Reprogramming Your Chevrolet Corvette's Automatic Transmission - Shifty Business

Changing a 700-R4's Character With a TransGo Performance Shift Kit

John Nelson Nov 1, 2002 0 Comment(s)
Vemp_0211_01_z Reprogramming_chevrolet_corvettes_automatic_transmission Shift_kit 2/21

Automatic transmission technology has advanced by leaps and bounds since the early days of Fluid Drives, Dynaflows, and Powerglides. The General took giant steps when it replaced the Turbo 350 with the TH 700-R4 four-speed automatic transmission in 1982; this same basic unit (now electronically controlled and called a 4L60E) handles gearbox duties in Corvette (albeit in a highly modified form for the C5) and other brands to this day. In fact, automatics handle these duties in most Corvettes. Starting with the '72 model year, sales of shift-it-yourself Vettes dropped below those of automatic-equipped cars, and that's the way it's been ever since.

This certainly makes sense for the OEMs. Automatic transmissions allow the factory to control factors such as fuel economy and emissions by controlling when the transmission shifts gears. This gear selection, in turn, is second only to the accelerator in determining what speed an engine runs at. This arrangement is also satisfactory for the vast majority of motorists. I don't know that I'm old enough to be a diehard, but it's always seemed to me that sports cars 'oughta have a manual gearbox. Computer controls notwithstanding, it takes driver input via gearbox and clutch to pick the perfect engine speed for a given driving situation-which is why us "diehards" spend so much time contorting our ankles into position for heel-toe maneuvers.

That being said, I now must admit that my own Corvette, an '84 I've labeled "The Bronze Bomber," has an automatic transmission. Despite the desire to row my own, transmission preference took second place to getting the best Corvette for the money I had. My first thought, transmission wise, was "So this is why they call them slushboxes." The shifts themselves were slow, and always happening too soon, leaving me in a higher gear than I would've liked. This was especially true when driving in the "OD" position; even a Corvette doesn't feel very performance oriented at 25 mph in Fourth gear.

Vemp_0211_06_z Reprogramming_chevrolet_corvettes_automatic_transmission Electrical_connector 3/21

With the console door opened, use a small, flat-blade screwdriver to pry the traction control up and out to access several of the console retaining nuts. Unplug the switch from its harness and the electrical connector from the accessory power outlet.

The scary thing is, my '84s 700-R4 was in perfect working order. By their very nature, from-the-OEM automatic transmissions are imprecise creatures- especially when the slushbox in question is a first-generation 700-R4. And in performance applications-like autocrossing-durability questions arise as well. One solution is to remove the transmission and have it re-built to hi-po specs. Another-the route I took-is to re-program the stock unit. Of course, I wanted civilized street behavior along with increased performance when it comes time to do a little racing.

Here's a grossly oversimplified version of how an automatic transmission works: the gears within are engaged in various combinations to create a given gear ratio. Which gears are engaged, how they're engaged, and when they're engaged, is controlled by "bands," which either hold a given gear in place or allow it to turn. The servos that activate these bands are in-turn controlled by hydraulic pressure-that's transmission fluid to you and me-which is controlled by a number of valves that reside in the transmission's valvebody.

That being said, here's the deal: We can't change the gears in a transmission, but we can alter how and when it shifts by altering the valvebody-and that's exactly what TransGo does with its Performance Shift Kits. The PSK is a do-it-yourself kit, and to put it briefly, it changed the character of my 700-R4.

"The original system is always designed so that when mamma drives the car, there won't be any complaints," according to TransGo founder Gil Younger. "With our design, we do everything that we can to add performance and durability without getting a 'rough complaint' at light throttle."

Vemp_0211_10_z Reprogramming_chevrolet_corvettes_automatic_transmission Shift_knob_insert 7/21

Slip the shifter into Fourth gear, then use the small screwdriver (again) to carefully pry the shift pattern insert out of the shift knob. Pry from the front of the knob and insert.

One thing that TransGo doesn't do is create transmissions with hard, "junior high" shifts. What Younger and crew are going for is short, precise shifts-which provide better response and increased durability, since the bands are engaged for shorter periods of time. The shift points are also changed, and the new points are more-closely tied to what the engine is doing, rather than always seeking a higher gear and lower rpm. The "new" trans also retains the original shift system, meaning that shifts get harder as more throttle is applied. Not that the reprogrammed shifts are harsh, however. To my pleasant surprise, they're just as I said-quick and precise.

The Performance Shift Kit is geared towards the do-it-yourselfer, with both written instructions and an excellent video included with the purchase. To facilitate taking pictures, however, I took the '84 out to TransGo's El Monte, California, facilties, where Brady (aka "Max Throttle") handled the install while I snapped away. We also added a couple of extras from the "Goodies" page that TransGo includes with each kit. The first, a .472-inch-diameter TV (throttle valve) boost valve, helped increase the transmission's hydraulic pressure. The other was a "special" 4th shift valve for early 700s, which had the wonderful effect of delaying the 3-4 shift progressively longer when more throttle is applied, and ultimately allowed full-throttle shifts to overdrive. This alone was worth the price of admission.

Given the thoroughness of TransGo's instructions, we'll only be showing you the installation highlights here. There is one thing we will note, however: Brady pointed out the importance of adjusting your Corvette's throttle cable once the installation is done. "It's the only thing that carries what the driver is doing with the throttle to the transmission," he pointed out. "If it's pulling too much, the trans thinks there's more torque than there actually is." And vice versa, of course. On older cars, it's a good time to check the cable clip; as we pointed out in our March 2000 issue (Slip Slidin' Away), a broken clip-and a malfunctioning cable-can keep line pressure from rising, leading to a toasted transmission.

