard cooling.
DINGING A N D FINISHING
Paint is quickly scuffed off sharp dents leaving
metal exposed to rusting and corrosion; therefore,
damaged panels should be repaired as soon as
possible. Proper metal finishing is required to
assure a smooth surface. Application of hammer
directly to panel tends to stretch the metal and
cause a great deal of unnecessary work. Whenever
possible, a spoon should be used under the hammer
when bumping a panel. Repair damaged panels by
forcing outward in direction opposite to force
which caused damage. In this way metal strains,
set up when damage occurred, are relieved.
G M C S E R V I C E M A N U A L
REPAINTING
sion products, grease, and other foreign matter
must be removed. Use of phosphoric base metal
conditioners, such as "Metalprep" (Neilson Chem­
ical Co.) or "Dioxidine" (American Chemical Paint
Co.) or equivalent is recommended in preparing
steel for painting. These materials vary in method
of application and use, and should be employed only
as directed by the manufacturer. Solvent cleaning,
pressure steam cleaning, wire brushing, and hand
sanding methods are recommended.
organic or alkaline solvents. However, if alkaline
removers are used, all traces of alkali must be
washed off before primer is applied. If old primer
is very difficult to remove, and if there is no evi­
dence of metal corrosion, old primer may be left
on, but all loose paint must be removed.
allow to dry. Use a good oxide primer obtained
from a reputable manufacturer.
quiring color, apply two coats of a good air-drying
black or other automotive lacquer.
paint in accordance with standard practice.
PAINTING NEW PARTS
cleaned and painted, as outlined previously under
"Repainting," after installation in vehicle. In addi­
tion, hidden surfaces of panels should be cleaned
and coated with one heavy coat of sheet metal
deadener.
WINDSHIELD GLASS REPLACEMENT
by a molded rubber weatherstrip with an insert-
type rubber seal as illustrated in figure 1. A single
windshield glass is used in the conventional cab
models whereas two glass sections are used on
steel tilt and "P" models.
is very important that the cause of the glass break­
age be determined and the condition corrected be­
fore a new glass is installed. Otherwise, it is high­
ly possible that a small obstruction or high spot
somewhere around the windshield opening will con­
tinue to crack or break the newly installed wind­
shield; especially when the strain on the glass
caused by the obstruction is increased by such
conditions as wind pressures, extrem es of temp­
erature, motion of the vehicle, etc.
GENERAL MAINTENANCE
PAINTING
1. Thorough cleaning is essential. All corro­
2. Completely remove old paint by use of
3. Apply primer, preferably by spraying, and
4. Apply finish coats:
a. For understructure or other parts not re­
b. To exposed body parts, apply surfacer and
New replacement parts should be thoroughly
Windshield glass is retained in cab opening
When replacing a cracked windshield glass, it
Sec. 1
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