Chevrolet 1991 Light Duty Truck Operating instructions

TRUCKS
CHEVROLET

.— - ------- —■*“

FOREWORD
This manual includes procedures involved in disassembly and assembly of components
listed in the "Table of Contents.
This manual should be kept in a handy place for ready reference. If properly used, it will .
meet the needs of technicians and vehicle owners.
CAUTION:
These vehicles contain some parts dimensioned in the metric system as well as in the
customary system. Some fasteners are metric and are very close in dimension to familiar
customary fasteners in the inch system. It is important to note that, during any vehicle
maintenance procedures, replacement fasteners must have the same measurements and
strength as those removed, whether metric or customary. (Numbers on the heads of metric
bolts and on surfaces of metric nuts indicate their strength. Customary bolts use radial lines
for this purpose, while most customary nuts do not have strength markings.) Mismatched or
incorrect fasteners can result in vehicle damage or malfunction, or possibly personal injury.
Therefore, fasteners removed from the vehicle should be saved for re-use in the same loca
tion whenever possible. Where the fasteners are not satisfactory for re-use, care should be
taken to select a replacement that matches the original. For information and assistance, see
your authorized dealer.
CHEVROLET MOTOR DIVISION
.General Motors Corporation
Warren, Mic igan
No part of this publication may be reproduced, stored in any retrieval system or transmit
ted, in any form or by any means, including but not limited to electronic, mechanical, photo
copying, recording or otherwide, without the prior written permission of the Chevrolet Motor
Division of General Motors Corp. This includes all text, illustrations, tables and charts.

CAUTION
To reduce the chance of personal injury and/or property damage, the fol
lowing instructions must be carefully observed.
Proper service and repair are important to the safety of the service techni
cian and the safe, reliable operation of all motor vehicles. If part replacement
is necessary, the part must be replaced with one of the same part number or
with an equivalent part. Do not use a replacement part of lesser quality.
The service procedures recommended and described in this service man
ual are effective methods of performing service and repair. Some of these
procedures require the use of tools specially designed for the purpose.
Accordingly, anyone who intends to use a replacement part, service pro
cedure or tool, which is not recommended by the vehicle manufacturer,
must first determine that neither his safety nor the safe operation of the
vehicle will be jeopardized by the replacement part, service procedure or
tool selected.
It is important to note that this manual contains various Cautions and No
tices that must be carefully observed in order to reduce the risk of personal
injury during service or repair, or the possibility that improper service or
repair may damage the vehicle or render it unsafe. It is also important to
understand that these ‘Cautions’ and ‘Notices’ are not exhaustive, because
it is impossible to warn of all the possible hazardous consequences that
might result from failure to follow these instructions.

1991
LIGHT TRUCK
UNIT REPAIR
MANUAL
When reference is made in this manual to a brand name, number, or specific tool, an equivalent
product may be used in place of the recommended item.
All information, illustrations, and specifications contained in this manual are based on the latest
product information available at the time of publication approval. The right is reserved to make
changes at any time without notice.
ST 333-91
©1990 General Motors Corporation
Printed in U.S.A. June, 1990
All rights reserved