Vemp_0211_11_z Reprogramming_chevrolet_corvettes_automatic_transmission Tightly_clamped 8/21

Now it's time for the Vise-Grips. There's a metal "T" retainer holding the shift knob in alignment on the shifter stick. Tightly clamp the Vise-Grips onto the retainer and pull it up and out. The retainer will probably be very tight so carefully rock the Vise-Grips from side to side as you work the retainer upward. It may help to tap the side of the Vise-Grips with a hammer. When finished, unscrew the knob and set it aside.

The bottom line here, however, is that this transmission feels more closely related to what the engine-and my right foot-is doing, and less like a slushbox. And all this without the neck-jerking shifts that compromise streetability.

"When the transmission's working properly, the whole car smiles," is part of Younger's philospohy. "When the transmission is ill-timed and has those hard bumps, the car's not happy." At this point, both driver and car are very happy.

Vemp_0211_16_z Reprogramming_chevrolet_corvettes_automatic_transmission Hex_nuts 12/21

Four 10mm hex nuts hold the "close out" rubber boot in place. Remove them and carefully (this will be reused) pry the boot up over the shifter. If there's a rubber band, remove it and throw it away.

Vemp_0211_17_z Reprogramming_chevrolet_corvettes_automatic_transmission Shifting_power 13/21

Isn't this a marvelous looking...thing? Let's get rid of it! Remove the four 3/8-inch hex head bolts that hold the factory shifter base to the extension housing, then lift the shifter up and out. There is an alignment pin on the front of the shifter base; remove the pin while lifting the old shifter out.

Vemp_0211_18_z Reprogramming_chevrolet_corvettes_automatic_transmission Hurst_billet_plus_shifter 14/21

Carefully pry the plastic cup bushing from the end of the factory shifter and, after lubing it with a small amount of grease, fit onto the corresponding ball socket end on the Hurst Billet/Plus shifter. It should snap into place with some gentle pressure.

Vemp_0211_23_z Reprogramming_chevrolet_corvettes_automatic_transmission Aluminum_base 15/21

Test the new shifter's operation. The stick should move freely and fully engage each gear. To adjust the shifter stops turn the stop screws out until they're flush with the inside of the aluminum base. Pull the stick firmly into Second and hold it there while turning the rear stop screw in until it contacts the stick, then back it out 1/4-turn. Hold the screw securely with a 3/8 hex key wrench while tightening the jam nut with a 9/19-inch box or open-end wrench. Repeat the same procedure on the forward stop adjustment, with the shifter stick in Third gear.

Vemp_0211_24_z Reprogramming_chevrolet_corvettes_automatic_transmission Hex_key_wrench 16/21

There should be a rubber gasket adhering to either the shifter base or the extension housing. If it's stuck to the housing, remove it and toss it in the trash. Then, clean the mounting surface on the housing. Next, place the Hurst shifter onto the housing, making certain that the plastic cup bushing fits cleanly into its socket within the housing. Be absolutely certain that the notch in the Hurst shifter stick's threads (for the shift knob) is facing rearward. Bolt the new shifter in place using the four 3/8-inch socket head screws that are supplied with the shifter and tighten evenly to 8-10 ft-lbs of torque with a 3/8 hex key wrench.

Vemp_0211_25_z Reprogramming_chevrolet_corvettes_automatic_transmission Better_looking_shifter 17/21

Doesn't that look better than the stock shifter? It works a LOT better!

Vemp_0211_27_z Reprogramming_chevrolet_corvettes_automatic_transmission Disassembly_process 18/21

For the most part, the balance of the job is a careful reversal of the disassembly process. One of the few changes that must be made is to the factory rubber "close-out" boot. You'll need to either cut out the inner portion of the boot or do as we did and simply roll the bottom edge of the boot inward and upward, flipping the ring inside out so that it will now face upward.

Vemp_0211_28_z Reprogramming_chevrolet_corvettes_automatic_transmission Tweeking 19/21

Minor side-to-side tension adjustments, if desired, are done by using a 1/4-inch hex key (Allen) wrench and turning the hex socket screws on the top of the shifter housing clockwise to increase tension or counter-clockwise to decrease tension. If the desired adjustments can NOT be achieved in a maximum of one full turn from the factory pre-sets, then the bias screws will need to be changed. There are two pairs of additional bias springs supplied; all it took to satisfy Tony was a very minor tweak from the factory settings.

Vemp_0211_29_z Reprogramming_chevrolet_corvettes_automatic_transmission Reinstallation 20/21

Now, re-install the close-out boot, re-using the four 10mm hex head bolts that originally held it in place.

Vemp_0211_30_z Reprogramming_chevrolet_corvettes_automatic_transmission Hammer_time 21/21

After threading the shift knob back in place, the "T" retainer must be refitted. It was exceedingly snug in Tony's '99, so we ended up persuading it into place with some judicious taps from the hammer.

Sources

PML
Inglewood, CA 90302
310-671-4345
www.yourcovers.com
Transgo
El Monte, CA 91733
626-443-7451
http://www.transgo.com/

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Check out TransGO's performance shift kit that allows you to reprogram your automatic transmission!
John Nelson Nov 1, 2002

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