T-5 to C4-C5

T-5 to C4-C5

This is a real common swap for people looking for a relatively cheap and very strong automatic. The c5 is a later version of the c4 found in early 80's model Mustangs that features some better case mods than the earlier c4's, but they are basically the same thing. The c4 can easily be modified to c5 specifications. One confusing factor about this swap is the difference between the big and small bellhousings that are available forthese transmissions. If you find an early model transmission (pre ~75), it will have the small bellhousing that is required with the 157 tooth flexplate. These 157 tooth flexplates are all a 28oz imbalance, so if you want to use it on a late model 50oz imbalance motor you will need an aftermarket 157 tooth flexplate that has been balanced to 50oz. The later c4 models have the big bellhousing from the factory, and they use the 164 tooth flexplate as found on AOD Mustangs.

Parts needed:

  • c4/c5 transmission
  • Big or small bellhousing
  • Bellhousing backing plate (AOD type works with big bell c4)
  • Shifter and bracket
  • Tranny cooler (B&M part # works excellent with high stall converters)
  • 2 fittings for cooler lines in transmission
  • 2 fittings for the cooler
  • Transmission fluid hose and 4 clamps
  • 5 quarts of ATF
  • New transmission filter
  • New pan gasket
  • Converter
  • Shifter cable
  • Valve body
  • Transmission pan
  • Modified crossmember, or a replacement piece

Swap time:

Pull the T-5 and bellhousing, flywheel, backing plate. Next take out the pilot bearing at the end of the crankshaft with a puller that you can rent from your local parts place, or using a few other methods such as with soap jammed into the hole etc. Replace your rear main seal since you are in there. Once all thats out, its time to pull your pedal/pedals. The easiest way to do this is to remove the clutch pedal by pulling the clip that holds it on, and then sliding the pedal out. If you want the auto pedal setup, that will add a bunch more time to this swap as its a big pain to get the assembly in and out.

The next thing that needs to be addressed is the transmission crossmember. The c4 will LIKELY require you to cut off the welds where the barrel type ends are connected to the crossmember. This will then allow the crossmember slide it back and forth to change where the transmission mount lines up with the bolt holes. This can be done before or after you put the transmission in. The AOD crossmember shouldn't need modification, but the T5 one will.

Once you have done that, its time find the clutch pedal switch that allows the starter to be triggered to start the car only with the clutch pedal engaged. The plug for this is black and has multiple wires coming together at two terminals. You need unplug it and then cut the wires off, and then either use an electrical connector to connect them all, or solder them together as I recommend doing (its kind of hard to get under there with the soldering gun though). After thats done, you need to climb under the car and cut the two wires that go into the plug that goes onto the nuetral safety switch, and then connect them together to effectively bypass that switch.

Now its time to deal with the shifter setup. There are many choices here, with aftermarket stuff having its own type of bracketry and cable that needs to be used with it. I will describe what needs to be done to adapt an AOD type shifter to work with the c4 as I have done in my project '88 GT. Once you have the shifter and your center console out, you will see that the mounting holes for the shifter are different than the holes you had for the T-5 cover plate. The two back holes line up perfectly with the floorpan holes and are there for the T-5, but the front ones go into air as the floor is different. This means its time for some customization! What I did is find a place as far to the left and right towards the front of the shifter, that allowed me to get the shifter bolted down and to use the threaded clips that were in the floorpan for the top two bolts of the shifter cover plate. This requires that the holes be drilled towards the end of the floorpan so the clips can go into the new holes you made. What I did is bolt the cable bracket to the floorpan using my new holes in the plate and the floorpan on the top left and right side, and then I bolted the shifter in using the back two holes through the bracket, and then into the floorpan. Once that was done, I decided to just bolt the shifter to the cable bracket using two nuts and bolts from the hardware store in order to get the shifter bolted down good and snug leaving the two bolts that hold the plate under the shifter. I used a late model 4cyl AOD shifter, but the mounting should be the same for all AOD shifters.

The next thing you need to deal with is the cable. When using the AOD shifter, the easiest way of accomplishing this is by using B&M's cable kit for adapting their ripper shifter for the AOD to a c4. There will be a bracket that you need to bolt to the tranny, and then you have a small bracket that needs to go onto the stock shifter cable bracket in order for the cable to mount. Besides that, you need to get the end of the cable onto the shifter. With my 4cyl shifter there is a bolt type thing that is threaded for a nut at the base of the shift lever. All I had to do was slightly enlarge the hole on the end of the cable in order to get it to fit over the bolt, and then I put the nut on and was done. On some shifters you will need to enlarge the hole to get it over a ball on the end of the shifter, and then have a washer or just a glob of mig welder wire welded on to the end of the ball to stop the cable from coming off.

Now its time to put the tranny in. Bolt in the valve body if thats not done, and put the bellhousing on, and then fill the converter with about 2 quarts of fluid and put it in the transmission. It should have 3 distinct clicks to make it fully seated. Once fully seated, there should be about 3/4 of an inch clearance between the converter mounting tabs and the end of the bellhousing. Now is also a good time to put in your tranny cooler fittings, which I used some hardware store pieces that had a 3/8 opening for the cooler lines and were 3/8 NPT thread. I used the same type for the cooler, except those needed 1/2 NPT thread. Once you have the top backing plate on, and have torqued down the bolts for the flexplate, its time to put the transmission in. Once you have the tranny up and bolted to the motor, you need to pull the converter towards the motor using the access hole at the bottom of the bellhousing where the lower backing plate goes. Torque each nut one at a time and rotate the motor to get each flexplate hole where you need it. Now its time to connect the cable to transmission, then put the access plate in, and pop your stock driveshaft into the back of the transmission. You can also put the pan on, and once the pan bolts are tight, its time to fill the tranny up. Put about 1 1/2 quarts of fluid in and then start up the motor and go through the gears to get the fluid to cycle through the system, then turn it off and check the level with your dipstick and add more as needed.