TABLE OF CONTENTS
The Table of Contents on this page indicates the sections covered in this manual. At the beginning of each
individual section is a Table of Contents which gives the page number on which each major subject begins.
SECTION SUBJECT CONTENTS
nGENERAL OA GENERAL INFORMATION
UINFORMATION
1B1 A6 AIR CONDITIONING 1B4 HR-6HE AIR CONDITIONING
COMPRESSOR COMPRESSOR
AAIR 1B2 V5 AIR CONDITIONING 1B5 SD-709 AIR CONDITIONING
1CONDITIONING COMPRESSOR COMPRESSOR
1B3 R-4 AIR CONDITIONING
COMPRESSOR
3STEERING 3B2 MANUAL STEERING GEAR 3B3 POWER STEERING
4B REAR AXLE 4C FRONT AXLE
4B1 7 1/2 and 7 5/8-INCH RING GEAR 4C1 8 1/2-INCH RING GEAR
4B2 8 1 /2-INCH RING GEAR 4C2 9 3/4-INCH RING GEAR
4B3 9 1 /2-INCH RING GEAR 4C3 7 1/4-INCH RING GEAR
4 AXLE 4B4 10 1/2-INCH RING GEAR 4C4 8 1/4 AND 9 1/4-INCH RING
4B5 DANA REAR AXLES GEAR
4B6 12 INCH RING GEAR 4C5 ALL WHEEL DRIVE—7 1/4-INCH
(ROCKWELL) RING GEAR
4B7 LOCKING DIFFERENTIALS
5 BRAKES 5 BRAKES
6ENGINE 6C THROTTLE BODY INJECTION
6A GENERAL ENGINE UNITS
-6A1 2.5L L4 ENGINE 6C1 TBI UNIT MODEL 220
6A2 2.8L V6 ENGINE 6C2 TBI UNIT MODEL 700
6ENGINE 6A3 4.3L V6 ENGINE 6D ENGINE ELECTRICAL
6A5 V8 ENGINES 6D1 SI SERIES GENERATORS
6A7 6.2L DIESEL ENGINE 6D2 CS-144 GENERATOR
6D3 SD STARTING MOTORS
6D4 DISTRIBUTORS
7A AUTOMATIC TRANSMISSION 7D TRANSFER CASE
7A1 4L60 AUTOMATIC 7D1 NEW PROCESS 205 TRANSFER
TRANSMISSION CASE
(7A2) 4L80E AUTOMATIC 7D2 NEW PROCESS 241 TRANSFER
7 TRANSMISSIONS TRANSMISSION CASE
7B1 5LM60 MANUAL TRANSMISSION 7D3 NEW PROCESS 231 TRANSFER {
7B2 117 MANUAL TRANSMISSION CASE
7B3 BORG-WARNER T5 MANUAL
TRANSMISSION

GENERAL INFORMATION OA-1
SECTION OA
GENERAL INFORMATION
CONTENTS
SUBJECT PAGE
0A- 1
OA- 1
0A- 1
0A- 2
0A- 3
0A- 3
0A- 3
0A» 4
OA- 5
0A- 5
OA-15
OA-16
Service Parts Identification Label
Vehicle Identification Number
Certification Label
Engine Identification Number
llansmission Identification Number
Model Reference
Metric Fasteners
Fastener Strength Identification
Six Lobed Socket Head Fasteners
Prevailing Torque Fasteners
Conversion Table
Decimal and Metric Equivalents
SERVICE PARTS
IDENTIFICATION LABEL
The truck service parts identification label is provided
on all models (figure 1). It is located on the inside of
the instrument panel compartment (or on an inner body
panel for Forward Control models). The label lists the
VIN (Vehicle Identification Number), wheelbase, paint
information and all production options or special equip
ment on the vehicle when it was shipped from the
factory. ALWAYS REFER TO THIS INFORMATION
WHEN ORDERING PARTS.
VEHICLE IDENTIFICATION
NUMBER
The VIN is the legal identifier of the vehicle. On all
models except the Forward Control, it is located on a
plate which is attached to the left top of the instrument
panel and can be seen through the windshield from the
outside of the vehicle (figure 2). On Forward Control
models, the plate is mounted to the top of the radiator
2
1. VIN 6 5
2. Wheel Base 5. RPO/SEO Codes
3. Model Number 6. Exterior Color WA Numbers
4. Order Number 7. Paint System pcArr
support. To find out the manufacturer, model and chas
sis type, engine type, GVW range, model year, plant
code, and sequential number, refer to figure 3.
CERTIFICATION LABEL
The certification label shows the GVWR, the front
and rear GAWRs, and the payload rating for the vehicle
(figure 4).
Gross Vehicle Weight (GVW) is the weight of the
orginally equipped vehicle and all items added to it
after it has left the factory. This would include bodies,
winches, booms, etc.; the driver and all occupants, and
the load the vehicle is carrying. The GVW must not
exceed the GVWR. Also, the front and rear gross axle
weights must not exceed the front and rear GAWRs.
The payload rating shown on the label is the maxi
mum allowable cargo load (including the weight of the
driver and all occupants) that the vehicle can carry
1. Typical VIN
F7557
Figure 1—Service Parts Identification Label Figure 2—VIN Location

