By: DAVID FREIBURGER
Photos by: David Freiburger
Reprint from Car Craft Magazine, January 2001
Gear Vendors. That means a lot to the hard-core towing and RV crowd, and it has practically a cult following among off-road and land-speed racers. These things are cool, and it’s about time to see them in more street machines.
Here’s the sitch: A Gear Vendors unit is a supplemental, planetary-gear transmission that replaces the extension housing of your existing automatic or manual trans and provides an extra gear with a ratio of 0.78:1. The immediate benefit is the 22-percent overdrive-you can either reduce your engine rpm by 22 percent any given mph, or increase your mph by 28 percent at any engine rpm. In reality that means a car that has a three-speed automatic, 4.10 axle gears, and 27-inch-tall tires could use the Gear Vendors to take the engine rpm at 65 mph from about 3,300 to just 2,500 (assuming no converter slippage). On the other hand, if you’re comfortable buzzing 3,00 rpm, your mph with the Gear Vendors could go from 65 to 83 mph.
The Science of Gear Splitting
The Benefits of overdrive are pretty well understood: Reduce engine rpm and wear, get better mileage, or just plain go faster. Right on. You can get all that with an overdrive automatic trans from the junkyard, and if overdrive alone is your only concern, that’s the
cheapest way to go. A Gear Vendors can ding you for $2,200. It ain’t cheap, but there are significant advantages over a regular overdrive, many of which stem from the fact that a GV tranny isn’t just an overdrive, it’s a gear splitter. That means the extra 0.78:1 gear can be kicked in no matter what gear your primary transmission is in. Therefore, a three-speed trans becomes a six-speed; a four-speed’s now got eight choices. Consider the perks:
Go faster by splitting gears.
If you’ve ever been at the dragstrip with a typical automatic trans, you’ve probably been disappointed by the shift from Second to Third. With a TH350, the Two-Three shift will net a drop in engine rpm of 34.2 percent-for example, form 6,000 rpm to about 3,900-which may be slowing you down by putting the engine well below its torque peak after the shift. It struggles in third, and you go through the beams well below the engine’s power peak. You may also be winging the engine higher than what’s really beneficial, or using a torque converter with too much stall speed, in an effort to keep the rpm from dropping too much after the shift. However, with a Gear Vendors, you can shift First, Second, Second Overdrive rather than going directly into Third. By adding the GV’s overdrive in Second, the drop in engine rpm is only 22 percent-for example, from 6,000 rpm to about 4,700. That’s enough to keep the engine bussing happily in it’s power band, and we doubt that many cars would require a shift to Third-you’d run through the lights in Second Over. The more peaky you power curve, the more benefit you’ll get from the Gear Vendors’ ability to operate the engine in a narrow rpm range. It’s even possible to drag race by shifting First, First Over, Second, Second Over (splitting each gear), but it takes practice because you don’t want to shift the overdrive off before the trans grabs the next higher gear.
Once we described our daily-driven 800hp goals and our desire for a full-manual valvebody, Dynamic Racing Transmissions advised a competition Turbo 400 with a standard-ratio gearset. We wanted a transbrake, but Dynamic felt that would be a poor idea because of the streetable 10-inch converter we were using. The company also advised maintaining the transmission’s vacuum regulator; if we didn’t, line pressure at idle would be very high, and combined with the comparatively low-stall converter, it would bang too harshly when shifting from Neutral to First. We’re way happy with the setup, and the trans barks the tires nice and hard like we like it.
Dynamic also advised a JW Performance UltraBell to replace the stock bellhousing so we’d have a dragstrip-legal, SFI-approved scattershield without having to cut our floor-boards to fit a bolt-on shield (see “The Ultra-Cool Ultra-Bell,” July 2000). The TH400 was a bolt-in swap to replace our old TH350, and we topped it up with TCI’s synthetic trans fluid.
