Circle D Transmission | 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.  Available: 4140 HTSR Billet Reinforced Output Carrier (Pictured). This custom output carrier with billet spline upgrade helps eliminate the OE spline failure in high horsepower vehicles. Also available is our custom Billet 4-5-6 Hub Shaft Assembly & Performance Clutch Pack, upgraded 3-5-R and 2-6 Clutch Packs with performance steels and added clutch capacity. The pump and valve body are also upgraded to exclusive CDT specs.  

Rebuild Levels:  

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 horsepower. 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.  Please contact us for tuner recommendations.  Once your final tune and log reviews meet our requirements we will document this in our records for warranty purposes. Please only drive the vehicle for tuning purposes until this process is completed.  

Auxiliary Cooler: You 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.

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 or something comparable.

Shipping:  If you need assistance shipping your transmission, we can arrange Domestic Shipping (averages $200 – $300 each way) for your transmission. Please complete the Shipping Form on our website if you would like us to arrange shipping.

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!


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