Rebuilding an Allison Transmission in an LB7 Duramax Engine

Rebuilding an Allison Transmission in an LB7 Duramax

The LB7 Duramax engine paired with the Allison 1000 5-speed automatic transmission is a powerful and reliable drivetrain combination found in many Chevrolet and GMC trucks from 2001-2004. However, even the most robust transmission can eventually wear out after years of hard use. When that happens, a rebuild is often the most cost-effective solution to get your truck back on the road.

Symptoms of a Failing Allison Transmission

Some common signs that your Allison 1000 is in need of a rebuild include:

• Delayed engagement when shifting gears
• Slipping between gears
• Burning smell from the transmission fluid
• Vibration or shuddering when shifting
• Noisy operation
• Leaking fluid
• Illuminated check engine light

If you experience any of these issues, it's wise to have the transmission inspected and rebuilt sooner rather than later. Allowing the problems to persist can lead to even more expensive repairs down the road.

Removing the Transmission

The first step in rebuilding an Allison 1000 is to remove it from the vehicle. This involves:

1. Lifting the truck securely on jack stands
2. Draining the transmission fluid
3. Disconnecting the cooler lines, wiring harness, and shift linkage
4. Unbolting the transmission from the engine and dropping it out

Having a transmission jack makes removal much easier. The Allison 1000 is heavy, weighing over 200 lbs, so safe lifting procedures are critical.

Disassembly and Inspection

With the transmission out of the truck, it's time to tear it down to the component level. The teardown process involves:

• Removing the valve body and sensors
• Splitting the transmission cases
• Extracting the planetary gear sets, clutches, bands, bearings, seals, and shafts

A thorough inspection of all parts follows the disassembly. Look for any damaged, worn, or cracked components. Pay special attention to the condition of the friction materials on the clutches and bands. Also check the transmission case for any cracks or other defects. Any compromised parts must be replaced.

Cleaning and Reconditioning

All reusable parts should be cleaned before reassembly. Use a degreaser to remove old fluid and debris. The valve body channels must be flushed completely clean as well. It's also wise to check shaft end play and runout to verify they are within spec after cleaning.

In addition to cleaning, some components may need reconditioning before being reused. This includes:

• Resealing bearings and bushings
• Replacing seals, gaskets, and O-rings
• Resurfacing sealing surfaces
• Checking springs for proper tension

Any reconditioning should only be performed by an experienced transmission rebuild specialist with the proper tools.

Reassembly and Installation

Once all parts have been inspected, cleaned, and reconditioned as needed, the transmission can start going back together. Here are the key steps:

1. Install bushings, bearings, seals, and gaskets
2. Assemble the planetary gear sets into the case
3. Install the shafts, clutches, and bands
4. Mount the valve body and torque fasteners to spec
5. Mate the case halves and bolt together
6. Reinstall modulator, sensors, PCM, hoses, wires, linkage
7. Add proper amount of transmission fluid

Take care to follow all factory assembly procedures. Double check torque values and lash adjustments where applicable. Proper reassembly is critical to a successful rebuild.

Once fully assembled, the transmission can go back into the truck. Take care aligning it on the mounting pads and inserting all attachments properly. Refill with transmission fluid and verify proper levels.

Post Rebuild Testing

After a complete Allison 1000 rebuild, the transmission should be road tested thoroughly. Drive the truck through all gears, and pay attention to how smoothly it shifts. Accelerate moderately and come to steady stops to feel for any vibration or slippage.

Also verify that temperature and pressure readings are within normal ranges. Address any leaks, noises, delayed engagement, or error codes immediately. It's much easier to diagnose and correct issues right after the rebuild rather than later down the road.

Assuming all checks out, your Allison transmission should now be good for many more miles of reliable service! Proper maintenance is always recommended to maximize longevity.

FAQs about Rebuilding an Allison Transmission

Here are some frequently asked questions about rebuilding an Allison 1000 transmission:

How much does it cost to rebuild an Allison transmission?

A professional Allison 1000 rebuild typically costs $2,000 to $3,000 in parts and labor. The exact cost depends on how many new parts are needed, if the torque converter is rebuilt, and local labor rates.

Is it better to rebuild or replace an Allison transmission?

For the LB7 Duramax application, rebuilding is usually better than replacing unless the transmission case itself is damaged. Rebuilding allows reuse of the high-quality OEM components while replacing worn parts.

How long does an Allison transmission rebuild take?

The total job can take 15-40 hours from transmission removal to reinstallation. The rebuild itself is typically 6-10 hours for an experienced transmission builder working in a fully equipped shop.

What causes an Allison transmission to fail?

Common reasons for Allison 1000 failures include worn friction materials, leaks, overheating, electrical issues, abuse/neglect, and excessive mileage. Regular fluid changes and proper driving can maximize longevity.

How long do rebuilt Allison transmissions last?

A properly rebuilt Allison 1000 can easily last over 200,000 miles if well-maintained following the rebuild. Sticking to the recommended fluid and filter service intervals is key.

Recap

Rebuilding the Allison 1000 5-speed automatic transmission in an LB7 Duramax is a cost-effective repair to get these hard-working trucks back on the road. Look for slipping, vibration, leaks, or error codes to indicate a worn transmission. A professional rebuild with quality parts can often be a better value than replacing the transmission outright. Proper teardown, inspection, cleaning, reassembly, and post-rebuild testing helps ensure a successful job. Taking care of your rebuilt Allison with regular fluid changes will maximize its longevity.

FAQs

What tools do I need to rebuild an Allison transmission?

Proper tools like an impact gun, torque wrench, specialty tools for disassembly/reassembly, transmission jack, and other standard mechanics tools are required. Renting or buying quality tools is recommended over trying to rebuild without the right equipment.

Can I drive with a failing Allison transmission?

It's not recommended to continue driving with a badly slipping or malfunctioning Allison transmission. Doing so risks further damage and more extensive repairs. Have it inspected and rebuilt as soon as possible.

Will a rebuild restore an Allison transmission to like-new condition?

Essentially yes - a proper rebuild with quality parts will return the Allison transmission to factory-fresh performance and longevity. Proper reassembly and testing helps ensure OEM-level quality.

How often should I service a rebuilt Allison transmission?

Follow the factory recommendations for fluid and filter changes, typically every 25,000-30,000 miles. Use only approved fluids to avoid damage and maximize the lifespan.

What is the warranty on a rebuilt Allison transmission?

Most professional Allison rebuild shops will provide a 12,000-24,000 mile or 1-2 year warranty on parts and labor. Longer warranties are sometimes offered for an added cost.