Here’s how the Gear Vendors works: the casting on the left is the adapter that replaces your transmission’s stock output housing. In the middle is the coupler that links the transmission output shaft to the under/overdrive, and to the far right is the universal Gear Vendors transmission.
Because our blown big-block had been internally balanced, Dynamic supplied a neutral-balance flywheel (right) to replace the original one that had a weight on it for a stock externally balanced engine (arrow). We also had to drill the holes in the flexplate oversize to accommodate the beefier 3/8-inch bolts used with the Dynamic converter as compared to stock 5/16-inch fasteners.
Our only glitch with the Dynamic trans installation was that the supplied dipstick tube was apparently for a truck and was way too long for the El Camino. We’re sick of messing with leaking, hard-to-install dipstick tubes anyway, so we upgraded to a Lokar flexible tube and dipstick with a firewall mount. These things are available for many applications and can cure problems with tight clearances and headers. We knew the trans would require bit-time cooling, so we fed aftermarket cooler with prebent lines from Classic tube. They fit perfectly, even with headers. However, we cut off the fittings that were intended for the original in-radiator cooler and coupled the hard line to AN line using some new fittings from Pure Choice that don’t require flaring the hard line.
Bolting the Gear Vendors to the trans takes only a few minutes. The challenge in some passenger-car applications is clearance to the floorboards. The GV trans is about the size of a two-pound coffee can, so you can use one to judge clearances. Gear Vendors has application-specific help sheets for some cars and says that a few quarter-sized dings in the tunnel are all it takes to fit the unit in GM A-bodies like ours. We got overzealous in our desire to fabricate a shifter stand for the car, so we just cut out a section of the trans tunnel for clearance and to level the floor.
The Gear Vendors adapters are designed to reuse the original trans mount and place them in the stock location for minimal fabrication during installation. The trans mounts from left to right are from Energy Suspension, Daystar, and GM. Note that the Energy unit is about a Â½-inch taller than the others, making it too tall to use in this application. We used the polyurethane Daystar version.
Oddly, we had to cut a notch (shown) in our Chevy’s original oval tubular crossmember to clear the sump of the Gear Vendors unit. Gear Vendors has noted that ’69-’71 A-bodies usually have a stamped crossmember with a flatter shape that can be swapped in to eliminate the need for any fabrication. Also shown here is the mount we made for the Gear Vendors signal generator (described later) and the speedo cable extension. After installation, the speedo is driven from the GV; a new gear and housing are provided with the kit, and it will be spec’d properly for your axle ratio and tire size.
Since the Gear Vendors installation adds significant length to the transmission assembly, the driveshaft need to be shortened; we had Wenco do the job. The FV uses a TH400-type 1350 output yoke that’s provided, and a matching yoke can be installed on the driveshaft at the time it’s shortened. Note that you may have to change your exhaust system to clear the GV, especially if you have a crossover pipe. Driveshaft safety loops will also need to be moved aft.
Here are the electronics for the AutoDrive option from Gear Vendors. Using a signal generator inline with the speedo cable, this computer calculates road speed so that the unit can operate seamlessly, just like a factory electronic overdrive. It automatically disengages the overdrive as you come to a stop. The switch panel also offers manual mode so you can activate the overdrive yourself with either a foot switch or a button on a modified shift handle.
Since it takes just 12 volts and a ground to trigger the Gear Vendors, we opted to omit the AutoDrive computer and simply powered the overdrive solenoid with an On/Off footswitch (arrow). We rigged an unused factory dash light to come on when the overdrive is engaged so we’ll always know when it’s on. That helps prevent trying to drive away from a stoplight with the overdrive engaged.
Finally, here’s the sheetmetal stand we fabricated for Hurst’s new Pistol Grip Quarter Stick to activate the Dynamic trans. It’s a bit of a pure-race item, but the Quarter Stick has always been a favorite street shifter, and the new aluminum handle looks trick and feels comfy. The painless Wiring switch panel will control lots of electrical functions, including the main power for the Gear Vendors.
