There are quite a few things between the engine and transmission that are important. One is the pilot bearing. This is a cheap part to replace if worn or missing. It goes into the center of the crankshaft under the Flexplate and the round part in the center of the converter goes into this hole and keeps the converter centered.

The next items are the flexplate and flexplate bolts. OEM Flexplate bolts are fine to use for lower power. There are flexplate spacers in OEM configuration for spacing the converter properly that goes on both sides of the flexplate. Flexplate spacers may or may not be needed and purely depends on the spacing in the converter and transmission. Crankshaft bolts should be OEM. The 17mm long option from the 1g 5-spd is about the right length. You can also use OEM ring gear bolts cut to length. Up to about 500whp, 100ft-lbs with red loctite works fine. Up to about 700-800whp, 130ft-lbs with red loctite works fine. Beyond this level, Kiggly is running 150ft-lbs on his drag car with loctite on the threads and grease under the bolt heads. All applications should clean the flexplate and crankshaft surfaces with brake clean during assembly and then coat them with red loctite to glue them together. The better fix to this issue at high power will be a 7-bolt crankshaft pattern with its bigger bolt circle and one more bolt to hold the joint.¹⁾

The OEM flexplates are not very strong at all. In fact in the early days of developing the platform flexplates used to be stacked. If you find yourself needing a flexplate then pick up a SFI certified on from Kiggly because the stock flexplate can be used up to somewhere in the 400-500whp range before the converter bolts start being near-impossible to keep tight. Kigglys flexplates are considerably stiffer and thicker, making it load the bolts more purely in shear rather than trying to rock the bolt heads loose. This helps with keeping the bolts tight. Above about 600-700whp, it is really difficult to keep the bolts tight with only 4 bolts and it is a good idea to step up to an 8-bolt converter to go with the Kiggly flexplate.

And last are the flexplate to converter bolts. In all applications, converter bolts should be tightened to 50ft-lbs or greater with red loctite. Re-torque the bolts after the first heat cycle. First gen applications with the coarse thread (91-92 used M10x1.5) can use 12.9 allen bolts or any variety of 10.9 bolts in an M10x16mm long. Either use OEM bolts which are a little short, or grind the bolt heads shorter on an M10x16mm. ²⁾

You will need a torque converter for the transmission you are running. If you are running a 1G transmission then you need a 1G converter. If you are running a 2G transmission then you need a 2G converter.

Main article: Converter

1g or 2g transmission? 2G transmissions were most desirable and popular initially due to having more space in the bell housing for a slightly larger converter and thus has better options. This has since become a non issue and you can get the same converter for either transmission. 2g transmissions are also lockup converter transmissions stock. In a performance application that is one of the first things that disabled. So to answer this you must ask yourself. Do i need lockup? If no then i suggest you get the trans that matches the shell your swapping the transmission in to.

RVR Transmission? To see if you have the weaker imposter RVR transmission then just know it visually looks like a 2G transmission but it is a non lockup transmission so it lacks the larger bell housing and lockup converter and its internal fluid circuit. To fully ID a RVR then it must have front and rear transmission mounts on the bell housing and rear of the case on top of the front differential housing there is bolt thread bosses around the speed sensor. Then you count the teeth on the front differential. If everything is aligning as a late 2G transmission then to differentiate them you slide a 1G or 2G converter into the transmission input shaft. If 1G converter sits just under flush with the bell housing flange then its a RVR. If the 2G converter sits just under flush with the bell housing flange then its a late 2G.

Main article: Transmission

Transfer case is specific to automatic. The center section of the case is different. It has taller mounting points on the automatic. The transmission output shaft that goes into the tcase is also automatic specific. These two items should match since there are 22 and 23 spline versions.

Main article: Transfer Case

These are the bolts that secure the transfer case to the transmission. Transfer case bolts are specific to automatic. For a bolt kit you will need 4x MF241319 bolts and 2x MD718549 bolts. JNZ Tuning carries these in stock.

You do need a automatic rear diff when swapping. The gear ratios are different. Easiest way to tell if its automatic or manual is to look at the code tag. This contains diff type, code, and the ratio.

Main article: Rear Differential

1G Auto Intermediate Shaft Technically the automatic axles are all different part numbers then manual. However you only really need one. the front passenger side axle has a bump on it to make it easy to pry the axle out of the transmission for servicing. The manual axle does not have this bump and it makes it harder to get it out of the transmission. The front driver side axle you can run a 5 speed axle. The rear axles should match your rear end in the matter of 3 bolt/4 bolt. The manual axles also work fine here.

Main article: Driveshaft & Axles

You do need the automatic roll stops and brackets for an automatic swap. The timing side mount you can use either manual or automatic.

Main article: Mounts

Main article: Wiring

If you intend to run a TCU then you will need it and the harness to make it plug and play. You can wire the TCU into the car if you know automotive wiring. Alternatively you can run a aftermarket TCU or run no TCU and run a ratchet shifter.

Main article: TCU

Technically speaking the engine harness is different in automatic cars. The auto harness goes through the engine harness as well as the under dash harness. It goes near the ECU for the TCU connection, Diagnostic port, center console, shifter, instrument cluster, and the overhead light.

The Center Console has a economy/sport switch and the shifter has the overdrive button and the light. The instrument cluster has the economy/sport indicator. The overhead light has a trans temp warning light that the harness connects to. The TCU is right above the ECU in the lower front center console.

Though when you are swapping a manual car you can get away with just the engine harness.

Main article: Wiring

The stock shifter is needed. It also has a trim ring and shift cables that are needed. Alternatively you can use a 3g eclipse tiptronic shifter with the use of a aftermarket TCU. You can also use a ratchet shifter with or without a aftermarket TCU if you wish to manually shift the car. The only issue here is the hole in the tunnel in which the auto cable passes through is covered. Unless you want to cut up your shell to make it work you have to be crafty and come up with something. Most people just pass the cable through and just zip tie the auto firewall bracket to the dash support in the area where the TCU and ECU are located. Or you can do what i did and take an old beat up pair of shift cables and cut the rubber grommet off and put it on the auto cable along with the manual shift cable metal plate and seal up the hole. However once you get the shift cable clips in on the shifter and the transmission you will notice that it is to long because you are not going through the bottom of the driveshaft tunnel and instead routing it out the manual shift cable hole shows the cable a little bit to long and will cause the shift cable to be a little on the tight side.

Main article: Shifter

Starters for 1Gs are the same and you can use a MT or AT starter. 2G starters you must use the 2G AT starter. The MT will fit but they will burn out because its not right. If you are using a 2G in a 1G then you use the 2G AT starter. If you have the wrong plate the starter will have issues and the trans could have issues as well.

To swap the car you need the brake pedal assembly with brake sensor. The brake sensor uses the clutch pedal sensor wiring. The gas pedal is also different because it has a gas pedal position sensor that the TCU reads.