ALTO 8L90 Performance Transmission Rebuild Kit & Billet Input Shaft - Level 3 (Added Clutch Capacity)
When it comes to a serious 8L90 rebuild, this kit is built for enthusiasts and professionals alike. It includes a billet input shaft, precision-machined for strength, engineered to resist heat and handle increased power and torque demands. If you’re replacing worn components or upgrading your automatic transmission, the added clutch capacity brings dependable performance in high-stress conditions.
Installation of this 8L90 rebuild kit is simplified with included instructions and you have the option to add a detailed service manual to eliminate guesswork. Whether you’re fine-tuning the valve body, adjusting gear ratios, or managing transmission fluid levels, having inside knowledge helps reduce risk and resolve challenges that arise during remanufacturing or upgrades.
This premium brand-level rebuild gives you full access to all essential parts, from o‑rings and seals to the durable billet shaft, all backed by a warranty that ensures confidence in long‑term use. When compared to comparable kits on the market, this offering stands out for its comprehensive scope and engineered resilience against overheating, wear, and shifting issues.
FREE UPS Ground to the contiguous United States (lower 48)
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.
Picture for representation purposes only - actual contents may vary as we continue to develop our product.
High-Strength Billet Input Shaft for 8L90 Transmission Rebuilds
This billet input shaft is a key component in any serious 8L90 rebuild, precision machined from 300M alloy steel and heat treated to maximize strength, durability, and long-term use. Designed specifically for high-performance automatic transmission applications, the shaft’s increased radius between the sealing rings helps reduce potential failure points under high power and torque conditions.
To streamline the installation process and reduce risk during assembly, this part arrives fully prepped with o‑rings and sealing rings already installed, making it a true drop-in component. This means you won’t need to buy separate ring sizing tools or a sealing ring installer, saving you time and money during your transmission remanufacturing or replacing process.
Engineered to be comparable with other leading brand components, this shaft is part of a full kit designed to improve the performance and reliability of your valve body, gear ratios, and overall transmission fluid control. Backed by a warranty, it’s a high-quality solution that helps resolve common issues associated with stock parts and elevates your upgrades for lasting performance across all gears.
⚠ Important: Multiple Versions Available
The 8L90 transmission uses different input shaft designs depending on model year, application, and torque converter setup. To ensure you receive the correct part, please confirm the following before ordering:
Model Year & Vehicle – The shaft design can vary between early and late model 8L90 units.
Shaft Style – Determine whether you have the early-style or late-style spline configuration.
Torque Converter Compatibility – Match the shaft to your converter hub size and spline count.
How to Verify:
Check your transmission’s build tag or serial number.
Measure your existing input shaft and count splines.
Text us a clear photo of your input shaft and converter hub to 713-895-7019.
💡 Tip: If you’re unsure, our team is happy to help confirm fitment before you order—avoiding downtime and return shipping delays.
Complete 8L90 Rebuild Clutch Pack & Overhaul Kit Breakdown
Our 8L90 rebuild solution features upgraded clutch packs and a precision-engineered overhaul kit designed for superior heat resistance, reduced wear, and long-term use. This is not a basic rebuild—it’s a high-performance upgrade that includes enhanced friction plates, steel plates, and specialized components tailored to improve power transfer, reduce risk, and help resolve common transmission issues. Every component is selected for compatibility with your automatic transmission, including GM’s latest OEM designs and Circle D’s trusted brand of modified parts.
C1 Clutch Pack (1-2-7-8-R) – OEM Spec
This C1 clutch pack is the newest OEM design from GM and provides the foundation for improved durability during remanufacturing or high-performance replacing. The thicker steel plates increase thermal resistance and minimize warpage, helping maintain correct gear ratios and shift quality.
C2 Clutch Pack (1-2-3-4-5-R) – Stock Capacity
3 Clutches
2 Steel Plates
1 Apply Plate
This C2 configuration maintains stock clutch capacity and is ideal for builds where retaining OEM parts while ensuring reliability and consistent transmission fluid flow is a priority.
C3 Clutch Pack (1-3-5-6-7) – CDT Modified Alto Power Pack
The C3 Power Pack adds one additional clutch over factory 4- or 5-clutch drums. The G3® friction material is formulated to resist heat and wear, optimizing power delivery and enhancing shift performance in all gears. These upgrades are ideal for those seeking comparable or better performance than other aftermarket brands.
C4 Clutch Pack (2-3-4-6-8) – CDT Modified Alto Power Pack
This flexible setup allows for either 1 additional friction plate (retaining the wave plate) or 2 additional frictions (by omitting it). It’s a strategic upgrade to increase clutch surface area, reduce slip, and extend the life of the transmission during demanding use cases.
C5 Clutch Pack (4-5-6-7-8-R) – CDT Modified Alto Power Pack
The C5 clutch pack adds an extra clutch and steel while retaining the factory wave plate. Like the others, it uses G3® friction technology for minimal wear, excellent heat management, and optimal pressure response in high-load conditions—helping prevent future transmission issues.
Overhaul Kit Highlights
Includes all essential parts for a complete 8L90 rebuild
Engineered with premium-grade materials for superior durability
Hi-Per Blue® Piston for C1 (1-2-7-8-R) made from high-performance Blue AEM material to resist extreme heat and chemicals while improving fit and function
Includes GM OEM filter for optimal transmission fluid filtration
Comprehensive sealing set with upgraded o-rings, gaskets, and sealing rings
This full kit offers unmatched access to elite-level performance, offering everything you need for a cleaner, stronger, and more efficient valve body and shaft assembly. When considering replacing or remanufacturing your 8L90, this package is an ideal balance of performance, cost, and peace of mind—fully backed by the Circle D warranty.
Frequently Asked Questions
Can a modified clutch pack help resolve gear slip issues during high-load towing?
Yes, upgrading to a performance clutch pack, especially with G3® friction plates and added steel plates, can help resolve gear slip under load. These parts increase surface area and heat resistance, allowing your automatic transmission to maintain consistent pressure and better control gear engagement during towing or heavy use.
How does heat affect the longevity of the 8L90 billet input shaft and sealing components?
Excessive transmission heat can degrade sealing rings, o-rings, and even warp internal parts like steel plates over time. That’s why Circle D’s billet input shaft is heat-treated and paired with high-temperature-resistant sealing materials, ensuring long-term use under demanding power and temperature conditions.
Is this 8L90 rebuild kit compatible with remanufacturing in a professional transmission shop?
Absolutely. This kit is ideal for both DIY users and professional transmission shops performing 8L90 remanufacturing. It includes complete access to the clutch packs, valve body-related parts, and upgraded sealing components, allowing pros to deliver a high-performance build with fewer post-installation issues.
Do the included steel plates affect shift timing or gear ratios?
The thicker and varied steel plates help improve clutch engagement timing and stability, which in turn contributes to more precise shifting and retention of factory gear ratios. These upgrades minimize transmission fluid overheating and help maintain consistent performance across all gears.
How do I know if I need to replace my Hi-Per Blue® piston during a rebuild?
If you’re experiencing delayed engagement, worn o-rings, or inconsistent pressure in your 1-2-7-8-R clutch pack, replacing the piston is strongly recommended. The Hi-Per Blue® piston included in this kit is a high-performance upgrade designed to resolve these issues and improve sealing under heat and chemical stress.
