Yeah, we got 25 percent better fuel economy with our big-block ’68 Chevelle, but our Gear Vendors overdrive packs even more fun than we counted on.

By: Johnny Hunkins
Photography by the author
Reprint from Hot Rodding Magazine, September 2008


TH400_mech_flatThe gear Vendors overdrive kit for the Turbo 400 had everything we needed to add a pleasant 0.78 overdrive to our big-block ’68 Chevelle. The kit costs $2,595 (PN 3D0400AFS), and includes everything except labor and a shortened driveshaft.

At $4.27 per gallon for 91 octane premium unleaded, the price to fill up the 20-gallon tank in our ’68 Chevelle just climbed well over $80. Yikes! On top of that, the actual distance yielded by that gas with our 496-inch big-block and Turbo 400 trans was only about 150 miles. We’ll do the math for you: That’s about 7.5 miles per gallon. Something had to give, so we contacted the overdrive specialists at Gear Vendors.

We’d head good things about Gear Vendors overdrives from friends and readers. For one thing, we’d lose none of the strength of our bulletproof TCI Turbo 400 like we might if we switched to a 700-R4, 200-4R, or 4L60E. We’d need none of the complicated programming electronics like we would for a 4L80E or 4L60E. We

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wouldn’t need to break out the chopsaw for tunnel clearance either—only a slight massaging of the tunnel with a rubber mallet would be needed. Traditional overdrive automatics also hunt worse that Elmer Fudd—and that ride is no fun on the highway. We could’ve gone with an overdrive five- or six-speed manual, but neither of these was right for the street/strip vibe of our Chevelle. The Gear Vendors was our obvious choice, so we made the call.

We spoke to Rick Johnson, the CEO of Gear Vendors, and he told us in no uncertain terms that his 0.78:1 overdrive unit would better our fuel economy by at least 25 percent. Not only that, but his overdrive would be practically indestructible—even behind our big-block—and loads of fun to boot. (Rick’s a big fan of splitting gears, which the Gear Vendors overdrive allows because its ratio is split numerically perfect between most transmissions’ gears.)

Rick invited us down to Gear Vendors company headquarters in El Cajon, California (near San Diego), where his crew installed one in our Street Sweeper ’68 Chevelle project car. What’s interesting to note is that a Gear Vendors installation is remarkably simple. Even with photos, we were out in about five hours. (Try that with a five speed manual swap.) But you don’t have to go to Cali to get one installed—there are certified Gear Vendors


The guts of the Gear Vendors overdrive: A bulletproof mechanical pump at the front of the housing (right) supplies pressure to engage a conical clutch that engages a planetary gearset residing inside an annulus. It’s essentially impossible to break, but the practical limit is right around 1,600 hp-not because that’s where they’re weak, but because the transmission in front of it usually breaks. Sounds like our kind of piece!

installation facilities all over the country (You can check the Web site or call to find one in your neck of the woods.) In fact, in order to sell a Gear Vendors overdrive, a retailer must be a qualified installation center for the entire Gear Vendors product line.

The short of it: For just under $2,600, you can get a kit for your Turbo 300-equipped GM A-body. Another $750 or so gets it installed for you (it’s about $100 less for Camaros and Firebirds), which also includes the cost of shortening your driveshaft. Many Gear Vendors kits

are available for Ford and Mopar musclecars, too, and that includes kits for four-speed manuals. While we were there, we got the chance to sample a late model C5 Corvette, a ’32 Ford street rod, and a ’56 Chevy truck with a Gear Vendors overdrive, and they were all just as fun to drive.

Yeah, we said “fun.” We didn’t really expect that an overdrive button could be so cool, but it was a blast to chirp the tires by clicking it on. Likewise, turning it off on the highway, into a non-overdrive passing gear, was a thrill, too. And the icing on the cake: blasting

“… A Gear Vendors installation is remarkably simple. Even with photos, we were out in about five hours.”

