1966 Chevy Chevelle Gear Vendor Unit Install - Split Decision
Gear Vendors Makes Cruising That Much Easier
From the January, 2010 issue of Chevy High Performance
By Sean Haggai
Photography by Courtesy of Manufacturer, The Car Craft Staff
It shouldn't be this way though. Running through the streets is always a good time; however, drivers should also be able to experience the open road where cruising at 70 mph and above (if you dare) is the norm. The slow lane is no place for muscle cars to hunker down. In the past, the only way to keep the highway rpm low was to install a lethargic set of rearend gears. While this made high-speed cruising tolerable it made for a fall-on-your-face personality on the street. Once those tires lose bite, forget about it.
In order for rodders to get their muscle cars to scoot on the freeway, some upgraded from a Turbo 350 or 400 (three-speed) to a more modern electronic overdrive transmissions such as the 700-R4 or by installing a higher rearend gear ratio. The 700-R4 allowed for an extra overdrive gear for freeway speeds, but the factory gear spread still kept engine speeds relatively high. Let's face it, we build our cars to be driven everywhere. Blasting freeway on-ramp entrances should continue all the way into the fast lane. Our car's driveablitly should in no way be limited by our transmission, the very component of the vehicle which harnesses the engine's torque allowing us to move about.
The vehicle in question is...
The vehicle in question is this '66 Chevelle. It's owned by Brett Voelkel of RideTech and packs a 460hp 383 small-block. The motor is backed by a Bowler 700-R4 automatic with a 4.10:1 gearset in the back. For the street, it's a great combo and cruises well. Since this car sees specific duty in autocross events and long road trips gearing is critical. Through the cones the Chevelle suffered from too short of a First gear, sending the motor to 7,000 rpm, only to bog once it shifted into Second gear. Voelkel didn't want to swap for a manual tranny, which would require a bit of work, nor changing to less rearend gearing which would hurt the car off the line. More gear would allow for better Second gear range but would kill the motor on the highway. In this case, the Gear Vendors unit would allow for the best of both worlds; great grunt down low and sufficient rpm drop once on the highway.
The only way to get more operating range from the engine is via a closer gear spread. Aside from adding a new tranny or fussing with the innards of it, piggy-backing a Gear Vendors under/over-drive unit to your already existing transmission can get the job done. Its key is the ability to split each gear with its own overdriven gear, essentially turning your three- or four-speed into a six- or eight-speed automatic. It won't matter if it's mated to a manual or automatic either and it doesn't care if you are a drag racer, autocrosser, or weekend hauler. Plus the unit can handle up to 2,000 hp. We took advantage of RideTech's '66 Chevelle that's backed by a 700-R4 to install a complete Gear Vendors unit. We put the 'Velle on the lift for a better view and got the skinny on how it's installed and what makes this component so special.
What We Did
Installed a Gear Vendors unit into a '66 Chevelle
Blast in the fast-lane with better driveability
$2,600 for 700-R4 (Call for pricing on other applications)
Everything was just as I had imagined. The pushbutton gear split was effortless and the short rpm drop made the car sound like a high-end exotic. The Chevelle used to run at about 3,000 rpm at 80 mph. Now it runs smooth and quiet at 2,300 rpm; talk about saving some fuel. On the autocross track, I can shift the car from First to First-Overdrive which keeps the engine right in the middle of its powerband without sacrificing starting line power or overrevving the engine. The shift is quite firm but can be modulated by throttle position to soften it. I can tell you that the car (and driver too) is much more comfortable and controllable than trying to wring the motor out in First or bogging into Second. I can't wait to get the car on a big track where I can use all four (now eight) gears. It is not too often a performance upgrade can be achieved with no compromise. -Bret Voelkel, RideTech
Guillermo Chavez began work...
Guillermo Chavez began work on the '66 Chevelle at Gear Vendors' headquarters in El Cajon, CA. There we placed the Chevelle on the racks for an easier install. The first order of business was to measure the angle of the differential and driveshaft. The differential came in at 4.5 degrees and the driveshaft sat at 1.2 degrees. It's important to check this because if the angle is too extreme it could cause unwanted driveline vibration.
