is it possible to sawp from usdm 5-speed mt with abs to a jdm 6-speed mt with DCCD and keep the abs? I have heard that the abs causes problems with the DCCD?

 

The DCCD requires speed sensor inputs from the ABS system. Installing the DCCD won't affect your ABS, but I am not certain if the signals are the same from the speed sensor of both cars.

 

This is what I think
1) ABS works best when the center diff is open
2) manual DCCD isn't necessarily open all the time (in fact most leave it at a certain percentage lockup)
3) The first DCCD tranny that works ABS comes with an auto mode (in the New Age STi), and require input from ABS
4) From all that I have read, older DCCD controller don't support ABS, and the new DCCD-A controller will keep the center diff open when ABS is active

So it looks like DCCD or ABS, but not both unless you have the whole TCU/ECU from an STi V8. The main reason for ABS needing to have the center diff open seems to be that if the diffs are not open and a wheel lock up, it might caused all other wheels to lock up, which makes it difficult for the ABS to detect vehicle speed (thus a G-sensor is needed on AWD vehicle with ABS). I'm not sure if that's enough of a reason why we just don't see DCCD w/ABS until recently.

On a side note, all I wanted was a 35:65 center LSD, but DCCD seems to be the only diff that has this property (Cusco Tarmac diff is open, other aftermarket diffs are all 50:50). My other guess is that upgrading to the 12kg/20kg STi center diff could seriously affect how ABS works given that they are more likely to lock.