Decoding Chevrolet Automatic Transmissions: A Comprehensive Guide

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Have you ever popped the hood on your Chevy and wondered, “What transmission do I have?” Identifying a Chevy automatic transmission can seem tricky, but this guide will walk you through how to ID all the popular GM auto transmissions used over the years.

A Brief History of Chevrolet Automatic Transmissions

Chevy has used several different automatic transmissions over the years in their vehicles. Here’s a quick overview:

  • Powerglide – Chevrolet’s first automatic transmission, used from 1950-1973 in rear-wheel drive cars. Simple 2-speed design with just 1st and 2nd gear.
  • Turbo Hydra-Matic – 3-speed auto introduced in 1964. Used in numerous rear- and front-wheel drive GM models over the years. Still in use today.
  • 700R4/4L60 – 4-speed overdrive trans. Debuted in 1982 and replaced the Turbo 350 in many applications.
  • 4L80E – Heavy duty 4-speed overdrive trans. Came out in 1991 for trucks and large SUVs.
  • 4T65E – Front-wheel drive 4-speed, introduced in 1997. Replaced the TH-125/4T40E.
  • 6L80/6L90 – 6-speed was introduced in 2006. Found in late-model rear-wheel drive cars and trucks.

There are some other oddball transmissions, but these are the major ones found in most Chevy vehicles. Now let’s look at how to identify each of these key auto transmissions.

Key Ways to Identify a Chevy Auto Transmission

Here are the main ways to ID which transmission you have in your Chevy:

1. Check the Vehicle Identification Number (VIN)

The quickest way is to check the VIN code. The 8th digit will indicate the transmission.

For example, if the 8th digit is “M”, that signifies a TH700R4/4L60. If it’s “T”, that indicates a 4T65E trans.

Here are the VIN codes for most Chevy auto transmissions:

  • M – TH700R4/4L60
  • 7 – TH200-4R
  • 8 – TH350
  • 9 – TH400
  • T – 4T65E
  • U – 4T80E
  • V – 4L80E
  • 5 – TH125/4T40E
  • R – MM5/5LM60

So check your VIN sticker on the door jamb or paperwork and look up that 8th digit code to quickly ID the transmission.

2. Check the Transmission PanBolt Pattern

The transmission pan shape and bolt pattern is unique for each model. Count the bolts and look for an ID tag.

For example, a TH350 pan is rectangular with 12 bolts. The TH700R4 uses a square pan with 16 bolts. A 4L60 has 16 bolts but a drain plug located in the right rear corner.

Truck transmissions like the 4L80E have a larger irregularly shaped pan. So bolting up a new pan is one way to confirm which trans you’re working on.

3. Count the Solenoids

Most modern transmissions are electronically controlled by solenoids. Simply count the number of electrical solenoids on the outside of the transmission case to narrow it down.

For example, the 4L60E has 5 solenoids. The newer 4L65E has 7 solenoids. A 4T65E has 8 solenoids on it.

So visually counting the solenoids can quickly eliminate certain transmissions that don’t match up.

4. Check the Gear Selector Positions

The gear selector PRNDL pattern can also offer clues as to which Chevy trans you have.

The TH350 and TH400 have a simple PRNDL pattern with no overdrive. The TH700R4 adds an overdrive (“D”) in the shifter pattern after 3rd gear.

Newer transmissions like the 6L80 have a manual mode (M) and tow/haul mode (T) selector on the gear shift lever.

So check your gear shift indicator which helps narrow down domestic transmissions. Import models may vary.

5. Look up the RPO Transmission Code

Chevy uses RPO codes to identify all installed components. This code can be found on the service parts identification sticker usually located in the glove box.

It is typically a three-letter code that looks like “MX0” or “MG5”. Enter this RPO into a decoder chart and it will specify the exact transmission model.

For example, MD8 decodes to a TH700R4, while M30 is a TH350 trans. These RPO codes eliminate any guessing since they pinpoint the precise transmission.

6. Research by Year/Make/Model

If you don’t have the VIN or RPO sticker, some research of the OEM transmission used for that make/model/year can get you pretty close. For example:

  • The Turbo 350 was used in most Chevy V8s thru the 60s and 70s.
  • The 2004 Chevy Trailblazer came with either a 4L60E or 4L65E trans.
  • All fifth-gen Camaros had the 6L50 transmission.

While not foolproof, checking reference guides for that vehicle’s drivetrain gives you an educated guess. Always confirm using the VIN if possible.

How to Tell if it’s 2WD vs 4WD Transmission

Another important factor is determining if you have a 2WD or 4WD transmission.

