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6L80 Performance Transmission Rebuild Kit - CDT Level 4

FREE UPS Ground to the contiguous United States (lower 48) | NO core required for output carrier

Rated up to 1000 RWHP, this kit is engineered for high-powered builds demanding superior transmission durability and reliability. While horsepower ratings are influenced by various factors such as tuning, vehicle weight, power adders, and driving conditions, this kit delivers proven performance for serious applications.

Designed specifically for 6L80 transmissions, this package features high-capacity 45-tooth 4-5-6 clutch plates for improved engagement and reduced clutch failure under heavy load. It also includes CDT’s Billet 4-5-6 clutch hub and intermediate shaft (CDT part number 104680-45), engineered for enhanced control and maximum torque handling. The upgraded 4-5-6 clutch pack provides 50% more surface area than stock, while the 3-5-R clutch pack offers an additional 50% increase in clutch area, boosting both power transfer and longevity.

Built to optimize the performance of GM’s six speed automatic transmission, this kit is ideal for users experiencing slipping, overheating, or clutch-related issues under stress. For complete system integrity, it pairs well with a high-performance torque converter, precision calibration of the transmission control module, and premium transmission fluid. All components are manufactured with a focus on quality, ensuring they can be confidently replaced and trusted in even the most demanding applications.
Availability: In stock
In stock items ship within 1-2 business days.
Picture for representation purposes only. Actual contents may vary as we continue to develop our products.

This performance transmission kit comes with printed instructions for all of the items in the kit except for the Sonnax items. For installation instructions for Sonnax items, click here. If you would prefer printed instructions please click the checkbox below:

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$3,975.00
SKU: CDTL4PK/80-P

6L80 CDT-BROC: Reinforced Output Carrier for High-Powered Applications

6L80 CDT-BROC (4140 HTSR Billet Reinforced Output Carrier) | NO core required for output carrier

The 6L80 CDT-BROC is a performance-engineered output carrier specifically built for 6L80 transmissions in high-powered applications. Designed for vehicles producing over 750 RWHP—including heavy-duty trucks, SUVs, CTS-Vs, and nitrous-assisted builds—this component delivers exceptional strength, reliability, and longevity under extreme load conditions.

Machined from 4140 HTSR (Heat Treated Stress Relieved) billet steel, the carrier offers increased hardness and high strength, which minimizes distortion and improves wear resistance during high-torque operations. This material choice significantly reduces the risk of clutch failure, stress fractures, and spline stripping, all common concerns when upgrading six-speed automatic transmissions for high-horsepower use.

The billet steel drive plate has been precision milled and contoured to fit seamlessly with the planetary housing, virtually eliminating the possibility of separation under dynamic loads. This level of control and component integration supports superior torque converter function and improves overall transmission performance.

As a drop-in part, installation is quick and efficient, with no need for a core return. For builders and technicians seeking OEM+ quality, improved power handling, and upgraded transmission components, the CDT-BROC is a trusted choice—engineered to meet demanding performance specifications while offering long-term reliability.

CDT456L4/80 (4-5-6 CLUTCH KIT)

  • 7 G3® Clutches
  • 9 Lindered Steels (varying thicknesses)
  • 1 Stepped Apply Plate
  • 1 Wide Backing Plate
  • 1 Snap Ring
  • 2 Hi-Per Blue® Bonded Pistons

CDT456L4/80 offers 50% more clutch apply area than stock. G3® friction material is formulated to achieve minimal wear and maximize heat resistance. Lindured is a chemical and heat treatment process that hardens the steel, which results in less wear. Hi-Per Blue® Pistons are manufactured with upgraded High Performance Blue AEM material for superior thermal and chemical resistance, with better fit and performance.

104680-45: Billet Intermediate Shaft & 4-5-6 Clutch Hub for 6L80 Transmission Performance

104680-45 (One-Piece Billet Intermediate Shaft & 4-5-6 Clutch Hub)

The 104680-45 billet intermediate shaft and clutch hub is a critical upgrade for maximizing performance and durability in 6L80 transmissions, especially in high-horsepower builds. Forged from premium 300M billet steel, this component is heat-treated and shot-peened to deliver unmatched strength, fatigue resistance, and long-term reliability under extreme torque and temperature conditions.

