Allison 1000 / 2000 / 2400 Transmission Guide: 5-Speed vs 6-Speed, ID & Parts
Allison's 1000, 2000 and 2400 Series (GM LCT1000) are one family of automatics for light- and medium-duty trucks: a 5-speed from 2001 to 2005 and a 6-speed from 2006 to 2019. Most people know the 1000 as the transmission behind the Duramax diesel in Chevrolet Silverado and GMC Sierra HD pickups. The same family went into medium-duty trucks, motorhome chassis and commercial vehicles. In 2020 the GM HD pickups moved to the newer 10-speed 10L1000.
Working on a 2020 or newer GM HD truck? That is the 10-speed Allison 10L1000. See our 10L1000 oil level & fluid capacity, clutch clearances and gear ratios pages.
Applications
- Chevrolet Silverado / GMC Sierra 2500HD and 3500 (2001–2019): behind the 6.6L Duramax diesel and the 8.1L Vortec gas V8
- GM medium duty: Chevrolet Kodiak / GMC TopKick, and the 2019-on Silverado 4500HD/5500HD/6500HD
- Motorhome and commercial chassis: including Workhorse motorhome chassis and the Ford F-650
5-Speed or 6-Speed? Duramax Years
| Duramax engine | Model years | Allison 1000 |
|---|---|---|
| LB7 | 2001 – 2004 | 5-speed |
| LLY | 2004½ – 2005 | 5-speed |
| LBZ | 2006 – 2007 | 6-speed |
| LMM | 2007½ – 2010 | 6-speed |
| LML | 2011 – 2016 | 6-speed |
| L5P | 2017 – 2019 | 6-speed |
The 6-speed came in for 2006, and the 8.1L gas V8 got it the same year. Model year is the quickest way to tell the generations apart: 2005 and earlier is a 5-speed, 2006 and later is a 6-speed.
Gear Ratios
Gears 1 through 5 are the same in both generations. The 6-speed adds a second overdrive.
| 1st | 2nd | 3rd | 4th | 5th | 6th | Reverse |
|---|---|---|---|---|---|---|
| 3.10:1 | 1.81:1 | 1.41:1 | 1.00:1 | 0.71:1 | 0.61:1 (6-speed only) | 4.49:1 |
Identify Your Valve Body and Electrical Parts by Year
Solenoids, the internal harness and the valve body changed several times. Order these by year, not just by "Allison 1000." Sonnax identifies four valve body versions: two 5-speed and two 6-speed (Sonnax: Identifying Allison 1000/2000/2400 valve bodies).
| Years | Valve body | Matching parts we stock |
|---|---|---|
| 2001–2003 | 5-speed, six solenoids, one tube on the bottom | Internal harness (1999–2003, 6-solenoid), solenoid kit (2000–2005) |
| 2004–2005 | 5-speed. Adds a seventh solenoid (solenoid G) in a small modulated main pressure housing. | Internal harness (2004–2005, 7-solenoid), solenoid kit (2000–2005) |
| 2006–2009 | 6-speed. A second tube from the modulated main housing, and a different converter clutch solenoid with a red connector. | Internal harness (2006–2009, gray connector), solenoid kit (2006–2019) |
| 2010 on | 6-speed, redesigned. Does not interchange with any earlier valve body. | Solenoid kit (2006–2019), or the alternate 2010–2019 kit for units with two PCS1 solenoids |
Overhaul kits are split the same way: 2001–2005 and 2006–2019. Internal filters come in shallow-pan and deep-pan versions, so check your pan before ordering.
Fluid and Level Check
- 2001–2005 (5-speed): factory fill was DEXRON-III.
- 2006 and later (6-speed): GM specifies DEXRON-VI.
- Check the level hot, with the sump at 160–200°F (71–93°C). A cold reading is only a reference. A filter and pan service on the stock pan takes about 7.4 quarts. Always finish by setting the level on the dipstick.
- Besides the internal filter in the pan, there is an external spin-on filter.
Common Parts We Stock
Rebuild and overhaul kits
- Custom Allison rebuild kit and the custom Superpak kit, where you choose the clutch pack for each position
- Overhaul kits: 2001–2005, 2006–2019. Molded rubber piston kits: 2001–2005, 2006–2015.
Clutch packs
- Raybestos Superpak kits: C1, C2, C3, C4, C5. Also the friction module and the steel module.
- Alto PowerPacks: C1 G3, C2 G3, C3 G3, C4 G3, C5. Also the C2 GPZ friction.
Service, filters and seals
- Filters: external spin-on, internal deep pan (1999–2009), internal deep pan (2010 on), internal shallow pan (1999–2006), internal shallow pan, 2nd design (2006–2018)
- Oil pan gasket, front pump seal, bell housing plate gaskets (front, rear), bell housing bolt seal
- Solenoid filter screen and the pan magnet
Electrical
- Solenoids: trim A (2000–2005), trim B (2001 on), shift C/D/E (2000–2005), plus the solenoid kits listed above
- Pressure switch manifold: 4-switch and 6-switch, with a seal set; speed sensor
Valve body, shift kits and converters
- Rebuilt Allison 1000 valve body, TransGo A1 shift valve kit, Sonnax lube regulator spring kit (1999–2003)
- TransGo shift kits: Allison SK (2001–2005), SK Jr (2005–2010); also the cooler bypass delete kit
- Torque converters: low stall with billet cover, medium stall, high stall, 2010–2017 13.5"
- Hard parts and tools: the TCS billet main shaft, output shaft nut sockets (2001–2009, 2010 on), and a holding fixture
Shop Allison 1000 / 2000 / 2400 parts · Shop 10L1000 parts · All GM & Allison transmission info
Not sure which year group your unit falls in? Send us your VIN or call us at (844) 298-6404, Monday–Friday 8–5 Eastern, or email sales@globaltransmissionparts.com.