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Thread: AWD->FWD - Debate with friend, need answers.

  1. #61
    SLi nOOb EJ22D's Avatar
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    Re: AWD->FWD - Debate with friend, need answers.

    Quote Originally Posted by hfxdesign
    Read the first post here. My duty C solenoid failed, I'm just saying I'm still getting a flashing light despite having the driveshaft pulled. I'm beginning to wonder if it's the TCU and not the solenoid itself. I've already pulled the code, and the only one I get is for a failed duty C. The transmission still shifts just fine, no problems whatsoever.
    The TCU is throwing the code for a failed Duty C but you can still drive it. It's just going to constantly remind you in that annoying way. I have never heard of a TCU "lying" or being messed up that badly. Not to say that it doesn't happen but if it says you have a failed Duty C, it is so. Just because you have it in FWD doesn't mean that the flashing will stop since the TCU isn't picking up an electrical signal from the Duty C.

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    Administrator Huffer's Avatar
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    Re: AWD->FWD - Debate with friend, need answers.

    Quote Originally Posted by Felipe
    Quote Originally Posted by Huffer

    Just remember what your car does (stock) and in what gear (D = 90/10 torque split, D3, D2, D1 = 50/50 torque split).
    What about in Reverse?
    Reverse... that would different. Besides the fact that your speed is severely limited by the gearing (R I think is as short as 1st gear) the "rear" wheels while moving in reverse have much greater turning capability. As far as torque split goes, you'd probably be the same as D4 - Rear wheels will still only 10% while the fronts get 90%. I guess you could say that while in reverse, you now have a mostly RWD car... LOL

    Quote Originally Posted by hfxdesign
    Read the first post here. My duty C solenoid failed, I'm just saying I'm still getting a flashing light despite having the driveshaft pulled. I'm beginning to wonder if it's the TCU and not the solenoid itself. I've already pulled the code, and the only one I get is for a failed duty C. The transmission still shifts just fine, no problems whatsoever.
    And you'll get a code because your failed duty C solenoid isn't part of the rear driveshaft. It's a sensor/switch inside the trans and it's failed. It's like unplugging your antenna and then saying your stereo still isn't picking up FM even though your CD player is still working.
    The trans will shift fine - because shifting has no bearing on how the rear wheels are turning. The rear diff isn't dependent on how the trans shifts - it's dependent on how the fast the driveshaft is turning based on the rear clutch packs. Because you've physically disconnected the driveshaft (which means under your car you now have a spinning pipe that's not anchored on both ends, which is really dangerous), you won't "feel" any difference in the transmissions shifting or how the rear wheels are turning.

    Oddly, you'd have achieved the exact same result just by inserting the FWD fuse in the engine bay. Much less work and far less dangerous overall.

    Quote Originally Posted by EJ22D
    6. I use my FWD switch very often, especially when I'm moseying around town & driving at street speeds & all with no ill effects. When I switch from FWD to AWD, I do it ALWAYS when the transmission is in park, even if I have to switch to park at a light. I use it, NOT abuse it as I am not yet certain what kind of effect that switching in motion will have on the Duty C.
    That's really interesting about your 4EAT in your 98 only locking into 50/50 in 1st and 2nd gear. I've had 2 98 GTs (sedan and wagon) and they locked into 50/50 in 3rd gear (on the freeway, doing 60mph in snow, based on RPMs). Granted I pay more attention to the engine speed and wheel speed more than I did gearing so I could be wrong - but all the literature I've read says 50/50 from D3 to D1.

    I'd really avoid switching the Duty C "off" mid-roll... I imagine the driveline shock might be a bit much over time, a bit like when someone jumps a gear or stalls out on a hill too many times.
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    Re: AWD->FWD - Debate with friend, need answers.

    Quote Originally Posted by hfxdesign
    Alright, me and my friend are getting in a heated debate about whether or not running my car on just the front wheels is gonna trash the transmission. The back story is this: The duty C solenoid in my car fizzled out, and I don't have the time to replace it, instead I removed the rear section of the driveshaft (4EAT transmission), leaving the rear differential / axle shafts in place.

    I'm not really seeing where there could be much of an issue, aside from extra stress on the front CV shafts. Anyone have some input on this to clear it up?
    So much BS in this thread (other post's)....

    Yes, you can run with the FWD fuse in.
    Yes, it may damage the trans
    Yes, it can be converted to FWD

    Removing the rear half of the driveline is not the best idea, but it can be done. If you are doing it to save MPG, it's pointless since you still have both rear axles installed as complete units. You might save a little. That trans is meant to run ALL 4 WHEELS!

    The FWD fuse is for towing and if you are using a spear tire. Thats the reason for it. Not because your trans is having problems.

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    Re: AWD->FWD - Debate with friend, need answers.

