Axle shims adjust the angle of a vehicle’s pinion axle by being placed between the axle and leaf spring. They are commonly used in four-wheel drive applications to combat severe driveshaft angles caused by excessive suspension lift. The pinion angle is determined by a gauge and adjusted through upper suspension rods.
Axle shims are thin pieces of metal that are placed between an axle and a leaf spring to adjust the angle of the vehicle’s pinion axle. Commonly offered in 2 to 8 degree angles, axle shims are designed to bolt to the bottom of the leaf spring package and are held in place by an interference fit between the spring and spring pad on the axle, as well as the center bolt of the spring pack. When using axle shims on a front axle, such as in a four-wheel drive application, extra care must be taken to correct front wheel set-up and camber after driving the shims into place.
A vehicle’s rear suspension is designed to give optimum performance at a predetermined pinion angle. Sprocket angle reflects the angle in degrees that the rear axle sprocket is positioned in relation to the ground or road. Generally, it is best to position the pinion gear at a slight downward angle on the driveshaft yoke. This is the angle that gives the tires the best bite on the road surface, providing the best traction and handling for the vehicle. While some degree of pinion angle is taken into account in the placement of the spring mount pads, certain alterations such as tire size, ride height, and spring wear can change the angle, requiring shims. shaft to correct the problem.
This pinion angle method is accomplished only with a leaf spring suspension. Coil spring suspensions use a four-link suspension setup with two upper and two lower suspension bars that position the rear axle. The pinion angle is not adjusted with axle shims, but through adjustment of the upper suspension rods. On either spring system, a pinion angle gauge is used to determine the amount of pinion angle to fit into the suspension. This is typically a mag gauge that sits against the rear end muzzle or against the rear axle sprocket yoke.
In a four-wheel drive application, axle shims are often used to combat severe driveshaft angle from excessive suspension lift. With excessive lift, the driveshaft can often run at a severe angle to the shaft, creating a universal joint bind. Placing axle shims in the spring pack can often alleviate the problem when moving the pinion axle up toward the driveshaft. The use of axle shims can only eliminate part of the problem before increasing negative or climbing angle begins to cause other problems within the suspension. On the front axle, axle wedges can severely alter roll and lean angles toward negative, creating a dangerously poor handling vehicle.
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