Spicer Ford Applications 1999-2011 Light Axle Parts User Manual
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How Limited Slip Differentials Operate
A conventional differential transmits all the ring gear torque through the differential gears to the axle shafts.
Torque is at all times equal on the axle shafts, and if one wheel slips, the other wheel can only put out as much
torque as the slipping wheel.
The Spicer Limited Slip differential has the same power flow as a conventional differential, plus a more direct
flow which automatically takes effect as driving conditions demand. This more direct power flow is from the
differential case to each axle shaft through a clutch plate and disc arrangement.
Arrangement of these plates and discs is at the option of the vehicle manufacturer, so care should be taken
during disassembly to note the arrangement of these components.
The Limited Slip construction permits differential action when required for turning corners and transmits equal
torque to both wheels when driving straight ahead. However, when one wheel tries to spin due to leaving the
ground, a patch of ice, etc., the clutch packs automatically provide more torque to the wheel which is not trying
to spin.
The Limited Slip differential resists wheel spin on bumpy roads and provides more pulling power when one
wheel tries to slip. In many cases of differences in traction, pulling power will be automatically provided until
both wheels start to slip.
In diagnosis of vehicle operators' complaints, it is important to recognize two things.
1. If, with unequal traction, both wheels slip, the Limited Slip Differential has done all it can pssibly do.
2. In extreme cases of differences in traction, the wheel with the least traction may spin after the Limited
Slip has transferred as much torque as possible to the non-slipping wheel.
How To Obtain Special Service Tools
Special service tools (see service manuals) can be obtained from the following company:
Kent-Moore
OE Tool and Equipment Group
SPX Corporation
28635 Mound Road
Warren MI 48092-3499
(800) 345-2233
www.servicesolutions.spx.com
POWR-LOK™
2-Piece Case
4 Pinion Mate Gears
TRAC-LOK™
1 or 2-Piece Case
2 or 4 Pinion Mate Gears
All Models except Models 70/267 and 80/286: The
Powr-Lok design is identified by its 2-piece case. The
Trac-Lok design is identified by its 1-piece case.
Models 70/267 and 80/286 only: Both the Powr-Lok and
the Trac-Lok use 2-piece cases in the model 70 (267)
and 80 (286) axle. The difference between the two is in
the shape of the holes for the cross shaft. The Powr-Lok
case will have cross shaft holes that are "U" shaped in
one case half and "V" shaped in the other case half.
The Trac-Lok case will have cross shaft holes that are
semicircles in both case halves.
Model 80/286 only: It is also possible to replace an
existing Powr-Lok unit with a complete Trac-Lok unit.
For this purpose, the differential case assembly must
be replaced.
How To Distinguish a Powr-Lok™ from a Trac-Lok™