Shop Talk: Anatomy of an Allison 3000 Transmission

Categories: Shop Talk, Transmissions

Allison 3000 Series Transmission Cutaway Illustration

What Does an Allison 3000 Series Transmission Look Like?

Craig Oster Mechanic

Curious about your medium-duty vehicle’s transmission? You’ve come to the right place. Today, US Transmissions Service Manager Craig Oster is providing a closer look at the Allison 3000 Series Transmission.

Why We Chose the Allison 3000

The Allison 3000 Transmission is the most-used transmission on the road today for trucks. In our last episode, Shop Talk: Check Transmission Light, we used an Allison 3000 Transmission as our example – not because it’s a problematic transmission, quite the opposite – because it is the workhorse transmission for medium-duty trucks most in use today.

The Allison 3000 has been in production since 1993. Medium-duty Class 6 trucks using the 3000 transmissions have an average age of 2.12 (the oldest on the road) and there are an estimated 2.155 million of these active trucks in service.

 

What is Considered a Medium-Duty Truck?

Freightliner.com has written extensively about medium-duty trucks. Medium-duty trucks fall into Classes 6-7 and have a gross vehicle weight (GVW) rating range of 19,501- 60,000 lbs. Medium duty trucks are used for a variety of lighter duty applications.

 

Allison 3000 Series Transmission Anatomy

 

Orientation

In this illustration, the right is the driver’s side and the left is the passenger side. The large end of the transmission faces the front of the vehicle.

Allison 3000 Series Torque Converter

Allison 3000 Series Transmission Torque Converter
Figure 1: Allison 3000 Series Transmission as Shown from the Front

 

Allison 3000 Series Transmission Torque Converter
Figure 2: Allison 3000 Series Transmission, Torque Converter Highlighted

 

The torque converter is located at the front of the Allison 3000 Series transmission in the center of the dial as highlighted in Figure 2 (above). Of course, with the transmission installed and functioning, there is no way to “see” the torque converter, but this is where it located.

Purpose of the Torque Converter

The transmission torque converter is a fluid coupling that enables the vehicle to get started. Then, as the speeds progress, it has a lockup clutch within the torque converter that applies to make it to make a 1-to-many connection.

 

Engine Speed Sensor

Allison 3000 Series Transmission, Passenger Side
Figure 3: Allison 3000 Series Transmission, Passenger-Side Profile
Allison 3000 Series Transmission Engine Speed Sensor Highlighted
Figure 3: Allison 3000 Series Transmission, Engine Speed Sensor Highlighted (Passenger-Side)
Purpose of the Engine Speed Sensor

The Engine Speed Sensor assessed the speed at which the crankshaft spins. This electronic control device sends crucial information to the transmission.

The PTO

The PTO can be driven off of either side of the transmission. Therefore, there are two plates on either side as shown below:

Allison 3000 Series transmission Driver's Side
Figure 5: Allison 3000 Transmission, Driver’s Side View
Allison 3000 Series Transmission Driver's Side PTO Access Cover
Figure 6: Allison 3000 Series Transmission Driver’s Side PTO, Highlighted
Allison 3000 Transmission, Passenger Side View
Figure 7: Allison 3000 Transmission, Passenger Side View
Allison 3000 Transmission, Passenger Side View PTO Access Cover Highlighted
Figure 8: Allison 3000 Transmission, Passenger Side View PTO, Highlighted

 

Dipstick Hole

Allison 3000 Series transmissions are manufactured with a dipstick hole on either side of the transmission. One side or the other will be in use; the side not in use will be plugged (see Figure 11 below).

Allison 3000 Transmission passenger side view
Figure 9: Allison 3000 Series Transmission, Passenger Side View
Allison 3000 Series Transmission Dipstick Hole
Figure 10: Allison 3000 Series Transmission, Dipstick Hole Highlighted (Passenger Side)
Figure 12: Allison 3000 Transmission, Plugged Dipstick Hole Highlighted (Driver Side View)

 

Allison 3000 Series Transmission Data Tag

The transmission data tag displays information such as the serial number and sometimes the part number, but most importantly, it displays how the transmission was built. This tells mechanics everything they need to know about how a transmission is built. This is located below the Dipstick Hole on the transmission (see Figure 13 below):

Allison 3000 Series Transmission, Data Tag Highlighted
Figure 13: Allison 3000 Series Transmission, Data Tag Highlighted (Passenger Side View), located below the Dipstick Hole.

