The Tremec TKO is a great choice for retrofitting into the old muscle cars, but it isn’t quite a direct bolt-in replacement for a four speed. There are a few areas that will require modification and/or custom parts for a TKO conversion into any muscle car.

The Tremec TKO’s three rail internal shift mechanism is positioned at the top of the transmission, making it taller, wider and flatter across the top than most of the old four speeds that were common in the 1960s and 1970s. Some cars such as the 1967-1981 Camaros and Firebirds typically have ample room to install a TKO without any tunnel modifications. Other muscle cars have transmission tunnels that are barely big enough for the old four speeds, and will interfere with the TKO. Body mounts that are in bad condition will make things worse, so make sure your body mounts are in good shape before installing a TKO. Some cars can get by with just dimpling the transmission tunnel in a few areas, but on others there just isn’t any way to get around cutting the tunnel and reshaping new sheetmetal around the transmission. However, the modifications can almost always be covered by the factory carpet, and with a console may be completely invisible from inside the car.

Your transmission crossmember or its location will have to be modified in some way due to the mount pad location on the TKO being further rearward than the mount pad on most four speeds. On some cars you can just move the crossmember further back on the frame rails and drill new holes, but others may require sectioning your factory crossmember and welding it back together, or possibly fabricating a new one. Before removing your old transmission, it is wise to record the height of the transmission output shaft relative to some fixed point on the car so that you have a reference point to shoot for when modifying your crossmember or building a new one. The transmission height may need to be raised or lowered slightly in the end in order to obtain acceptable driveline angles, so keep that in mind if you are fabricating a new crossmember.

The TKO at 24.07″ long is not exactly the same length as any factory four speed, although it is very close to some versions of the Ford Toploader. Plan on either having your old driveshaft modified or having a new one built to work with the TKO. The TKO requires a Ford C6 pattern 31-spline slip yoke, but there are slip yokes available that will adapt the TKO to common 1310, 1330 or 1350 universal joints. You may want to keep your original driveshaft intact in case you ever decide to sell your car and want to convert it back to the original configuration.

Most four speed transmissions use a solid bronze pilot bushing in the crankshaft, but a roller pilot bearing is a good idea with almost any transmission. The TKO requires one. Make sure you install a roller pilot bearing along with the TKO.

The Tremec TKO has tapered roller bearings supporting the input shaft, and is designed with relatively tight tolerances. It doesn’t have the “slop” in the input shaft that the old 4-speed transmissions have. Tremec requires that you perform a bellhousing runout check to make sure that the transmission is properly aligned with the crankshaft. If you have more than 0.005″ of misalignment, you will need to install offset dowel pins to correct it.

Some cars have other challenges to overcome, such as the torsion bar front suspension on Mopar muscle cars. The support structure that the rear ends of the torsion bars attach to interferes with the TKO. A Mopar installation will either require a specially modified transmission, a serious amount of fabrication and reinforcing after removing the torsion bar support structure, or a new front suspension that eliminates the torsion bars altogether.

The areas of concern above are common to almost all TKO installations. Even considering these obstacles, the benefits of increased fuel mileage and decreased noise, heat and engine wear are worth the effort if you plan on driving your muscle car any further than just across town very often!