1991 Chevy Chyaene will not go into 4-wheel drive. Transfer gear engages, 12 volts present at front punkin but no light on the 4-wheel drive indicator at the shifter. Have not yet checked the oil level

Depending on the make and model, it could be the control switch on the dash or the switch that moves the gears in the transfer case.

Vehicles: 2002 Chevrolet Trailblazer 4WD 4.2L SFI DOHC 6-cylinder

Your front 4WD Transfer case is low on Gear Oil.
On warm days, the Gear Oil expands slightly, and is less viscous, so the "Service 4WD" light stays off. On colder days/mornings the story changes.

The following paragraph has info applying to the manual differential only:
The 2002 Trailblazer (the first year Chevy made the Trailblazer) has a Front Differential using 1.11 (that's 1 and 1/9th) Quarts Gear Oil, and a Rear Differential with a capacity of 2.29 (thats 2 and 2/7ths) Quarts Gear Oil.
The Gear Oil needed is GM Part No.12345349 or GM Part No.1052931 (they're identical), also known as "GM Synchromesh"(R), which is a type of GLS (Gear Lubricant, Special), also known as "Manual Synchromesh Transmission Fluid 5W30". A synthetic version of which sells for $12.70/qt (USD) at
http://www.amsoil.com/storefront/mtf.aspx

This is not to be confused with 5W30 motor oil (which can be had for $3.00/qt (USD)).

The 2002 Trailblazer 4WD Transfer Case (NV126 Transfer Case) capacity is 0.8 Liters of GM Part No.12378508 (US), also known as "GM Auto Trak II"(R).
Note that one Quart (US) = 0.946 Liter, so 0.8 Liter = 27.06 ounces.

Red Line sells something that they say replaces both GM Synchromesh and GM Auto-Trak II for $12.14/Qt and $44.55/Gal (US) at
http://www.shopwiki.com/Red-Line-MTL-70W80-GL~4-Gear-Oil-%281-Quart%29

13 Manufacturer Recalls apply to the 2002 Chevrolet Trailblazer (model year 2002 was the first year Chevy offered the Trailblazer), and two recalls pertain to the 4WD Transfer Case. Note that one of the recalls applies to only 895 units, so your vehicle is unlikely to be affected by this Transfer Case recall.

2002 Trailblazer Recall ==========================
OCT 17, 2001 ' Recall ID# 54221

Recall Reason POWER TRAIN:TRANSFER CASE (4-WHEEL DRIVE)
Recall Date OCT 17, 2001
Model Affected TRAILBLAZER
Potential Units Affected 78004

Recall Summary
VEHICLE DESCRIPTION: SPORT UTILITY VEHICLES EQUIPPED WITH 4-WHEEL DRIVE. THE CALIBRATION OF THE TRANSFER CASE CONTROL MODULE COULD CAUSE INSUFFICIENT HIGH SPEED GEAR ENGAGEMENT.

Consequence
IF THE GEAR IS NOT ENGAGED, THE VEHICLE CAN ROLL WHEN THE TRANSMISSION IS IN "PARK" AND A CRASH COULD RESULT WITHOUT WARNING.

Remedy
DEALERS WILL UPDATE THE TRANSFER CASE CONTROL MODULE CALIBRATION TO INCREASE GEAR ENGAGEMENT. OWNER NOTIFICATION BEGAN NOVEMBER 6, 2001. OWNERS WHO TAKE THEIR VEHICLES TO AN AUTHORIZED DEALER ON AN AGREED UPON SERVICE DATE AND DO NOT RECEIVE THE FREE REMEDY WITHIN A REASONABLE TIME SHOULD CONTACT CHEVROLET AT 1-800-222-1020 OR GMC AT 1-800-462-8782.

Notes
GENERAL MOTORS CORP. 01064/01065

2002 Trailblazer Recall ============================
SEP 05, 2001 ' Recall ID# 26006

Recall Reason POWER TRAIN:TRANSFER CASE (4-WHEEL DRIVE)
Recall Date SEP 05, 2001
Model Affected TRAILBLAZER
Potential Units Affected 895

Recall Summary
VEHICLE DESCRIPTION: SPORT UTILITY VEHICLES (4 WHEEL-DRIVE). SOME OF THESE VEHICLES WERE BUILT WITH A RANGE SHIFT COLLAR IN THE TRANSMISSION TRANSFER CASE THAT CONTAINS CRACKS.

Consequence
THIS CONDITION COULD RESULT IN A COMPLETE FRACTURE OF THE RANGE SHIFT COLLAR AND SUBSEQUENT LOSS OF VEHICLE FORWARD AND REVERSE GEARS, AND THE INABILITY TO MAINTAIN "PARK" POSITION. THIS INCREASES THE RISK OF A VEHICLE CRASH RESULTING FROM UNINTENDED MOVEMENT OF A PARKED VEHICLE.

Remedy
DEALERS WILL REPLACE THE TRANSFER CASES AND UPDATE THE CONTROL MODULE CALIBRATION. OWNER NOTIFICATION BEGAN SEPTEMBER 6, 2001. OWNERS WHO TAKE THEIR VEHICLES TO AN AUTHORIZED DEALER ON AN AGREED UPON SERVICE DATE AND DO NOT RECEIVE THE FREE REMEDY WITHIN A REASONABLE TIME SHOULD CONTACT CHEVROLET AT 1-800-222-1020 OR GMC AT 1-800-462-8782.

Notes
GENERAL MOTORS CORP. 01061


Read about all (13) 2002 Chevy Trailblazer recalls at:
http://www.internetautoguide.com/10-12-2002-16-1287/2002-chevrolet-trailblazer-recalls.html

replace the 4 wheel drive acuator if in 4wd with selector and the wheels are still free then the acuator is bad even tho you 12v the acuator may not be pulling back to lock in the hub for 4 wd. simply replace it as their is a small spring on the acuater that over time becomes week and can no longer hold the presure that is created when it activated.

check on the frontend, some of the chevys have an electricl controlled vaccum actuator that locks the frontend in, it will be close to the punkin. if the vaccum line is off or has a hole in it, it will not engauge in 4 wheel drive. hope this helps

my 2000 chevy tahoe 4wheel drive light indicator wont stay on even when i tryto angage automatic 4 wheel

Does the vehicle still have 4 wheel drive... or is it just the light that isn't working. I don't mean to insult you, I'm just asking if that's the case. You may just have a burnt out light. Most of these lever shift transfer cases are pretty straight forward, they either work, or they're so busted up inside that they make terrible noise.

Normal thing that happens as long as onone (worked) on it, is the vacume hose going to the engage sevevo under the battery box has fell of on either end or is brocken on the way there. Then the once or now leaky battery acid ate up this same servo. then the cable going to the front axel breaks sticks falls off or even someone needing one climbed under your truck while parked somewhere to get one to replace their brokeen one now you don't have one then theaxel engage arm or gearset is damaged

Front hubs need to be taken off and inspected for damage,
Replace as necessary.

There is a vaccuum operated switch located on the transfer case that sends vaccum to the accuator that pulls a cable that locks the front end in. Check for vac coming in and out of this switch if no vac out replace it. This switch is a very common problem. You can find them at most parts stores in the help section #49315. please rate.

I have a 1999 chevy blazer that stuck in 4 wheel drive. How do you get it out.