Gear out alignments and worn out gears parts most likely the caused,must be check out and replaces gears parts by those transmission professional like in AMCO,Many,Moe and Jack for transmission repair and replacement of parts
SOURCE: my 2001 f150 super crew won't shift from 2wd to 4h
Best to check by jacking the truck up ( taking safety precautions,
parking brake, chock the wheels, jack stands, etc ), turn the key to
the run position and place into 4WD.
If the front drive shaft turns, the problem is in the transfer case.
If the front drive shaft does not turn, the problem is in the front axle.
I
would suspect the front shaft does not turn, and the most common cause
of this is the vacuum motor on the front axle, the vacuum lines to it,
or the vacuum solenoids.
The vacuum shift motor is what locks the
front wheels in, and without this action, the PM does not get the
confirm that the truck is good to go, and illuminate the cluster
indicators ( 4x4, and if 4L the Low Range lamps ).
There are 2 vacuum solenoids, one is 4WD one is 2WD ( to move the motor one way or the other ).
Start
with checking for vac on the vacuum motor ( actually it is a diaphragm
). The pink line should have vacuum when in 4WD, the blue line should
have vacuum when in 2WD. If not, time to work back towards the
solenoids. Use a short length of hose on the vacuum solenoids, and
retest.
If still missing vacuum on the 4WD solenoid, I would
suspect it is bad, but best to test on the other side of it, to make
sure the vacuum reservoir ( mounted behind the battery box ) is
supplying vacuum to the solenoids.
This is just the most common
cause, best to confirm with the 1st test above, to know if you should
look to the trans case, or axle.
This is what the vacuum shift motor looks like on the front axle
These are the vacuum shift solenoids
Testimonial: "Thank you for your help.I was working on it this morning and found alot of moister in the vacuum shift motor. "
SOURCE: My 2002 GMC Envoy XL
Check to see if any of the other switch selections ( A4WD, 4LO) turn on a light, if not, the problem could be the switch itself or the TCCM (Transfer Case Control Module). If you get a flashing light condition for a switch selection, then the problem could be the actuator on the Transfer Case.
SOURCE: 1998 gmc senoma owner manual
Check this download in 1998 GMC Sonoma Owner's Manual
Hope helps.
From N to 4H
Stop the vehicle completely, place the
transmission in "N" (Neutral) and depress
the brake pedal and the clutch pedal fully
(if equipped), then push in and turn the
switch to shift into "4H".
From 4H to 4H LOCK
You can operate the transfer switch either
when the vehicle is stopped or while the
vehicle is moving.
Position the front wheels straight ahead
and turn the switch to shift into "4H LOCK".
If the vehicle is moving, we recommend
that the speed be less than 100 km/h (60
mph) during this operation.
NOTE:
• When shifting between the transfer
switch position and the transfer gear
position is unmatched, all 4WD indicators
will blink and the buzzer will sound.
• If it is difficult to shift between "4H" and
"4H LOCK" while the vehicle is moving,
try accelerating and decelerating your
vehicle several times after turning the
transfer switch. Be sure to wait until traffic
conditions allow you to accelerate and
decelerate safety before using this procedure.
From 4H LOCK to 4L LOCK
Stop the vehicle completely, place the
transmission in "N" (Neutral) and depress
the brake pedal and the clutch pedal fully
(if equipped), then push in and turn the
switch to shift into "4L LOCK".
From 4L LOCK to 4H LOCK
Stop the vehicle completely, place the
transmission in "N" (Neutral) and depress
the brake pedal and the clutch pedal fully
(if equipped), then push in and turn the
switch to shift into "4H LOCK".
From 4H LOCK to 4H
You can operate the transfer switch either
when the vehicle is stopped or while the
vehicle is moving.
Position the front wheels straight ahead
and turn the switch to shift into "4H". If the
vehicle is moving, we recommend that the
speed be less than 100 km/h (60 mph) during
this operation.
NOTE:
• When shifting between the transfer
switch position and the transfer gear
position is unmatched, all 4WD indicators
will blink and the buzzer will sound.
• If it is difficult to shift between "4H" and
"4H LOCK" while the vehicle is moving,
try accelerating and decelerating your
vehicle several times after turning the
transfer switch. Be sure to wait until traffic
conditions allow you to accelerate and
decelerate safety before using this procedure.
From 4H to N
64J209
Stop the vehicle completely, place the
transmission in "N" (Neutral) and depress
the brake pedal and the clutch pedal fully
(if equipped), then push in and turn the
switch to the mark (1) at the left of the "N"
position, and hold the switch in this posi-
tion for 5 seconds until the "N" indicator
blinks, then turn the switch to the "N" position.
When you turn the transfer switch to the
"N" position, "N" indicator will come on with
the buzzer sound.
CAUTION
• Be sure to stop the vehicle completely
before operating the transfer
switch to shift between "N" and
"4H", or between "4H LOCK" and
"4L LOCK".
• Do not shift between "4H" and "4H
LOCK" unless the front wheels are
in the straight-ahead position and
we recommend that the vehicle
speed be less than 100 km/h (60
mph).
Do not operate the transfer switch
while tires are racing.
• Do not operate your vehicle in "4H
LOCK" or "4L LOCK" on dry, hard
surfaces.
(Continued)
CAUTION
(Continued)
• Do not operate the vehicle while a
4WD mode indicator is blinking
except when shifting between "4H"
and "4L LOCK".
If you operate the vehicle while a
4WD mode indicator is blinking, a
buzzer will sound and the transfer
will shift to "N" (Neutral) to prevent
transfer case damage.
In this case, use the following procedure.
1) Depress the clutch pedal fully (if
equipped) or shift the automatic
transmission gearshift lever to the
"N" position.
2) Turn the transfer switch to the
position previously selected.
3) Operate the transfer switch again.
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