Keisler A41 Automatic Transmission - Geared To Go
Keisler's Automatic Overdrive Conversion Will Bring Your Mopar Into The 21st Century.
From the August, 2009 issue of Popular Hot Rodding
By Steve Dulcich
Photography by Steve Dulcich
There's a lot to love about a vintage muscle car. We can swoon over the seductive styling, the purposeful simplicity, and intangible raw element of power that seems to emanate from these classic American machines. While a classic muscle car fits in your garage like a jewel in a case, bringing that beast onto the streets in a usable fashion often presents an entirely different concept of reality. Technology has been steadily moving forward in the decades that have elapsed from those automotive glory days, and taking to the streets in old iron is enough to drive the point home.
Our project Satellite is a perfect case in point. Although currently far from achieving the status of artful garage decoration, the visual, spatial, and auditory elements are all there. With a high-winding 340 small-block working through deep gears, the sounds and action were ready to thrill, however, put this machine to use and reality sinks in. On the wide-open expanses of asphalt where such a machine should thrive, it did nothing but disappoint. Even with the "compromise" rear gear ratio of 3.55, the hydraulic and mechanical realities of nearly 10 percent torque converter slip and gear ratio had the engine trying too hard, and going nowhere fast.
A sustained 4,000 rpm on the wide-open highway is enough to get you thinking about those reciprocating engine components needlessly eating away at themselves. Cutting down the pace to a more sustainable level brings nothing but humiliation as the old Mopar chokes the flow of cheap imported tin moving down the road. And, what reward for all the misery? There was nothing to show for all the open-road drama but excessive noise, engine heat, and vibration from the overworked drivetrain. There is a definite disconnect between the promise of sweet performance, and the reality of highway inadequacy.
Gearing UpNow this shortcoming is not without its cure. The real problem lies in the fact that the OEM transmissions of the era were limited to three forward gears, with tightly spaced gear ratios cumulating at 1:1. In practical terms, what this means is that the limitations of the transmission ratios present a choice: gear it for acceleration, or gear for outright speed. Making this choice via the rear axle ring-and-pinion ratio presents the enthusiast with no correct answer. Consider the alternatives. Taking the path of a low gear ratio will provide the rocket-like acceleration expected of a performance machine, but at the expense of any real semblance of utility on the road. Gear it for high speed, and the muscle has just been removed from your muscle car. Strike a compromise gear ratio and try not to be overly disappointed when the car simply does nothing very well. When it comes to gearing using the old '60s drivetrain technology, we really have a strict A or B choice, with opposite goals and outcomes.
OEM manufacturers solved this paradox decades ago with transmissions featuring deep overdrive ratios, wider ratio spreads, and lock-up torque converters. In examining each of these characteristics, their individual advantages are clear, but more importantly these features work together to a cumulative advantage. An overdrive alone will drop the rpm at speed, but the lockup torque converter is what really makes overdrive gearing shine in an automatic transmission application. Taking a 30 percent cut off the transmission input shaft speed puts a standard hydraulic torque converter down to a speed well below its efficiency range, making for lazy operation, inefficiency, and excessive heat. The lock-up with the overdrive solves this problem. A wider gear ratio spread brings the entire package together, allowing a moderate final drive ratio (with the associated lower driveline speeds), while providing far greater gear multiplication on the initial hit to get rolling in a hurry.
Keisler's A-41 is based on...
Keisler's A-41 is based on a modified 4L60E, engineered specifically for the Mopar retrofit application. The trans can take some punishment, with units available to handle 450, 550, or 650 lb-ft of torque.
Our 904 Torqueflite was working...
Our 904 Torqueflite was working great, but the 1:1 top gear ratio and normal torque converter slip, working through our Satellite's 3.55 rear gear ratio, made the car a pig on the open road when compared to any new car. We were happy to see the archaic transmission go.
Stock Mopar torque converters...
Stock Mopar torque converters carry an integral starter ring gear, while the Keisler system uses a GM-style flexplate with the ring gear built in. All of the required hardware came packaged in the A-41 transmission retrofit kit.