Here are some tips for identifying 2WD vs 4WD Chevy transmissions:

  • 2WD – Typically have longer, skinny bell housings. The drive shafts hook directly to the tail shaft.
  • 4WD – Use shorter, wider bell housings to accommodate the transfer case. Driveshafts connect to the transfer case output.
  • VIN – 2WD versions have a “W” for 4th digit. 4WD models use an “N”.
  • Trans ID – 4WD models are labeled with “HD” or “NP8”. Examples: 4L80HD, NP8HD
  • Case Length – Measure front to back. 14″ case is 2WD, while the 4WD measures around 12″.
  • Tailhousing – 2WD tails are longer and removable. 4WD has integrated non-removable tail sections.
  • Fluid Lines – 2WD has cooler lines on the driver’s side. 4WD lines are on the passenger side.

So pay attention to VIN, measurements, and hardware differences to discern between 2WD and 4WD transmissions. Matching hardware is critical during swaps to avoid driveline vibrations.

Identifying Individual Chevrolet Transmissions

Now let’s dive into the unique features and identifiers of each major Chevy auto transmission family:

Powerglide

  • The first automatic trans-Chevy was produced starting in 1950 for rear-wheel drive cars.
  • Simple and durable 2-speed design (1st and 2nd gear only). No park gear so had to use a hand brake.
  • Used until 1973 in Chevy cars and trucks. Also popular in drag racing for reliability.
  • Aluminum Powerglide case with drain plug in the middle of the pan. Hard to misidentify this vintage 2-speed transmission.

Turbo Hydra-Matic 350 and 400

  • TH350 came out in 1969 as a 3-speed automatic designed for high-torque V8s.
  • Strong performance reputation but lacks overdrive so highway RPMs are higher.
  • Bellhousing bolts are staggered in two rows rather than a single row like most transmissions.
  • Rectangular oil pan drained through the indent Guide Pins on the passenger side.
  • TH400 introduced in 1964 was a heavier-duty 3-speed for trucks and muscle cars.
  • Same lack of overdrive but with extra-wide gear spacing for fast launches off the line.
  • Look for the “TH400” ID tag on the case to confirm what you’ve got.

700R4 and 4L60E

  • The 700R4 emerged in 1982 as a 4-speed overdrive transmission for GM rear-wheel drive cars and trucks. Replaced many TH350s and TH400s.
  • 4th gear is 0.7:1 overdrive which lowers highway RPMs for better fuel economy.
  • Uses a 16 bolt square pan. Dipstick is located on the passenger side near the firewall.
  • Electronic shift controls were added in 1993, hence the name change to 4L60E. Same case as 700R4, just upgraded internals.
  • Overall one of the most widely used late-model GM transmissions well into the 2000s.

4L80E

  • Beefed-up heavy-duty version of the 700R4 introduced in 1991. Sometimes called the “Turbo 400 with overdrive.”
  • The signature extra-large bell housing and shift lever are located in the center of the case.
  • Typical in 3/4 and 1-ton GM trucks, full-size vans, and commercial vehicles. Rare in SUVs or cars.
  • Mostly electronically controlled 4L80E, but some early hybrid versions had a TV cable shifter.

Front Wheel Drive Transaxles

GM began introducing front-wheel drive models in the 1980s. Key transaxles found in cars like the Chevy Cavalier include:

  • TH125/4T40E – Early Rangers, Sprints and other FWD cars. Had 3 speeds plus reverse. Light duty low torque rating.
  • 4T60E – Upgrade to the TH125. Used in mid-90s FWD GM vehicles. Medium torque capacity.
  • 4T65E – As the name suggests, a 4-speed evolution to the 4T60. Heavier duty and higher torque rating. Used in Malibus, Aleros, Grand Ams.
  • 6T70/6T75 – 6-speed FWD transaxles. Introduced in 2008. Higher torque capacities thanks to 6 gears. Found in newer Malibu, Impala, Buick LaCrosse models.
  • Compared to rear-wheel drive transmissions, FWD transaxles have side-mounted cases and no tail shaft since the axles exit the front.

6L Transmissions

The latest generation of Chevy automatics:

  • 6L50 – 6-speed RWD trans introduced on performance cars like the 2008 CTS-V. Handles up to 565 lb-ft torque.
  • 6L80 – Heavy duty truck version launched in 2006 for pickups and SUVs. Also 6 speeds but built for higher 665 lb-ft ratings.
  • 6L90 – Closely related to 6L80 with minimal changes to internal components. Found in late-model trucks and performance sedan applications.
  • These modern 6-speeds deliver greater efficiency, better acceleration, and enhanced towing capability compared to their 4-speed predecessors.

Conclusion

Identifying unknown Chevy automatic transmissions can seem daunting. But using VIN codes, counting solenoids, inspecting bell housings, and understanding model evolution will help you decide which transmission is sitting in your Chevy.

The key is matching hardware to avoid potentially destructive driveline vibrations. Many Chevy transmissions interchange within drivetrain families, but component compatibility must be checked.

With this comprehensive guide, you now have the knowledge to positively ID the most popular Chevrolet auto transmissions. So grab a wrench and start wrenching!

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