SubaruFred Posted October 19, 2011 Share Posted October 19, 2011 the FWD fuse is left in or the TCU is bypassed and the duty C is controlled by a manual switch? FWIW, I tried flushing the ATF, Trans-X and a new duty C but the only thing that fixed my TB was bypassing the TCU and hard-wiring the duty C to a switched +12V power source. The problem was that the TCU kept determining that the duty C was bad and defaulting to 50/50 torque split. This ensured that TB was always present since the TCU wouldn't send any voltage to the duty C. Sending +12V to the duty C via a switch has eliminated all TB and allows 50/50 AWD on-demand at the flick of a switch. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 19, 2011 Share Posted October 19, 2011 You probably have a bad driver circuit in your TCU. I would replace the TCU if it fails to recognize the new Duty-C. Would seem the logical and simple solution - either that or there's a wireing issue somewhere and in that case running a new set of wires to the TCU would seem to be the most prudent course. Ruining a new Duty-C by putting constant 12v to it seems counter-productive. That's supposed to be a temporary solution and for diagnostic purposes only. GD Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted October 19, 2011 Share Posted October 19, 2011 It's probably not ideal to drive the duty c continuously like that. There used to be an endwrench document I believe that indicated the TCU controlled the solenoids from 5% to 95% duty cycle at around 50 Hz. So none were ever continuously energized (100% duty cycle). Quote Link to comment Share on other sites More sharing options...
idosubaru Posted October 19, 2011 Share Posted October 19, 2011 (edited) GD has a good point - the TCU's are very easy to swap and they very rarely fail so there's zero demand meaning they're not worth anything (they're cheap). the FWD fuse is left in or the TCU is bypassed and the duty C is controlled by a manual switch? it's a counter productive question because every thread ends up exactly the same way - tons of commentary and little, if any, real world experience. that doesn't help you. most people are going to say don't do it because something bad will happen. first they're wrong, because i've done it. second, who cares since it's already hosed!? it's a no brainer: 1. possibility of zero work and maybe needing to replace later. 2. replace now. #1 is a great fit sometimes and saves a bunch of time and money. no one has actually ever seen this cause a Duty C to fail, so that's rather good news. and i've driven a long time exactly like this, about 2 years, controlling the Duty C by a switch. if you're worried about it and dont' need 4WD - run it without the Duty C and remove the rear half of the driveshaft. Edited October 19, 2011 by grossgary Quote Link to comment Share on other sites More sharing options...
987687 Posted October 19, 2011 Share Posted October 19, 2011 It is possible for the transistor in the TCU responsible for the duty C to get fried... eulogious has a post about that is his tread about paddle shifters As has been said, look in the computer, or plain replace it. Quote Link to comment Share on other sites More sharing options...
SubaruFred Posted October 19, 2011 Author Share Posted October 19, 2011 Thanks guys. I agree that replacing the TCU would be the ideal solution, if that's all it takes. The thing that worries me is that my TCU does control the duty C correctly much of the time. It's only when the TCU decides the duty C has failed and stops sending it any current that my TB occurs and remains until I re-cycle the ign switch (and TCU). I also agree that theoretically it's not a great idea to run a intermittent duty solenoid at 100%. However I was looking more for real world success and failure data like below: no one has actually ever seen this cause a Duty C to fail, so that's rather good news. and i've driven a long time exactly like this, about 2 years, controlling the Duty C by a switch. Thanks again grossgary. 2 years is a long time and if my duty C lasts that long wired this way I'll be satisfied. Quote Link to comment Share on other sites More sharing options...
Dylan Posted October 19, 2011 Share Posted October 19, 2011 and i've driven a long time exactly like this, about 2 years, controlling the Duty C by a switch. Same here, I installed a dash switch a few months ago. It has about 1000 really really hard miles on it. Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted October 20, 2011 Share Posted October 20, 2011 fred, look at it this way. if replacing the tcu fixes it you are done. if not you are no worse off. if you had put your repair effort into the tcu instead of the switch, you would know now if it worked. if the tcu does not fix it, you can just leave the switch in for 2 years. Quote Link to comment Share on other sites More sharing options...
SubaruFred Posted October 20, 2011 Author Share Posted October 20, 2011 fred, look at it this way. if replacing the tcu fixes it you are done. if not you are no worse off. if you had put your repair effort into the tcu instead of the switch, you would know now if it worked. if the tcu does not fix it, you can just leave the switch in for 2 years. John, you make some very valid points but I already had the switch, wire and connectors in hand so this mod only took under 2 hours total. I've already spent over 2 hours searching for a replacement TCU and still haven't found one. Do you know where I can find a known-good TCU for a 1993 Legacy AWD non-turbo? Maybe I can leave the switch in for 10 years? We don't really know how long the duty C will last at 100% duty cycle. My original lasted 175,000 miles and 18 years running at 90% duty, 95% of the time and was still good when I replaced it. If I can find a TCU for a good price I may try it but frankly this car will probably be sold or scrapped when the tires wear out in ~40,000 miles. It's rusted, the paint sucks, it's no classic and has very little re-sale value. Thanks again for what I consider to be very good advice, even if I don't take it. That's on me and I may or may not regret it. Only time will tell. P.S., I have a 12V PWM fan speed controller laying around. What if I wired that into the duty C circuit? Instead of a +12-14V switch I could manually control the duty C the same way the TCU does. I may try this. ~1 hour and free. Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted October 20, 2011 Share Posted October 20, 2011 did you look here, www.car-part.com ? usually i sort by distance, but shipping on a trans computer is going to be cheap, so i would sort by price or part grade. Transmission, 4WD (L. strg col), LHD, w/o turbo http://www.car-part.com/cgi-bin/search.cgi?userSearch=int&userPID=1000&userLocation=All+States&userIMS=&userInterchange=CB%3DA%3D&userSide=&userDate=1993&userDate2=1993&dbModel=70.6.1.1&userModel=Subaru%20Legacy&dbPart=591.1&userPart=Computer%20Box%20Not%20Engine&sessionID=600000000000000000007906968&userPreference=price&userZip=24015&userLat=37.2556&userLong=-79.9796&userIntSelect=606117&userUID=0&userBroker=&iKey=&userPage=2 Quote Link to comment Share on other sites More sharing options...
SubaruFred Posted October 20, 2011 Author Share Posted October 20, 2011 No, I didn't look there. Thanks for the link! How can I tell which TCUs will work with my car? Will any 92-94 AWD Legacy TCU work? Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted October 20, 2011 Share Posted October 20, 2011 when you search for a 93, the software only returns parts that are known to fit. so all shown will work unless the guy at the parts yard entered the info incorrectly. the interchange software on that site is very conservative. it does not know that a 96 outback auto trans will work in a 97 - 98 outback. we have learned this thru real world experience. but if it shows the TCU will work, it should. Quote Link to comment Share on other sites More sharing options...
SubaruFred Posted October 21, 2011 Author Share Posted October 21, 2011 Thanks again. It's always good to have options. Quote Link to comment Share on other sites More sharing options...
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