Roush, rear lowering springs ???
06-13-2011, 05:51 AM
#12
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Question for suspension gurus. Is it necessary to loosen and retorque the upper trailing arm after installing these springs?
Found the following in the Roush instructions for ROUSH Wheel Hop Reduction Kit Part # R06030084 and wonder if this step should be included for the springs installation.
"As packaged, the Bracket and Upper Trailing Arm are preassembled in
the required position to function properly on a stock ride height Mustang GT. If the vehicle ride height has been altered, it will be necessary to loosen the forward bushing bolt and retorque the assembly with the components in the vehicle and the axle positioned at the intended ride height (neutralized). Failure to do this will result in dramatically shortened bushing life and probable increased wheel hop. "
Found the following in the Roush instructions for ROUSH Wheel Hop Reduction Kit Part # R06030084 and wonder if this step should be included for the springs installation.
"As packaged, the Bracket and Upper Trailing Arm are preassembled in
the required position to function properly on a stock ride height Mustang GT. If the vehicle ride height has been altered, it will be necessary to loosen the forward bushing bolt and retorque the assembly with the components in the vehicle and the axle positioned at the intended ride height (neutralized). Failure to do this will result in dramatically shortened bushing life and probable increased wheel hop. "
What's happening is that the lowering puts the OE bushing material under stress when the car is at its "unloaded" ride height, which increases the stress in the bushings every time the car goes into "bump". IOW, with 1.5" lowering, a bump that used to be 1.5" down from the bushing zero load position would effectively become a 3" downward motion (with double the bushing stress in this case).
Virtually all OE rubber bushings are bonded to the inner sleeve (that the bolt runs through and holds tight because of the bolt torque/clamping load) and also to the outer shell (that's captive via press fit in the arm). When you lower the car, the inner sleeve wants to rotate relative to the shell, which loads up the rubber. When you loosen the bolt, the inner sleeve "slips" into a new "zero bushing stress" position. Basically, you're just resetting the bushings.
FWIW, when you double the bushing stress in bump, its life does not necessarily become only half. In the absence of specific bushing fatigue data, I wouldn't even expect it to last 10% as long.
Norm
Last edited by Norm Peterson; 06-14-2011 at 05:28 AM. Reason: bad spelling
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