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.
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.
We headed over to Icon Engineering, where proprietor Mike Schultz showed us the basics of what it takes to cram the Passon goodies into an existing A833 Chrysler four-speed. If you've never rebuilt a manual transmission, you might want to get some help from somebody who has. It can be a little tricky for the uninitiated, and a large hydraulic press is needed. In our situation, the Passon components cost $2,339.50, $1,695.00 of which paid for the basic OD Hemi conversion kit, and the rest of which paid for service parts and the modified shift handle. Icon Engineering charges about $700.00 for labor to convert a transmission (not including removal or installation in the car) for a total cost of just over three grand. That's very competitive with the other Mopar overdrive solutions on the market, but again, this is the only one that hides in plain sight and requires absolutely no vehicle modifications. Scope it out.
CRUISING RPM FOURTH GEAR TIRE SIZE REAREND RATIO RPM SPEED 1.00:1 28 inches 4.10:1 3,248 65 mph {{{80}}}:1 28 inches 4.10:1 2,580 65 mph A833 GEAR RATIOS STOCK OVERDRIVE STOCK REAR RATIO