Spreading a Dana Differential

This is in reference to recent ARB Air Locker models
that suit Dana/Spicer shim adjusted Salisbury axle housings.
(Model #s RD100, RD101, RD102, RD103, RD104, RD105,
RD109, RD113, RD116 & RD117)

It has come to our attention that some of our stockist network has been experiencing difficulty
when installing some of our recently released Dana/Spicer model differentials which include a
replacement carrier bearing for both ends of the carrier. The problem seems to arise from the
necessity of holding a shim pack onto the carrier bearing (RH side or side opposite the air entry
side) while installing the differential assembly to achieve a certain degree of pre-load.

The newer Air Locker models listed above employ higher rated carrier bearings and heavier
bearing journal cross sections than were available on the factory designs. Unfortunately because
of this the Air Locker unit does not support re-using the existing Dana shims which are located
under the bearing cone because the bearing journal diameter of these models is larger than that
of the original model. As a replacement for these, ARB includes a full set of shims to use on the
outside of the supplied bearing cup. The difficulty then seems to lie in squeezing the differential
center into its cavity at the same time as the desired thickness of shim.

We have investigated this and found that if the assembly has been adequately spread using a
common differential housing spreader (as detailed in the Air Locker Installation Guide and the
vehicle manufacturer’s service manual) then no such difficulty exists. Once spread enough to
accommodate the differential, bearings and shims, an Air Locker can be simply placed into the
housing by hand.

We are, however, aware that this installation is sometimes attempted without the use of any form
of differential housing spreader. This is a practice that ARB cannot support. Dana Spicer and
the vehicle manufacturer explicitly detail the importance of using a differential housing spreader
and demands it of all of their approved service technicians. These tools are readily available for
sale at reputable axle service shops, and most designs are adjustable to suit the whole range of
Dana axle applications. 

During heavy off-road driving, high torque at the axle means that the ring gear on the differential
carrier can get pushed away from the drive pinion gear with so much force that it partially
disconnects the two halves of the carrier bearing on the opposite side. In a factory differential
this temporary misalignment can result in ring and pinion gear damage, as well as carrier bearing
damage to both sides. In an Air Locker installation a misalignment condition of this type could
also result in damaged O-rings leading to air or oil leaks. To combat this the factory equipped
Dana differential assembly was designed to run with a great deal of tension holding the assembly
together known as pre-load. You can easily identify this design by the existence of the spreader
sockets provided.

Although some fitters may think that by hammering it into a tight fit situation they are still “preloading a differential” – It is not possible to fully and adequately pre-load a Dana differential using this method. Without the use of a spreader a properly pre-loaded differential is actually too tight to even just remove without difficulty, and next to impossible to refit.

Spreading a Dana shim type axle assembly will not only reduce the installation time and effort
required to set up an Air Locker, but it will also allow for the preload necessary to support the
increased torque demands of off-road use on a locked differential, increase overall bearing life,
and insure that your Air Locker seals run reliably for many, many years of use.

Attached are some instruction manuals for commercially available differential housing spreaders below for your reference.