9
Fig. 1 Drop-out
Fig. 2 Measure Drop-out
FOX FORX use hydrodynamic lubrication. In our system, oil is force fed into the tall slotted bushings during the
compression stroke. When the fork cycles up and down the oil is trapped between bushings, upper tubes and seals.
Thermal expansion rates can cause the bushings to close in on the upper tubes causing high friction and binding
during normal operation. Correct bushing clearance is critical to prevent binding of fork during normal operation.
Geometric dimensioning and tolerancing is a design practice used to insure parts will work / fit during the manufactur-
ing process. Bushings are sized before installation and rechecked for size after installation. Correct bushing tolerance
is a diametric clearance of .0015”-.0090”.
Show Room Testing - As you rock the fork back and forth while stopped with the front brake applied, the bushings have
only a small amount of lubricant separating the bushing / upper tube. At this time you may notice a small amount of
bushing play. Fork bushings must have clearance to perform correctly. Too little clearance will cause high friction,
binding or bushing seizure when hot.
Real World Testing - During normal riding conditions, hydrodynamic lubrication occurs when there is a complete
separation of the upper tube from the bushing by a thin film of oil. Hydrodynamic lubrication is characterized by very
low friction and no wearing of the bushings or shaft since there is no metal to bushing contact. During hydrodynamic
lubrication normal bushing clearance will not be noticeable.
Bushings should be checked annually for excessive wear. If excessive fore and aft movement is detected between the
upper tubes and lower legs, contact an Authorized FOX Racing Shox Service Center or FOX Racing Shox for further
instructions. Grasp the lower legs at the drop outs (axle). Push the fork straight back towards the rear wheel. Then pull
it towards you. Next grasp the fork near the upper tube/seal junction and try the same thing. If excessive movement is
noticed, refer to page 4 of this manual and contact FOX Racing Shox or an Authorized FOX Racing Shox Service
Center.
Bushings Technology and Inspection
Over time the knurled surfaces of the hub on the front wheel and quick-release skewer wear the drop-out region of the
lower leg. (Fig.1)
Inspect and measure the thickness of the dropouts every 6 months or 100 hours that any point on the surface is above
the minimum specification of 6.20mm. (Fig. 2)
Replace the lower leg assembly if the drop-out thickness is at the
minimum specification or smaller.
Drop-out Thickness Inspection
