The Complete Honda K-Series Transmission Guide

Introduction

Over the years, Honda released a wide range of K-Series manual transmissions designed for different vehicles and applications. Because they were used in everything from everyday economy cars to high-performance models, they offer plenty of gear ratios, final drives, and configurations to choose from.

The good news is that many of these parts are interchangeable, so you can mix and match components to build a gearbox that’s perfectly suited to your setup.

Use this guide as a resource to learn about the different K-Series transmissions, how to identify them, and what you should consider before buying a gearbox. We’ll also help you determine the best fit for your project and cover common modifications, upgrades, and replacement parts along the way.
 

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1. Identify the Transmission Case

The major differences between K-Series transmission cases generally come down to their mounting locations. There are essentially two main mounting styles, though some applications use a combination of both.

These mounting locations matter because they determine which conversion or swap mounts you’ll need. They can also help you narrow down the transmission family, generation, and, in some cases, the engine or vehicle the gearbox originally came from.

What to Look For:

Case shape
There are essentially two shapes of K-Series transmission cases (excluding AWD), easily identified by their mounting locations. 

Mounting locations
Top Transmission Mounting location

Style 1 has a three-bolt top transmission mount. This is typically found on the K20A, K20A2, K20A3, K20Z1 and K20Z3 transmissions. (The K24A1 AWD CRV also has a three-bolt top, but a different rear. *see notes sections below*)

Style 2 will have a two-bolt top transmission mount. This is typically found on the K24A2, K24A4 and similar K24 transmissions. (This excludes the K24Z7)

Rear Mounting LocationStyle 1 has a three-bolt rear mount, usually called a T-bracket. There will be a thru bolt at the top and two bolts at the rear section of the differential area. 

Style 2 has a different two-bolt mounting section on the rear case. These are typically found on all K24 transmissions. (Excluding the K24A1 AWD gearbox.)

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2. Check the Gear Selector

The K-Series manual transmission has two different types of gear selectors. 

It's very important to identify which type of gear selector you have. This will determine which shifter cables and shifter you should use. Even though the gear selectors are (for the most part) interchangeable between transmission cases, the cables that connect to them and the shifters that work with them are NOT interchangeable. 

Style 1

These are typically found on the K20A, K20A2, K20A3, K20Z1 & K24A1 transmissions. They can be found in the DC5 Integra, EP3 Civic and 5spd CR-V AWD. This style gear selector has the forward / back ( RED ARROW) shift selector located on the inside of the left / right (YELLOW ARROW) connection.  

Style 2

These are typically found on the K24 gearboxes; however, they are also on the K20Z3 and the K20A CL7 Euro R, FN2 Type-R, and FD2 Type-R. Basically, anything after MY 2006 has this style of gear selector. This style has the forward / back ( RED ARROW) shift selector located on the OUTSIDE of the left / right (YELLOW ARROW) connection, which is why your RSX shifter stuff does not work correctly. 

IMPORTANT: Gear selectors can be swapped between some transmissions, so the selector should be treated as another identification clue rather than definitive proof of the transmission model.

Also, every Honda Transmission, regardless of engine, has a counterweight on the gear selector. This is always the front-to-back motion of your shift. 

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3. Check the Shifter Cable Bracket

On the K-Series transmissions, there are essentially three types of shifter cable brackets. They are not interchangeable and are specific to the gearbox case, shifter mechanism, and shifter cables. 

STYLE 1

These gearboxes have a specific shifter cable bracket for a few reasons. 

1. They are stamped and welded from steel. 
2. They are designed to bolt to the K20A, K20A2, K20A3, K20Z1 & K24A1 gearbox cases. 
3. Part number: 24601-PNS-000
4. View in store

STYLE 2

The STYLE 2 cable brackets differ than the others because: 

1. They are cast aluminum
2. They attach shifter cables using clips.  
3. There are a few different versions, but the CAST aluminum brackets can be found on most newer transmissions. (2006+)
4. K20Z3 - Part number: 24601-RPN-000 (view in store)
5. K24Z2, K24Z3, K24Z7 - Part number: 24601-RPW-000 (view in store)

STYLE 3

The last K-Series shifter cable bracket focuses on what you'd find in the 03-07 Honda Accord or 04-08 Acura TSX. The brackets are specific because:

1. They are cast aluminum
2. They retain shifter cables with bolts. 
3. Commonly used on the K24A2, K24A4, and K24A8 transmissions.
4. Part Number: 24601-RAP-010

IMPORTANT: Cable brackets can also be changed and modified to fit, so compare the bracket with the case and gear selector before identifying the transmission. A helpful tip is to NEVER change the cable bracket without verifying that it works with the cables and shifter you plan to use. Cable brackets are essential to proper cable and gear change geometry.  

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4. Locate the Vehicle Speed Sensor

Honda installed two types of speed sensors on their transmissions. There are two versions, one being more common than the other. 

K-Series Transmission Speed Sensors

K-Series transmissions use two different vehicle speed sensor (VSS) designs: low frequency and high frequency.

Low-Frequency Transmissions (VSS)

Found in the 2002–2004 RSX and 2002–2005 Civic Si. (Also JDM DC5 R & Honda CR-V K24A1)

The speed sensor is located at the rear of the transmission and reads from the final drive, producing a low-frequency signal. This signal is sent directly to both the ECU and gauge cluster.

