GM, Duramax Diesel Transmission Guide

General Motors Automatic & Manual Transmission Ratios, Model Years

The Duramax diesel is not nearly as popular as the Duramax-Allison combination; the Allison 1000 transmission has played a significant role in the growth and development of General Motors' ventures in the diesel segment. Originally released as a five speed unit, a second overdrive gear was added to the Allison 1000 for the 2006 model year, and the six speed gearbox continues to grow with the 6.6L Duramax diesel. The combination is popular enough that it is much less typical to see manual transmissions in GMC and Chevrolet HD pickups than those of competing brands.

Transmission

Type

Manufacturer

Model Years

1st
(:1)

2nd
(:1)

3rd
(:1)

4th
(:1)

5th
(:1)

6th
(:1)

R
(:1)

TH400

3 spd auto

General Motors

1982 - 1990 6.2L diesel
(3/4 & 1 ton only)

2.48

1.48

1.00

n/a

n/a

n/a

2.07

SM465

4 spd manual

Muncie

1982 - 1991 6.2L diesel

6.55

3.58

1.57

1.00

n/a

n/a

6.09

NP440/NP833

4 spd manual

New Process

1982 - 1987 6.2L diesel

3.09

1.67

1.00

0.73

n/a

n/a

n/a

TH700R4

4 spd auto

General Motors

1982 - 1989 6.2L diesel
(1/2 ton only)

3.06

1.63

1.00

0.70

n/a

n/a

2.29

4L60E

4 spd auto

General Motors

1990 - 1993 6.2L diesel
(1/2 ton only)

3.06

1.63

1.00

0.70

n/a

n/a

2.29

4L80E

4 spd auto

General Motors

1991 - 1998 6.2L, 6.5L diesel
2001 - 2005 6.6 Duramax Vans

2.48

1.48

1.00

0.75

n/a

n/a

2.07

NV4500

5 spd manual

New Venture

1992 - 1994 6.5L diesel

6.34

3.44

1.71

1.00

0.73

n/a

6.34

NV4500

5 spd manual

New Venture

1995 - 1998 6.5 diesel

5.61

3.04

1.67

1.00

0.75

n/a

5.61

ZF S6-650

6 spd manual

ZF Friedrichshafen

2001 - 2006 6.6L Duramax

5.79

3.30

2.10

1.31

1.00

0.72

5.23

Allison 1000

5 spd auto

Allison Transmission

2001 - 2005 6.6L Duramax

3.09

1.81

1.41

1.00

0.71

n/a

4.48

Allison 1000

6 spd auto

Allison Transmission

2006 - current 6.6L Duramax

3.09

1.81

1.41

1.00

0.71

0.61

4.48

6L50

6 spd auto

General Motors

2005 - current 2.8L Duramax

4.07

2.37

1.55

1.16

0.85

0.67

3.20

Prior to introducing the Duramax-Allison combination, many transmissions made they're way into GMC and Chevrolet diesel applications. The NP440, sometimes referred to as the NP833, is notably rare but relatively easy to spot thanks to the acronym "OD" labeled on the shift knob in the 4th gear position. The transmission is a bit of an oddity in that it is a four speed, overdrive transmission. Do to its wide ratio spread and relatively tall first gear ratio, it's not often sought after in 6.2L diesel applications.

For all intents and purposes, the TH700R4 and the 4L60E are identical transmissions, however GM began using a different name convention in the early 1990s. This transmission was only available in 1/2 ton 6.2L diesel applications. 3/4 and 1 ton diesel applications received instead the TH400 and later 4L80E as the higher GVWR necessitated the need for a stronger transmission.

The NV4500 is a popular manual transmission in 6.5L diesel applications, although two versions have been used by GM. The 1992 to 1994 model year edition features a lower first gear ratio and favorably higher overdrive ratio. The NV4500 did not find its way into the Duramax platform, GM choosing instead to offer a ZF 6 speed manual transmission. GM has not offered a manual transmission in a Duramax equipped Silverado/Sierra pickup since the 2006 model year.