Specifications

Here is a case study right out of the Chevy P Chassis manual:
“GM CASE STUDY: A motor home was loaded to a maximum GVW, both front and rear. Sufficient air
was applied to a typical after-market leveling device to establish a 'dead-level' frame. In this case study, wheel
travel was limited to ¾ inch before the after-market device “went solid metal-to-metal” between the rear axle
and the frame. This severe limitation on wheel travel promoted a “crash-through situation” on even the
slightest bump. The force from this “crash-through situation” was transmitted into the vehicle frame, rear
axle and the coach itself. GM has determined that these types of after-market leveling devices can be very
damaging to the motor home and also can affect vehicle handling and are therefore potentially very
dangerous.
“If vehicle weights cannot be shifted due to vehicle build, consideration should be given to adding spring
leaves or spacer blocks.”
The spacer blocks mentioned above refer to making the side-to-side rear ride height
measurement equal. (This supposes that the weight is not in excess of the axle rating and you
have moved your moveable stuff around to help balance the side-to-side weight.) Spacer blocks
are fabricated in local machine shops.
NOTE: The addition of a spacer block ( 2 ½” wide, 6” long, thickness as needed) can actually
improve overall ride quality while the addition of a leaf tends to reduce the ride quality of the
vehicle.
The thickness of the spacer block is determined by the difference in the side-to-side
measurements at the rear axle. Once the thickness is determined and the block fabricated, a ¾
inch hole is drilled in the center. A slip-fit dowel, as long as the thickness of the spacer block, is
inserted into the hole of the block. This keeps the center of the axle and the existing spring
properly aligned. The U-bolts will need to be replaced with longer ones if the spacer block is
more than ¾” thick. Also, the rear flexible brake hose that runs from the frame to the axle may
need to be lengthened since you are increasing the distance from its mount on the frame to the
connection on the axle. Check by slowly lifting the rear by the frame and allow the rear axle to
http://users.sisna.com/cebula/P-Chassis-AlignmentProcess.pdf 16 Version 0.7 –Sep 14, 2005