Leaf Spring Shackle Bushing with Fitting Position Front, Rear for 1977 GMC K25 Base

Nolathane leaf spring shackle bushings renew the pivots that let a shackle swing as your GMC K25's leaf spring flexes. Every time the spring compresses, it gets longer, and the shackle has to rock back to make room. A worn leaf spring shackle bushing turns that smooth swing into a loose, knocking joint, and the rear end tells you about it over every bump.

Polyurethane shackle bushings bring the pivot back to a firm, quiet fit on trucks, pickups, and 4x4s that tow, haul, or spend time off the pavement. Each listing shows the shackle position, bushing dimensions, pin size, and whether it suits your GMC K25.

The Shackle?s Job in the GMC K25 Leaf Spring Suspension

A leaf spring is a curved arc. When weight lands on it, the arc flattens and the distance between its two eyes grows. The front eye is bolted to a fixed hanger, so all of that extra length has to go somewhere, and the shackle is what takes it.

The shackle is a short link with a pivot at each end. One end connects to the spring?s rear eye and the other to the frame. As the spring compresses and rebounds, the shackle rocks back and forth through a small arc, thousands of times on every drive.

That makes the shackle the busiest pivot in the whole spring assembly. It moves on every bump, every change in load, and every bit of axle wrap under power or braking. With two pivots working constantly, shackle bushings usually wear out before the front eye bushing does.

The shackle also sets the spring?s working length, and with it the rear ride height. A shackle that hangs at the wrong angle because its bushings have collapsed can drop or raise one corner and change how the spring behaves under load.

GMC K25 Shackle Bushing Positions

A shackle has bushings at both ends, and the right replacement depends on which end you?re working on and how the frame side is built.

Rear Eye to Shackle

This is the spring end of the shackle. The bushing sits in the spring?s rear eye, and the shackle pin passes through it to join the eye to the shackle plates. This position sees the most movement, because it rotates with both the spring and the shackle.

Frame Shackle (Hanger)

At the top of the shackle, a second bushing connects it to the frame shackle, also called the hanger. Some vehicles use a common frame shackle design with a separate pressed-in bushing. Others use a molded frame shackle, where the bushing is formed as part of the hanger assembly. The two need different parts, so check which design your GMC K25 uses before ordering.

Front Shackles on Leaf-Sprung Front Axles

Older 4x4s and trucks with leaf springs on a solid front axle often carry a shackle at the front of the vehicle, too. Those shackle bushings handle steering loads as well as spring movement, so wear shows up as wander and vague steering, not just noise.

Signs of Worn Shackle Bushings on Your GMC K25

Shackle bushing wear tends to announce itself with noise before anything else. Watch for:

• A clunk or knock from the rear over small bumps, driveway lips, and expansion joints
• Clunks as you pull away or come to a stop
• A shackle that sits at an odd angle compared with the other side
• Squeaks or groans as the rear end moves
• Ride height that differs from one side to the other
• Bushing material pushed out past the shackle or eye, or cracks in the rubber

Because the shackle moves so much, even a small amount of play here gets loud quickly. Grab the shackle with the weight on the wheels and try to rock it. Any movement you can feel or hear at the pin means the bushings are due.

Polyurethane Shackle Bushings and Greasable Pins for the GMC K25

Factory shackle bushings are usually rubber bonded to a steel sleeve. The rubber twists with every swing of the shackle, so it?s under constant stress, and it eventually tears away from the sleeve or wears into an oval.

Polyurethane works differently. The bushing doesn?t twist; instead, the shackle pivots on a lubricated center sleeve that turns freely inside it. The result is a firm pivot that keeps the shackle on its intended path, with less of the slop that lets the rear end shift under load. Polyurethane also stands up well to abrasion and resists oil, grease, ozone, and weathering, which matters at a shackle that sits right in the spray from the rear tires.

Greasable shackle pins take that a step further. They carry a zerk fitting and an internal passage, so you can push fresh grease into the pivot during routine maintenance. That flushes out water and grit and helps stop the pin from seizing in its sleeve, a common problem on trucks that see mud, salt, or water crossings.

Choosing Shackle Bushings for Your GMC K25

Shackle bushings have to match both the shackle and the frame side, so it pays to check a few details first. Each listing shows the dimensions and fitment you need to compare.

Bushing Outside Diameter and Shackle Pin Size

The outside diameter has to suit the bore in the spring eye or frame shackle, and the inside has to match the pin. Measure both if you?re unsure, especially on an older or modified truck.

Frame Shackle Type

Confirm whether your GMC K25 uses a common frame shackle with separate bushings or a molded frame shackle. Ordering for the wrong design is the most common fitment mistake at this position.

Shackle-Only, Eye-and-Shackle and Complete Kits

Some kits cover only the shackle positions. Others include the rear eye, or the complete set for both ends of the spring. If the eye bushings are as old as the shackle bushings, doing them together saves a second teardown.

Pins and Shackle Hardware

A new bushing can?t work properly on a pin that?s worn, stepped, or rusted. Replace any pin that shows a ridge where it rode in the old sleeve, and fit new nuts where the old ones are corroded.

Replacing Shackle Bushings on Your GMC K25

Shackle bushing replacement suits a qualified installer or an experienced home mechanic. The general sequence looks like this:

• Support the frame on jack stands and support the axle separately, so the spring is unloaded
• Remove the shackle pins and lower the spring end away from the shackle
• Press out the old bushings and sleeves
• Clean the bores in the spring eye and frame shackle
• Fit the new bushings and sleeves, greasing them with a polyurethane-safe lubricant
• Refit the shackle using new pins and nuts if the old ones are worn
• Lower the vehicle onto its wheels and torque the pins to specification at ride height
• Pump grease into any greasable pins once your GMC K25 is back on the ground

Tightening at ride height matters. A pin torqued with the axle hanging leaves the bushing loaded in the wrong position, which causes binding and early wear. Check the torque again after the first few hundred miles.

GMC K25 Shackle Bushing Limitations and Trade-Offs

Polyurethane shackle bushings are a strong upgrade, but they have limits:

• Polyurethane transmits slightly more road noise and vibration than soft rubber
• It can squeak if it isn?t greased with the right lubricant
• New bushings can?t fix a bent shackle, a cracked hanger, or a sagging spring
• Longer lift shackles are a different part, and they change the spring angle and ride height
• Fitting new shackle bushings next to worn eye bushings leaves play in the system

Compliance and Insurance

Inspection and towing rules vary from state to state, including rules for trailers where they apply. Make sure your GMC K25 still meets the requirements of the state where it?s registered, and let your insurance company know about any suspension modifications.

Warranty and Support

Nolathane shackle and eye bushings carry a lifetime warranty against manufacturing defects in material and workmanship, for the original vehicle. Shackle sets, pins, and other hardware are backed by Nolathane?s warranty. If you?re not sure which frame shackle type you have or which kit to order, our local support team can help you match the right part.

Shop Leaf Spring Shackle Bushings for Your GMC K25

Replace the shackle end and the front eye together with leaf spring bushings from the same polyurethane bushings selection.

Find the leaf spring shackle bushings for your GMC K25 and order online with fast shipping. Every part comes with our fitment guarantee, and universal or dimensional kits are guaranteed to match the dimensions shown in the listing.