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Old 06-04-2010, 06:09 AM   #1
BLSTIC
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Default Using later model 'centre diff' autos in early model cars

I'm not sure if you US boys got them, but in NZ they have Gravel Express Imprezas, which are essentially WRX wagons, most of which were automatic.

I'm thinking of getting one of these as a base for a project, as they are cheap and have many of the basic parts I can use in my project (such as the auto computer, the correct pedals, and a turbo/computer setup that will do for running in my uber-motor).

I want to get the latest model auto I can get my hands on (for the computer controlled centre diff), and I'm wondering whether they will fit, and what to do about controlling the centre diff.

I will leave the shift patterns under the control of the computer (with various adjustments to the input signals if required, and probably change the signal going to the line pressure control solenoid later in the game), and wire in a (rather large) resistor to wire that would normally control the rear drive clutch. I was thinking of using a PWM signal to control the lockup, controlled by a thumbwheel by the shifter, with no other controller.

Alternatively I could try and use a later model trans computer (which would come with the right programming to control the centre diff), but I am only interested in going fast in a straight line, so this may be a lot of work for little benefit.

Has anyone done this before? What did they do?
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Old 06-04-2010, 08:29 AM   #2
Storm
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If I'm understanding this correctly, you want to put a DCCD unit into an older 5speed manual transmission?

It can be done.
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Old 06-04-2010, 08:35 AM   #3
BLSTIC
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Using a manual transmission was never mentioned in any part of my above post. The title says auto, the first line has automatic in it. The second sentence specifies auto computer, the third says 'late model auto'. The fourth line talks about computer controlled shift patterns, line pressure, and rear drive clutch. Even the 5th bit says 'trans computer'.

Where did you get the idea that I wanted to use a manual gearbox?
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Old 06-04-2010, 09:03 AM   #4
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This is probably something you should be asking on an Australian forum, as we did not get those models here in North America.
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Old 06-04-2010, 09:06 AM   #5
BLSTIC
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No, but you must have got some version of an automatic subaru. As far as I know all of the autos up to 1998 (and all Impreza's up to 02) were FWD full time with the rear drive computer controlled.

Basically, putting an auto with a centre diff into a car that came with the "FWD Fuse"
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Old 06-05-2010, 01:27 PM   #6
Storm
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Quote:
Originally Posted by BLSTIC View Post
Using a manual transmission was never mentioned in any part of my above post. The title says auto, the first line has automatic in it. The second sentence specifies auto computer, the third says 'late model auto'. The fourth line talks about computer controlled shift patterns, line pressure, and rear drive clutch. Even the 5th bit says 'trans computer'.

Where did you get the idea that I wanted to use a manual gearbox?
I saw "computer controlled centre diff" and thought of a DCCD since the 4EAT uses a TCU to control the entire operation of the transmission, including the center diff lockup. This made me revert back to a worldwide plethora of terminology used by different people over the years to describe things. Doesn't matter to me, I just try to help.

If you wanna alter the centre diff operation within a TCU, I think you'll be treading new ground. The FWD fuse grounds ("earths" in Kiwi-speak) a signal to the TCU that opens the center diff. A preliminary search of "Torque-mada lite" will show of folks who've installed a simple switch to apply 12v to the diff, locking it up. Expand on that for a controller based function separate of the TCU.

Good luck,
Jay
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Old 06-06-2010, 12:38 AM   #7
BLSTIC
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I thought more about it, and I'm thinking of using the TCU's original rear drive signal, which is more than likely electrically compatible and comes into play at similar times (The request for more traction will work), and I get to keep my snow mode switch (that locks the front rear drives together and starts in second gear). But then I thought about the likely motorsports use of the car and I am quite likely to want manual control over the diff at times. So i have my solution...

Use the computers rear drive output to lock the centre diff during normal driving, and have an additional switch and thumbwheel. They would control a circuit that provides a pulsewidth modulated signal to my centre diff. The switch would change the device providing the signal (ie from TCU to my ciruit, making an auto-manaul switch) and the thumbwheel would control the manual lock. The handbrake switch will kill the signal to the centre diff in manual mode only.

Basically I'm adding DCCD to an automatic car. I'll let you all know how it works when I actually get another subaru...
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Old 06-06-2010, 01:27 AM   #8
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So are you asking about using the VTD center differential from a Phase II 4EAT instead of the MPT style found on Phase I 4EATs?

Or using the Phase II 4EAT with a Phase I TCU? Or am I totally missing the point.
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Old 06-06-2010, 03:23 AM   #9
BLSTIC
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Using the 'phase II' gearbox in a car that should have the 'phase I' gearbox equipped, and driving the whole thing (diff included) with the phase I computer. But also having control over the locking of the centre diff on command (ie DCCD, DIY style)
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Old 06-07-2010, 08:44 AM   #10
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Old 06-08-2010, 03:04 AM   #11
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Not sure if this helps, but it's worth a shot.
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