Engineered as a one-piece design, the shaft eliminates common failure points seen in multi-piece factory shafts. It significantly boosts transmission performance by doubling oil flow to the 4-5-6 clutch pack, enhancing heat resistance and extending clutch life, even in demanding applications like heavy-duty trucks, performance cars, and nitrous-assisted vehicles.

Designed to fit seamlessly with 45-tooth clutch plates, this shaft provides increased control and improved power transfer. Its OE damper-less design reduces internal friction and rotational mass, contributing to smoother clutch shifting, quicker response times, and better overall automatic transmission efficiency.

Whether you’re upgrading for racing, towing, or high-load street use, the 104680-45 delivers the material quality, precise specifications, and performance-focused components required to handle increased torque without compromise.

CDT35RL4/80 (3-5-R CLUTCH KIT)

  • 6 Borg Warner® High Energy Clutches
  • 6 Kolene® Steels (varying thicknesses)
  • 1 Steel Plate
  • 1 Apply Ring
  • 1 Backing Plate
  • 1 Snap Ring

CDT35RL4/80 offers 50% more clutch apply area than stock. High Energy material maintains consistent frictional behavior and tolerates extreme thermal stress applications. Kolene® Steels provide a surface treatment that enhances wear & fatigue resistance.

CDT26L4/80 (2-6 CLUTCH KIT) 

  • 5 Red Eagle® Externally Splined Clutches                                     
  • 5 Red Eagle® Internally Splined Clutches   
  • 1 Externally Splined Plate                                                 
  • 1 Snap Ring                                             
  • 1 Hi-Per Blue® Bonded Piston

Red Eagle® Clutches are designed to limit the amount of slip providing a shorter apply time, generating less heat. Hi-Per Blue® Pistons are manufactured with upgraded High Performance Blue AEM material for superior thermal and chemical resistance with better fit and performance.

CDT1234L4/80 (1-2-3-4 CLUTCH KIT)

  • 5 High Energy® Clutches
  • 5 Steels
  • 1 Backing Plate
  • 1 Snap Ring
  • 1 Spiral Snap Ring
  • 1 Snap Ring Kit
  • 1 Hi-Per Blue® Bonded Piston

Hi-Per Blue® Pistons are manufactured with upgraded High Performance Blue AEM material for superior thermal and chemical resistance with better fit and performance.

CDTLRL4/80 (LOW-REVERSE CLUTCH KIT)

  • 5 High Energy® Clutches
  • 5 Steels
  • 1 Hi-Per Blue® Apply Piston

Hi-Per Blue® Pistons are manufactured with upgraded High Performance Blue AEM material for superior thermal and chemical resistance with better fit and performance.

CDTVBPKL4/80-90 (VALVE BODY & PUMP KIT)

  • 2 Boost Valve Springs
  • 2 Clutch Regulator Valve Springs
  • 1 Center Support Seal Kit
  • 1 Pressure Regulator Valve Kit
  • 1 Line Pressure Booster Kit
  • 1 O-Ringed End Plug Kit
  • 1 Pump Slide Spring

CDTMKL4/80 (MASTER KIT)

  • 1 High Performance overhaul kit engineered utilizing premium materials for racing.
  • 1 Bonded OE Valve Body Plate
  • 1 Bushing Kit (includes extension housing bushings)
  • 1 Pan Gasket
  • 1 Filter
  • 1 Oversized Pump Washer

We do not include welded hubs in Kit. In the beginning of R&D on this transmission we thought this area needing strengthening. However, in all the units that we've rebuilt we've NEVER seen one broken. Therefore, we deemed it unnecessary. Also, we do not include a billet pump rotor because the factory pump rotor has proven itself reliable (we have never seen one broken) unlike the 4L60E.

Frequently Asked Questions

What are the benefits of upgrading to a billet intermediate shaft in a 6L80 transmission?

Upgrading to a billet intermediate shaft—like the 104680-45—provides enhanced strength, increased oil flow to the clutch pack, and superior heat resistance. These features help reduce the risk of clutch failure and improve transmission reliability in high-performance or heavy-duty applications.

How does a 4140 HTSR billet output carrier improve 6L80 transmission performance?