Â· Go faster by gearing down. What if you’ve already chosen your axle gears such that you don’t need Overdrive? In that case, the Gear Vendors can really help you bottom-end acceleration. First, because gear splitting is a huge plus for tall-geared cars at the dragstrip. Second, you can add lower axle gears for better acceleration, then add the Gear Vendors to maintain your highway style. Just multiply your current axle ratio by 1.28 (the reciprocal of the Gear Vendors’s ratio); if you have 3.08s, you can put in 3.90s for acceleration, yet your cruise rpm and speed with the GV engaged will be identical to your old setup.
Â· Better Street Cruising: We like cams that are too big for our own good. As a result, we often find ourselves cruising on the street in First gear and living with a bit too much rpm because a shift to Second drops engine speed enough to make it run ratty. With a Gear Vendors, we cruise the streets in First Over. Less rpm that First, more driveable that Second, less overheating. Perfect.
Other Reasons to Go Gear Vendors
In addition to the pluses offered by gear splitting, there are some other points that make the Gear Vendors cool:
Double Overdrive. The units are available for all the common four-speed automatics, so a Gear Vendors can add deep overdrive like a factory six-speed manual. Put one on a 700R-4 with a 0.71:1 Fourth gear and the Gear Vendors knocks it down to 0.55:1. You could have axle gears as low as 4.56 and still cruise 85 mph at 2,600 rpm! If you really wanna go nuts, stack two Gear Vendors units inline for ratios as high as 0.43:1.
Trans Braking. With the exception of Ford’s AOD, we don’t know of any full-manual, trans-brake valve bodies available for automatic-overdrive transmissions. With a Gear Vendors, you can have a strong, trick race tranny like a TH400 or a Torqueflite 727, plus an equally beefy overdrive.
Reliability. Did we mention that we don’t really trust typical overdrive trannies with huge power? The Gear Vendors is rated to 1,200 hp out of the box, and they can be tuned for 2,000. They don’t flinch at a 30,000 GVW, and are designed to last a quarter-million miles. A Gear Vendors with a TH300 trans was standard equipment in Callaway Corvettes (normal Vettes had 700-R4s back then).
They can be price-practical. Despite the high price, a Gear Vendors can be a bargain if you’ve already dumped a bunch of money into a good tranny and converter and have now decided you want overdrive. When we put a 4L80E trans in our big-block Chevelle project car, the price was over $3,200-and we can’t split gears with it.
Towing.Not that you care about towing with your hot rod, but if you do have a tow vehicle, the Gear Vendors is the single biggest improvement you can make for hill climbing with a heavy load. Much better mileage too.
But Howâ€™s It Drive?
For this story, we stabbed a Gear Vendors into our ’72 El Camino to show you how an installation works. We combined the GV with a full-manual-valve-body TH400 race trans from Dynamic Racing Transmissions and also used a 10-inch Dynamic converter. We got the Elco running with the Gear Vendors/Dynamic setup hooked to our 12-second 454, but the ultimate plan is to feed it the 830hp blown 496 that was on the August 2000 cover. We intend to drive the blown combo every day.
Once the huffer motor is in the car, we’ll give you even more feedback, but we’ve
experienced the Gear Vendors in several vehicles and have always dug it. On a radical street machine like our planned 10-second Chevy, the Gear Vendors makes the difference between highway driveability or not, and going down the dragstrip using Second Over instead of Third is usually worth a tenth or two. The Gear Vendors can be shifted at full throttle with an auto trans, and it does so firmly enough to chirp the tires. The GV provides a great driving experience, with lots of gear-snatching that really adds performance. You don’t think you need those extra gears until you have them, then they’re indispensable. You can always keep your engine in its sweet spot, it makes the exhaust shriek nicely, and it’s just plain fun. We’ve proven that even ludicrous engines get better mileage with overdrive, and they don’t overheat as
readily, either. Moral of the story: expensive, but way worth it.
DYNAMIC RACING TRANSMISSIONS