Hello, I'm new to this Audi forum, and I'm posting this question to help my dad out.

He's got an 1990 3 speed 100 and the transmission is acting up. He found a 91 100 4 speed transmission and doesn't think that he can swap it out. He got the radiator and some other parts when he took the 4 speed out and noticed that the wiring harness is different, and believes that the ECU may also be different.

I might not be getting all the details correct...remembering what he told me.

So is it possible to swap these out? What all would he need to change?

Thanks guys!!!

 

While I have not done the swap, it is possible but it’s not going to a straight swap. The 3-speed is mostly mechanical unit while the 4-speed is electronically controlled. So you will need the wiring harness, ECU, sensors, cables, shifter, mounting hardware, etc. You will also need am OEM service manual. Often manufacturers will use the same wiring harness so it might be a good idea to carefully check the donor car.