bwfci

in my 2002 chevrolet silverado with a 4.3 l v-6, which i just bought
used with
46,000 miles, a
strange problem, occurs whether in 1st, 2nd 3rd or 4th gear,
while driving, at around rpm 1100 very noticable engine vibration will
occur. if i keep at that speed (rpm stays the same), vibration will
be constant. if i increase or decrease speed (rpm), vibration will
disappear.

mechanic friend says all chevy 4.3 's have similar problems/qirks

hoping someone will access to TSB's can look it up.

many thanks

bwfci

received email from someone, as below. i am posting it incase anyone
else has similar problem. looks to be a common issue.
================================================== ========
it is the v6 and the exhaust heres the bulletin ,steve

Exhaust Moan/Vibration (Install Exhaust System Flex Pipe Kit)
#02-06-05-003C - (02/05/2004)
Exhaust Moan/Vibration (Install Exhaust System Flex Pipe Kit)
1999-2004 Chevrolet Silverado 1500 Series Extended Cab or Regular
Cab/Long
Box Pickups (New Style)

1999-2004 GMC Sierra 1500 Series Extended Cab or Regular Cab/Long Box
Pickups (New Style)

with 4.3L Engine (VINs W, X-- RPOs L35, LU3) and Automatic
Transmission (RPO
M30)

This bulletin is being revised to add the 2004 Model year. Please
discard
Corporate Bulletin Number 02-06-05-003B (Section 06 --
Engine/Propulsion
System).

Condition
Some customers may comment on a moan or vibration at low vehicle
speeds
between 900-1200 RPM under load.

Cause
Exhaust system resonance that is transmitted through the powertrain
mounts
into the body may cause this condition.

Correction
An exhaust system flex pipe kit is available to correct this
condition. If
diagnosis leads to this condition, install the applicable exhaust
system
flex pipe kit listed below using the following procedure. Refer to the
Parts
Information for kit applications and usage.


Important
This fix and the kit part numbers are specific to vehicle frame type.
A
Level 3 frame was introduced interim 2000 model year (approximately
January
2000). With a Level 3 frame, the transmission crossmember was moved
forward
of its previous location. Pre-Level 3 frames will require the
installation
of additional components to correct the condition.


1999-2000 4WD Models Built Prior to 1/20/00 and All 2000-2004 2WD and
4WD
Models Built After 1/00
These models only require the installation of a flex coupling. The
flex
coupling has adapter sleeves for the installation of U-bolt clamps.
This
procedure uses the U-bolt clamps, but the preferred installation
method is
to weld the flex coupler to the exhaust pipe.

1.. Raise the vehicle.
2.. Locate the first available straight section of pipe rearward of
the
mid-joint flange and forward of the muffler assembly.
3.. Measure approximately 228 mm (9 in) on the straight pipe and
mark.
4.. Using a suitable cutting tool, cut out the marked section of the
pipe
and remove.
5.. Remove any burrs, if necessary, before installing the flex
coupler
pipe.

6.. Install the flex coupling (1). Expand the sleeves of the flex
coupler,
if necessary, to properly fit over each pipe end. The centerline of
the
installed flex coupling should run parallel to the straight section of
pipe
(no bends in the coupling) for optimum performance.
7.. Install the U-bolt clamps (2) on each sleeve end of the flex
coupling.
Tighten
Tighten the U-bolt clamps to 30 N·m (22 lb ft).

8.. Lower the vehicle.
1999-2000 2WD Models Built Prior to 1/00
These models will require the installation of a flex coupler, two
Y-pipe
support brace rods w/integral U-bolt clamp assemblies on the LH and RH
sides
of the transmission rear mount and new transmission mount studs and
nuts.
The Y-pipe support braces are used in combination with the flex
coupler to
reduce exhaust moan.

1.. Install the flex coupler using steps 1-7 of the above procedure.
2.. Support the transmission with a suitable adjustable jack stand.
3.. Remove the two bolts and nuts from the transmission rear mount.
4.. Position the transmission rear mount and install two new studs
to the
mount.
5.. Install the new studs supplied with the kit to the transmission
mount.

6.. Loosely position the Y-pipe support braces w/integral U-bolt
clamps
(LH and RH) to the underside of the transmission rear mount and the
crossover pipe as shown. The top ends of the braces attach to the
underside
of the transmission rear mount. The bottom ends of the braces attach
to the
crossover pipe using the integral U-bolt clamps. The braces support
the LH
leg of the Y-pipe where it crosses over the vehicle to meet the Y-pipe
collector.
7.. Install the two nuts to the transmission rear mount and the two
nuts
to the U-bolt clamps. Tighten
a.. Tighten the new transmission mount nuts to 25 N·m (18 lb ft).
b.. Tighten the two U-bolt clamps to 30 N·m (22 lb ft).
8.. Lower the vehicle.
Parts Information
Part Number
Description
Usage

15076982
Exhaust System Parts Package
1999-2000 2WD Models Built Prior to 1/00

15076990
Exhaust System Parts Package
a.. 1999-2000 4WD Models Built Prior to 1/20/00
b.. All 2000-2004 2WD and 4WD Models Built After 1/00


a.. Kit P/N 15076982 includes a flex coupler, two support brace rods
w/integral U-bolt pipe clamps, two U-bolt pipe clamps (for use with
flex
coupler) and two new transmission mount studs w/fasteners.
b.. Kit P/N 15076990 includes a flex coupler and two U-bolt pipe
clamps.