GMC 4000 Series Service Manual page 472

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information pertaining to fuel filters and fuel pumps.
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GENERAL DESCRIPTION
FUEL TANK MOUNTINGS
In general, fuel tanks are located on side of
chassis and lay lengthwise to frame side rail. A
mounting of two metal straps anchor tanks to mount­
ing brackets which are bolted to frame side mem­
ber. Metal-to-metal contact between tank and
brackets and straps is prevented by use of anti­
squeak material.
FUEL TANK CONSTRUCTION
Typical frame mounted tanks consist of an
upper and lower half, each with a wide flange and
baffles which are pressed into the tank halves. The
two tank sections are seam-welded at the flange
around the entire tank to assure leakproof con­
struction. Exceptional stiffness is secured by the
combination of the welded flanges and depressed
ribs in both upper and lower tank sections. Baffle
plates are incorporated to provide additional stiff­
ness and to prevent the surging of gasoline within
the tank.
FILLER CAPS AND NECKS
Fuel tank filler caps and neck assem blies con­
form to the latest S.A.E. Standards for filler caps
and related filler neck cam s. Upper and lower
filler necks vary as to size, length, and shape,
depending on model requirements. Filler necks
are treated so that rust will not form and get into
the fuel system . In general, lower filler necks are
first bolted or riveted to the tank and then sweat
soldered in place to eliminate any possibility of
leakage. All tanks are equipped with a vented filler
neck cap.
FUEL PICKUP PIPE
The fuel pickup pipe is built integrally with
the tank gauge unit, located at the top of the tank
G M C S E R V I C E M A N U A L
SECTION 8
8A Fuel T a n k .........................................................
8B Exhaust System ..............................................
NOTE: Refer to ENGINE FUEL SYSTEM (SEC. 6M) for
SECTION 8A
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Page No.
in line with safety recommendations. A large area,
fine-m esh screen is located on the bottom of the
fuel pickup pipe. This screen is designed to pre­
vent the entrance of dirt or water into the fuel
system . See "Fuel Gauge System" later in this
section for complete description of tank sending
unit.
FUEL TANK REPLACEMENT
DRAINING FUEL TANK
If fuel tank does not incorporate a drain plug,
it will be necessary to siphon fuel from tank. The
following procedure is recommended:
1. Obtain an 8 to 10-foot length of 3/8", or
slightly less, I.D. hose and cut a flap type slit 18"
from one end. Refer to figure 1.
NOTE: Hose with larger than 3/8" I.D. is not
recommended as it is difficult to erect and main­
tain a siphon using this method with a larger hose.
2. Insert a small nipple (at least 1/8" larger
O.D. than the hose I.D.) into opposite end of hose
from slit.
3. Insert nipple end of hose into tank until it
strikes bottom.
4. With the opposite end of the hose in a suit­
able container which is positioned below bottom of
fuel tank, insert an air pressure hose nozzle into
CUT SLIT TO
A C C O M O D A T E AIR CHUCK
PIPE NIPPLE
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Figure 1— Tank Siphon Construction
Sec. 8A
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— FUEL FLOW — ►
( L -----------1 8 " ----------
10 FT. -------------------------
T -5 7 6 3