The only "tunnel" work required...
The only "tunnel" work required to fit the four-speed Keisler transmission into a B-body Mopar is to fold back the pinch weld where the firewall meets the floor. We used an air hammer, and smoothed the flange well flat for maximum clearance.
OEM manufacturers did not come to the current state of the art in transmission and drivetrain technology in a single leap. The evolution began with overdrives, often without the lockup feature, meaning driving continuously through the converter stall just going down the road. With the addition of the lockup feature, the disconnected feeling was eliminated, along with the excessive heat and lost energy generated in the slipping converter. Still, these early transmissions were problematic, with a hydraulic control mechanism relying on unstable balances of hydraulic fluid pressure, spring tension in the various valve body circuits, and mechanical linkages to command the transmissions functions. Hydraulic controls just lack the precision to reliably and accurately control the transmission, a problem that was eventually overcome through the use of modern electronic controls.
A modern electronically controlled, lockup, overdrive four-speed transmission is simply at a whole different level compared to an old Torqueflite three speed. It doesn't take much proof to come to this conclusion beyond getting out of a modern vehicle and then hitting the open road in your vintage Mopar. Upgrading to a modern transmission is obviously a worthy goal, but the application presents some difficulties. Chrysler's own electronically controlled four-speed automatics do work well in later model trucks, but swapping one into an older muscle car is more than a little problematic.
The Chrysler 46RE (and the earlier hydraulically controlled A-518) transmission was an evolutionary design, created as a modification of the same old A-727 automatic transmission used since the early '60s. The overdrive portion was stuffed onto the back of the existing planetary architecture in the tailhousing, resulting in a functional four speed, but one that is too bulky to fit in the older passenger car chassis. With these Chrysler four-speed automatics, the bulbous overdrive tailhousing interferes directly with the existing torsion bar crossmember. Attempting this swap will require a major reworking of the suspension crossmember and floor pan. Due to this fit issue, the swap to a late Chrysler automatic has never become popular.
The Keisler A-41
Given the problems with the Chrysler automatic four-speed swap, most Mopar enthusiasts were simply out of luck when looking for a truly modern automatic transmission upgrade. Keisler Engineering, a company that has made a name for itself in the Mopar community with their overdrive manual conversions, set out to finally provide a solution. The answer was found based upon the GM 4L60E, a state-of-the-art electronically operated four-speed automatic. This transmission has an integral overdrive gear, so the fit problem associated with the 46RE/A-518's oversize tailhousing is not an issue. The real beauty is that the transmission features a detachable bolt-on bellhousing. Keisler designed and cast specific OEM-quality bellhousings for Chrysler applications, making the transmission bolt on as though it was designed for the Mopar engines. This was the genesis of the Keisler A-41.
The Keisler bellhousing allows the transmission to mate to the engine, but there are many other aspects of such an installation that needed to be addressed before this retrofit could become a reality. Keisler's approach is to accomplish a "perfect-fit" conversion, complete and ready to go. Among the many special components developed are a unique flexplate for the Mopar engine with an integral starter gear, a universal Throttle Position Sensor arrangement, a revision to the tailhousing to accept a mechanical speedometer drive, and of course all the required hardware, and the crossmember mount.
There is some bench prep required...
There is some bench prep required before swinging the A-41 transmission in place, namely installing the shift selector, some fittings, and braided lines for the transmission cooler.
Anyone who has wrenched those...
Anyone who has wrenched those difficult-to-reach cooler line fittings on a factory Torqueflite can appreciate these flex lines used on the A-41 conversion. The braided steel lines provide an easy hook-up to the new hardlines run from the radiator along the right side framerail.
In order to account for the...
In order to account for the difference in starter ring gear placement, the bellhousing comes with a spacer/adaptor that is used in conjunction with the factory starter. We used a late-'90s Ram truck starter, which is much smaller, lighter, and more powerful than the original.
