Symptoms
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.
The fix, step by step
- Raise and support the front, remove the wheel, then remove the automatic hub assembly, its retaining ring and the drag sleeve parts.
- Check the wheel bearings and the spindle nut adjustment, and repack or replace the bearings if they're dry or rough.
- Fit the internal-style manual hub kit to suit your axle (10-bolt or Dana 44, spline count).
- Then check that 2WD and 4WD both engage.
Tools & part numbers
- Snap-ring pliers
- spindle nut socket
- bearing grease
- torque wrench
Where to buy the parts
Warn internal-style locking hubs for GM 10-bolt or Dana 44 (all 1/2-ton)Offroad Design ↗Amazon ↗
Yukon Hardcore locking hub set, '79+ GM 8.5-in front and Dana 44 (19-spline)Offroad Design ↗Amazon ↗
Locking hub listings, 1987 BlazerRockAuto ↗Amazon ↗
Hunting a used or discontinued part? Search eBay Motors for Chevrolet K5 Blazer (1973–1991) parts →
Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.