Gear Vendor's Overdrive - Mopar How-To! 3+1=6
Convert Your 727 To A Six-Speed Overdrive With Gear Vendors' Tailshaft-Mounted Overdrive Unit.
From the June, 2000 issue of Mopar Muscle
The Gear Vendors overdrive...
The Gear Vendors overdrive cutaway displays that it is a self-contained, two-speed, auxiliary transmission with direct drive and a .78:1 overdrive ratio. The mechanical basis of it is a planetary gear set, similar to those in any automatic trans.
King of the Road? Well past the muscle car days and into the '80s, there was no question about it. The performance edge on the open road was there with almost any sensibly-geared muscle car. For the first two decades after their production years, with the 55mph speed limit and pathetic Detroit offerings, muscle cars reigned supreme. In the '90s, the picture began to turn, speed limits went up, and new cars picked up in performance, but more importantly, in gearing.
Originally incorporated to increase fuel economy, overdrive transmissions in both standard and automatic form have become the norm for any new car or truck. With the overdrives came the additional benefits of reduced engine wear, noise, and effortless high-speed cruising. Crank any new vehicle up to 90 mph, and it's a Sunday drive. With the high-speed gearing provided by overdrive ratios, under the hood, the engine is quietly spinning along at a lazy rpm. On the open road, drivers of newer vehicles unconsciously use the capabilities afforded by modern gearing, and average road speeds have steadily risen well beyond today's higher speed limits.
Driving a muscle car on the open highway out West can be downright humbling today. Hit the fast lane in our 440-powered '71 Charger R/T, crank up to just shy of 4,000 rpm on the tach, and watch the traffic back up behind you. A never ending stream of minivans, late Euro-cruisers, and Hondas duck to the inside to make the move past. You know the chassis is there, you have 500 lb/ft on hand, but it just sucks as that gal in the Geo Metro effortlessly blows by. And that's with those 3.55 gears that once seemed so sensible. Sure, a hot 440 will spin 6,500 rpm+, and will rocket to insane speeds, devouring all comers-but it's fleeting. You really just can't, and don't want to, hold it at a screaming rpm just cruising along.
If your muscle car activities are confined to the track, showfield, or occasional burger-joint cruise, even 4.56s won't be a problem. Otherwise, the benefits of higher-speed gearing are clear, even if it's just to reduce wear on that fresh mill. There are a number of alternatives to give older Mopars the open road gearing advantages of a modern vehicle, some with more compromises than others. The easiest and cheapest thing to do is ditch the drag gears for a higher rear ratio. A set of 2.76s out back will make for a great freeway flier, but it comes at a steep cost in off-the-line oomph. Those low gears you started with were in there for a reason: more torque multiplication off-the-line and through the gears. A high-stall converter will help the launch in an automatic car, but the ratio spread will turn the machine into a two speed at the drag strip.
First time for everything-I...
First time for everything-I let the guys at Gear Vendors handle the installation, and just worked the camera. The big lift made the job a breeze, but the straightforward installation can be done in your driveway.
Another choice is to drop in a late-model four-speed 518/618 overdrive auto. The late auto overdrive swaps are popular with some makes; however, the fact is it's not a great swap in early Mopars. A big-block version of the Mopar four-speed auto was never produced, requiring the use of an adapter plate and the related mods and expense. Even in a small block application, the bulk and positioning of the fat overdrive tailhousing on the Mopar overdrive auto causes problems. Serious surgery is required to the critical torsion bar crossmember in the area of the trans tunnel. It's just not a good fit down there. Most of these trannies were built with lock-up torque converters, poorly matched to the power curve of a performance V8; and nowhere near as capable of handling serious output as a conventional converter. Finally, the swap means pulling out and tossing that reliable 727 TorqueFlite. The late-overdrive trans swap can be successfully pulled off, but weigh the downside.
The Gear Vendors
What if you could take the 727 that's already there and add some gears? It would be nice. With the Gear Vendors' overdrive conversion it's not only possible, but it's a simple bolt-in, without even having to remove the tranny. The Gear Vendor is a self-contained, two-speed, auxiliary transmission with direct drive and a .78:1 overdrive ratio, taking its operating principles from the LayCock/DÈNormanville overdrive. The mechanical basis of it is a planetary gear set, similar to those in any automatic tranny. The main difference is that the planetaries are activated by a cone clutch, engaged by two hydraulic servos. The servos and the unit's lubrication are provided by a mainshaft-driven, cam-operated pump drawing oil from the unit's own sump. A 12-volt electrical solenoid valves oil to the servos to engage the cone clutch, setting the planetaries and overdrive into motion. The hydraulic actuation system, operating at 650+psi, makes for near instant shifts.
The cone clutch and planetaries provide for extremely efficient transfer of torque and unbelievable power handling capabilities-the manufacturer claims it takes less than 1 horsepower per 400 to operate, and in standard form can handle 1,200 horsepower, or modified up to 2,000-plus horsepower. Owing to the clutch/planetary design, the overdrive can be shifted at that power level-at full throttle. Obviously, we haven't tested these rates, but we do know that the Gear Vendor is the overdrive unit of choice by builders in extreme horsepower applications, from blown street rods, drag cars, and land speed cars, to OE applications such as the Mopar-powered Jensen Interceptors and, we hate to say it, the Callaway Twin Turbo 'Vettes (the GM overdrive auto was too weak).