    Quote Originally Posted by Dead91silvia
    ...The FWD fuse is for towing ...
    Here is a question in regards to this. Is it for towing something with the car, or the car being towed?

    My understanding was to put the car into FWD for an unavoidable front-wheel tow (as in, not a flatbed tow) so as to not destroy the transmission, but if you are using the car to tow a trailer or whatever to leave it in AWD as you would be putting a larger load on the front axles than normal.

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    Re: AWD->FWD - Debate with friend, need answers.

    Alright, well I'm planning on replacing the Duty C, anyone know where I can get one for a decent price?

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    Re: AWD->FWD - Debate with friend, need answers.

    @rkrenicki That's what 1, 2, and 3 are used for, as stated, most 4EATs lock into 50/50 in the numbered gears, and yes you want it full time AWD when towing a trailer, on the AWD subarus the front CV shafts are slimmer than the ones on the FWD versions, so they're not as sturdy.

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    Re: AWD->FWD - Debate with friend, need answers.

    Not to stray away from this convo any further than it has lol. But is it ok to drive in 3 thru city like areas? Obviously not highway. So lets say under 50mph.
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    Re: AWD->FWD - Debate with friend, need answers.

    Quote Originally Posted by Huffer
    That's really interesting about your 4EAT in your 98 only locking into 50/50 in 1st and 2nd gear. I've had 2 98 GTs (sedan and wagon) and they locked into 50/50 in 3rd gear (on the freeway, doing 60mph in snow, based on RPMs). Granted I pay more attention to the engine speed and wheel speed more than I did gearing so I could be wrong - but all the literature I've read says 50/50 from D3 to D1.

    I'd really avoid switching the Duty C "off" mid-roll... I imagine the driveline shock might be a bit much over time, a bit like when someone jumps a gear or stalls out on a hill too many times.
    I only switch on/off at complete stops & in P, never during a roll. I don't have the courage to test that out & I don't want to gain it! But yes, my 4EAT doesn't not lock into 50/50 in 3rd gear, only 1st/2nd. There is no bind when I put it into 3rd but it immediately comes up when 1st/2nd is selected. My old L did it in 1st, 2nd, & 3rd. I have had this transmission checked & it is in great shape for its age.

    To the OP,
    1. You can run with the FWD fuse in & it is recommended for you to do so should you have any problems with the transmission.
    2. You're likely to break a C/V joint long before you'd ever hurt the transmission due to them not being as strong as those in the FWD version.
    3. The transmission is a FWD based transmission, so it is good to use if you have to do it.
    4. Even if you drive in FWD mode, you will save gasoline. 3mpg at best but its still a gain over being in AWD. I don't know about you but 15k+ feet is quite the distance.
    5. The 4EAT is a FWD based transmission that has AWD as a "secondary response", so to speak. Most times when you're driving at lower speeds, the transmission has a 90/10 split, essentially making it a FWD car.
    6. It is true that you are to use FWD when you're towing a load or when you have a flat but when that flat happens, the wheel speed sensors sense the difference in tire speed & will cause the transmission to bind, much like what will happen with a failed Duty C, hence why the FWD fuse is there to use.

    Quote Originally Posted by Grimmrican
    Not to stray away from this convo any further than it has lol. But is it ok to drive in 3 thru city like areas? Obviously not highway. So lets say under 50mph.
    Any time you have the transmission out of Drive & if its binding, you are essentially in 4WD (50/50) & the stress of all 4 wheels turning at the exact same time causes extra heat/stress on the transmission itself, which tears up the fluid much faster & will leave you with a blown Duty C & very damaged clutch packs. I hope this answers your question.

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    Re: AWD->FWD - Debate with friend, need answers.

    Ok so it depends really if 3rd binds or not which I don't feel when it does only in 2nd. But ok good to know ill avoid it unless I desperately need to use it
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    Re: AWD->FWD - Debate with friend, need answers.

    Duty C was destroyed due to 4 different tires being on the car, which also destroyed the rear diff. New tires put on today, rear driveshaft will stay disconnected as the Duty C is so far gone the FWD fuse no longer works anyway. Still deciding whether to replace the solenoid, or get a plug for the front / center diff, remove the whole driveshaft and rear diff, and stub off the rear hubs (essentially convert it to FWD completely).

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    Re: AWD->FWD - Debate with friend, need answers.

    Quote Originally Posted by hfxdesign
    Duty C was destroyed due to 4 different tires being on the car, which also destroyed the rear diff. New tires put on today, rear driveshaft will stay disconnected as the Duty C is so far gone the FWD fuse no longer works anyway. Still deciding whether to replace the solenoid, or get a plug for the front / center diff, remove the whole driveshaft and rear diff, and stub off the rear hubs (essentially convert it to FWD completely).
    That will do it.
    All tires on our AWD systems must be of the same type, size, tread, & psi.
    It would be better if you restored the car's AWD system piece by piece as it being non-functional will affect the resale value of the car.
    Also, it would also be great to have that extra control when you need it but if you're going to go through all of that extra effort, you may as well swap in a FWD transmission so you don't have the dead weight of the inert AWD parts stopping your car from being as efficient as can be.

