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manual transmission swap basics

Transmission Swap Basics

What is the purpose of a Transmission Swap?

In simple terms, a transmission swap involves switching the transmission in your vehicle from the Original Equipment Manufacturer (OEM) or factory spec transmission to another that initially was not offered on the assembly line. Typically, when discussing the topic of swapping a transmission, it refers to an automatic to manual transmission swap. However, it also applies to any change for performance benefits. To understand better what these benefits might be, let’s look at a common transmission swap.

 Comparing Transmissions

G Force LS Cummins Tranmission Adapter Kit

While the advantages are familiar to the experienced car enthusiast, the similarities between transmissions might cause a novice to question why one would choose to swap one transmission for another.

As an example, the 4L60, 700R4, and TH2004R are all 4 speed automatic transmissions. However, when comparing the two aftermarket transmissions to the OEM part, the factory transmission cannot withstand high power. In addition, it does not offer electronic tunability, which is critical for optimal performance.

Unlike the TH2004R, the 4L60 is computer controlled. This means that modifying shift points, torque converter lockout, and other tuning parameters is as simple as adjusting a program. On the other hand, the TH2004R requires full disassembly to make those same modifications.

In Pursuit of Performance

Moreover, the 4L60 can hold higher output ratings. It has a maximum torque rating of 360 ft lbs compared to the 250 ft lbs of the TH2004R. The higher torque rating means that once the transmission swap is complete, drivers get the easy tuning adjustability electronics provide along with the ability to run higher horsepower. These features ultimately result in a faster quarter mile.

What Does the 700R4 Offer Over the TH200R4?

The TH2004R and 700R4 came from the same era and are, in fact, surprisingly similar. Thanks to the introduction of additional overdrive gears that increased fuel efficiency as much as 30%, both transmissions were considered more fuel-efficient replacements for the TH400 or the TH350 transmission. Also, both transmissions are four speeds and use a TV cable as their controller.

undercarriage of car for transmission swap

Perhaps the biggest difference is gearing. When compared to the TH2004R, 700R4 transmissions have a slightly shorter overdrive and longer gears, making it more appealing to those looking to use the transmission for drag racing.

However, either transmission is an excellent aftermarket option as modern manufacturers have made these transmissions reasonably bulletproof. In the end, the 700R4’s longer production run means more support in the automotive community, making it a favored transmission swap for the enthusiast.

Comparing the 4L60 to the 700R4

As previously mentioned, GM responded to consumer interest in more fuel-efficient vehicles with the TH2004R and 700R4. In 1990, the 700R4 transmission went through a name change and was designated the 4L60. This was only a name change with no mechanical modifications between the transmissions.

It wasn’t until 1993 that engineers swapped the traditional hydraulic shifting system for an electronic system and introduced the 4L60E. Now controlled by computers, the 4L60E allowed for a broader range of tuning options. This change made it a popular transmission swap option.

Later, General Motors introduced a two-piece case that allows for different bellhousings and, ultimately, a more adaptable or swappable transmission. Then in 2001, updates to the 4L60E resulted in a more robust 4L65E transmission. In the end, although the 700R4 and 4L60E share similar internals and dimensions, continued updates made for a stronger, more tunable, reliable, and swappable transmission. The 4L65E is a more popular transmission choice.

Pairing Transmission Swap with Motor Swaps

Sometimes car enthustiasts take on a transmission swap project without a motor swap to enhance car performance. Other times they happen as part of a engine swap. While often not a primary consideration when completing a motor swap for your car, the transmission you install deserves careful thought. Ultimately, which one you choose impacts your satisfaction with the final result.

Although it is fun to brag about how powerful the motor in your car is, your ability to put that power to the ground is sometimes more important. Without the right transmission, a powerful engine doesn't mean faster lap times. And, odds are, if you're going through the hassle to change your motor, you're doing so to make more power.

So, if power is what you're looking for, the factory transmission might not hold the added power you're putting through it. That's when it's time to consider a transmission swap too!

RCG-700 crossmember

For more information regarding what GM transmission will work with motor swaps such as LS, Vortec, or other GM small blocks, check out our related article

G Force Performance Crossmembers are the perfect solution to support your new transmission.

Find out more about our RCG-700 Crossmember. It’s performance-engineered for swapping a TH2004R to a 700R4 transmission or 4L60 transmission in G-Body cars.

Looking for more information about LS Swaps? You may find these blog articles helpful.


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