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Automatic transmission to TREMEC T-5 small block swap

Installing a TREMEC T-5 in place of an automatic, behind a small block Ford is relatively straight forward. Using many of the same components and concepts as used in Fox body Mustangs in the '80's and '90's simplifies the process.

Bell housing

Start by using a TREMEC T-5 bell housing assembly from an 1984-93 mustang 5.0L and a Modern DriveLine clutch cable kit or the new Hydraulic Master/Slave kits.  This is the easiest way to solve many swap issues. The T-5 bell housing fits both the Windsor blocks (289/302/351) and the T-5 without use of an adapter plate.  A Modern Driveline clutch cable conversion kit or Hydraulic kit removes the need to use the 3 or 4 speed clutch linkage and provides smoother operation. Both the cable kit and hydraulic kit bolts to the stock clutch pedal in just minutes.

65-66 mustang cable kit

65-66 Mustang Cable Kit

Using the T-5 bell housing with a clutch cable kit or hydraulic kit will require using a diaphragm pressure plate found in Fox body Mustangs. 302 engines dated 1981 and earlier will need a 157 tooth 28oz imbalance flywheel, as do the 289 and 351 blocks, regardless of year.  302/5.0L engines will need a 157 tooth 50oz imbalance flywheel or otherwise known as a 5.0L flywheel.  We offer flywheels with fixed and removable counter weights depending on the need. Removable weights are handy when there are plans to swap motors in the future that require different counter weights.

Cross member

T5 crossmember 65-70 Mustang

Mustang T5 Cross members

T-5's have a ¾” longer input shaft which sets the transmission back. Since it is set back ¾” and has a lower transmission mount, a replacement T-5 transmission cross member is needed. Not all cross members are built the same.  Most cross members on the market don’t provide enough exhaust clearance or proper mounting of the e-brake lever. The Modern Driveline cross member solves these problems. We have provided enough clearance to fit convertibles where exhaust system clearance is very tight.  It is also built to withstand just about any type of use. The cross member is designed for use with the stock early transmission mount, so don’t make the mistake of purchasing a Fox body T-5 transmission mount as it will not work.


The drive shaft will have to be shortened about ¾” to make up for the ¾” back set. (Caution:  Measure the length required first.  We have seen too often, driveshafts which were wrong to begin with.)  This can be done at any driveline service shop or purchase a custom made one from us in steel or aluminum (We will ask for measurements and build to fit).


The shifter on a T-5 lines up with the shifter hole in the floor. Just a little of the floor has to be removed on the front and right side of the opening. The T-5 shifter has two threaded holes to mount almost any kind of shift lever desired.  We offer both stock like appearance shift lever, ball and boot and the Hurst classic style.  For those who like the Hurst look of the 60’s, there are several chrome levers to choose from. Hurst also offers five speed pattern shift balls in white and black or T-handles found in 69-73 Mustangs.


Be sure to save the automatic transmission speedometer cable, as it will be reused. You will, however, need to install a T-5 speedometer driven gear, which are available in a variety of tooth counts to match your differential gear and tire combinations. Installing the new speedometer driven gear is simple, it requires removing the c-clip and pulling the old gear off and sliding the new one on.

Neutral Safety Switch

Automatics have a neutral safety switch, so that the car can only be started in park or neutral. Manual transmissions don't need the switch, which must be by-passed or the motor will not start. On early Mustangs the four-plug harness sticks out of the firewall above the master cylinder. Two of the wires control the reverse lights; the other two control the neutral safety switch. Splice those two wires together and you've bypassed the neutral switch.


The starters from early 289-302 Fords with automatic transmissions work just fine. The starter from any '85-'95 Mustang 5.0, auto or manual, will work. When header clearance is an issue, 1992-95 5.0L Mustangs use a high-torque which will run about $130.

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