Allison 1000 Transmission

Allison 1000 Specs & Ratios

The Allison 1000 has been the standard automatic transmission for the Duramax diesel since its inception in 2001. At this time, transmission's size, strength, and versatility far exceeded anything available from the Duramax's direct competitors. The Allison 1000 was a five speed transmission from 2001 to 2005 model years, while a significant upgrade for the 2006 MY included the addition of a second overdrive gear, making it a six speed transmission. Allison's specialty is commercial grade automatic transmissions for medium and heavy duty applications, which includes everything from transit buses to tractor trailers. Acquired by General Motors in 1929 following the death of the company's founder, Allison's history includes the development of propulsion systems for aircraft and other military applications prior to the end of the WWII. GM sold Allison Transmission in 2007, although Duramax powered pickups continue to use their transmissions.

Allison 1000 Transmission Features

Moderate changes have occurred to the transmission throughout the years however the platform itself has, for all intents and purposes, remained the same since 2001. The most notable modification has been the transition from a five to six speed model, which lowered cruising rpm by roughly 14% in high gear. This addition is particular attractive in terms of fuel consumption, as the lower engine speeds create an opportunity for greatly improved fuel economy on the highway. Rather than becoming outdated, the Allison has evolved to match the performance characteristics and demands of the Duramax turbodiesel, which has undergone significant changes itself through the years.

Manual transmissions are relatively rare for Duramax powered GMC/Chevrolet pickups, the primary reason being the attractiveness of the Allison 1000. General Motors was the first of the "Big 3" to phase out a manual transmission option for their diesel - the ZF 6 speed was last offered for the 2006 model year. Modern automatic transmissions, such as the Allison 1000, are far superior to manual transmissions in almost every category. While a manual transmission is obviously a much simpler machine, there can be no integration between engine parameters and transmission shift schedule; such communication between powertrain components brings us innovative features that include engine braking and dynamic shift schedules. Additionally, the Allison 1000 is rated with a far greater input torque capacity than any outgoing manual transmission.

The Allison's external filter eliminates the need to frequently service the internal filter and greatly reduces maintenance time/cost. It also relies on adaptive technology which integrates the transmission with the engine control module to continuously monitor driver input and calculate ideal shift strategies for the particular driving conditions.

Allison 1000 Ratios








3.094 : 1

1.809 : 1

1.406 : 1

1.00 : 1

0.711 : 1

0.614 : 1

4.480 : 1

* 6th gear available in 2006+ model years.

Allison 1000 Specs


Allison 1000

Production Plant:

White Marsh, Maryland (Baltimore)


• Light/medium duty diesel trucks
• All Duramax diesel equipped Chevrolet/GMC trucks with auto trans

Production Years:

• First produced in 1999
• Produced for Duramax applications 2001 - present


• 5 speed, 2001 to 2005 model years
• 6 speed, 2006 to present model years


~ 330 lbs dry

Max Input RPM:

3,300 rpm (2015 MY spec)

Nom. Max Input Torque:

• 520 lb-ft (01 - 05 MY)
• 565 lb-ft (05 MY)
• 650 lb-ft (06 - 07 MY)
• 660 lb-ft (08 - 10 MY)
• 765 lb-ft (11 - 16 MY)
• Not currently available for 2017 MY


Dexron-III (5 spd models) or Dexron-VI ATF (6 spd models), roughly 13 quart total fluid capacity and 7.4 quart refill capacity w/ filter change.

Allison 1000 Strengths & Weaknesses

The Allison's obvious strength is its robust size, as the 1000 series transmission is designated for medium duty applications. Intuitively, this demonstrates that the transmission is inherently sufficient for class 3 and 4 GMC/Chevrolet pickups. The six speed model also has dual overdrives, with the second overdrive ratio being rather high. This allows for low engine speeds at cruising rpm and ultimately opportunities for significantly reduced fuel consumption in relative terms.

The Allison is not without a few weaknesses, which include insufficient lubrication to the C3 clutch and the off-center engagement of the C1 and C2 clutches. Low fluid flow to the C3 clutch has been known to be a leading cause of premature failure in the Allison, although it's not generally a cause for concern and there exists no phenomenon of widespread failures as a result of this issue. The C1 and C2 clutch pistons engage their respective clutch systems from the side (off-center), which typically causes uneven wear on these clutch packs. Again, the problem is frequently noted during transmission rebuilds, but has not been largely attributed to premature transmission failure.

A common occurrence for Duramax owners who chose to install aftermarket tuners/programmers (for performance improvements) is experiencing the transmission's "limp mode". This is a safety feature built into the Allison's programming which locks the transmission in 3rd gear if rapid or excessive slippage is detected. The concept is to protect the owner from being stranded as the result of serious transmissions problems, as the system identifies the slippage as abnormal and possibly a sign of severe problems. When this occurs, owners will experience a significant decrease in engine performance and reduced vehicle speed (performance and ratio limited).