Info - Allison Automatic Transmission Valve Body Hardware Changes

The valve body for the Allison® Series 1000 transmission has been revised for the 2004 model year to add modulated main pressure control. This revision will provide additional transmission oil cooler flow and reduced pump load during certain low speed operating conditions. The revised components will be installed on all 2004 transmissions and will be functional on the L18, 8.1L gas engine and LLY, 6.6L diesel engine but not on the LB7, 6.6L diesel engine.

Visible changes to the valve body assembly include an added modulated main valve body assembly, a control solenoid and a revised internal wiring harness. The modulated main valve body and solenoid are located on the bottom, near the front of the valve body assembly and are connected to the wiring harness by an additional wire and connector.

Important: This revised valve body will be used to service all 2001-2004 models. The modulated main pressure components will not function on the 2001-2003 models as the TCM is not equipped with the calibrations necessary to make these components operate. Installation of a modulated main equipped service valve body on a 2001-2003 transmission will not affect transmission operation.

Interchangeability

The current valve body assembly, P/N 29541572, is fully interchangeable with any 1000/2000/2400 SeriesTM production main case. The shift body, the main body and the separator plate are not interchangeable between the two generations of hardware. The current design incorporates a relocation of the dowel pin in order to prevent mixing of current and former designs.

Parts Modifications

Passageways and orifices have been added/modified to allow for the implementation of the Modulated Main Pressure feature. Mixing of former P/N valve body components will not be possible. Relocation of dowel pins and modification of separator plates is not allowed to facilitate the assembly of former and current components.

New Service Procedure

Removal and installation procedures for the complete assembly have not changed with this modification. However, it is important to know that the correct Wire Harness, P/N 29539792, must be used. This harness includes an additional connector for the current G solenoid. When securing the G solenoid to the Modulated Main Valve Body, be certain to insert the retaining clip from the "Main Body" side. The clip needs to become trapped between the two components. There are now six gold colored bolts (longer 65 mm (2.56 in) that secure the modulated main body to the valve body assembly and also to the main case.

Parts are currently available from GMSPO.