 

Main Transmission Connector or 20-Way Connector

The 20-Way connector is located beside and behind the dipstick hole as shown in Figure 14 (below). It is considered the transmission’s artery, running from the computer to the transmission’s main solenoids, transmission, and to the switches.

Allison 3000 Series Transmission, Main Transmission Connector, 20-Way Connector, Highlighted
Figure 14: Allison 3000 Series Transmission, Main Transmission Connector, 20-Way Connector, Highlighted

 

Dipstick Tube Mounting Hole

The bolt hole directly above the 20-way connector is the mounting hole to the dipstick tube (see Figure 15 below).

Allison 3000 Series transmission Output Fly-In
Figure 15: Allison 3000 Series Transmission Output Fly-In (Passenger Side View)

 

Allison 3000 Series Transmission Output Speed Sensor

The output speed sensor is located at the lower rear of the transmission, behind the 20-way connector (see Figure 17 below). In our previous discussion, Shop Talk: Check Transmission Light, we recommended checking the Output Speed Sensor.

 

The Allison 3000 Series transmission’s Turbin Speed Sensor is located inside the transmission.

Note: The Allison 1000 Series, 2000 Series, and 4000 Series transmissions have three external speed sensors:

  • On the front lower passenger side: the Engine Speed Sensor
  • In the middle: Turbin Speed Sensor
  • One in the back passenger side: Output Speed Sensor
Allison 3000 Series Transmission, Right Lower Rear, Passenger Side View
Figure 16: Allison 3000 Series Transmission, Right Lower Rear (Passenger Side View)
Figure 17: Allison 3000 Series Transmission, Output Speed Sensor Highlighted (Passenger Side View)
Figure 17: Allison 3000 Series Transmission, Output Speed Sensor Highlighted (Passenger Side View)

 

Allison 3000 Series Transmission Control Module (Underside of Transmission)

Allison 3000 Series Transmission, Underside View
Figure 17: Allison 3000 Series Transmission, Control Module (Underside View)

Two Filter Areas on Either Side of the Transmission

There is a Main Filter (Figure 18: Right Side) and a Lube Filter (Figure 18: Left Side). The filters come in a kit that contains the filters, seals, and gaskets.

Allison 3000 Series Control Module Filters Highlighted
Figure 18: Allison 3000 Series Control Module, Filters Highlighted

Allison 3000 Series Transmission Oil Flow

Oil leaves the transmission to be cooled (see Figure 19 below) via the To Cooler Port and returns to the transmission (see Figure 20 below) via the From Cooler Port. Notice the Arrow pointing up to a plug labeled “To Cooler.”  The To Cooler Port is where the oil leaves the transmission and goes to an oil cooler to be cooled. In Figure 20 below, notice the incoming arrow pointing down towards the Lube filter. This is the From Cooler Port is where the cooled oil returns to the transmission.

Allison 3000 Series Transmission To Cooler Port
Figure 19: Allison 3000 Series Transmission, Control Module, To Cooler Port
Allison 3000 Series Transmission From Cooler Port
Figure 20: Allison 3000 Series Transmission, Control Module, From Cooler Port

 

Allison 3000 Series Transmission Clutches

The Allison 3000 Transmissions allows for the capability to check individual clutch pressures. We can diagnose each individual clutch. In Figure 21 (below), notice the individual clutch numbers. Those, predictably, correspond to that specific clutch.

Allison 3000 Series Transmission, Control Module, Clutches Highlighted
Figure 21: Allison 3000 Series Transmission, Control Module, Clutches Highlighted

 

So these are the main components of the Allison 3000 Series Transmission. We hope this tour has been helpful to those who want to better understand the location of the main components of this transmission.