Let's get down to business. Schultz always smiles when he ponders the wonders of overdrive. Let's get down to business. Schultz always smiles when he ponders the wonders of overdrive These are great times for Mopar musclecar owners who want to hit the highway with steep gears spinning inside the rear axle. Finally, after years of jealously watching the GM and Ford guys motor on by with the added convenience, economy, and performance of overdrive transmissions, Mopar owners can now choose from several excellent new ways to cut those engine revs while cruising on the open road. For some, the minor floor cutting required for the addition of a modern five- or six-speed manual transmission kit isn't a big deal. For those who don't want to cut, there's the possibility of those cool add-on overdrive units that bolt to the end of the transmission and effectively double the number of speeds in the transmission. But for those who want an absolutely invisible overdrive upgrade for their stick-shifted Mopars, Passon Performance offers a great conversion kit for existing Chrysler A833 manual gearboxes. This cluster gear comparison shows how the Passon gear (bottom) is machined from 9310 steel versus the 8620 steel used in stock Chrysler gearsets. The replacement alloy is harder but has a specific heat-treatment process that adds forgiveness to prevent fractures. Jamie Passon tells us he has sold more than 60 OD conversion kits, including one to former pro wrestler Bill Goldberg, whose Hemi Dart can't break it. This cluster gear comparison shows how the Passon gear (bottom) is machined from 9310 stee But wait, didn't Chrysler beat Passon to the punch back in the mid-'70s with all those overdrive four-speed-equipped Darts, Dusters, Volares, Aspens, pickups, and vans? Yes and no. While it's true that Chrysler re-engineered the A833 four-speed around 1975 to yield a 0.76 overdriven top gear, those gearboxes suffer from general weakness and were never intended for high-performance use. Drawbacks include the fact that most were built with somewhat flexible aluminum cases that expand-and explode-with high loads. And while the 0.76 top gear is great at dropping engine revs by 24 percent versus a 1:1 box, the ODs (like most earlier Slant Six four-speed A833s) are stuck with super-low 3.09 First gear ratios. The problem is that when these gearboxes are used with rear-axle ratios above 3.55, the total gear multiplication zings the motor to redline much too soon and forces a premature shift into Second that wastes energy, kills the 60-foot time, and dulls the overall e.t. The Passon overdrive kit corrects all these issues by including an 18-tooth Hemi-spec input-shaft upgrade and redesigned gearsets that yield a 2.65 First gear (same as factory stock) and a 0.80 overdrive top gear. What results is a best-of-both-worlds transmission unit that combines-for the first time ever-the economy of the Chrysler OD four-speed and the unmatched strength of the Chrysler Hemi four-speed in a totally stock-appearing package. So, if you're running a 4.10 gearset in the rear axle, pop it into Overdrive and engine speed will perform like 3.23 highway gears! Likewise, 4.56s will behave like a 3.56:1 ratio. Best of all, it's all made here in the USA, so the craftsmanship is superior. The Hemi part of the conversion consists of this beefy, 18-spline input shaft, also known as the drive pinion. Only factory-assembled Hemi and 440 Mopars got the bigger 1.14-inch, 18-spline shaft, thus the term "Hemi box." All the rest (383s, 340s, and so on) got smaller, 0.960-inch, 23-spline inputs (top). The new pinion requires a matching 18-spline clutch disc. The Hemi part of the conversion consists of this beefy, 18-spline input shaft, also known Thanks to the Hemi drive pinion's added thickness, a new front bearing retainer is required. If you don't have an original Chrysler part kicking around, Passon offers the billet-steel replacement on the left for $99.00. There were three different bearing-retainer flange diameters used in production, so Passon tells customers to call with their measurements to ensure the new retainers will suit their bellhousing/blow-shield configurations. Naturally, you'll also need to change the throwout bearing to match the new, large bearing retainer. Thanks to the Hemi drive pinion's added thickness, a new front bearing retainer is require To affect the ratio change, the three stock main shaft gears must be replaced. They're also machined from superior steel and feature fresh bushings (foreground). To affect the ratio change, the three stock main shaft gears must be replaced. They're als 1 | 2 | 3 | » | View Full Article Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!