Leaf Springs: A Reliable Suspension System for Vehicles

The purpose of this instruction is to address the issue of possible squaking noises in installed dual fastener type aftermarket leaf springs.

This applies to all leaf springs supplied by The Universal Group with a deisgn that includes more than one center bolt fastener in order to prevent leaf fanning. The design might require two center bolts or a center bolt and a roll pin.

1. Primarily, the U-bolt provides the force required to clamp the leaf springs and related components firmly together. In addition to the leaf spring, these components include the top plate, axle seat, axle, and bottom plate.
2. The properly installed U-bolt eliminates any flexing of the leaf spring in the area between the U-bolts. This is particularly critical since the hole for the center bolt in each leaf acts as a stress concentration which would lead to rapid leaf breakage if spring flexing was not totally eliminated by the U-botl clamping force. By firmly clamping the spring to the axle seat the horizonal forces acting on the center bolt are greatly reduced which in turn prevents shearing of the center bolt.
3. Proper clamping of the spring by the U-bolts provides the desired spring stiffness and contributes to maintaining the vehicle ride height and handling characteristics as originally specified for the vehicle.
4. Lack of U-bolts proper clamping in the particular case of dual fastener design springs allows the leaves to rub against at least one of the fasteners (center bolt, pin) and produce tell-tale squeaky noises.

1. Do not reuse U-bolts. A previously toqued U-bolt will suffer from distorted threads from the engagement of the deep nut. Deep nuts should be tightened once and retorqued, never loosened and re-tightened.
2. Re-tighten U-bolts after the first 500 to 1,000 miles. As new or repaired springs wear in, some settlin of the spring stack will occur. Even a minor amount of settling can cause a dramatic reduction in the U-bolt clamping force. If possible, re-torquing of U-bolts should be done with the vehicle under load.
3. Inspect for signs of loose U-bolts. Virtually all leaf spring failures near the center hole are caused by inadequate U-bolt clamping. Look for signs of movement within the area between the U-bols. Worn or polished surfaces on axle seats or top plates are sure indicators that unwanted movemnt has occurred.
4. In the case of dual fastnere design springs, squeaky noises indicate insuficient U-bolt clamping as well.

Recommended torque levels from the vehicle or suspension manufacturer should always be used where possible. If these specifications are unknown, the following chart can be used as a guide:

Examples of spring part numbers that are using the dual fastener design:
34-1451
34-1453
34-1455
34-1459
34-1461
34-1465
34-1467
34-1485
34-1487
34-1497
34-1499
43-1551
43-1553
43-1555
43-1679
43-1781
43-1783

Superior Spring offers a wide variety of leaf brings for multiple vehicles. Take a look at the products we offer!

Leaf springs have been a trusted suspension system for vehicles for many decades. Their load-carrying capacity, shock absorption capabilities, and durability make them an excellent choice for a variety of applications. Whether it's a pickup truck on a construction site or a heavy-duty commercial vehicle on long-haul routes, leaf springs continue to play a vital role in ensuring a smooth and stable ride.