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6L90 Performance Transmission Rebuild Kit - Level 3

Rated up to 750 RWHP, HP ratings are contingent on numerous factors, such as tune, vehicle weight, power adder, use, etc. | Detailed Instructions Included | FREE UPS Domestic Ground Shipping

Kit is designed with 45-tooth 4-5-6 clutch plates. CDT's Billet 4-5-6 clutch hub and intermediate shaft (CDT part number 104690-45) is included in this kit. The 4-5-6 clutch pack provides 45% more surface area than a stock clutch set up. The 3-5-R clutch pack offers 40% more clutch area than stock.
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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CDT456L3/90 (4-5-6 CLUTCH KIT)

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

CDT456L3/90 offers 45% 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.


One-piece 300M steel forging is heat treated and shot-peened for maximum durability. This shaft doubles oil flow to the clutch pack for improved resistance to heat and longer clutch life. The hub is designed for use with Powerglide-style, 45-tooth frictions. This shaft is designed for use without OE dampner.

CDT35RL3/90 (3-5-R CLUTCH KIT)
7 Borg Warner® High Energy Clutches
7 Kolene® Steels (varying thicknesses)
1 Steel Plate
1 Apply Ring
1 Backing Plate
1 Snap Ring

CDT35RL3/90 offers 40% 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.

CDT26L3/90 (2-6 CLUTCH KIT) 
7 Red Eagle® Externally Splined Clutches                                      
6 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.

CDT1234L3/90 (1-2-3-4 CLUTCH KIT)
6 High Energy® Clutches
6 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.

6 High Energy® Clutches
6 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.

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

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.

PLEASE NOTE: GM has a transmission that has the same outside dimensions as a 6L90 but uses one less clutch in all the clutch housings compared to a true 6L90. We call this transmission a 6L90LCC (less clutch capacity). Please refer to "Stock Clutch Capacity Chart" and "Length of Main Case Chart" on the "Transmission Specs" tab below to determine if you have a 6L90 or 6L90LCC. When ordering this part, please indicate in the Notes textbox above that you have a 6L90LCC. If you are unable to determine if you have a 6L90 or 6L90LCC, we will determine which transmission you have from the VIN.

We recommend the Billet Reinforced Output Carrier for vehicles producing over 750 RWHP, Nitrous or Heavy Vehicles (including trucks, SUV's and CTS-V's.) Note: We have seen the stock output carrier (planetary) break in vehicles with less than 750 RWHP. We do not warranty the stock output carrier (planetary.) We highly recommend that you purchase the billet reinforced output carrier. We offer a 6L90 Level 4 Kit that includes this part.

transmission specs worksheet

  • 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

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 are mandatory. All 6L80/90’s are torque base shifted units. The torque signal is calculated thru the ECM. Therefore, transmission performance & 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 & fin style cooler) rated for 25,000 GVW. The ideal operating temperature for this transmission is 180°or less. These transmissions have a tendency to run very hot – the cooler will lower operating temperature and recovery time which in turn will extend the life of your transmission.

Limited Warranty Statement

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

Improperly Stored
Improperly Installed
Improperly Tuned (EMC or TCM)
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

Circle D Transmission will not pay for any fluids replaced in the event of a 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 Kit components. We will not provide you with any cash refund except as many 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.