We also measured from the...
We also measured from the front of the transmission extension housing gasket to the center of the U-joint on the transmission drive yoke. This measurement allowed us to determine which extension housing to use.
To gain better access, we...
To gain better access, we removed the transmission mount from the 700-R4. Next, we used a 9/16-inch socket and wrench to remove the transmission crossmember from the framerails.
The path was clear and we...
The path was clear and we removed the transmission extension housing with a 9/16-inch socket. Be cautious, as some transmission fluid will leak out. We were sure to place a drip pan underneath to prevent a nasty mess.
With the extension housing...
With the extension housing removed the output shaft is exposed. Chavez measured how much of the shaft to trim off. Since the GV unit uses a coupler to connect the original transmission shaft to the GV shaft, if it's too long the GV unit won't be able to bolt up. Note: most kits do not require this step, but the specific kit for a 4L60E in a '66 Chevelle does.
GV Extension Housing
GV Extension Housing
Gear Vendors offers a full line of transmission extension housings and adapters for popular GM two-, three-, or four-speed transmission applications such as 4L60E, 4L80E, 700-R4, Muncie, Powerglide, T10, and TH350 or TH400. In our case, we went with the 350S extension housing since the 350SS was going to be a bit short. Note: Some transmission crossmembers may need to be modified for proper fitment.
Using a zip tie as a reference,...
Using a zip tie as a reference, Chavez used the measurement and shortened the shaft. Then, with a cutting wheel Chavez trimmed 13/8 inches off of the shaft.
After the shaft was trimmed...
After the shaft was trimmed we could mock up the GV tailhousing for floor clearance. Normally, with the shorter TH350 space wouldn't be an issue; since the Chevelle utilized a 700-R4 with a shifter bracket located in a funky position there were some clearance issues to contend with. We used an air hammer to create more space where it was needed.
When installing the GV tailhousing,...
When installing the GV tailhousing, there is no guesswork on its position, as the word "TOP" is cast on the housing. Still, should you encounter any fitment issues, the transmission crossmember can be flipped 180 degrees. In this instance, the fit was a slam dunk and the GV tailhousing fit in the same location as the 700-R4's location.
The auto-drive control unit...
The auto-drive control unit is the brains of the operation. It's an interface which can control up-shifts into a split overdrive based on speed or rpm. Each Gear Vendor unit comes with this unit and it's a cinch to install cleanly under any dash. Since the 700-R4 already has an overdrive gear (4) from the factory, Gear Vendors used their dash switch delete option. Simply put, there is no AutoDrive (automatic engagement at cruising speed of the Gear Vendors like you would want with a 3 speed automatic). Dashswitch delete still gives you AutoLaunch for the automatic application of First over at the dragstrip and turns the overdrive off (if you have forgotten to) at low speeds so you always take off in First.
Next, we installed the coupler...
Next, we installed the coupler which adapts the smaller output shaft of the 700-R4 to the larger 32-spline input shaft in the GV unit.
We used a straight edge to...
We used a straight edge to confirm we had the length correct (shims provided). The accuracy of this measurement will ensure the two flanges will meet together and bolt up.
We screwed in the 10-inch...
We screwed in the 10-inch speedometer cable into the speed sensor on the GV unit. From there we placed the other end of the GV speedometer cable into the factory speedometer cable.
This end also contains the...
This end also contains the sensor that converts the speed info to the electronics using a VSS signal.
Since the GV unit hangs farther...
Since the GV unit hangs farther off the back of the transmission, a shorter driveshaft must be placed back in. Our new driveshaft was actually the original unit from the car that was cut down 1211/16 inches and balanced.
With the driveshaft installed...
With the driveshaft installed we filled the overdrive up with 27oz of Castrol Syntorq LT (GM # 12346190). We also checked the main trans fluid level while idling in park. Finally, we could get the car back down to the ground.