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    Re: AWD->FWD - Debate with friend, need answers.

    Well the only piece it needs is the solenoid...It's just a very time consuming process to replace it, not to mention finding the part I need. I've already replaced the rear differential, disconnected the driveshaft to avoid damaging it. Taking it to a dealer to have them do it would cost more than what I paid for the car ($700) Swapping for a FWD transmission would probably cost about the same, and if I was going to do a transmission swap I'd just get a known good AWD 4EAT (4.11FD) transmission. So you can see my dilemma.

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    Administrator Huffer's Avatar
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    Re: AWD->FWD - Debate with friend, need answers.

    Quote Originally Posted by rkrenicki
    Quote Originally Posted by Dead91silvia
    ...The FWD fuse is for towing ...
    Here is a question in regards to this. Is it for towing something with the car, or the car being towed?

    My understanding was to put the car into FWD for an unavoidable front-wheel tow (as in, not a flatbed tow) so as to not destroy the transmission, but if you are using the car to tow a trailer or whatever to leave it in AWD as you would be putting a larger load on the front axles than normal.
    Yep.

    The only time it is recommended to use the FWD fuse slot is:
    1. for an emergency tow where you would have the front wheels off the ground, but the rear wheels on the ground. This allows the rear wheels to free-roll without damage.
    2. For diagnosing a torque bind situation that usually results in duty c solenoid going/gone bad or burnt transfer clutch packs inside the trans.
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    Re: AWD->FWD - Debate with friend, need answers.

    Quote Originally Posted by hfxdesign
    I'm not using the fuse, I have the rear section of the driveshaft physically removed. He thinks it's going to destroy the transmission since there's no power to the rear tires.
    I drove mine for several hundred miles with the rear drive shaft removed. No damage to the transmission, but if you get ANY snow, it will be a zero wheel drive vehicle.

    Edit. Mine was 5MT so nevermind.

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    Re: AWD->FWD - Debate with friend, need answers.

    An open differential will only send power to one front wheel if there is slippage, which results in the wheel with the least traction spinning while the other wheel sits there helplessly. Open diffs are designed with turning in mind - the wheels can be driven while still rotating at different speeds (around corners) so you don't end up with "wheel hop" when you drive around a corner.

    LSDs help send power to both wheels in a slipping condition while retaining the ability for each wheel to turn at a different speed, like around corners. Many upper model Subarus have rear LSDs (Legacy GT, Outback, Forester XS/XT, WRX, STi) while very few have front LSDs (STi, possibly others that I'm not aware of).

    On newer Subarus with VDC, the car has the ability to brake the spinning wheel on one side to allow the wheel on the other side with more traction to regain power. It's kind of a compromise with LSDs & locking diffs, but a system that works pretty well in slippery conditions.

    You could have 50/50 power split across the front/rear wheels if you locked the diffs (a feature not available on modern Subarus), but that would cause the wheels to turn at the same speed, even around corners which causes wheel hop & other annoying side effects. That's why locking diffs are only used in slow, off roading conditions, generally.

    From what I've read about the DutyC on autos, you can burn it out by locking it 50/50 with a resistor mod, and possibly by using the FWD fuse too long (only in theory though) but to the OP that doesn't matter as it's wrecked anyways. Of course, the FWD fuse might not work with the duty C ruined.
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    Re: AWD->FWD - Debate with friend, need answers.

    Sorry to resurrect this post. I just got new tires on the car and re-connected the driveshaft. Still getting torque bind, but far less severe than it was, still have the 16 flashes of AT oil temp, and FWD fuse does nothing. Pretty much 99.8% sure the duty C is shot. Would driving it like this risk further damage? If so, what kind of damage? I'm not exactly made of money and don't have alot of time to work on it. My only A-B vehicle ATM so I can't have it 'in the shop' per se.

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    Re: AWD->FWD - Debate with friend, need answers.

    Bump

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    Re: AWD->FWD - Debate with friend, need answers.

    you run the risk of snapping the transfer shaft if you let it continue to run with torque bind
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    Re: AWD->FWD - Debate with friend, need answers.

    So pretty much back to square 1: fwd

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    Re: AWD->FWD - Debate with friend, need answers.

    That would be our safest bet. At least until you have the money to fix it right.
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    Re: AWD->FWD - Debate with friend, need answers.

    I meant if the transfer shaft broke.

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    Re: AWD->FWD - Debate with friend, need answers.

    yeah, that would be the end of the transmission's awd ability without a decent bit of work/money.
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    Re: AWD->FWD - Debate with friend, need answers.

    Oh well, New transmission incoming anyway

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