Since the Gear Vendor overdrive can be found working reliably behind 8-second drag cars, we knew that its power handling capabilities were far beyond what our modified 440 would deliver. Power handling we weren't worried about, and the two-year unlimited mileage warranty told us the manufacturer wasn't worried about reliability. Looking at what the unit had to offer in our application, it seemed like the most logical solution to our gearing problems. Plus,we'd get to keep our excellent B&M-equipped 727. With the Gear Vendors overdrive, our 3.55 ratio would drop down to 2.77 in overdrive top, more than enough to get the revs down at a high speed cruise. Finally, and often overlooked, the Gear Vendor would give us gearing in Third over, which is compatible with our Holeshot B&M converter.
Converter stall speed has to be taken into account when considering overall gearing. Our converter stalled at 2,900 rpm. Running at the anticipated cruise speed, the converter shouldn't be too far below the stall range, or the converter will slip excessively, costing efficiency, heating the tranny, and negating a portion of the gearing potential of the overdrive. That's why manufacturers universally use lock-up converters with their overdrive autos-to work with the extremely tall overdrive ratio of their automatics. The 22 percent overdrive of the Gear Vendor would give us an almost ideal ratio for a high-speed cruise, while not being so drastic that we would need to reduce the stall speed or require a lock-up converter to operate efficiently. The Gear Vendors seemed to be the perfect choice for our R/T, so we went out to get one.
First the angle of the engine/trans...
First the angle of the engine/trans is measured and recorded, then the trans is supported and the crossmember removed.
After pulling the driveshaft...
After pulling the driveshaft and speedo cable, the tailhousing was unbolted from the trans case. Spreading the snap ring under the cover just fore of the mounting pad releases the housing from the bearing and it slides off.
The original snap ring and...
The original snap ring and park pawl lock is removed from the stock extension and fitted into the replacement Gear Vendors adapter.
The adapter replaces the extension...
The adapter replaces the extension housing and is flanged to mount the overdrive unit at the output end. Slide it on, engage the locking snap ring, and bolt it up.
At the time of our installation,...
At the time of our installation, the Gear Vendors' extension was not cast with a provision for the slapstick shifter lower linkage bracket, so this bolted-on angle iron mounting bracket was added (arrow). The mounting ears have since been added.
Next, the coupler was slipped...
Next, the coupler was slipped in place over the trans's output splines. The clearance was set to specs with shims (part of the Gear Vendors kit) to provide the required clearance to the input of the overdrive unit.
To make the checking of the...
To make the checking of the overdrive unit's fit easy, an empty dummy case was used. Do-it-yourself installers would just swing up the McCoy.
Breaking from our usual jack-it-up-in-the-driveway install, when Rick Johnson of Gear Vendors offered to install the unit at the factory, we figured we'd check out their production plant and let them handle it. We set an appointment at the Gear Vendors facility near San Diego, about an hour and a half of freeway time from our digs in Los Angeles. Driving down, we decided to take the desert highway route to avoid traffic. Settling in the fast lane at our cruising rpm of 3,500 rpm, the Charger soon began bottling up the high speed desert freeway traffic. Trying to keep up with the assorted mini trucks and Hondas coming up on our tail, we edged the tach up to about 4,000 rpm, and they still kept coming. Finally, looking in the rearview, we saw a guy in the service van behind us throw his hands up in disgust. We gave up, moved over to the slow lane, and dropped it down to 3,500 rpm for the rest of the trip.
The actual installation of the Gear Vendor is simplicity in itself. The original tailhousing is pulled off the back of the 727, and the Gear Vendor's adapter is bolted in its place. The adapter is flanged to bolt onto the 727 case at one end, and at the output side is flanged to receive the overdrive unit, placing it in position to engage the original output shaft through a short splined coupler. Some massaging of the driveshaft tunnel with an air hammer was all that was required to give adequate clearance for the compact overdrive unit-an area about 3-inches wide by 1 1/2-inches tall on the right side of the tunnel.
With the overdrive bolted in, the drivetrain angle was adjusted back to the stock specs (measured earlier), and the trans secured using the stock crossmember with a few minor modifications. Since the adapter/overdrive assembly replaces the stock tailhousing, the speedo drive is provided for in the overdrive unit. A compact 90-degree adapter was needed for our Mopar application, and the Gear Vendors' technician calibrated it for our gearing and tire size. With the Gear Vendors unit now hanging off the back of our 727, the driveshaft was then shortened. To finish the job, the Gear Vendors' electronic control package was installed, which provides for full automatic operation of the overdrive unit, while allowing the overdrive to be switched off or used in a full manual mode through an auxiliary switch. For the manual control, we went with their recommended floor mounted switch, although all manner of shifter- or steering-wheel-mounted switch gear can be used.
