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C3 Corvette Transmission - Maximum Overdrive
Installing An American Powertrain ProFit3 Five-Speed In Project C3 Triple-Ex
Oct 21, 2010
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C3 Corvette Transmission - Maximum Overdrive
It's well known that a five-speed transmission is one of the best upgrades you can perform on your classic Corvette. Now, American Powertrain makes the conversion much easier with its ProFit3 kit.
Project C3 Triple-Ex has come a long way during the year since we pulled it off the trailer...
...with new brakes, suspension, paint, and interior. This month we'll add the conveniences of a modern five-speed by installing an American Powertrain ProFit3 kit.
The ProFit3 kit is based around the Tremec TKO five-speed. Aside from the trans, driveshaft, and specially designed shifter, there aren't many parts needed to install the kit in a T-10 manual-equipped Corvette like ours. Kits for automatic or Muncie-equipped cars include the bellhousing and other necessary items.
Tremec TKO transmissions are known for their durability and torque tolerance in high-performance applications. Additionally, the shift linkage is internally lubricated and sealed from the elements for years of precise gear changes.
The ProShift3 offset shifter mechanism is what allows the Tremec transmission to be installed in the Corvette while retaining the factory shifter location. By design, the shift tower and shift handle are removable to facilitate installation.
The ProShift3 is contained in a billet housing, which is installed and sealed to a machined port in the trans tailhousing.
The entire system is then encapsulated in a new cover plate. The offset link connects to the main shift rail at a 1:1 ratio, so shifts feel clean and controlled, with no slop.
Following the instructions included with the kit, we removed the distributor, the console cover, and the shift handle before putting the car on the lift and disconnecting the exhaust.
Using a screw jack, the engine can be supported so the transmission mount can be removed. It's also easiest to remove the shifter and all of the linkage at this time.
Since the rear crossmember in the C3 is fixed, the transmission won't drop straight out. You'll definitely need the help of a friend here, as a trans jack won't support the transmission at the extreme angles necessary.
Side by side, the Tremec 5-speed is noticeably bigger than the Borg-Warner T-10. Given the constraints of the Stingray's transmission tunnel, we knew this was going to be a tight fit.
The T-10 and the Tremec are dimensionally identical in the front, so we didn't need a bellhousing or clutch with our kit. This really was a simple installation, and the clear instructions helped make the job even easier.
The trick to getting the larger Tremec in place is to lower the back of the engine as far as possible, remove the bellhousing, and then, with the tailshaft supported on the fixed crossmember, rotate the bellhousing and transmission into place together.
With the pieces lined up, the trans and bellhousing can be slid into place together. New fasteners are included with the kit where necessary.
At the rear crossmember, the factory bracket is replaced by this new MIG-welded and powdercoated bracket. This bolts directly in place of the stock bracket using the same bolt holes, so no drilling or fabricating is required.
The transmission is mounted with the new polyurethane mount provided with the kit...
...and then held in place with the new crossmember bracket.
Another nice feature of this kit is the speedometer-cable extension. Rather than having to get behind the dash to replace the entire cable, a simple adapter cable is provided to connect the original unit to the new Tremec trans.
Since the shift tower and replica shift handle are easily removable...
...they're installed last from inside the car. The result is a shift mechanism that looks stock, but feels anything but. Both the upper and lower factory shift boots are retained with this conversion.
Tremec transmissions use a specific fluid: American Powertrain recommends either GM or Pennzoil synchromesh gear oil.
To depict the new shift pattern, a cover plate is provided for the original console cover. This simply attaches over the factory piece with double-sided tape, and looks enough like the original that you'll likely have to point it out to passengers.
With our installation complete, we lowered the lift and ran the car through the gears, checking for proper operation and leaks.
Everything checked out OK, so we took C3 Triple-Ex out on the road to really test the performance of our new transmission and shifter.
Rowing through the gears, the improvement was nearly indescribable. Gear selection is precise, and the shifter throws are short and defined, with a smooth click of the shift handle. The improvements had us smiling already as we eased our Stingray up to highway speeds.
Cruising on the interstate, the car used to rev to around 3,000 rpm at 70 mph, making for a noisy ride. Now we simply select Fifth gear, and rpm drops to a comfortable 1,900 at the same speed. In addition to dramatically decreasing cabin noise, our new overdrive transmission will improve our C3's acceleration and fuel mileage.
Best of all, our Stingray is now even more fun to drive, encouraging us to take it on the road more often. The American Powertrain ProFit3 five-speed conversion is a great upgrade, improving the C3 in a multitude of ways. Best of all, this conversion is compatible with all Corvettes, from stock to highly modified, since the Tremec TKO can handle significantly more power than any of the factory transmissions found in early Vettes.
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