Installing Classic Motorsports Group’s
Elite TKO Overdrive Transmission Kit
Into a 1973 Dodge Challenger
By
Tony Edler
Classic Motorsports Group

Overview
The following is a description of the installation of a Tremec TKO-600, 5-speed overdrive transmission into a 1973 Dodge Challenger. To provide a little background, my car has a 400 HP, 340 based small block motor. The car was originally equipped from the factory with the 833 4 speed transmission and the awesome Hurst Pistol Grip shifter and a center console.

In total, from the removal of the original 833 4-speed to having the TKO installed and running, it took about 10 hours to complete the job with the help of a friend. If you have a reasonable level of skill, a friend to help you, and the proper tools, you should be able to successfully complete this swap without too much difficulty.

The Installation
First, I removed my passenger side seat, sill plate, and console so I would be able to access anything I needed in the interior of the car. I then jacked up the car onto jack stands as high as possible in order to be able to slide the TKO under the car while it is on the transmission jack. I positioned the jack stands underneath the rear axle, not at the rear frame rails. Next, I disconnected and removed my exhaust at the collectors to just before the mufflers to create a bit more room to work. Note that the configuration of your exhaust may cause an issue with the removal and the re-installation of the new transmission.  I then removed my driveshaft, cross member, old transmission, bellhousing, clutch & pressure plate. Next, I installed my bellhousing, clutch disc, pressure plate, clutch fork and TO bearing. After everything was in place, I set the TKO on a small jack and lifted it into the tunnel and with the help of a friend slid the transmission into the bellhousing.

Note: In order to install the larger TKO transmission into the tunnel, it is often necessary to cut the tunnel to allow for proper fitment. The kit comes complete with a template and sheet metal patch for the proper cutting and repairing of the transmission tunnel if this occurs.

Crossmember
The Classic Motorsports Group kits include a custom crossmember specifically designed for E-Body Challengers and Cuda’s and later B-Body Road Runners and Chargers. It is a direct bolt in replacement for the stock cross member requiring no modifications to the car.

Custom crossmember


Cross member and transmission installed

Driveshaft
The Classic Motorsports Group kit also comes with a custom made driveshaft complete with u-joints and C6 slip yoke.

Final under car work
After installing the new driveshaft I then focused on the electrical connections. For the reverse light switch, I simply hooked up my cars reverse light wires from the wiring harness to the reverse light switch located on the driver’s side of the transmission case. I used a custom made pigtail connector that easily snaps on to the reverse light switch on the transmission. This part is included with the kit
Next, I attached the mechanical speedometer cable to a pick-up located on the drivers side of the transmission. The kit is supplied with a custom cable that attaches to the back of the original speedometer and to the new transmission.

Mechanical Speedometer Cable

Before leaving the underside of the car, I filled the transmission with 3 quarts of GM Syncromesh transmission fluid.

Interior & Console
The custom designed side-mount shifter that is inluded with the Mopar kit is a high quality unit and works excellent in this application. This shifter fits in the stock Mopar center console without having to modify the console in any way. The original Hurst Pistol Grip shifter that came with my car bolts directly the Classic Mopar shifter and set the height of the handle in the factory position. The only modification to the shifter handle is the addition of a custom 5-speed bezel to the top of the Pistol Grip – this bezel was included in the kit. All I needed to do was to install the shifter boot, the center console, reinstall the carpet and trim pieces, and the interior was done! You can’t tell you have a 5-speed in the car without crawling under it.

Factory shift stick positioning

Break In & Test Drive
It is necessary to properly break-in the transmission. To do this, I put the car on jack stands, started the car, and ran through the gears for 10-15 minutes.
All that was remaining was the test drive. The shifting is noticeably smoother and tighter than my 833. The first gear of the Tremec worked well with my 3.55 rear gears that are in my car and the gear ratios between gears is spot-on with no big rpm drops. The throw between gears is nice and short and the shifter has a nice feel to it. But the best thing, by far, is the overdrive! I am now able to cruise on the highway at 70 MPH at 2200 RPM's. With my old 4 speed, I was at 3500 RPM's at 70 MPH - what a difference! The Tremec TKO-600 is everything I had hoped for and my car is now much more enjoyable to drive. To complete this installation I used the Classic Mopar 5 Speed Elite Kit for 1970-74 E-Bodies and 71 to 74 B-Bodies.

Interior After Installation