Circle D Transmission | 6L80/6L90 Modifications

Services: 6L80/6L90 Modifications

Circle D Transmission | 4140 HTSR Billet Reinforced Output Carrier 4140 HTSR Billet Reinforced Output Carrier

Circle D Transmission is ready to turn your 6L80/90 into a performance beast. We’ve been a leader in the transmission industry since 1976. Our continued development in custom modifications and billet upgrades makes your choice an easy one. Now available: 4140 HTSR Billet Reinforced Output Carrier (Pictured). This custom output carrier with billet spline upgrade helps eliminate the OE spline failure in high HP vehicles. Other CDT modifications include our custom Billet 4-5-6 Hub Shaft Assembly & HD Clutch Pack, upgraded 3-5-R and 2-6 Clutch Packs with nitride treated steels and added clutch capacity. The pump and valve body are also upgraded to exclusive CDT specs. Our 5th generation shop Camaro is steadily used for R&D of parts & tunes so that we can help push your vehicle to its peak performance. The majority of the vehicles that we upgrade or rebuild with a 6L80/90 transmission have between 500 – 800 RWHP. We have been successful with vehicles that have up to 1200 RWHP. There are two options to choose from: you can either ship your transmission to us: Bench Package or you can transport your vehicle to us: Vehicle Package.


Transmission Tuning: Proper tuning of the transmission pressures, shift points and lock-up are all MAJOR components that ensure the vehicle can handle the additional HP. There is not one tune that meets every vehicle’s need. 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 run the risk of premature transmission failure. If we are supplying you with the Bench Package, you will need to pull the tune from the TCM & ECM with either HP Tuners or EFI Live and then e-mail it to us. Once we have completed the tune modifications we will e-mail it back to you. You will need someone that is very experienced at tuning, drivability and making log files to complete the installation. THIS IS A TIME CONSUMING AND CRITICAL STEP! There are occasions where it is necessary to reset the transmission adapts with an MDI Scan Tool (this is a factory GM scan tool.) This is one of the many reasons that we strongly suggest that you transport the vehicle to us. Please also complete the Performance Vehicle Questionnaire located under the 6L80/90 tab of our website. More details/instructions will follow on tuning once the project is underway. There may be additional charges to tune ECM.

You may need to install a stacked plate auxiliary transmission 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.

We cannot stress enough the importance of flushing the cooler(s) and lines that circulate transmission fluid, even if they are new. We recommend using a Hot Flush Machine or something comparable.

Make sure that you send your vehicle to us with suitable tires for aggressive driving. This is very important for several reasons, the first being safety the second is to minimize wheel spin.

Thank you for the opportunity to assist you. We look forward to transforming your 6L80/90 into a performance beast. Please email us with your questions OR call us during business hours (7:30 am – 5:30 pm CST, Monday thru Friday). The crew at Circle D Transmission is here to answer all of your questions!