Auxiliary Spring Shim Evaluation - ProGear Hendrickson HN FR Series Service Manual

HN ® FR Series

AUXILIARY SPRING SHIM EVALUATION

The HN FR suspension uses a dual spring design to achieve a good empty ride while maintain-
ing a stable ride when loaded. When empty, the vehicle rides on the bolster springs and there
is an air gap between the auxiliary springs and the Vee bracket. When loaded, the weight of
the vehicle compresses the bolster springs until the auxiliary spring engages the Vee bracket,
thereby increasing roll stability. However, vehicles with a high unladen tandem weight or a high
center of gravity may require high roll stability at all times. On these vehicles, auxiliary spring
shims may be added until the auxiliary spring and the Vee bracket are engaged at all times. This
will eliminate any gap between the auxiliary springs and the Vee bracket. A maximum of five (5)
shims may be installed above each auxiliary spring.
NOTE Both sides of the HN FR suspension must have an equal number of shims in place or a vehicle
lean may result.
Most production vehicles are manufactured with three (3) auxiliary spring shims above the
auxiliary spring, see Figure 7-6. However, some vehicles are manufactured with only one shim to
minimize the need for adjustment after the body equipment is installed.
To achieve optimal ride quality and stability the unladen tandem weight of a vehicle will dictate
the auxiliary spring shim arrangement necessary above the auxiliary spring, see chart below for
details.
DISASSEMBLY
1. Chock the wheels.
2. Loosen the nuts that attach the auxil-
3. Remove or install additional shims as
ASSEMBLY
1. Re-assemble fasteners and tighten
2. Remove the wheel chocks.
Alignment & Adjustments
Pro Gear and Transmission • 906 W. Gore St. Orlando, FL 32805 • 1 (877) 776-4600 / (407) 872-1901 • parts@eprogear.com
TABLE 7-1
RECOMMENDED AUXILIARY SHIM CONFIGURATION
UNLADEN TANDEM WEIGHT WITH BODY / EQUIPMENT / EMPTY TRAILER INSTALLED
10,000–18,000 lbs.
STD–3 Shims
iary spring assembly to the saddle.
recommended.
locknuts to 90-105 foot pounds
torque.
FIGURE 7-6
22
18,001–28,000 lbs.
2 Shims
17730-285