OA-2 GENERAL INFORMATION
VEHICLE INDENTIFICATION NUMBER
(VIN)
Nation of Origin
1 - U S Built
2 - Canadian Built
3 * Mexican Built
Manufacturers
G « General Motors
Code Make
A Chevrolet Bus*
B Chevrolet Incomplete
C Chevrolet Truck
D GMC Incomplete
H Oldsmobile MPV
J GMC Bus*
K GMC MPV
N Chevrolet MPV
T GMC Truck
* Van seating exceeds
10 passengers
~ T H ,
Code Series
1'k Ton
2 ^ Ton
3 1 Ton
GVWR/BRAKE SYSTEM
Code GVWR Range Brake System
B3001-4000 Hydraulic
C4001-5000 Hydraulic
D5001-6000 Hydraulic
E6001-7000 Hydraulic
F7001-8000 Hydraulic
G6001-9000 Hydraulic
H9001-10,000 Hydraulic
J10,001-14,000 Hydraulic
K14,001-16,000 Hydraulic
Code Body Type
0Chassis Only
1Hi-Cube/Cutaway Van
2Forward Control
3Four-Door Cab/Utility
4Two-Door Cab
5 Van
6 Suburban
7Motor Home Chassis
8Utility (Blazer/Jimmy)
9Extended Cab/
Extended Van
Code Year
M1991
Assembly Plant
B Baltimore, MD
E Pontiac East, Ml
F Flint, Ml
J Janesville, Wl
S St. Louis, MO
V Pontiac, Ml
Z Fort Wayne, IN
0 Pontiac, Ml
1 Oshawa, ON
2 Moraine, OH
3 Detroit, Ml
4 Scarborough, ON
5 London, ON
7 Lordstown, OH
8 Shreveport, LA
Line and C assis Type
C assis
Code Line Type
C Conventional Cab 4x2
RConventional Cab 4x2
D Military Truck 4x4
KConventional Cao 4x4
VConventional Cab 4x4
GVan 4x2
P Forward Control 4x2
S Sm Conventional Cab 4x2
TSm Conventional Cab 4x4
MSm Van 4x2
L Sm Van 4x4
HChassis Cutaway 4x2
Engine Type and Make
Code Producer Type RPO
ACPC 2.5L L4 EFI L38
BCPC 4.3L V6EFI LU2
CCPC 6.2L V8 Diesel LH6
ECPC-North 2.5L L4 EFI LN8
HCPC 5.0L V8 EFI L03
JCPC 8.2LV8 Diesel LL4
KCPC S.7LV8EFI LOS
NCPC 7.4L V8 EFI L19
RCPC 2.8LV6EFI LL2
ZCPC 4.3L V6 EFI LB4
F8850
Figure 3—Vehicle Identification Number
19 I 2/86
MFD. BY GENERAL MOTORS CORPORATION
anm Mum IT MW* M
U/ftf
ra n 4649/21 OS 2100/953 260MB 80
P195/75R15 — Pm /75R 15
M l 15 X 6 JJ ^m i5 « f a u
m /ift CeU 35/241 ^ f » 3 5 / w r
WAX TIM i X 4T
AL L APPLICABLE FEDE-
|Cl.TSAFETY STANDARDS IN EFFECT
MANUFACTURE SHOWN ABOVE.
100001 MPV
T IS VtMCli m i FM 1000/453 IBS. PATUMO
SEE OWNER’S MANUAL FOR ADDITIONAL INFORMATION
F0597
Figure 4—Certification Label
based on all factory installed equipment on the vehicle.
The payload rating is reduced if any accessories or
other equipment is added to the vehicle after final date
of manufacture. The weight of these items should be
determined and deducted from the payload rating.
The vehicle may also have a GCWR (Gross Combi
nation Weight Rating). The GCW (Gross Combination
Weight) is the total weight of the loaded tow vehicle
(including passengers) and a loaded trailer.
The tires on the vehicle must be the proper size and
properly inflated for the load being carried. The vehicle
certification label shows the originally equipped tire
size and recommended inflation pressures.
On C/K and R/V trucks, M vans and G vans, the
certification label is located on the trailing edge of the
driver’s door. On S/T trucks, it is located on the door
lock pillar on the driver’s side. The label for Forward
Control models is shipped separately and installed by
the body manufacturer.
ENGINE IDENTIFICATION
NUMBER
Refer to figures 5, 6, 7, 8 and 9 to determine the
location of the engine identification number.

