A STRONG CASE FOR THE GM 200-4R IN PERFORMANCE STREET MACHINES
By Terry Cole
There was a time when performance car builders didn’t give a second thought to what transmission was going to be used to transmit power from the engine to the rear wheels. In fact, if you go back far enough, there wasn’t even a choice. A manual gearbox was the only thing available, and shifting became a staple of a performance machine. Catch phrases such as, “banging gears,” “double-clutch,” and “power shift,” were mainstays on the boulevard and quarter-mile track.
When the factory muscle car era was ushered in during the late 1950s, virtually all the high-power rides came standard with a manual transmission – usually a “three-on-the-tree” – thus the reference to “standard” when referring to the car’s gearbox. The next wave of cool names like “Rock Crusher,” “Top Loader,” and “Super T-10,” rolled off the lips of enthusiasts as the trend in high-power machines led enthusiasts to the dealerships in the 1960s when big-inch engines upped the power ante and four-speeds replaced the column-shifted three-speeds. Enthusiasts used these transmission names proudly while pointing out what was in their rides. To order anything else was considered an affront to performance and a “lazy-man’s option.”
Of course, over time the automatic transmission chipped away at the manually shifted world and became a viable alternative for those serious about getting to the finish line – or next stoplight — first. Not only did the automatic transmission, bearing monikers such as “Powerglide,” TorqueFlite,” “C-6,” and “Turbo Hydramatic” do the work of upshifting for the driver, but minimalized the wear-and-tear associated with clutches, pressure plates and throw-out bearings. Not to mention that automatics were easier on suspension components and could be dialed in for better launching off the starting line. A good torque converter with the appropriate stall speed was the key to getting the car to work best.
After the downturn in performance brought on by the global “Fuel Crisis” era, manual gearboxes were in small demand in American cars, despite their known advantage in fuel economy over their automatic sibling. The general public simply lost its desire to shift manually and some mainstay machines, like Corvettes and Camaros, which traditionally had manual transmissions, found Powerglides and TH 350s in the tranny tunnel instead.
That leads us to the second coming of performance and the advent of computer-controlled machines. While not dead, the manual gearbox gave way in the performance world to the automatic overdrive transmission. In the early 1980s, with fuel-injected engines taking the automotive world by storm, General Motors released a lineup of overdrive, four-speed automatics that were up to the task of harnessing the tremendous torque being produced by the fuel-injected power plants. Most well known from that era is perhaps the GM 700R4, a big, bulky and electronic-laden transmission that was found in everything from Corvettes to SUVs. These transmissions were an instant hit with custom car builders and enthusiasts and found their way into everything from street rods to tow vehicles. The overdrive fourth gear allowed the owner to run a lower rearend ratio for quicker performance and the 700’s gear ratio spread meant more efficient use of an engine’s power band.
But the 700R4 had a few things working against it. First and foremost, it was expensive initially, and often cost-prohibitive to repair and/or modify. Plus it was an electronic-controlled unit, making its adaption into a vintage muscle car more complicated in those early years of electronics. It was big and bulky and weighed considerably more than a Powerglide or TH 350.
For those who searched out alternatives there is one transmission that has transcended the generations to be more popular today than ever. The GM 2004R was released a year before its bigger brother and immediately found a cult following among diehard performance enthusiasts and racers who embraced its simplicity and smaller footprint. These attributes made it a perfect replacement for the old TH lineup of 350s and 400s and a no-brainer to replace the antiquated Powerglides.
Quietly, GM knew they had a workhorse in the 2004R as they slipped it into a new generation of muscle cars other than the Camaro and Corvette. The Buick Grand National, with its potent turbocharged V6 was the perfect proving ground for the 200. The Buick had tons of power, and was a heavy, rear-wheel-drive mid-size coupe in need of a strong gearbox, but one that would withstand the torque from the turbocharged engine and still maintain a level of economy to allow it to pass the strict fuel efficiency requirements of the federal government. And, its smaller footprint made it the perfect choice.