On The Road
With the hardware in, we rolled off the rack, and Rick took the wheel to show us the Gear Vendors' overdrive in action. Just cruising in automatic mode, the electronic control shifted the 727/Gear Vendor combo as though we had a factory four speed automatic down below. In automatic mode, the Gear Vendor-equipped tranny provides four shifts, with overdrive automatically kicking in at the programmed automatic shift point in the Gear Vendors' electronics package, typically 47 mph.
Once on the open highway, in automatic mode, the overdrive is already on by the time you reach freeway speeds. RPM at a high speed cruise was down from 4,000, to just under 3,200 at 85 mph, and about 2,700 at 70 mph-perfect. This is just where it needed to be to work efficiently with our torque converter, yet leaving plenty of revs available should the need arise. Remember, with the overall higher gearing effect of the overdrive in action, the run from 3,200-4,000 rpm is worth a 28 percent higher mph gain than with the direct drive ratio at work. Stabbing the throttle at speed, we got something we didn't expect, as the tranny kicked down to Second Over, and the Charger rocketed up to well over triple digits before shifting to Third Over. Without the Gear Vendors, top speed for grabbing an automatic kickdown had been about 65 mph. With the overall gearing effect of the overdrive engaged, we now had an extra passing gear-automatically-into Second Over at a 28 percent higher road speed. Very impressive.
We pulled off the freeway. It was time to put the Gear Vendors' unit through its paces in manual mode. There are now 6 forward speeds available: First, First Over, Second, Second Over, Third, and Third Over. With the TorqueFlite's wide gear ratio spreads, and the moderate ratio of the Gear Vendor, there is no overlap in ratios, with each intermediate range providing a useful gear split. The ratios run sequentially from first as follows: 2.45, 1.91, 1.45, 1.13, 1.00, and 0.78. With our blessing, Rick nailed the throttle, and proceed to bang through all six ratios. "Outrageous." That's the only way to describe 440 cubic inches screaming through six closely spaced ratios. He'd obviously done this a few times before. Rick told us that because the engine stays near the peak of its power curve, drag race users typically see meaningful ET gains, usually shifting in the First, Second, Second Over, and Third, firing that extra torque multiplication where it's needed most, between the two-three shift (First Over will usually blow-off the tires in a fast drag car)
Taking the wheel, we found getting the most from the Gear Vendors overdrive in manual mode takes a bit of practice. The actual shifts are tire-chirping quick, but with a slight delay from the moment the button is hit. Upshifting from an overdrive ratio to the next higher gear in direct, such as First Over to Second Direct, or Second Over to Third Direct, you have to hit the switch to kick-out the overdrive while slapping the shifter to the next higher gear. The thing you don't want to do is kick-out the overdrive before the tranny gears up, or you'll be going down half a gear instead of up. With a little practice, being conservative, and upshifting first, the feel for the shift timing will come, and then it becomes almost instant. Even sloppily done, the vehicle is under full power acceleration while all the shifting is taking place. It didn't take long until we were able to pull off the rapid-fire six-gear change show with the best of 'em.
With its gear-splitting ability, high-speed kickdown, and powerful upshifts, the Gear Vendor delivered more than the simple overdrive we expected. There was genuine performance to be found in the unit, beyond the bonsai-run ability and reduced engine wear and tear we sought. The thing is downright fun. With the demo over, we packed our gear for the long drive home-rightfully in the fast lane this time.
|Gear Ratio Chart: Torqueflite 727|
|Trans||Ratio|| ||Final Drive Ratio|
Some massaging of the floorpan...
Some massaging of the floorpan was indeed needed in one spot to give adequate clearance at one stud on the upper right. Nothing serious here; it was taken care of with some quick work of an air hammer with a flat plannishing tip.
The speedo is read off the...
The speedo is read off the output shaft of the overdrive to register. A compact 90-degree adapter is utilized to make the best use of the available clearance. Calibrating the Gear Vendors' speedo drive ensured our speedo would be right on.
Bolted up, the compact Gear...
Bolted up, the compact Gear Vendors' overdrive tucks nicely in the driveline tunnel. Our muffler shop-bent exhaust pipe just cleared the corner of the unit. Any contact with the exhaust, chassis, crossmember, or floorpan will transfer vibration, so make sure everything clears as it should.
Next, the trans mount. The...
Next, the trans mount. The ears at the upper corners of the crossmember's mounting bracket kissed the adapter extension's mounting pad. Clipping the corners of the ears fixed that.
The mount went in for a trial...
The mount went in for a trial fit, and a check of the engine/trans angle. The unit had to come down slightly at the tail to preserve the stock angle.
Adjusting the angle was accomplished...
Adjusting the angle was accomplished by redrilling the crossmember tabs for the trans mount's lower cross bolt (arrows). Bolt in the mount, and make sure there is clearance between the crossmember and extension, since they are closer together with the redrilled holes. Ours just cleared, but otherwise, clearance the crossmember or lower rib of the extension as required.
The driveshaft was sent out...
The driveshaft was sent out to be shortened, the supplied new 1350-series yoke installed, and then balanced.
The last step is to hook up...
The last step is to hook up the Gear Vendors' electronic controls. We had the auto/manual mode switch mounted under the dash (arrow), while the manual control switch we used was floor mounted. That's it, bang shifts and drive on.