GENERAL INFORMATION OA-3
TRANSMISSION IDENTIFICATION
NUMBER
Refer to figures 10 through 13 for determining trans
mission identification numbers and code meanings.
MODEL REFERENCE
Refer to figures 14 through 19 for determining the
vehicle model. C, R, and S models are two wheel
drive. K, V, and T models are four wheel drive.
METRIC FASTENERS
The vehicle models are primarily dimensioned in the
metric system. Many fasteners are metric and are very
close in dimension to well-known customary fasteners
in the inch system. It is most important that replace
ment fasteners be of the correct nominal diameter,
thread pitch and strength.
Original equipment metric fasteners (except “beau
ty bolts, such as exposed bumper bolts, and cross
recess head screws) are identified by a number mark
ing indicating the strength of the material in the fasten
er as outlined later. Metric cross recess screws are
identified by a Posidriv or Type 1A shown in figure 20.
Either a Phillips head or Type 1A cross recess screw
driver can be used in Posidriv recess screw heads, but
Type 1A cross recess screwdrivers will perform better.
NOTICE: Most metric fasteners have a
blue color coating. However this should not
be used as positive identification as some
fasteners are not color coated.
General Motors Engineering Standards, along with
other North American Industries, have adopted a por
tion of the standard metric fastener sizes defined by
ISO (International Standards Organization). This was
done to reduce the number of fastener sizes used and
yet retain the best strength qualities in each thread
Figure 6—2.8L Engine I.D. Location
size. For example, the customary 1/4-20 and 1/4-28
screws are replaced by the metric M6.X1 screw which
has nearly the same diameter and has 25.4 threads
F7552
I.D.
I.D. (Optional Location)
Figure 7—4.3L Engine I.D. Location

OA-4 GENERAL INFORMATION
1. Engine I.D.
2. Engine I.D. (Optional Location) F7553
Figure 8—5.0L, 5.7L, 7.4L Engine I.D. Location
Figure 9—6.2L Diesel Engine I.D. Location
per inch. The thread pitch is in between the customary
coarse and fine thread pitches.
Metric and customary thread notation differ slightly.
The difference is shown in figure 21.
FASTENER STRENGTH
IDENTIFICATION
Most commonly used metric fastener strength proper
ly classes are 9.8 and 10.9 with the class identification
embossed on the head of each bolt. Customary (inch)
strength classes range from grade 2 to 8 with radial
line identification embossed on each bolt head. Mark-

GENERAL INFORMATION OA-5
JULIAN DATE
(OR DAY OF THE YEAR)
MODEL YEAR
<1 -1991) [HYDRA MATIC 4L601
TczT
1 .YK, M 209 ,A^
MODEL SHIFT BUILT
A & B » FIRST SHIFT
C 4 H - SECOND SHIFT
1. Transmission I.D. Location
F9368
Figure 10—Hydra-matic 4L60 Transmission
I.D.Location
ings correspond to two lines less than the actual grade
(i.e.grade 7 bolt will exhibit 5 embossed radial lines on
the bolt head). Some metric nuts will be marked with
single digit strength identification numbers on the nut
face. Figure 20 shows the different strength markings.
When replacing metric fasteners, be careful to use
bolts and nuts of the same strength or greater than the
original fasteners (the same number marking or high
er). It is likewise important to select replacement fas
teners of the correct size. Correct replacement bolts
metric fasteners available in the aftermarket parts
channels were designed to metric standards of coun
tries other than the United States, and may be of a
lower strength, may not have the numbered head mark
ing system, and may be of a different thread pitch. The
metric fasteners used on GM products are designed to
new, international standards that may not yet be manu
factured by some non-domestic bolt and nut suppliers.
In general, except for special applications, the common
sizes and pitches are:
M6 x 1
M8 x 1.25
M10 x 1.5
M12 x 1.75
SIX LOBED SOCKET
HEAD FASTENERS
Six lobed socket head (Torx) fasteners are used in
some applications on vehicles covered in this manual
(figure 22). The door striker bolt is of this design.
Tools designed for these fasteners are available com-
1. Transmission I.D. Location
MODEL YEAR
(1-1991)
1
BUILD DAY OF MONTH
01 . 1ST DAY
15-1 5TH DAY
N T B 1 7
BUILO MONTH
A - JANUARY
B - FEBRUARY
HM 117 C - MARCH
D - APRIL
E - MAY
H - JUNE
K - JULY
M - AUGUST
P - SEPTEMBER
R - OCTOBER
S - NOVEMBER
T - DECEMBER
2. Transmission Identification Tag
OXXY
—I SERIAL NUMBER I
HjMUNCNE
610XXYMXXXXXX
F9371
Figure 11— Hydra-matic HM-117 Transmission
I.D.Location
mercially. However, in some cases, if the correct tool is
not available, a hex socket head wrench may be used.
PREVAILING TORQUE FASTENERS
A prevailing torque nut is designed to develop an
interference between the nut and bolt threads. This is
most often accomplished by distortion of the top of an
all-metal nut by using a nylon patch on the threads in
the middle of the hex flat. A nylon insert may also be
used as a method of interference between nut and bolt
threads (figure 23).
A prevailing torque bolt is designed to develop an
interference between bolt and nut threads, or the
threads of a tapped hole. This is accomplished by dis
torting some of the threads or by using a nylon patch
or adhesive (figure 23).
RECOMMENDATIONS FOR REUSE:
1. Clean, unrusted prevailing torque nuts and bolts
may be reused as follows:
a Clean dirt and other foreign material off the nut
or bolt.