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through all the gears, splitting them with the overdrive (that’s six in all for out Turbo 400-equipped Chevelle). It was so fun, we almost forgot the initial impetus for going overdrive: better gas mileage.
A careful measure of fuel economy before and after the Gear Vendors installation revealed that even under ideal conditions (55-mph top speed, no full-throttle blasts), the best we could muster on the highway without overdrive was 7.5 mpg. After the install, we easily pulled down 10 mpg, and we were going way faster than 55 mph, more like 65 mph. That’s an improvement of 25 percent. Put another way, we could go the same amount of miles from our fill-up for about 20 bucks less—and still have 5 gallons left in the tank. The only questions we’re asking now is: “Why didn’t we do it sooner?”phr


Note that all Gear Vendors sales outlets must meet the requirements of being an installation center—hence no mail-order deals. What that means is that your driveshaft will be shortened for you as part of your total installation (650 for most cars, $750 for GM A-bodies). If you do it yourself, you’ll need to make some basic measurements of your driveshaft, then sent it out for shortening before you begin your installation. Our Inland Empire aluminum shaft needed to be shortened by 14 5/16 inches.


The ’64-72 GM A-body (Chevelle, Skylark, Cutlass, and LeMans) was designed specifically for bench seats, which means unlike the Camaro and Firebird, there’s a big pinch in the tunnel right where the Gear Vendors needs to be tall and wide. No problemo—just get out the mallet and hammer the area in front of the crossbrace. This is why there’s an extra $100 cost associated with installation in an A-body versus an F-body.

“Yeah, we said ‘fun.’ We didn’t really expect that an overdrive button could be so cool, but it was a blast to chirp the tires by clicking it on.”
3This shot shows both the tunnel mod (foreground, near brace) and how easy it is to bolt up the Gear Vendors extension housing, which mates the Turbo 400 to the overdrive unit.


Next, bolt the Gear Vendors overdrive/tailhousing assembly to the extension housing. If you haven’t clearanced the tunnel enough, you’ll find out now. This is the time to add fluid to the overdrive—about 28 ounces of Dextron II for this flat-sump model. Oil change intervals are about 5,000 miles.


Screw in the speedometer cable extension included in the kit. If you’re doing the install yourself, you will have previously measured your tire diameter, and supplied it to Gear Vendors (along with your rear gear ration) when ordering your unit. This will guarantee the right speedo gear is inside your overdrive housing.

Scroll down for more installation pictures.

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The first thing most people think about when contemplating the purchase of a Gear Vendors overdrive is the improved fuel economy. The thought coming just after that is imagining what it would be like to extend the life of a high-performance engine by another 25 percent before needing an expensive rebuild. If the credit cart isn’t out by then, you’re a really tough customer, and you may also need to ponder the improved quality of the driving experience that allows you to, say, hold a non-screaming conversation with a passenger, or listen to the radio at a reasonable volume level. We would also like to offer you another reason: gear splitting.

In a drag racing scenario, it is the average power applied over time—rather than fuel economy—that trumps all else. In a perfect world, the drag racer would keep his engine at peak power continuously for the entire run to maximize his e.t. But that can’t happen, partly because the transmissions in use behind high-powered engines tend to be simple, beefy two-speed Powerglides, or three-speed Turbo 400s. These transmissions can take loads of abuse, but their limited number of gears necessarily forces the engine out of its optimal operating range at some point.

Enter the Gear Vendors overdrive. For our purposes here, we can take the overdrive concept and turn it on its head. Whatever numerical rearend gear ration that was optimal (without overdrive) for peak power going though the top end can now be multiplied by a factor of 1.28 for even more grunt off the line. (If you were using a 3.73 gear, a 4.88 gear will now give you close to the same finish-line rpm.) At the point where you run out of gear without the overdrive, kick it into overdrive for the dash to the finish line right in the meat of your power curve. The end result is that your engine stays near its peak longer-and quicker e.t.’s and faster trap speeds are the outcome (you may even find yourself needing only a nominally shorter gear as a result).

But the advantage doesn’t end with just having an overdrive. Try splitting the gears between one-two (and two-three if you have a three-speed like a Turbo 400 or Ford C4). You’ll stay near peak power for even longer, for improved e.t. Don’t believe us? We found Jim Luttrell, a veteran Super Comp racer for Apache Junction, Arizona, using a Gear Vendors overdrive in just such a fashion—with race-winning results. We spoke to Jim about his experience racing a dragster at over 200 mph with a Gear Vendors overdrive, and here’s what he had to say:
“I Run a Powerglide, and we’ve worked to split the gear with our Super Comp dragster. For a while, I was just using it as an overdrive to bring the rpm down—to bring it back into the torque curve—at the top of the track. Then we moved to NHRA Super Eliminator in NHRA Division 7, and with the Gear Vendors, we were the only Dragster in the division running over 200 mph on a 7.90-second index—right at 204 mph. With the gear splitting, you take off the First gear, then at a set rpm, the Gear Vendors goes into First-over, with the Gear Vendors engaged. When the transmission shifts into Second—which is High gear in a Powerglide—the Gear Vendors will switch back out. Then later on down the track, the Gear Vendors comes back in to keep the rpm down in the engine’s

