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4LHD/4LHDX Application Manual
Powertrain Control Solutions
REV 1.1
2.3.5 Overow Vent
During operation the transmission is subjected to heating and cooling. A breather tube is provided to prevent the inside
of the transmission from becoming pressurized. Refer to Section 1.1.2 or Figure 2.3.5-1 for location of the breather tube.
In the event that transmission uid is overlled, some uid may be expelled from the breather passage; therefore the
breather opening must not be directed at any hot components. The breather opening can be located remotely by attaching
a hose to the existing breather tube. The hose length and diameter shall be such that the pressure of the inside of
the transmission is always ±4.0 psi of atmospheric. A hose must not have any low spots that would allow any uid or
condensation to collect and prevent the free movement of air. The end of the hose shall be located at a position that does
not inhale environmental or vehicle contaminants.
Remotely attached breathers are required, new designs must be provided by the vehicle manufacturer to be reviewed
with Powertrain Control Solutions Engineering. PCS overow vent kits serve this purpose and are available for purchase.
Reference the PCS OEM Parts Catalog for part numbers.
Overow Vent Kit Installation
The following procedure should be applied when installing an overow vent kit. Improper installation could result in
transmission uid expelled from the hose and onto potential heat sources.
1. Apply lubricant to inner circumference of transmission vent hose. Secure hose 19 mm onto transmission vent tube.
2. Secure overow vent kit to local features on transmission or body. The uid relase vent should be routed toward rear
of transmission to avoid leakage onto transmission and vehicle components. The pressure release vent should be
moved towards the top of the bellhousing to prevent uid from accumulating in the hose.
3. The release vents referenced in Figure 2.3.5-1 must be directed away from potential heat sources, such as exhaust
or catalytic converter.
Figure 2.3.5-1: Overow Vent Kit Attachment
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