Today, the acceptance and use of the 2004R in the performance world is secure. And one of the reasons for its stellar reputation among muscle-car enthusiasts, racers and street-rod builders is due to the research and development by California Performance Transmissions and its owner Art Carr. A longtime staple in the performance and racing world, and Hot Rod Hall Of Fame member, Carr has refined and perfected the 2004R to the point where it is a direct bolt-in replacement for many classic muscle cars whose owners are looking for modern drivability and increased fuel economy without any sacrifice in performance. For more than six decades, Carr has been building performance transmissions and the modifications he has incorporated into the 2004R are designed to exceed the capabilities of any big-power muscle car or street rod.
With four different versions available, this venerable transmission can be tailored to fit every budget or horsepower rating. And with dimensions almost identical to the time-proven TH 350 three-speed automatic, major modifications to the body’s tunnel and/or firewall are unnecessary and, in most applications, the stock crossmember is retained.
To get a first-hand perspective on just how easy this swap is, we took a drive over to Carr’s Huntington Beach, California facility where they had a customer’s beautiful big-block-powered ’66 Chevelle SS on the lift ready to undergo the swap from the TH 400 to the new 2004R and its accompanying 2500-stall-speed converter.
This particular Chevelle had been fully restored, but with a few subtle updates sitting hidden beneath its skin it was outfitted for today’s world of traffic conditions and economic environment and at the same time provide the driver with the blast-from-the-past power of a big-block motor beneath the hood. The original TH 400 was still residing in the tunnel behind the Fat Rat; while the new 2004R was on the transmission stand ready to be put in place.
Taking out the old trans was straightforward, with no removal of the custom dual exhaust necessary. Once the bolts were removed from the torque converter and bellhousing, it was simply a matter of disconnecting the stock shifter cable, removing the driveshaft’s rear U-joint straps and the crossmember fasteners to the tranny mount and frame. The crossmember came out easily when the trans was lifted up off its rear mount about an inch or so. The driveshaft, due to the exhaust pipes running close together just beneath it was removed once the transmission was lowered.
Once out, the old TH 400 was rolled off to the corner of the shop and the 2004R was lifted into place. Installation was basic and simply a reversal of the process used for removing the old trans. Only other procedures required were a straightforward installation of a Shiftworks adapter so that the original shifter can be retained (and work with the four forward gears), a new shorter driveshaft yoke was installed on the driveshaft and a high-efficiency transmission oil cooler was incorportated inline with the original radiator unit, for added cooling of the fluid.
The oil cooler was positioned in front of the radiator off to the passenger side behind the grille. Fitting it required careful positioning of the unit and custom brackets so as not to damage the fins on both the radiator and cooler. The fluid lines were brought in from underneath and routed away from the lower radiator hose and any interference with the fan or harmonic balancer. The clean install with no kinks in any of the hoses was achieved by carefully routing the rubber hoses as short as possible, while staying clear of any potential obstacles.
Once the 2004R and remote trans cooler were in place, buttoning up the swap was a snap, with the TV cable attached to the carb throttle linkage and the Shiftworks adapter positioned inside the factory shift mechanism. Both of these procedures require some attention to detail, but are pretty straightforward with clear instructions. The Shiftworks adapter required taking the top of the console off to expose the shifter handle mechanism. Once in place, the new detent plate coordinates with the 2004R’s shift cable to ratchet through all four forward gears as well as positions for reverse, neutral and park. Basically, it just adds one stop for the overdrive. Included in the update is a factory looking shift indicator panel reflecting the addition of a 4th gear.
Attaching the TV cable, which will provide throttle position shifting and passing gear, is a basic install onto the throttle plate of the carburetor. The cable provides a link that is simply attached to an existing hole in the plate, while the cable bracket is attached to the left-rear carb hold-down stud.
