Allison Gen 4 / 5 B400R / B500R Valve Body Assemblies
Allison Valve Bodies:
Allison valve bodies for Gen 4 / 5 are the same in layout, springs, solenoids and spool valves. But between the B400R and B500R there are differences between some springs and spool valves, but all solenoids are the same.
For ordering parts for a transmission, use the transmission serial number to cross reference the correct parts.
Allison Valve Body Layout:
Solenoid Valve Body Assembly:
Main Valve Body Assembly:
Diagnostic Switch PS-1:
The diagnostic switch PS-1 has two functions:
1. When the C5 clutch is filled, It verifies pressure to the C3 clutch pack in reverse, neutral, and 1st range are attained.
2. When the C5 clutch is exhausted, it verifies the positions of the C1 and C2 latch valves.
If incorrect pressure is sensed by the switch, the signal will be sensed by the TCM, and a DTC will be logged.
Note: C1 and C2 latch valves control fluid pressure between clutches. They also control limp mode operation.
⇒ PCS-2: Controls the C2 clutch pack, but in reverse it will control the C3 clutch pack.
⇒ PCS-3: Controls the C3 clutch pack, but in neutral, reverse and 1st range it will control the C5 clutch pack. The C5 clutch pack has no assigned solenoid.
Filter Life Switch PS-2:
The filter life switch PS-2 monitors filter life deterioration when the filters need replacing. When unfiltered main pressure (pressure on the outside of the filter) becomes greater than filtered lock up pressure (pressure after the filter). The unfiltered main pressure will increase and activate the PS-2 switch, sending a signal to the TCM. This signal will activate the Prognostics service icon on the shifter that filter service is needed.
Retarder Valve Bodies:
The retarder is a bolt on hydraulic brake at the rear of the transmission to help slow the vehicle down. The valve body receives activation commands from the TCM to apply the retarder. The PCS-5 solenoid is PWM which controls retarder application. How much retarder application, depends on driver input demand.
Note: All retarder valve mounting bolts to retarder housing are M8 bolts that are torqued at 18-21 lb. ft. (N m 24-29).
⇒ The metal separator plate between retarder valve body and retarder housing is coated with a sealing agent. No paper gaskets are used.
Valve Body Torque Specs:
Internal valve body torque specs are as follows:
Note: Control valve body mounting bolts to transmission case and filter nuts are M10. Torque to these bolts or nuts are 38-45 lb. ft. (51-61 N m).