High-Frequency Transmissions (CSS)

Found in the 2005–2006 RSX, 2004-2008 TSX & Accord, and 2006–2011 Civic Si.

The speed sensor is located at the front of the transmission and reads the teeth on 3rd gear, producing a high-frequency signal. This signal is sent to the ECU, which converts it to a low-frequency signal for the gauge cluster.

Matching the Speed Sensor System

For the ECU and speedometer to function correctly, the following components must match the low- or high-frequency design:

• Transmission speed sensor frequency
• Engine and dash wiring
• ECU speed-signal conversion
• ECU speed-signal output to the gauge cluster

Low-frequency wiring splits the transmission signal between the ECU and dash. High-frequency wiring sends the transmission signal to the ECU first, which then sends a low-frequency signal to the dash.

In Hondata KManager, low frequency is the default. High-frequency transmissions require the “Countershaft Driven Speed Sensor” option.

If these components are not matched, the ECU vehicle-speed reading, dash speedometer, or both may not function.

What to Look For:

• Sensor location (front or back?) 
  • Front -> CSS
  • Rear -> VSS
• Sensor type
  • VSS -> Gear Driven
  • CSS - Hall Effect 
• Electrical connector
  • The VSS and CSS wiring connectors are NOT the same and will NOT plug into each other without shaving and modifying.
• Transmission applications that use each design
  • K20A, K20A2, K20A3, K24A1 - > VSS
  • All other transmissions -> CSS 

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5. Factory Transmission Codes

Each factory transmission was given a barcode when built new. 

The first four digits of the barcode will identify which car the transmission came from originally. In some cases, transmissions are painted, cleaned or worn so they can come off. If you have a gearbox with a barcode, use the following chart to identify 

There are a few locations where you'll find the barcode. 

Examples:

AST5 -> K24A3 03-08 Honda Accord (CL9 - US TSX Equivelent*)

SY1M -> K24Z7 2012-2015 Civic Si 

7RPN -> NOT A CODE. This is a manufacturing barcode, not the gearbox serial number. 

Use the chart below to identify the gearbox by code.

6. Limited Slip or Open Differential?

Some factory K-Series transmissions were equipped with a limited-slip differential. They are commonly found on the "performance" version models, specifically ALL 06-15 Honda Civic Si's. In general: 

1. No USDM K20A2 or K20Z1 transmission had a factory LSD. (The K20A2 UK Spec EP3-R transmission DOES have an LSD)
2. No K24 transmission was equipped with an LSD (Except the K24Z7*)
3. Most LSD equipped transmissions are JDM imports from the DC5, CL7, FD2, FN2, etc
   

LSD

You can easily identify a gearbox equipped with a factory LSD by looking through the differential hole. An "open" hole means the transmission has a factory LSD installed. 

Open Differential

You can identify open differentials, or "NON-LSD" transmissions, by the center bar through the differential. They are not straight through like the LSD, so if you can't see through it, it's an open differential. 

IMPORTANT: Don't rely exclusively on the transmission code to determine whether a used transmission currently has an LSD. Differentials can be changed during the transmission's life. This applies to OEM Honda parts; it may not apply to aftermarket differentials. 

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7. Factory Gear Ratios

Once you've identified the transmission, use the chart below to determine its original application, individual gear ratios, final drive, and other specifications.

Review the chart below to understand the gear ratios in each factory application. 

K-Series Transmission Ratio Chart

Understanding Gear Ratios

Shorter Gearing:
Short gearing benefits an all-motor K-swap because it keeps the engine higher in the RPM range, where it makes the most power. With less torque than a turbo setup, shorter gear ratios improve acceleration and reduce the RPM drop between shifts, helping the engine stay in VTEC and in its powerband.

Taller Gearing:
Taller gearing is beneficial when you want higher speeds in each gear and fewer shifts. The longer ratios can work well with higher-power K-swaps, especially turbocharged setups, where the engine has enough torque to pull the taller gears while staying in the powerband. It can also improve traction and reduce unnecessary shifting at higher speeds.

Final Drive:
The final drive ratio affects all of the transmission’s gears at once. A higher numerical final drive, like a 4.7 compared to a 4.3, makes every gear effectively shorter, improving acceleration but reducing the speed you can reach in each gear. A lower numerical final drive makes the gearing taller, allowing more speed per gear and lower cruising RPM, but with less mechanical advantage for acceleration.

K-Series Gear Ratio Chart

Quick K-Series Transmission Identification Checklist

When identifying an unknown K-Series transmission, work through these steps in order:

1. Identify the Case

2. Check the Gear Selector

3. Check the Cable Bracket

4. Locate the Speed Sensor

5. Check the Barcode

6. Check for an LSD

7. Use the Chart to Verify the Gear Ratios

Don't rely on a single feature to identify a used transmission. Cases, selectors, cable brackets, differentials, and internal gearsets may have been changed over the years.

Factory specifications do not prove what is inside a used transmission or whether it fits your swap. Check the actual unit and modification history before buying!

Shop Replacement Parts & Upgrades

Transmission bearings

Transmission Gears, Gear sets, LSDs and more

Transmission boots, seals, etc

Transmission brackets & hardware

Transmission springs

Transmission Rebuild information - coming soon!