A 4140 HTSR billet reinforced output carrier strengthens the spline area and prevents separation under load, which is especially important in vehicles making over 750 RWHP. Its heat-treated steel construction enhances durability, torque control, and resistance to stress fractures in demanding environments.

Can I install a 6L80 billet clutch hub without modifying the transmission housing?

Yes, most billet clutch hubs—such as the 104680-45—are designed as direct drop-in components. They are contoured and milled precisely to fit the planetary housing, making them compatible with OEM specifications and easy to install without requiring custom machining.

What causes clutch failure in 6L80 transmissions, and how can it be prevented?

Clutch failure in 6L80 transmissions is often due to heat buildup, inadequate fluid flow, and low-grade friction materials. Upgrading to high-performance kits with enhanced clutch packs, billet shafts, and improved fluid dynamics helps reduce wear and extend service life.

Is a 6L80 transmission overhaul kit necessary for high horsepower builds?

Yes, for vehicles producing high horsepower—especially over 750 RWHP—using a complete 6L80 overhaul kit ensures all critical components (clutches, pistons, shafts, valve bodies) are upgraded for performance and durability. These kits help maintain torque converter efficiency and prevent transmission damage under heavy load.

 

transmission specs worksheet

Recommended Transmission Tools

  • Transmission holding fixture
  • Calipers
  • Dial Indicator Set
  • Bushing Drivers & Arbor Press for Bushing Installation (Bushings should only be replaced as needed)
  • Sealing Ring Protector and Sizer
  • Various Clutch Spring Compressors
  • Output Carrier/Shaft Lifting Tool
  • 1-2-3-4 & 3-5-R Clutch Housing Installer
  • Large Snap-Ring Pliers
  • Pump Alignment Tool

Misc. Transmission Information

Upgraded Parts: If you have an early pump cover (stator) that does not utilize anti-rotational tabs on the sealing rings or an early 1-2-3-4/3-5-R clutch housing that does not have the matrix stamp, you will need to install a factory-upgraded pump cover and clutch housing.

Transmission Tuning: Please understand that proper tuning of the TCM and ECM is mandatory. All 6L80/90’s are torque-based shifted units. The torque signal is calculated through the ECM. Therefore, transmission performance and longevity are directly dependent on the delivered torque signal that’s calculated in the ECM. If this is not done properly, you will experience premature transmission failure. We also do not recommend maxing out pressures or deleting torque management completely because it will cause seal failure and/or hard part breakage.

Flushing Cooler & Lines: We cannot stress enough the importance of flushing the transmission cooler(s) and lines, even if they are new. We recommend using a Hot Flush Machine Flush Machine or something comparable.                                      

Auxiliary Cooler: You need to install a stacked plate auxiliary transmission cooler (not a tube and fin style cooler) rated for 25,000 GVW. The ideal operating temperature for this transmission is 180°or less. These transmissions tend to run very hot, so the cooler will lower the operating temperature and recovery time, which in turn will extend the life of your transmission.

Transmission Rebuild Kit Warranty

Limited Warranty Statement

Circle D's Transmission Rebuild Kits carry a 1 year, parts-only warranty, exclusively against manufacturer’s defects. The warranty period begins at the date of purchase. There is no warranty under the conditions listed below. This includes, but is not limited to:

  • Improperly Stored
  • Improperly Installed
  • Improperly Tuned (EMC or TCM)
  • Misapplication
  • Altered, either by Owner or Their Technician
  • Torque Converter Failure
  • Inadequate Flushing of Transmission Cooler
  • Improper Fluid Level
  • Water/Engine Coolant in Transmission
  • Excessive Power
  • Accident
  • Neglect

Circle D Transmission will not pay for any fluids replaced in the event of a rebuild kit failure.

Under no circumstances shall there be any labor warranty or other warranty coverage on Circle D Transmission Kits beyond the replacement of individual rebuild kit components. We will not provide you with any cash refund except as may be required by law. Consequential and incidental damages are not recoverable under this warranty and are expressly excluded.

There is no warranty on broken parts such as, but not limited to, twisted splines, broken shafts, or broken planetaries.

Warranty issues will be considered on an individual basis.