Restoring a classic car is a commitment to performance, longevity, and craftsmanship. Whether you're building a weekend cruiser or a show-worthy masterpiece, the transmission you choose (and how you upgrade it) will play a critical role in how your classic rides, shifts, and performs under pressure.
At Auto Matic Kings, we’ve spent over two decades helping rebuilders source and upgrade automatic transmissions across all makes and models. If you're restoring a classic, here are the top 5 transmission upgrades every serious rebuilder should consider.
If you're rebuilding a classic with performance in mind, start with the torque converter. A stock converter might get the job done, but it won’t handle added horsepower or torque the way a performance-grade unit will. Upgrading to a high-stall or lock-up torque converter improves launch, throttle response, and drivability—especially in cars with upgraded engines.
Pro Tip: Don’t just grab the first high-stall converter you see. Take the time to match the stall speed to your camshaft profile, rear-end gearing, and intended use of the vehicle. If you’ve got a big cam and steep gears, a higher stall can really wake things up off the line. But if you’re cruising or doing some light towing, a lock-up converter with a moderate stall might serve you better.
Want crisp, consistent shifts? A shift kit is a must-have. These kits recalibrate hydraulic circuits inside the valve body, reducing slippage and increasing line pressure. That means faster, firmer shifts and improved clutch durability.
Shift kits are especially useful in classics with automatic transmissions originally designed for smoothness over performance. Think of it as recalibrating your transmission to match modern expectations, without changing the classic feel of the vehicle.
Pro Tip: Not all shift kits are created equal. Some are tuned for street performance, while others are built for full-on racing. Be clear about your goals before installing one. If your classic is a weekend cruiser, a mild or stage 1 kit will firm things up without making shifts feel harsh. But if you’ve got a big block under the hood and want that drag-strip feel, a more aggressive kit will deliver the punch. When in doubt, give us a call at Auto Matic Kings—we’ll point you to the right kit for your transmission and build.
Heat is the enemy of any transmission—especially in classics that weren’t designed for today’s high-temp, high-traffic conditions. Adding a transmission cooler is a simple upgrade that makes a big difference. It extends transmission life, prevents fluid breakdown, and reduces the chance of overheating in performance builds or during long drives.
If you're doing any towing or just pushing more power than stock, don’t skip the cooler.
Pro Tip: Make sure your cooler is properly sized for your specific setup. If you're running a built motor or a heavy tow rig, you'll need a larger cooler or even a dual cooler setup to handle the extra heat. Also, pay attention to the placement—mounting it in a spot with good airflow is crucial for keeping your transmission running cool, especially on those long highway stretches.
This one is a game-changer. Classic cars built before the mid-1980s typically lack overdrive, which means high RPMs at highway speeds and terrible fuel economy. Upgrading to an overdrive transmission—like the 700R4 or 4L60E—adds a modern touch that dramatically improves fuel efficiency and driveability.
With an overdrive unit, your rebuilt classic can cruise at 70 mph without sounding like it's screaming down a drag strip.
Pro Tip: Don’t just swap in any overdrive transmission—make sure it’s compatible with your engine and rear-end gearing. The wrong gear ratios can make the overdrive less effective, or worse, lead to poor performance. Also, think about adding a lock-up torque converter. It keeps engine RPMs even lower at cruising speed, making the most of your overdrive and maximizing fuel savings on long drives.
For rebuilders doing a full teardown, don’t reuse worn stock clutches and bands. Upgrade to performance-grade friction materials designed to handle more power, heat, and pressure. This is especially important in muscle cars or turbocharged builds, where OEM components simply won’t hold up.
A well-built transmission is only as strong as its internal components—make sure yours are built to last.
Pro Tip: When selecting performance clutches and bands, look for high-quality materials like carbon composite or Kevlar. These materials can withstand higher temperatures and provide better grip, ensuring your transmission can handle the extra power and torque of your rebuild.
Before you start upgrading, make sure you're working with the right transmission to begin with. Matching the transmission to your engine, weight, gearing, and intended use is critical. Not sure what works best? That’s what we’re here for.
Auto Matic Kings has 20+ years of experience sourcing hard-to-find automatic transmissions and building them for everything from ‘60s muscle to rare European classics. We know the classics inside and out—and we’ll help you build it right, from the ground up.