Common problems · 1973–91
Square Body K5 Blazer problems: 8 things to check
The problems owners and specialists flag most on the Chevrolet K5 Blazer (1973–1991), the repairs they end up doing and what those cost, plus the years and recalls to watch. Sourced, not scraped.
Square Body K5 Blazer problems to check before you buy
- Frame cracks at the steering boxThis is the classic K5 fault. On CK5 and GMSquareBody, owners say the frame cracks around and behind the steering-box bolts, often on the inside of the rail. You may not see the cracks with the box bolted on. Unbolt it if you can, or have someone rock the steering wheel while you watch for the frame moving. A properly welded reinforcement plate is fine; a bolt-on brace over an old crack isn't a fix.
- Rust in the usual placesCK5 members list the rockers, the front floor and the front seat-belt anchors, the rear wheel arches, the tail pan, the bottoms of the doors and tailgate, the cab mounts and the rear floor supports by the tailgate hinges. Pull up the carpet and smell for mildew. If the paint is bubbling from outside, the rust underneath is usually already serious.
- Tailgate window and top sealTry the rear window. It winds down inside the tailgate by crank or motor, the motor and its drive cable are known to fail, and a safety switch stops the glass going up if the tailgate isn't latched. Ask whether the top has been removed. Owners disagree on whether that always causes leaks, but the seal between the top and the body is the usual leak point.
- Is it really a 350?One CK5 member warns about 305s being sold as 350s, engines described as 'rebuilt' that never were, and a TH350 in a truck that should have a 700R4. Look for clean grease between the engine and transmission, which suggests nothing has been apart. Check the freeze plugs for weeping.
- Identify the axles and transfer caseOn the front axle, a 10-bolt cover is nearly round with no flat sides, while the Dana 44 has the familiar Dana shape. Mismatched gear ratios front and rear, or a missing front driveshaft, mean someone has swapped parts. NP205 and NP203 cases carry ID tags above the front output. On 1989–91 NP241s, a leaking slip-yoke rear output is common.
- Hubs and 4WD engagement1981 and later trucks came with automatic locking hubs, which seize with age. One King of the Hammers K5 owner bought a truck with a 'blown transmission' that turned out to be a transfer case stuck in neutral and seized automatic hubs. Engage 4WD on the test drive, and budget for manual hubs.
- Previous owners' workLook for hacked-in wiring, stereos and lights, cheap lift blocks and poor welding. One CK5 member says to pay extra for a properly done one-ton axle swap (8-lug axles) rather than a cheaply lifted 6-lug truck. Another suggests 1987–91 trucks for fuel injection, with 1989–91 the favorites.
- M1009 specificsCheck whether the 24/12-volt system is original or has been converted. If the resistor pack has been bypassed for 12-volt glow plugs, the starter, the alternator and the NATO slave receptacle in the grille also need dealing with. Expect 3.08 gears, 10.00-15 tires and a governed 55 mph top speed as delivered.
The repairs Square Body K5 Blazer owners end up doing
| REPAIR | SYMPTOMS | DIFFICULTY | TIME | COST |
|---|---|---|---|---|
| Repair and brace a cracked steering-box frame rail | Wandering steering, a box that visibly moves on the frame when someone turns the wheel, or hairline cracks running from the steering-box bolt holes. Big tires and hard wheeling make it worse. | 4 / 5 | ≈ A weekend (more if the rail needs welding) | Parts plus welding labor |
| Swap a worn or leaking steering box | Play at the wheel, wandering on the highway, fluid weeping from the box's seals, or a box that has been loosened by a cracking frame. | 3 / 5 | ≈ 3–4 hours | Parts plus labor |
| Convert seized automatic hubs to manual locking hubs | The truck won't pull with the front wheels in 4WD, grinding from the hubs, or front wheels that drive at one corner only. Automatic locking hubs arrived with the NP208 for 1981 and are now old. | 2 / 5 | ≈ 2–3 hours | Parts only for DIY |
| Reseal an NP208 or NP241 and fix a leaking slip yoke | ATF dripping from the rear output, a driveline clunk, or a slip yoke pulling out as the suspension droops on a lifted truck. A worn chain can also skip or slap. | 4 / 5 | ≈ A day (case out of the truck) | Parts plus labor |
| Rebuild the front axle ends (ball joints, U-joints, bearings) | Death-grip steering, clunks over bumps, uneven tire wear, a front end that won't hold alignment, or clicking from the axle U-joints in tight turns in 4WD. | 3 / 5 | ≈ A weekend | Parts plus labor |
| Renew leaf spring bushings and shackles | Clunks, wandering and axle wrap. Sagging rear springs are also common, and cracked rubber bushings often squeak. | 3 / 5 | ≈ A day | Parts plus labor |
| 6.2 diesel glow plugs and controller | Hard cold starts, long cranking, white smoke until warm, or a wait light that misbehaves. On an M1009, a bad resistor pack or a mixed 12/24-volt conversion can cook new plugs. | 2 / 5 | ≈ 2–3 hours | Parts only for DIY |
Each repair links to a step-by-step guide with tools, part numbers and where to buy the parts.
Square Body K5 Blazer recalls and service bulletins
- Rear brake drum balance weights can loosen aluminum wheels ↗ 1982 · NHTSA 82V128000On 1982 Blazer, Jimmy and C10/C15 trucks with aluminum wheels, the drum balance weights could contact the wheel, loosen the lug nuts and break the studs (1,633 vehicles).
- Composite front brake rotors can separate from corrosion ↗ 1988–1991 (Blazer listed for 1988–92) · NHTSA 93V119000Road-salt corrosion at the joint between the stamped steel center and cast outer section of the rotor could let them separate. The campaign covered Blazer, K10/K20, Suburban and GMC equivalents (341,364 vehicles).
Check any VIN for open recalls at nhtsa.gov/recalls ↗, or see the recall tracker.
Take the printable Square Body K5 Blazer inspection checklist: every check on this page plus the model-specific ones, on one sheet. Get the checklist →
Sourced from owners, specialists and factory documents; full sources are on the Square Body K5 Blazer guide. Verify torque figures and procedures against the factory service manual (disclaimer).