torque peak. It basically makes a two-speed Powerglide into a four-speed.” “We then figured out how to use an MSD rpm-activated switch with a lock on it, and also on the shifter, with another rpm-activated switch. The shifter on the Powerglide and the shifter on the overdrive are not connected—the rpm switch on the shifter turns the overdrive on, and the one on the NSD turns it off. Basically, I don’t have to do anything. If there’s some human involvement, it isn’t going to be consistent. In Super Comp, consistency is the key to winning. The reason why the lock is so important is that on the top of the track, I want the overdrive to stay engaged to where if something happens, I don’t want to over-rev the motor.”

“I’m making right around 1,900 hp, and this Gear Vendors unit has never come apart, or been checked out …It’s been in at least three different dragster since 1997 …” — Jim Luttrell, NHRA Super Comp racer

“Then we wanted even more simplicity, so we stopped using the rpm switches and changes over to timers to activate the overdrive. We still had the switch on the air shifter to deactivate the overdrive on the on-two shift. We also used a second timer to engage the overdrive on the top end. It gave us more consistency. After a few runs on a test and tune day, we could easily move any of the shift points before race day. We did pretty well. We actually won a Wally Award with it in Super Eliminator at the National Open in Division 7.” “I’m making right around 1,900 hp, and this Gear Vendors unit has never come apart, or been checked out. It’s still together. I couldn’t even guess how many passes I put on it-it’s got a minimum of al least 400 passes. It’s been in at least three different dragsters since 1997, and behind everything from a carbed big-block Chevy, to a blown Keith Black Hemi. Rick Johnson at Gear Vendors keeps wanting to take it apart and inspect it, but I don’t see any reason to. Those guys have just been above and beyond for me.”


Jim Luttrell of Apache Junction, Arizona, has used the Gear Vendors overdrive unit to great competitive advantage in his NHRA Super Comp dragster. His current (and only) Gear Vendors unit has run strong without a rebuild for 11 years—in fact, it’s outlasted three different race cars.

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At the terminus of the Gear Vendors speedo cable extension (where your factory speedo cable screws in) is a speed sensor with two wires. These should be run to the Gear Vendors electronic control box, which you’ll mount inside the cockpit under the dash.


These two wires energize the overdrive control solenoid, and must be routed to the Gear Vendors electronic control box.


We’re deviating from the standard Turbo 400 A-body installation because our Chevelle originally came with a 307 small-block and a Turbo 350. Las year when we swapped over to the Turbo 400, we just reused the Turbo 350 crossmember in different framerail holes. This put the crossmember in a slightly different place than normal, necessitating a boxed notch to clear the sump on the overdrive. Unless you are mixing and matching engines, transmissions, and crossmembers, you won’t need to do this.

9Here’s the Gear Vendors electronic control unit mounted safely under out dash, with connections already made for the solenoid control, speed sensor input, 12-volt power, thumb button control, and indicator lights.

“After the install, we easily pulled down 10 mpg … That’s an improvement of 25 percent.Put another way, we could go the same amount of miles from our fill-up for about 20 bucks less …”

10We elected to mount the two Gear Vendors indicator lights on our Stewart Warner gauge panel. The red light (left) is the Autostart indicator. When the overdrive button is engaged from a stop or a very slow roll, this light will come on. It lets you know that overdrive will automatically engage once you exceed approximately 15-20 mph (the in-shift threshold). The green light is the overdrive indicator, and tells you that the overdrive is now engaged. Overdrive automatically disengages (the out-shift threshold) when vehicle speed dips below 5 mph.

“The only question we’re asking now is: ‘Why didn’t we do it sooner?'”


You can choose a floor-mounted stomp switch, a dash-mounted slider switch, or a shifter-mounted switch to activate your Gear Vendors overdrive. We chose one on the shifter.gv This switch from B&M is stocked by Gear Vendors, and fits all B&M Bandit-style shifters. It also happens to fit our TCI Outlaw shifter perfectly. Now it’s time to hit the road and try it out…