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.