Help on swapping out 3sp for 4 sp transmission

[ToyotaBuba]

Am looking to swap out the existing 3sp automatic transmission that is in a 98 prizm (a corolla clone) that currently has a worn out 3 sp automatic in it that came from a 99 corolla. For those not aware, the prizm, except for trim, virtually all mechanical (except things like A/C system) are corolla).

I am getting conflicting feedback from mechanics, suppliers and salvage yards etc. as to what is compatible and what needs to be changed out, so any help would be appreciated.

1) Stats list interchangability between 3sp and 4sp auto with 98 and 99 years, but one wrecking yard said 2000 4sp can be used on 98 if you use your old i.e. 3sp torque converter. Is this true? Does this mean that for 98 and 99 years they don't have a lockup torque converter, but that the 4sp trans in the 2000's is the same as what's in the 98 and 99's, but that the 2000's have a lockup torque converter? Does this mean that the 4sp automatic transmission itself for the 98 and 99 years are the same as in the 2000?

I thought the 4sp’s used a lockup torque converter which the 3sp’s don’t use if I understand things so this area is currently not clarified for me at all.

2) There are 2 wiring harness connectors on a 98 3sp. I understand the 4sp shifting is electronically controlled (computer). Are the wiring harness connectors the same on the 4sp and interchangeable/compatable with the 4sp trans?

3) Any linkage issues other than having to salvage and use the 4sp shifter and console panel face plate etc?

4) It looks like the shift cable between the 3 and 4 speed are the same, but are they? Do I need to also get a cable off a car that has a 4sp in it?

5) And most important... Is the ECU on a 98 with a 3sp already compatable and able to control the 4sp automatic transmission? My understanding is that where shifting in the 3sp is mechanically controlled, the 4sp is electronically controlled. Also, is there any external electronics that I need to make sure I salvage off the a car with a 4sp that is used to control the 4sp? Does an ECU out of a 99 need to be gotten in order to control the 4sp transmission?

Thanks!

[zythr]

Originally Posted by ToyotaBuba

Am looking to swap out the existing 3sp automatic transmission that is in a 98 prizm (a corolla clone) that currently has a worn out 3 sp automatic in it that came from a 99 corolla. For those not aware, the prizm, except for trim, virtually all mechanical (except things like A/C system) are corolla).

I am getting conflicting feedback from mechanics, suppliers and salvage yards etc. as to what is compatible and what needs to be changed out, so any help would be appreciated.

1) Stats list interchangability between 3sp and 4sp auto with 98 and 99 years, but one wrecking yard said 2000 4sp can be used on 98 if you use your old i.e. 3sp torque converter. Is this true? Does this mean that for 98 and 99 years they don't have a lockup torque converter, but that the 4sp trans in the 2000's is the same as what's in the 98 and 99's, but that the 2000's have a lockup torque converter? Does this mean that the 4sp automatic transmission itself for the 98 and 99 years are the same as in the 2000?

I thought the 4sp’s used a lockup torque converter which the 3sp’s don’t use if I understand things so this area is currently not clarified for me at all.

2) There are 2 wiring harness connectors on a 98 3sp. I understand the 4sp shifting is electronically controlled (computer). Are the wiring harness connectors the same on the 4sp and interchangeable/compatable with the 4sp trans?

3) Any linkage issues other than having to salvage and use the 4sp shifter and console panel face plate etc?

4) It looks like the shift cable between the 3 and 4 speed are the same, but are they? Do I need to also get a cable off a car that has a 4sp in it?

5) And most important... Is the ECU on a 98 with a 3sp already compatable and able to control the 4sp automatic transmission? My understanding is that where shifting in the 3sp is mechanically controlled, the 4sp is electronically controlled. Also, is there any external electronics that I need to make sure I salvage off the a car with a 4sp that is used to control the 4sp? Does an ECU out of a 99 need to be gotten in order to control the 4sp transmission?

Thanks!

Hi: I think you've answered your concerns/questions. The 4 speed is indeed electronically controlled, so you'll need the wires and the ECU that would control the shifts. Both the 3 speed and 4 speed have lock up torque convertors as well, difference is, of course the 4 speed has another gear. Also, I'm not too sure, but I believe the 4 speed also has the O/d lockout either on the shift lever or the instrument cluster as well.

[Jjona5]

My car has one on the shifter

[ToyotaBuba]

Well, I went digging in a local wrecking yard today and it turns out I did find a 98 corolla with a 4sp. Sadly, the trans was in pretty bad shape but it had the shifter with overdrive button of course and 4 sp positions, so I dismantled the dash and console and pulled the shifter mechanism. Since they did in fact offer 4sp autos on the 98's, would think (but am guessing) that the wiring harness of a car with a 3sp in it, would have the connector there to plug into the shifter base for the overdrive button since I doubt they would build different wiring harnesses for different 'options' on a specific model/year, but would sure like some feedback from someone that's had direct experience in this topic and the Q's above.

[ToyotaBuba]

Just an update... some other posters I've run across clarified that in addition to the ECM from a 1998 or 1999 that has a 4sp in it as well as input from a toyota tech that it also takes the engine wire harness from a car of those years with a 4sp already in it in order for the conversion from a 3sp to 4 sp. Someone also indicated the possibility of needing different transmission mounts but I've yet to confirm that. Anyone know if the top and 2 bottom transmission mounts are the same for the 4sp and 3sp, or are any of the three different ?

Thanks!

[Buurin]

Originally Posted by ToyotaBuba

Just an update... some other posters I've run across clarified that in addition to the ECM from a 1998 or 1999 that has a 4sp in it as well as input from a toyota tech that it also takes the engine wire harness from a car of those years with a 4sp already in it in order for the conversion from a 3sp to 4 sp. Someone also indicated the possibility of needing different transmission mounts but I've yet to confirm that. Anyone know if the top and 2 bottom transmission mounts are the same for the 4sp and 3sp, or are any of the three different ?

Thanks!

Mounts: Front same, top probably same, back likely different.

Yup, wire and ECU from 98-99 needed.