Specifications

One last item to check before attempting to measure the ride height. You are looking for a bent
rear axle housing. Indications are found by noticing the inner dual tires wear more than the
outer ones. Also look for grease lube leaks at the bottom of the axle housing at the differential.
A split gasket near the bottom area almost always indicates an overload, or flex and housing
distortion, which destroys the gasket between the carrier and the housing. Failed rear wheel
bearings may be another possible indication to prompt a check for a bent axle housing. They
can also fail because of a lack of rear differential lube. (You didn't forget to check this during
the last lube did you?) A couple of potholes at high speed on a heavily-loaded motorhome can
do the trick. However, if the previous owner of the motorhome took care of these leaks and
replaced bearings, it is difficult to spot a bent housing except for inner tire wear.
Also, since the wheel bearings are supplied with lube from the differential, make sure that it 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.)
http://users.sisna.com/cebula/P-Chassis-AlignmentProcess.pdf 15 Version 0.7 –Sep 14, 2005