4EAT Diff-Lock Switch and Handbrake Mod - "Torquemada Lite" - Page 7 - Subaru Impreza GC8 & RS Forum & Community: RS25.com
 
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4EAT Diff-Lock Switch and Handbrake Mod - "Torquemada Lite"
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Old 03-15-2009, 07:10 PM   #61
reddragons
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hey defcon i'm new here. been on nasioc for a quite awhile but i got a new car with an automatic and have been researching it.

aaaaand this came up and looks pretty damn sweet. i could def use this in the snow. my lag time for the rear end to kick in is horrible, and the packs are slipping a bit so i get a good clucnk when the rear really kicks in.

anyway i'm pretty interested in yore little project and i think this is what i need next winter for sure. awesome job!

Last edited by reddragons; 03-15-2009 at 07:27 PM..
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Old 03-18-2009, 08:34 PM   #62
StartRestart
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Just installed on a 1998 L, the TCU pinout is different, 3 connectors versus your 2.. but, as logic would deem, the coloring between your TCU pins and Mine was the same.

I used a DPDT switch so it also would light a LED when it was enabled.

http://img21.imageshack.us/img21/7307/lightoff.jpg
http://img12.imageshack.us/img12/2672/lighton.jpg

Great writeup, I'll post pics of my weird TCU and the wire to use and of course the resistors/sinks i used tomorrow, need sun!


>That other switch enables the FWD Relay in my ebrake light circuit... Flip it and whenever the ebrake light in the dash lights up it essentially plugs in the FWD fuse, obviously not good to drive on, which is why its used to corner in the deep snows up here in northern MN.
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Old 03-18-2009, 10:49 PM   #63
obsolete
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^ Cool.

I am working on a version that uses a single three-position switch with relays to do 4WD-AWD-FWD + handbrake mod.

Got the schematic and parts, just need to do assembly and testing, which could be weeks away with my current schedule, unfortunately...

Hasn't got any LEDs, though...that's neat.
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Old 03-19-2009, 06:39 AM   #64
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Quote:
Originally Posted by StartRestart View Post
Just installed on a 1998 L, the TCU pinout is different, 3 connectors versus your 2.. but, as logic would deem, the coloring between your TCU pins and Mine was the same........
.....Great writeup, I'll post pics of my weird TCU and the wire to use and of course the resistors/sinks i used tomorrow, need sun!
This just came up with one of the guys that I built a kit for (limited). He's got a a 98 Legacy GT and has the three connector TCU as well.
It's good to know that the wire color appears to be a constant (so far), but if you could post pictures of your TCU and connectors, that'd be great. I'm trying to track down a decent source for Legacy and Forester service manuals in case thiser are more TCU options out there

Great install - I know that DPDT switch well. It's the only reasonable 'DT' switch that Radio Shack sells. One note - did you run the LED off of +12v, or is it fed off of the TCU wire? If you fed it from the TCU, the maximum voltage to the LED will be around 11v (vehicle in park). At any other speed, voltage will drop and the LED will dim. You'll also get varying voltage as you drive, and the LED will dim and brighten accordingly, and you'll probably get some flicker due to Subaru's low frequency PWM signal.
Certainly not a deal-breaker - in fact, it might be cool. But if it drives you nuts, now you know how to fix it..
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Old 03-19-2009, 07:09 AM   #65
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Quote:
Originally Posted by reddragons View Post
my lag time for the rear end to kick in is horrible, and the packs are slipping a bit so i get a good clucnk when the rear really kicks in.
Welcome reddragons. Glad you like the project. I feel your pain with the delayed rear lockup, but in researching it further, I don't think the 'clunk' that you're hearing is a worn clutchpack. It's a fault in Subaru's AWD mapping.

Under normal acceleration from a stop, the system works perfectly. It proactively shifts a large amount of torque to the rear wheels, and does so with no clunking. I would even go so far as to say it's a very good 'predictive' system.
Where it fails, is at speeds above 10-20 mph. When you hit the gas on slippery surfaces at those speeds, the sytem is purely 'reactive'. If the wheels spin, the TCU senses the spin and locks up the Duty C solenoid - sometimes politely, sometimes not. Lag and lockup percentage are dependent on a ratio of wheelspin to throttle position.

That is exactly the phenomenon that drove me nuts in Rallycross - it makes for a very ill-handling car. Now that I've fixed it, my results haven't gotten any better, but I attribute that to my distinct inability to drive like a sane person. Sideways may be slow, but it sure is fun!
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Old 03-19-2009, 12:49 PM   #66
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For both LED's I bummed 12v from the cigarette lighter right there.

As for the '98 4EAT TCU:
Location of it
http://img12.imageshack.us/img12/9373/98tcu.jpg

The wire for Duty Solenoid C ("AWD Solenoid"), note the way I am holding the tcu in this picture.
http://img16.imageshack.us/img16/4690/wiresolenoidc.jpg

For the resistor pack I used the same values but different housings.
2x 50 Ohm, 2x 100 Ohm, and 2 of these heatsinks to tie it all together.


just sits under the plastic between the shifter and center console piece.

Last edited by StartRestart; 03-19-2009 at 01:04 PM..
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Old 03-19-2009, 06:47 PM   #67
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If I'm not mistaken, The wire for the Solenoid C is the bottom connector right? with the TCU laying on the back end of the panel.

Like Defcon5 said, I have a 1998 Legacy and it's also has the 3 connectors instead of 2. I'm not sure what has change between the years. Hopefully it's still the same wire (white/green stripe) leading to the solenoid.
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Old 03-19-2009, 07:37 PM   #68
reddragons
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thanks for the welcome defcon. you see i thought it was slippy packs cuz someone told me that. i really didn't know. my last subie was a 95 impreza L awd manual, so i never had this problem. i should build this and install it before next winter for sure....
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Old 03-19-2009, 07:50 PM   #69
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Nice work on the photos StartRestart. Those are some impressive resistors! The resistor/sink assembly looks like a small satellite..

To answer limited's question; yes it looks like the bottom most plug (when mounted) contains the Duty C solenoid wire, and as luck would have it it, it matches the color of the 99 Impreza wire (wht/grn) Hooray!!

Now I just need to start a list of all the different TCUs we come across and add them to the actual DIY. Thanks for the reference photos StartRestart. If anyone else has installed one of these and has a different TCU than I picture, please let me know what model and year, and I'll do my best to come up with some specific documentation for each variation.
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Old 03-19-2009, 09:24 PM   #70
defcon5
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Quote:
Originally Posted by reddragons View Post
thanks for the welcome defcon. you see i thought it was slippy packs cuz someone told me that. i really didn't know. my last subie was a 95 impreza L awd manual, so i never had this problem. i should build this and install it before next winter for sure....
No problem - I thought the exact same thing. I was pretty much prepared to buy a new transfer clutch and install it. This would have been a very messy, involved installation, and could easily cost several hundred dollars - even on the cheap.

After I did a little research and plugged my meter into the car, I was able to narrow down the general problem. That's when the idea for the switch was born

You can build and install this switch/resistor assembly in an afternoon. You'll spend less than $40 in parts and tools, and you'll have the power to make the clunking go away whenever you want.

When you decide to do your install, I'm always available via PM if you get stumped.
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