What to Consider and How to Fit a TREMEC Transmission in Your Classic Car

Photography: Cole Quinnell

Installing an aftermarket 5- or 6-speed has become one of the most popular upgrades for classic cars and trucks, thanks to the features, strength and performance offered with TREMEC five- and six-speed transmissions. One of the most common questions we are asked, though, is how to make a TREMEC transmission fit into a muscle car or other older vehicle. To address that, we’ve put together this short overview of the typical transmission fitment issues that you might face when installing a TREMEC 5-speed TKO or 6-speed Magnum.

The TREMEC Magnum 6-speed has alternative shifter positions, helping it to fit well in a variety of muscle cars and other vehicles.
  1. Transmission Tunnel Fitment

Unlike the old OE four-speeds that were relatively small and narrow, modern five-speed and six-speed manual transmissions are larger in width, height and length. Generally speaking, 1970 and older vehicles will need significant changes to mid and rear sections of the transmission tunnel to accommodate the larger transmission. Later vehicles came with larger automatic transmissions and transmissions tunnels that accommodated them. These may only need tunnel modifications near the shifter location.

  1. Shifter Location

Another common fitment issue is the location of the shifter on modern manual transmissions versus the location on older three and four-speeds. The original transmission in many muscle cars had shifters mounted on the side of the transmission, and relatively far forward in the chassis. On a modern transmission, the shifter mounts on/through the very top of the transmission case. Because of how much longer the modern transmission is, it often ends up being located further rearward in the car. The TREMEC Magnum has multiple shifter location options to help you position the shifter in a natural position in a broad range of vehicles.

  1. Bellhousing

Getting the correct bellhousing to bolt your TREMEC transmission behind whatever engine you have is easy, thanks to a variety of aftermarket bellhousings and/or adapters. In many cases, you can even get an SFI spec bellhousing that is approved for use in racing if your application requires it.

Many people installing a TREMEC transmission into an older car choose to upgrade to a modern hydraulic-clutch system as well.
  1. Mechanical or Hydraulic Clutch Actuation

Another consideration when converting to a modern manual transmission is whether you will convert from a mechanical clutch to a hydraulic clutch actuation system. All vintage three-speed and four-speed transmissions use a mechanically operated clutch system, consisting of a pivot arm connected to the clutch pedal via a mechanical linkage. Modern clutches use a hydraulically actuated system, with a master cylinder actuated off the clutch pedal similar to the brake system, which operates a slave cylinder mounted inside the bellhousing that pushes on the pressure plate to release the disc. Some adapter bellhousings are available to retain certain mechanical linkage systems, while many people opt to convert to a hydraulic system. Aftermarket solutions are available for both.

  1. Speedometer Drive

A fairly basic consideration, but one that is often overlooked, is hooking up the speedometer on a classic vehicle to a modern five- or six-speed. Older transmissions used a cable drive connecting the speedometer to the transmission, with a gear spinning the cable at the correct speed to give an accurate speed indication on the gauge. Modern OEM transmissions do not have a mechanical speedometer output, and instead use a Hall Effect sensor that generates an electric signal. The electric signal is sent to the vehicle’s computer where the signal is processed and then sent to the speedometer to display the vehicle’s speed. Many people with classic cars convert the instruments to electronics, and adapters are available. The TREMEC Magnum 6-speed has a provision for a mechanical speedometer drive.

Each of these topics can be a full technical paper by themselves, and we will be bringing you more details in the coming weeks and months on the TREMEC Blog. Many TREMEC dealers offer kits and individual solutions to make each of these challenges easy to overcome. Check our list of authorized dealers for more information. Upgrading to a modern TREMEC five- or six-speed easier today than ever before! Click here to download the TREMEC Performance Aftermarket Product Guide.

5 thoughts on “What to Consider and How to Fit a TREMEC Transmission in Your Classic Car”

  1. I have a 72 Nova 402 big block with a 700r4 and bench seat. Your article trans tunnel info makes me think that if I change to a 6sp Tremac I will have to change to bucket seats due to a larger tunnel. Is that the case?

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