One of the most common calls sales staff will get is for a clutch pack or OEM posi unit to
correct the "chatter" or "crow hopping" effect on all the Ford F150 5.4L 12 bolt rear differentials
with a severe chatter problem, this is an OEM design problem and replacing the clutches does not
rectify the problem, Ford came out with a shim kit to install with the new clutch pack and this still
has not solve the problem, the best fix on the market is to replace the posi traction unit with an
Auburn posi 542090 (763B715A) and ignore Ford's oil recommendation and use 80W90 gear oil with
the additive that is included with the unit.