Background

The stock shackles on most trucks can be easily upgraded. Remember that you are only changing the height of one end of the spring, and that the middle of the spring is where the axlehousing mounts, so two inches of additional shackle length only amounts to about one inch of actual lift between the wheels and the frame. Longer shackles don't significantly change the spring rate, so they won't change the ride much -- though grease-able bushings can improve ride slightly.

There are several reasons for longer shackles:

• Aftermarket shackles are stronger, with thicker side plates and a reinforcing crossbar. Some designs omit the crossbar for slight improvements in articulation caused by the deflection of the shackle, but this deflection can also occur on pavement and make your handling squirrelly.
• You can upgrade to grease-able polyurethane bushings. Rubber bushings can be more compliant than urethane bushings, but are susceptible to dry rot and oil contamination when exposed to gas, oil, or grease. Softer poly bushings are now available that retain the long life of polyurethane but flex better. For more information, please view another excellent Off-Road.com article on polyurethane bushings.
• Longer shackles force the frame up from the spring, and are often the cheapest, easiest way of attaining moderate lift. Longer shackles can allow a longer sweep at the end of the spring, providing potentially greater travel.

And also a few reasons against longer shackles and polyurethane bushings:

• Longer shackles place more leverage on their frame mounts.
• They may potentially induce handling problems. Longer shackles are longer lever arms that may increase axle-steer.
• Longer shackles hang down further, and drag more often, than shorter shackles.
• Too hard a bushing may transmit too much ride harshness.
• The squeaking from poorly lubricated polyurethane bushings may drive you batty.

Installation

1. Chock the front wheels securely.
2. Jack up your truck until the rear wheels are well clear of the ground.
3. Use jack stands to secure the truck's frame.
4. Position your jack's lifting pad under one set of u-bolts.
5. Undo the nut that holds the bolt which connects the leaf and the shackle.
6. Jack the axle up far enough to unweight the spring at the shackle but not so far that you compress the spring. If done just right, the spring eye bolt will be loose enough to pull out by hand. You can use a pry bar to move the spring up and down a bit, but its easier to just set the right height with the jack. If you can't quite get the bolt out by hand, use a centerpunch and a hammer to drive the bolt out.
7. The shackle should now be connected to the truck only at the frame. Remove that connecting bolt and set aside the old shackle.
8. If you are replacing bushings, you'll have to remove the old ones, which can be nearly impossible. You can upgrade to grease-able polyurethane bushings. Rubber bushings can be more compliant than urethane bushings, but are susceptible to dry rot and oil contamination when exposed to gas, oil, or grease.
   • If you are lucky, a hammer and screwdriver will be sufficient persuasion. You won't be that lucky.
   • I've pressed a handful out successfully with a C-clamp and a couple of sockets. If you can take the springs fully off the vehicle, a bench vise also works.
   • If these fail, then burn them out with a torch. This is a smelly, nasty mess, but works almost every time. Adequate ventilation is a must -- and don't drip molten rubber on concrete you care about.
   • Some bushings are vulcanized to an outer metal sleeve which must be cut and pounded out.
   • When the bushings are out, use emery cloth to clean any left over rubber or metal fragments out of the spring eye.
   • If you are using polyurethane replacement bushings, be sure to grease them up with the manufacturer-provided grease or regular heavy bearing grease. You may need to use the C-clamp (or bench vise) and sockets to force the new bushings into the spring and frame eyes.
   
9. Loosely bolt the new shackle to the frame hangar.
10. Lower the axle down far enough to line up the spring and the longer shackle. If you get it exactly right, you'll be able to insert the spring eye bolt by hand. As noted above, you can use a prybar to move the spring up and down a little, but it is far easier to set the right height with the jack. If you can't quite get the bolt in by hand, use a hammer to gently drive the bolt across the shackle and through the bushing. Be careful not to munge the threads.
11. Tighten the shackle bolts until the nuts just touch the shackle side plates. Do not overtighten these fasteners.
12. Lower the axle with the jack until the wheels are back on the ground and the truck's weight is fully on the spring and shackle assembly.
13. Tighten the shackle bolts to the recommended torque. This torque should be enough to sandwich the bushing firmly between the shackle and spring but not pinch it. Pinching the bushings can shorten their life and interfere with normal suspension travel. With nylock nuts, you can keep them a little less tight, and get a little more travel. Too much play can lead to sloppy handling and axle-steer.
14. Repeat the above steps on the opposite side of the vehicle.
15. Jack up the truck, remove the jack stands, and lower the truck.

     

    Things to Check

    After you are done, you might want to check a few things. None of these issues will likely be a problem if you keep your shackle lift within reason:
    • Suspension travel and frame interference with the longer shackles.
    • Check for too-short brake lines, emergency brake cables, or differential vent lines with the suspension at full droop travel.
    • Check also to make sure your shocks are not limiting travel. Off-Road.com has an excellent shock fitment guide.
    Lifting one end of the leaf does change the suspension geometry, drive line angle, and pinion angle. Drive with caution until you are confident that these effects are minimal

     

    Larger Tires?

    With so many different tire sizes available, you'll have to measure and carefully plan what will fit on YOUR truck.

     

    Sources

    • CALMINI's carries shackles and new shackle bolts for Isuzus, Suzukis, and Nissans. If you want to use polyurethane bushings, Energy Suspension carries them. Contact CALMINI at: CALMINI Manufacturing, 6600-B McDivitt Dr, Bakersfield, CA 93313 U.S.A. Phone: 1-800-345-3305 Fax 805-398-9555 For more information email CALMINI.
    • Daystar Products carries shackle bushings for Isuzus, and though they have yet to put together a grease-able kit, they have all the parts required to source the grease-able bolts and bushings. Daystar does not sell directly to the public, but Accessories Plus carries their line of products. Contact them at 1-800-729-4294.
    • Energy Suspension carries polyurethane bushings for Isuzu products. Contact them at: Energy Suspension, 1131 Via Callejon, San Clemente, CA 92673. Sales: 1-714-361-3935.
    • Northwest Off-Road Specialties (NWOR) carries grease-able bushings and bolts for Toyotas. Contact NWOR at: Northwest Off-Road Specialties, P.O. Box 1617, Bellingham, WA 98227-1617. Phone (360) 676-1200 or FAX (360) 676-5401.

    Please mail the Isuzu ORC Staff if you have questions or comments about this page.