How to Replace a Transmission (Full DIY Guide)

Introduction

This tutorial will guide you through the process of replacing a transmission in your vehicle. Whether you're dealing with a worn-out clutch, a leaking rear main seal, or simply swapping out for a rebuilt transmission, this step-by-step guide will provide clear and actionable instructions. While the example focuses on a rear-wheel-drive 1998 Mustang, the principles apply to many vehicles, including front-wheel-drive and automatic models.

Step 1: Lift and Support the Vehicle

• Use 12-ton jack stands for better stability and height.
• Place jack stands far apart from the transmission area to allow for the transmission jack.
• Slide additional safety supports (like ramps or wheels) under the front tires for extra security.

Step 2: Disconnect the Battery

• Open the battery cover.
• Unscrew the clamp on the negative battery terminal and slide the cable off.
• Ensure the cable does not touch the battery post.

Step 3: Remove the Shifter

• Ensure the car is in neutral.
• Unscrew the shift knob and remove the shifter trim.
• Unscrew the nuts holding the shifter lever and remove the lever.
• Unscrew the bolts holding the shifter boot and remove it.

Step 4: Remove the Exhaust

• Check if your model requires exhaust removal.
• Disconnect oxygen sensors from the wiring harness rather than unscrewing them.
• Remove the nuts holding the downpipes and the X-pipe.
• Use penetrating fluid on rusted fasteners for easier removal.

Step 5: Drain the Transmission Fluid

• Locate the transmission drain plug.
• Use a 3/8 ratchet to crack open the drain plug and let fluid drain into a pan.
• Once drained, securely tighten the drain plug back.

Step 6: Remove the Driveshaft

• Engage the parking brake to prevent movement.
• Use a 12-point wrench to remove the driveshaft bolts.
• Heat stubborn bolts if necessary for easier removal.
• Slide the driveshaft out, using a catch can to collect any remaining fluid.

Step 7: Remove the Starter

• Identify the starter location at the engine-transmission interface.
• Remove the three bolts holding the starter in place.
• Disconnect any wires if necessary, but it can hang without complete removal.

Step 8: Disconnect Wiring Harness

• Disconnect the wiring harness clipped into the top of the transmission.
• Use a trim removal tool for clips and unplug the speed sensor and reverse light switch.

Step 9: Remove the Transmission Mount

• Support the transmission with a jack.
• Unbolt the transmission mount using two bolts and remove it.

Step 10: Unbolt and Remove the Transmission

• Remove the nine bolts securing the transmission to the engine.
• Use a long extension and universal joint for hard-to-reach bolts, especially at the top.
• Spray water inside the bell housing to minimize dust exposure before removal.
• Carefully separate the transmission using a pry bar and remove it from under the vehicle.

Conclusion

Now that you've successfully removed the old transmission, you can replace any worn components like the throw-out bearing or clutch. Follow the reverse order of these steps to install the new transmission, ensuring all parts are securely fastened and fluids are properly filled. Remember to test drive the vehicle gently for the first 500 miles to allow the new components to break in. For further assistance, check out related videos on clutch replacement or specific vehicle maintenance.