Allison B-Trim Pressure Control Solenoid
Part Number: 29533075
The Allison B-Trim Pressure Control Solenoid (29533075) is an OE-style replacement solenoid designed for 2001–2005 GM Duramax LB7 and LLY trucks equipped with Allison automatic transmissions. The B-Trim solenoid installs in the valve body and works in conjunction with the A-Trim solenoid to refine and smooth hydraulic pressure application during shifts.
While the A-Trim solenoid manages primary pressure, the B-Trim solenoid is responsible for fine-tuning clutch apply rates and shift timing. Proper B-Trim function helps control how quickly and smoothly clutches apply, reducing shift flare, harsh transitions, and erratic shift behavior under changing load conditions.
A worn or failing B-Trim solenoid can cause inconsistent shift timing, flare during gear changes, or harsh shifts even when overall line pressure appears normal. Replacing the B-Trim solenoid restores precise pressure modulation, improving drivability and ensuring predictable, repeatable shift quality during daily driving, towing, and higher-mileage operation.
Key Features and Benefits
- OE-style replacement for Allison B-Trim pressure control function
- Fine-tunes clutch apply rates for smoother, more controlled shifts
- Helps reduce shift flare and erratic shift timing
- Improves overall shift consistency and drivability
- Direct-fit valve body solenoid for service or rebuild work
- Recommended replacement during valve body service or high-mileage repairs
Common Symptoms of a Weak or Failed B-Trim Solenoid
- Shift flare during upshifts
- Inconsistent or erratic shift timing
- Harsh shifts not corrected by line pressure adjustments
- General drivability complaints related to shift quality
Applications
- 2001–2004 Chevrolet Silverado 2500HD 6.6L Duramax LB7
- 2001–2004 Chevrolet Silverado 3500 6.6L Duramax LB7
- 2001–2004 GMC Sierra 2500HD 6.6L Duramax LB7
- 2001–2004 GMC Sierra 3500 6.6L Duramax LB7
- 2004.5–2005 Chevrolet Silverado 2500HD 6.6L Duramax LLY
- 2004.5–2005 Chevrolet Silverado 3500 6.6L Duramax LLY
- 2004.5–2005 GMC Sierra 2500HD 6.6L Duramax LLY
- 2004.5–2005 GMC Sierra 3500 6.6L Duramax LLY
Fitment note: Proper operation of the B-Trim solenoid is critical for smooth clutch apply and shift refinement. For best results during valve body service, A-Trim and B-Trim solenoids are often replaced together.
