ENGINE SUPPORT
Weak link: Engine crossmember
Models affected: '73-'84 trucks and SUVs
What happens: Snowplowing or hard trail use flexes the frame enough to completely break or crack the engine crossmember.
Sturdy fix: There are several options. You can build a new crossmember, weld the broken one, or replace it with an '85-and-up crossmember, which is a better design and less prone to cracking. The challenge, though, is that it is almost impossible to remove the crossmember from a donor vehicle unless the engine is already out of the vehicle. Missouri Off Road Outfitters offers a bolt-in replacement crossmember for vehicles lifted more than 4 inches (shown), and as a bonus it also facilitates the use of a straight drag link in crossover-steering conversions.
Contact: Missouri Off Road Outfitters.
SAGGY DOORS
Weak link: Door hinges
Models affected: '88-and-up trucks and SUVs
What happens: The door hinges on pre-'88 models wore out fast, but the '88-and-up hinges wear even faster. When they wear, they cause door misalignment. This problem is even more prevalent on lifted trucks where the door is used as a grab handle for passengers to enter the vehicle.
Sturdy fix: Replace the hinge pins and bushings.
Contact: Your GM part supplier or your local body shop.
WEAK IDLER ARM
Weak link: Steering system two-bolt idler arm
Models affected: '88-'92 trucks and SUVs
What happens: The two-bolt idler arm is not very stout, and it wears quickly.
Sturdy fix: Replace the two-bolt idler arm with a later model three-bolt idler arm. The swap requires drilling a new hole at the point where it mounts to the frame, but it uses the same end at the steering system, so it is a retrofit. The three-bolt idler arm is much stouter and heavier than the two-bolt idler arm.
Contact: Your local GM dealer to order the three-bolt idler arm.
DRIVE SLEEVE
Weak link: Drive sleeve connecting either the Turbo 350 or SM465 transmissions to the NP205 transfer case
Models affected: '84-and-older
What happens: In normal off-highway use they don't usually break, but once they start to wear they tend to break quickly. When the internal drive-sleeve splines strip, the transmission is effectively disconnected from the transfer case. In this photo you can see a worn drive sleeve (left) compared to a new drive sleeve.
Sturdy fix: Replace with a new drive sleeve, available from Off Road Design.
Contact: Off Road Design.
STEERING WOBBLE
Weak link: Steering column tilt assembly
Models affected: '73-'91 vehicles equipped with tilt steering.
What happens: As these trucks age, the tilt assembly comes loose and wobbles. Most people believe that the column is worn out, but this is not the case. For some reason, GM did not use thread-lock on the four screws on the tilt assembly so they loosen, causing the wobble. This is especially found on lifted trucks where the steering column is used as a grab handle during entry.
Sturdy fix: Disassemble the steering column and reinstall the four screws using thread-lock compound. This will permanently solve the problem.
Contact: Do-it-yourself fix.
4WD FAILURE
Weak link: Thermal Linear Actuator
Models affected: '88-'98 trucks and SUVs
What happens: An overly complex device called the Thermal Linear Actuator (TLA) fails, and four-wheel drive won't engage. See, when you engage the transfer case, the left-front axle begins to turn, and the TLA is engaged. The TLA creates an electrical current that heats an inert gas, causing it to expand and move a plunger. The left axle and intermediate shaft are connected by spider gears in the differential, and the thermal actuator, once heated enough, extends approximately 1 inch to slide the shift collar and fork over the intermediate shaft to connect it to the right-front axle. Other drawbacks to the TLA include the fact that four-wheel-drive engagement can slow considerably in cold weather and it can disengage if submerged in water.
Sturdy fix: Sure, you can replace the TLA with a new unit, but the hot ticket is to eliminate this horrible idea altogether and install the 4x4 Posi-Lok (shown). It allows the driver to engage the shift collar and fork from inside the cab with simply a 1-inch pull on the 4x4 Posi-Lok cable. As a bonus, it allows you to disengage the front axle when in low-range, thus allowing two-wheel-drive low-range operation.
Contact: 4x4 Posi-Lok.