For our '71 Satellite, the swap looked like a winner, since we were favoring retaining an automatic transmission. The transmission is available in torque ratings of 450, 550, or 650 lb-ft, so we were confident in the power handling capabilities. Keisler custom tailors each kit to each customer's needs, and for our 340-powered Satellite, we specified a 550 lb-ft unit with a 2,800-rpm stall converter. The converter stall speed can be had at a wide range of ratings, depending on the specific requirements of the installation, and the beauty is that once the trans goes into lockup, all of the lost rpm and slip normally associated with a loose converter are gone.
We took our car to D&P Classics, an authorized Keisler dealer, to install the A-41 conversion. Basically, the job consists of two parts, the mechanical aspects of getting the old trans out and bolting in the A-41, and the electronics portion required for the transmission control. The Keisler kit comes with a harness that is fully terminated, so it is just a matter of plugging the harness ends into their associated connectors. A control unit is part of the package, and though it is fully programmable for altering the transmission functions, it is already set up by Keisler with a base calibration that is ready to go. Any changes to the calibration are simply made with Keisler's included software package via a laptop computer.
We quickly had the original 904 Torqueflite on the ground, and then pre-routed the harness into position as indicated in the thorough Keisler instruction manual. The control unit was mounted behind the driver's kick panel, and we moved on to hoisting the new trans into position. Any time a non-original retrofit is attempted, there is a question about just how well the parts will fit. Keisler makes a note of some minor clearancing of the firewall pinch weld, and no other "massaging." We swung the A-41 up to the waiting block, bolted it up, bolted up Keisler's custom crossmember mount, and it was in just like that! From there, the actual nuts and bolts of the install was no more complicated than a normal transmission replacement: hooking up the cooler lines, the shifter, torque converter bolts, and starter. Each kit comes with a custom driveshaft, and we ordered the upgraded aluminum 'shaft.
We wrapped up the full swap at D&P, spun the Satellite around the block to check the function of the A-41, and then it was trial by fire in the form of a 200-mile trip back home. With a trip of similar duration down to the shop still fresh in our mind, the contrast was staggering. The Satellite was at its worst in open highway driving, winding tight in the slow lane while traffic whizzed past. The noise vibration and harshness that were all part of the driving experience were gone. We slipped into the left lane with the hammer down, making time at a leisurely 2,400 rpm, a difference as clear as night and day. With the lower first gear ratio of 3.06, the launch off the line was the equivalent of a set of 4.30 gears with the old Torqueflite. Up into overdrive, and the final drive equivalent is an easy-cruising 2.51. That is the advantage an extra gear can make to the ratio spreads.
Keisler's control unit actually accepts two calibration programs, selectable from a dash-mounted toggle. We had a "cruise" calibration for normal driving, and a "performance" setting a switch click away. The A-41 and our converter combination, with the gear ratios involved simply made the car an animal in "performance" mode. Gear multiplication, perfect stall, and solid, quick shifts make that happen. The final upshot is the trans will just shift into overdrive, then lock the converter, and you're moving down the road like you never figured an old Mopar could.
The trans is staged in position...
The trans is staged in position under the car, but before heaving it all the way up and in place, the wiring harness is run down and routed, and all of the wiring connections are made. The only portion of the original harness retained are the factory neutral safety switch and reverse light wires, which are fitted with a new connector.
Upon completing the preliminary...
Upon completing the preliminary connections, we carefully maneuvered the trans into position. While removing the exhaust H-pipe would have facilitated our efforts, we were able to angle the transmission around the pipes to mate with the rear of the block.
At the tail of the transmission,...
At the tail of the transmission, the factory crossmember mount is discarded for a custom unit designed to mate the A-41 trans with the B-body chassis. We were impressed to find it bolted right in position as though it was OEM.