OA-6 GENERAL INFORMATION
2. Transmission Identification Tag
I MODEL |
oxxu
| SERIAL NUMBER [—
p | plan tT
Hm u n c ie '
61OXXUMXXXXXX
F9372
CALENDAR YEAR
BUILT
I MODEL LETTERS I
MODEL
YEAR
I JULIAN DATEl
HYDRA-MATIC
SERIAL NO. 0*V. OF GEN. MTRS CORP.
.9 1, . ,BCP
MODEL
LETTERS
1. Transmission I.D. F9135
Figure 13—Hydra-Matic 4L80E Transmission
i.D.Location
Figure 12—Hydra-matic 5LM60 Transmission
I.D.Location
b. Inspect the nut or bolt to insure there are no
cracks, elongation, or other signs of abuse of
overtightening. (If there is any doubt, replace
with a new prevailing torque fastener of equal
or greater strength.)
c. Assemble the parts and hand start the nut or
bolt.
d. Observe that, before the fastener seats, it
develops torque per the chart in figure 23. (If
there is any doubt, replace with a new prevail
ing torque fastener of equal or greater
strength.)
e. Tighten the fastener to the torque specified in
the appropriate section of this manual.
2. Bolts and nuts which are rusty or damaged should
be replaced with new parts of equal or greater
strength.

GENERAL INFORMATION OA-7
R-V MODELS
Pickup, Bonus/Crew Cab
—/qm2
— U
Utility Vehicle
Jimmy (Blazer)
F7558
Suburban
Figure 14—R/V Models

OA-8 GENERAL INFORMATION
G VAN MODELS
Rally (Sportvan)
Cutaway Van
Extended Van
h ~Tl- ** ] -s
[ a | c |
L_
“ g fc/ ------------------ — X W "
Vandura (Chevy Van)
Magnavan (Hi-Cube Van)
F7569
Figure 15—G Models

GENERAL INFORMATION 0Ah9
Value Van (Step Van)
(Aluminum)
Value Van (Step Van)
(Steel)
GIP Cutaway Cab
P MODELS
Motor Home Chassis
Forward Control Chassis
F7570
Figure 16—P Models
F4481
Figure 17—C/K Models

0A-10 GENERAL INFORMATION
S/T PICKUP, EXTENDED CAB
4 DOOR S/T UTILITY VEHICLE
JIMMY (BLAZER)
S/T UTILITY VEHICLE
JIMMY (BLAZER)
S/T CHASSIS CAB
F9136
S/T PICKUP, REGULAR CAB
Figure 18—ST Models

