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Allison 1000 Transmission - Inside The Allison 1000

A Look At The History, Strengths, And Weaknesses Of GM's Iconic Transmission

Text By , Photography by Courtesy of General Motors Corp.

In the last two decades, the diesel powerplants offered in diesel pickups have come with ever-increasing horsepower and torque numbers. But, in order for manufacturers to meet durability standards, stronger powertrain components were needed. As the parent company of Allison (from 1928 to 2007), General Motors engineers knew which automatic transmission would be capable of handling its Duramax engine's 300 hp and 520 lb-ft at the turn of the century.

Beginning with the '01 Chevy and GMC 2500 HD and 3500 trucks, customers purchasing a Duramax-powered Silverado or Sierra had the option of backing it up with the legendary Allison transmission. No doubt, the Duramax and Allison combination provided one of the most bulletproof packages on the market, and many people bought GM trucks based on Allison's reputation.

Breaking Into The Light-Truck Market
According to the Society of Automotive Engineers (SAE), Allison conducted extensive studies of the North American light-truck market before the Allison 1000 was on the drawing board. Noticing a torque growth in diesel engines' torque rating of approximately 15 lb-ft per year (from 1990 to 1994), Allison's engineers believed diesels would be making 470 to 510 lb-ft by 2000. And with the Duramax's debut torque rating coming in at 520 lb-ft, we'd say they were spot-on in their power prediction.

Allison LCT 1000
Spawning from the success Allison had with its AT542 automatic transmissions in the medium-duty segment, the Allison LCT 1000 was a much-improved version to say the least. The Allison 1000 came with some key features that the AT542 lacked, such as a parking pawl, Overdrive gear, and a torque converter clutch. Production of the Allison LCT 1000 began in 1999.

Adaptive Learning and the Aftermarket
One of the most advanced features found in the Allison 1000 is its use of adaptive learning technology. The adaptive learning process refers to the transmission's constant comparison of key shift parameters to pre-programmed (ideal) shift conditions. The electronic transmission controls then make hydraulic adjustments to assure the key shift parameters match the engine's torque to create the ideal shift strategy for the next shift. This is done to keep the driving experience comfortable and avoids any rough shifting instances. This adaptive shifting process continues for the life of the vehicle to provide consistent, optimized shifts.

While being completely electronically controlled makes the Allison 1000 a modern technological marvel able to adapt to your current driving style and provide utmost comfort, it often hampers its abilities to perform in the aftermarket. The Allison's adaptive learning technology can actually work against it in the performance-oriented world because the transmission tuning tells it to expect stock torque values.

According to Allison, "The transmission controls have been highly integrated with Duramax diesel engines in GM pickups. Part of this integration is that the TCM has a map of each engine's torque output throughout its operating rpm. The TCM uses shift energy management (SEM) logic to control each shift. During most range shifts, there is more power available than necessary to maintain acceleration. The unused engine power traditionally goes into slipping clutches and results in additional heat without adding to vehicle performance. Through engine/transmission communication, SEM is the electronic control process that reduces torque during range upshifts to a level resulting in consistent transmission output torque before and after the shift. The net result is optimized shift quality as well as reduced clutch energy. Needless to say, when engine torque is increased significantly via various aftermarket methods, [the SEM logic] is greatly compromised."

Limp Home Mode
Many Duramax owners have experienced the Allison transmission's limp mode after they've modified their engine. This occurs when the computer senses excessive slippage, or if the transmission loses communication with the TCM. In limp mode, no signal is sent to the shift solenoids, and the only forward gear available is Third. Reverse and Neutral are usable, but by only allowing one forward gear to move the truck, the owner has no choice but to limp the vehicle home, or to the nearest shop, hence the name. While it can be considered a bad thing, limp mode is yet another testament to the Allison's success in that a mobile option still exists, even after some internal damage has been done. To be fair, the few weaknesses found in the Allison 1000 shouldn’t discourage anyone from owning a Duramax-powered Chevy or GMC truck. It’s a given that the aftermarket will find weaknesses in any manufacturer's transmission, so owners and potential buyers should always be reassured that, in stock form and if maintained properly, their Allison should last the life of the truck it motivates.

TORQUE CAPACITIES ('01 TO '10):
2001: Input torque capacity: 520 lb-ft
2005: Input torque capacity: 565 lb-ft
2006: Input torque capacity: 650 lb-ft
2008: Input torque capacity: 660 lb-ft
2010: Input torque capacity: Projected to be up to 750 lb-ft

ALLISON 1000 SERIES GEAR RATIOS ('01 TO '10):
1st 3.10, 2nd 1.81, 3rd 1.41, 4th 1.00, 5th 0.71, 6th* 0.61
Reverse 4.49

* For the '06 model year, a Sixth gear was added, giving the Allison 1000 the double-Overdrive option found on heavier-duty transmissions within the Allison family.

ALLISON 1000 FEATURES:

* The Allison 1000's transmission control module (TCM) receives information from the engine, torque converter turbine, output speed sensors, pressure switches, and range selector shaft position switch. It controls shifting using two pulsed solenoids in the transmission's valvebody.

* A power take-off (PTO) is optional on the Allison 1000 in the 3500 cab and chassis trucks. The PTO is driven off the torque converter turbine and is rated for 250 lb-ft of torque.

* The gearbox module (main case) consists of the geartrain, valvebody, input retarder, park pawl, and PTO gear.

* The '06-to-present transmissions feature the following modes: gear selection mode, park warm-up mode, low-traction mode, and cruise control grade braking.

* The Allison transmissions can use either TranSynd (recommended by Allison), or DEXRON-III (recommended by GM) ATF.

* An external, spin-on transmission filter simplifies service intervals (the internal filter only requires replacement in the event of an overhaul).

* The Allison 1000 uses a modular case design.

* The Allison 1000 is rated for a 5,000-rpm input shaft speed capability.

* The approximate dry weight of the transmission is 330 pounds with the PTO gear.

THE ALLISON'S WEAKNESSES:

* Adaptive Learning: The Allison compares key shift parameters to pre-programmed (and ideal) shift conditions and engine torque values on a continuous basis. Because of this, the transmission has to adapt to gain pressure rise. Going from city driving or towing to drag racing does not give the electronics a chance to prepare to make adequate, harder, faster shifts.

* C3 Clutch: Suffer from lack of lubrication. The only time this clutch receives fluid is when it is applied.

* C1 and C2 Clutches (five-speed only): The apply pistons that engage these clutches are off-centered, leading to uneven pressure being applied. Because of this, when they are worn, they are only 50 percent worn.

SOURCES
SAE International
755 W. Big Beaver, Suite 1600
Troy
MI  48084
248-273-2494
www.sae.org
Inglewood Transmission
500 S Raymond Ave
Inglewood
CA  92831
714-870-7300
www.inglewoodtransmission.com
Allison Transmission
4700 W. 10th St.
Indianapolis
IN  46222
317-242-5000
www.allisontransmission.com
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