While the transformation of this ’66 Chevelle SS 396 was pretty straightforward, with quality parts and ease of installation, the true value in this performance upgrade is the increase in drivability and economy. The latter, of course, not the primary concern when taking a muscle car with a big block for a spin to the local drive-in. But all things considered, it is nice to know that a gallon of gas will go a little farther when hitting the highway for the trip back home.
CALIFORNIA PERFORMANCE TRANSMISSION
5502 Engineer Drive, Dept. CMX
Huntington Beach, California 92649
TOUGH INTERNALS MAKE THE DIFFERENCE
The GM 2004R is not the first modern four-speed overdrive automatic to gain acceptance among the GM aftermarket street machine crowd. That title most likely is awarded to the venerable 700R4, which adorned the transmission tunnels of Corvettes and F-bodies during the rebirth of performance in the mid-1980s. The 700 offered street machine and street rod owners the availability of an extra forward gear, and one that featured an overdrive ratio, thus allowing enthusiasts to run a lower (higher numerically) final drive rearend ratio and still enjoy a fair amount of fuel economy.
But using the 700R4 was no easy task in terms of expense and adaptation. They were costly in the beginning years. But even the initial cost wasn’t the only concern when they were employed in high-powered applications. The most notable drawback was the weal input shaft and drum assembly of the 700. Made from aluminum, this posed a problem for vehicles with more than 500 horsepower under the hood. The power rating being even less if it was a heavy machine.
The strength issue was only one strike against the 700. Compared with the 200, which made use of better materials for the input and drum, other drawbacks include an overly steep 3.06 first-gear ratio, compared with the 200’s less-aggressive 2.74:1 number. This was especially important since most performance machines had an abundance of torque from their V8 engines. With a more friendly first gear, coupled with the other three ratios (1.57, 1.1 and 0.67) being closer, meant there was less of an rpm drop between shifts, which would mean that the engine was staying in its power range throughout the entire shifting process. While this may not amount to much with street-only machines, it was a definite improvement at the track. Another caveat of the 700 that applies more to spirited driving than just basic transportation mode is that the 700 would not go into overdrive under full-throttle acceleration. The 2004R has no such limitation and can handle the torque of that Rat motor from first through fourth at wide-open-throttle!
As mentioned, California Performance Transmission offers varying degrees of performance levels with its 200-4R gearbox. Whether your car’s engine is a relative sedate 400-horsepower or a brute with more than 1000 ponies on tap, Art Carr and his team of experts can assemble a transmission dedicated to your specific application. Differences, like most other upgrades in engine combination and suspension systems, depend entirely on what the overall intention is for the part. Aside from the basic refinement to areas like the second-gear shift band, stator support and factory clutch pack, Carr can build the 2004R with stealthy parts like an input shaft fully machined from 300m steel, featuring longer splines for a more secure engagement into the shift drum. Valve bodies can be custom tailored for virtually any type of shifting requirement. Not a fan of factory-style lockup torque converters, Carr replaces the original lockup valve in the oil pump and replaces it with a steel valve machined to alter the hydraulic fluid circuits to match more closely with a non-lockup converter.
Another area given a lot of attention and tuning depending on horsepower capability is the internal line pressure. OE specs using the stock pressure regulator, boost valve and spring read as follows: 60-psi in Park and Neutral; 110-psi in Reverse; 120-psi in First; 130-psi in Second; and 60-psi in both Third and Overdrive. To increase these pressures to better handle higher horsepower levels, Carr will custom fit replacement components that effectively double the line pressure up to 300-psi for the first two gears. Talk about grip and hold capability, the 2004R will hold back slippage whether power comes from a torque monger big-block Rat motor or a high-winding, high-horsepower small-block.
With different components and configurations on hand, the 200-4R conversion will effectively make any high-performance street or track machine much more efficient, whether it’s in terms of better economy while cruising the freeway or better use of the engine’s power and torque while going all-out to the finish line.