GENERAL INFORMATION OA-11
PASSENGER VAN
CARGO VAN
EXTENDED VAN
F9134
Figure 19—M Models
1. Grade 2 (GM 200-M)
2. Grade 5 (GM 280-M)
3. Grade 7 (GM 290-M)
4. Grade 8 (GM 300-M)
5. Manufacturer’s Identification
6. Nut Strength Identification
7. Identification Marks (Posidriv Screw Head)
___________________________________ F0695
Figure 20—Bolt and Nut Identification
1. Customary Bolt—Va-20
2. Metric Bolt—M6.0x1
A. Vd-inch
B. 6 mm
C. 20 Threads Per Inch
D. 1 Thread Per Millimeter
(25.4 Threads Per Inch) F0705
Figure 21—Thread Notation

OA-12 GENERAL INFORMATION
E - External Drive
______________________________________ B2221
Figure 22—Six Lobed Socket Head Fasteners

GENERAL INFORMATION OA-13
(I°I)
8
6
o
A
6 & 6.3 8 10 12 14 16 20
4,5 Nm 0.4 0.8 1.4 2.2 3.0 4.2 7.0
In. Lbs. 4.0 7.0 12 18 25 35 57
1,2, 3, 6,
7, 8,9 Nm 0.4 0.6 1.2 1.6 2.4 3.4 5.6 In. Lbs. 4.0 5.0 10 14 20 28 46
B
.250 .312 .375 .437 .500 .562 .625 .750
4,5 Nm 0.4 0.6 1.4 1.8 2.4 3.2 4.2 6.2
In. Lbs. 4.0 5.0 12 15 20 27 35 51
1,2, 3, 6,
8.9 Nm 0.4 0.6 1.0 1.4 1.8 2.6 3.4 5.2
In. Lbs. 4.0 5.0 9.0 12 15 22 28 43
A. Metric Sizes
B. Inch Sizes 1. Top Lock Type
2. Center Lock
3. Dry Adhesive Coating
4. Out Of Round Thread
5. Deformed Thread Profile
6. Nylon Strip Or Patch
7. Nylon Washer Insert
8. Nylon Patch
9. Nylon Insert
B2406
Figure 23—Torque Nuts and Bolt Chart
P

Figure 24—Conversion Table
CONVERSION TABLE
Multiply by to get equivalent number of: Multiply to get equivalent
by number of:
LENGTH ACCELERATION
Inch
Foot 25.4
0.304 8 millimeters (mm)
meters (m) Foot/sec2
Inch/sec2 0.304 8 meter/sec2 (m/s2)
0.025 4 meter/sec2
Yard
Mile 0.9144 meters TORQUE 1.609
AREA kilometers (km) Pound-inch
Pound-foot 0.112 98 newton-meters (Nm)
1.355 8 newton-meters
Inch2 645.2
6.45
0.092 9
0.836 1
VOLUME
millimeters2 (mm2)
centimeters2 (cm2)
meters2 (m2)
meters2
POWER
Foot2
Yard2
Horsepower 0.746 kilowatts (kW)
PRESSURE OR STRESS
Inches of water
Pounds/sq. in. 0.2491 kilopascals (kPa)
6.895 kilopascals
ENERGY OR WORK
Inch3 16.387
16.387
0.0164
liters
3.785 4
mm3
Quart 0.946 4
Gallon
liters (I)
liters
BTU
Foot-pound
Kilowatt-hour
1 055 joules (J)
1.355 8 joules
3 600 000 joules (J * one W)
Yard3 0.764 6
MASS meters3 (m3) or 3.6 x 10®
LIGHT
Pound
Ton 0.4536 907.18 kilograms (kg)
kilograms (kg) Foot candle 1.076 4 lumens/meter2 (Im/m2)
FUEL PERFORMANCE
Ton 0.907
FORCE tonne (t) Miles/gal
Gal/mile 0.425 1 kilometers/liter (km/l)
2.352 7 liter/kilometer (l/km)
Kilogram 9.807 newtons (N) VELOCITY
Ounce 0.2780 newtons Miles/hour 1.609 3 kilometers/hr. (km/h)
Pound 4.448 newtons
TEMPERATURE
Degree
Fahrenheit (t°F-32)-r 1.8 degree Celsius (C)
OA-14 GENERAL INFORMATION