We noted on the Keisler website that a paddle shifter arrangement is offered as an option on the A-41. Without any previous experience with such a device, we thought about whether or not it would be worthy. After all, our old Mopar made good with nothing but a floor-mounted Slap Stik shifter. With an electronically controlled transmission, the shift functions are all commanded by the control unit. This opens the opportunity to tell the control unit what to do through the same electronics. That is basically what the paddle shifter does--command the transmission via an electronic signal to shift now, and it has to oblige. With the switching for this manual control right at hand, and the transmission reacting at the speed of the electronic impulses, the result is a transmission that will follow your commands to shift up or down, one gear at a time--instantly.
After some debate, we opted to include the paddle shifter, and without it you really don't know what you're missing. Our trans was built with an engine-braking function, so the result is much more mechanical than the normal free-wheeling feeling of an automatic. Up or down--just a quick flip of the paddle and you grab the next gear. One thing we didn't realize is that the multi-function display included with the paddle shifter provides a digital read out of a multitude of chassis and engine functions. Besides the current gear position, the display shows the engine, driveline, and turbine rpm, the trans and engine temperature, and vehicle speed among its many functions. No question about it, the paddle shifter is a worthy addition to the A-41 transmission.
Keisler's conversion kit comes...
Keisler's conversion kit comes with a custom driveshaft for the application. We went with the optional aluminum driveshaft due to the inherent advantage in smoothness at high driveline speeds in comparison to standard steel.
There are a variety of shifter...
There are a variety of shifter options with the Keisler transmission swap, including the option of retaining the OEM shifter. We elected to retain our factory console-mounted Slap Stik. Keisler provides a new detent plate that makes it work the extra gear.
A new four-gear indicator...
A new four-gear indicator lens is also available when retaining the factory shifter. Our original was aged and chalky in contrast to the crystal-clear replacement.
The Keisler A-41 shift selector...
The Keisler A-41 shift selector is operated by a control cable rather than the OEM mechanical linkage used with the factory Slap Stik installation. The required bracket and cable adaptor are part of the Keisler kit if the Slap Stik is retained. Given the shabby looks of our old shifter, in retrospect we should have just upgraded to a new shifter from Keisler.
At the transmission end, the...
At the transmission end, the cable terminates at the shift selector unit. A sturdy and direct mount anchors the cable to the transmission at the pan flange, and there is plenty of adjustment provision to allow a perfect synchronization of the gear detents to the shifter indicator.
While we retained the radiator's...
While we retained the radiator's OEM internal transmission cooler, we also added Keisler's accessory transmission cooler to the circuit, mounting the unit to the radiator right behind the valance grille.
The brains of this electronically...
The brains of this electronically actuated transmission are all contained within the circuits of Keisler's Transmission Control Unit (TCU). A single trunk connection attaches it to the harness. We conveniently mounted the unit behind the driver side kick panel.
With full electronic operation,...
With full electronic operation, the software package allows complete control of the transmission's functions, making shift points, kick-down, shift firmness, and converter lock-up functions fully user controlled. We started with the base calibration from Keisler, and found it worked exceptionally well. A few keystrokes raised the wide-open-throttle shift points to match the rpm requirements of our 340 small-block.
At first, we were a little...
At first, we were a little skeptical about the paddle shifter option, but all doubts were dispelled once we tried it. Precise and instant up and down shifts were right at the fingertips; a multifunction display with info has proven indispensable.
|TRANSMISSION GEAR RATIOS |
| ||1st ||2nd ||3rd ||4th |
|TorqueFlite: ||2.45 ||1.45 ||1 ||None |
|Keisler A-41: ||3.06 ||1.63 ||1 ||.70 |
|WHERE THE MONEY WENT |
|A-41 Perfect Fit transmission kit (Stage 1*), 450 lb-ft ||$3,795 |
|Stage 2 550 lb-ft transmission upgrade ||$500 |
|Transmission engine braking upgrade ||$200 |
|Paddle shifter kit ||$695 |
|Kit upgrades (aluminum driveshaft, $200; Slap Stick kit, $99; torque converter, $95) ||$394 |
|Total: ||$5,584 |
*Stage 1 base kit starts at $3,295