is full to the appropriate level and changed on a regular basis. All lubricants lose
effectiveness over time. Every four oil changes ('normal' or 'dusty' cycle) will do the job. The
differential can run a temperature approximately 100 degrees above the ambient
temperature. Air passing over the housing is the only thing that carries away this heat. Make
sure the housing is not severely covered with dirt or dried mud which will insulate and help
retain and increase the heat. (Go back to the car wash and hit the housing with the high-
pressure spray.) The exhaust pipe shouldn't be too near the housing. Don't mix lubricant
brands – this can cause foaming and reduce heat transfer. If you run at high speeds, it can
cause aeration and heat transfer capability will be diminished.
Ride height for the P Chassis rear is checked on each side between the top of the axle tube
and the bottom of the frame above the axle tube. You are looking for this “D” measurement
to be equal side-to-side. If these are not equal, your weight side-to-side may be unequal or
springs may be sagging. In any case, an attempt should be made to get these as equal as
possible. Check Appendix B for information on the rear spring capacities for various P
Chassis models. (The illustration has a single on the left and a dual on the right because it
applies to either situation including non-motorhome versions of the P Chassis.)
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
Main Body Page 12 of 38 Total Pages
