Allison 1000 Problems: Causes, Fixes & Repair Costs

Sun West Transmissions — Glendale, AZ. Free estimates, honest diagnosis and a 3-year / 40,000-mile warranty on qualifying rebuilds and replacements.

The Transmission Behind the Duramax

The Allison 1000 is the heavy-duty automatic paired with the Duramax diesel in Chevy Silverado and GMC Sierra 2500HD and 3500HD pickups for many years, and it also appears behind some gas engines, in medium-duty trucks and in motorhome chassis. It started as a five-speed and later became a six-speed. Allison built its reputation on commercial transmissions, and the 1000 series is generally considered one of the toughest automatics in a pickup.

Tough does not mean trouble-free. Heavy towing, added power and Arizona heat all take a toll, and certain failure patterns show up again and again.

Common Allison 1000 Problems

Clutch Slip With Added Power

A stock Allison 1000 is designed around the factory torque rating. When a Duramax is tuned for significantly more power, the clutches, especially those applied in the lower gears and during heavy acceleration, can begin to slip. Slip codes, flare between shifts and burnt fluid are typical signs. Built transmissions with upgraded clutches and pressure control are the common fix.

Speed Sensor and Wiring Faults

The Allison uses input, turbine and output speed sensors. Damaged wiring, corroded connectors and failed sensors cause erratic shifting, harsh shifts and limp mode with speed sensor codes. These are among the easier Allison problems to fix. See code P0717 for related information.

Harsh Shifts and Adaptive Learning

The Allison controller adapts shift timing as clutches wear. After a battery disconnect, reflash or repair, adapts may need to be reset and relearned. A transmission that has hit the limits of its adapts shifts harshly or inconsistently, which can signal internal wear.

Solenoids and Pressure Switches

Shift and pressure control solenoids and the pressure switch assembly can fail, triggering codes and limp mode. These components are serviceable with the right tools and procedures.

Torque Converter Problems

Converter clutch wear causes shudder or slip codes at cruise, especially in towing trucks and those with added power. A failing converter also contaminates the fluid.

Overheating and Cooler Problems

Pulling heavy fifth-wheels and equipment trailers in summer heat can push fluid temperatures high. Restricted coolers, leaking cooler lines and a weak engine cooling system all contribute. See why transmissions overheat.

Leaks

Cooler line fittings, pan gaskets and seals can leak with age. Low fluid in an Allison causes slipping and heat quickly.

What You Can Safely Check

• Check fluid level using the procedure for your truck, with the fluid at operating temperature.
• Watch the transmission temperature reading if your truck displays it, especially when towing.
• Look for leaks at the cooler lines, pan and output seal.
• Note any codes, flashing lights or limp mode and when they occur.

If the truck slips or overheats while towing, pull over safely, let it cool and avoid further heavy towing until it is inspected. Read towing and your transmission.

How Sun West Diagnoses the Allison 1000

We scan the transmission controller for codes and review live data, including clutch slip values, adapt data, speed sensor readings and fluid temperature. We check wiring and connectors, inspect the fluid and pan debris, and road test loaded when needed. That tells us whether the problem is electrical, hydraulic or a worn clutch. Learn about our diesel transmission repair and heavy-duty truck transmission repair.

Repair Options

• Sensor, wiring and connector repair.
• Solenoid or pressure switch service.
• Adapt reset and relearn after repairs.
• Torque converter replacement, with heavy-duty options for towing.
• Cooling improvements, including an auxiliary cooling system.
• Rebuild with upgrades for power and towing. See our Allison 1000 rebuild page and transmission upgrades.

What It Costs

Cost depends on whether the problem is a sensor or a worn clutch pack, and on the upgrades you choose for your power level and towing needs. Call (623) 473-9800 for a free quote. Qualifying rebuilds and replacements include our 3-year / 40,000-mile warranty with no deductible on covered repairs, and financing is available.

When to Stop Driving

If the transmission slips under load, flashes a warning and goes into limp mode, or the temperature climbs into the red, stop towing. If it slips without a trailer or loses gears, stop driving and call.

Allison 1000 Problems: FAQ

Can a stock Allison handle a tuned Duramax?

Mild changes may be tolerated, but significant power increases often cause clutch slip. A built transmission is recommended.

Are Allison speed sensor problems expensive?

They are usually far less involved than internal repairs. Diagnosis tells us exactly what failed.

Do you work on Silverado and Sierra HD trucks?

Yes. See our Silverado 2500HD and Sierra 2500HD pages.