dave833 Posted June 12, 2007 Share Posted June 12, 2007 I am just FULL of questions! How long can I drive my '95 Legacy 5 speed without the rear section of the driveshaft with no damage? I removed it as a temporary solution to the center diff coupling binding, but the front section to the bearing and of course the rear axles and diff are still in place. No fluids leaking out anywhere that I can see (it's a 5 speed.) Quote Link to comment Share on other sites More sharing options...
idosubaru Posted June 12, 2007 Share Posted June 12, 2007 in short, best to fix it, but i'd do it. if your center diff is fried, then you'll probably be fine to drive it as long as you please. on the older generation stuff you can run them with the center diff locked and the rear shaft out for as long as you please...i suppose some internal parts are seeing more load than normal, but assuming you don't drive crazy, race the car and install a turbo i'd guess you won't have any problems. i know a guy with an EJ trans just like yours, with torque bind and he's running it in 2WD (RWD actually). Quote Link to comment Share on other sites More sharing options...
jamal Posted June 12, 2007 Share Posted June 12, 2007 The viscous coupling will fry, and the rear output section will just spin. It won't move and gear oil will leak out the rear of the transmission. Quote Link to comment Share on other sites More sharing options...
svxpert Posted June 13, 2007 Share Posted June 13, 2007 The viscous coupling will fry, and the rear output section will just spin. It won't move and gear oil will leak out the rear of the transmission. "but the front section to the bearing and of course the rear axles and diff are still in place." Quote Link to comment Share on other sites More sharing options...
nipper Posted June 13, 2007 Share Posted June 13, 2007 If yuou dont leak trany lubricant, you will be fine. Worst thing your going to happen is that you hit X speed and you get a vibration, and then it may or may not work. nipper Quote Link to comment Share on other sites More sharing options...
jamal Posted June 13, 2007 Share Posted June 13, 2007 front section to what bearing? If you disconnect drive to the rear wheels the car won't go anywhere. The center diff cannot transfer 100% of the power to the front, so it will move until the viscous coupling loses all ability to resist shear, which would occur in about 10 seconds. Quote Link to comment Share on other sites More sharing options...
nipper Posted June 13, 2007 Share Posted June 13, 2007 front section to what bearing? If you disconnect drive to the rear wheels the car won't go anywhere. The center diff cannot transfer 100% of the power to the front, so it will move until the viscous coupling loses all ability to resist shear, which would occur in about 10 seconds. Car us always delivering power to the front wheels, the rear wheels as long as they keep up with the front are there for the ride. Also with very little inertia on the rear driveshaft, it will be turning right along with the front with very little delay. He is talking about disconnecting the rear half of the driveshaft, between the carrier bearing and the rear diff. He already has a fried VC so its basically locked up. nipper Quote Link to comment Share on other sites More sharing options...
jamal Posted June 13, 2007 Share Posted June 13, 2007 A fried Viscous Coupling does not lock up. The fluid overheats and loses it's ability to resist shear, and thus do anything. The VC acts to limit speed differences between the front and the rear of the center differential, not as a coupling to transfer power to the rear. Once you've fried the VC, the center differential is open. This means it won't transfer any power to the front if the rear wheels aren't connected. Quote Link to comment Share on other sites More sharing options...
dave833 Posted June 13, 2007 Author Share Posted June 13, 2007 Been driving the car all day with NO rear section of the driveshaft. Front section is in place from the tranny to the carrier bearing, as is the rear diff and axles. I'm not sure what the VC is doing, but sufficient power is definitely getting to the front wheels. I haven't noticed any really unusual vibrations or noises, and it definitely eliminated the torque bind issue I was having! I'm not planning to leave it this way, but I wanted to verify it was a VC issue before I dropped $500 on a new one. (see my other post for the accompanying brake snafu that MAY have been a contributing factor!) Quote Link to comment Share on other sites More sharing options...
Andyjo Posted June 13, 2007 Share Posted June 13, 2007 I'm thinking about doing this w/ my OBS until i get new parts, but it has a 4eat, anyone think there'd be a problem with that? Quote Link to comment Share on other sites More sharing options...
nipper Posted June 13, 2007 Share Posted June 13, 2007 I'm thinking about doing this w/ my OBS until i get new parts, but it has a 4eat, anyone think there'd be a problem with that? maybe. The car might be limited to 50mph by the TCU/ECU. Its the same as driving with a bad VSS sensor. The car will try to correct the the speed difference between axles. In the past when somone with an auto has driven with a blown front axle the car limits itself to 50 mph. On the other hand, the car may just spin the rear driveshaft ( 90/10 split) and not really care. You wont hurt anything by trying. nipper Quote Link to comment Share on other sites More sharing options...
jamal Posted June 13, 2007 Share Posted June 13, 2007 With a 4eat all you have to do is put in the fuse and it won't try to engage the center clutch pack. It's not recommended to drive around like that for long periods of time. As far as the 5mt, the center diff and clutch pack are not capable of transferring all the power to the front or rear. So driving and accelerating slowly it might handle it, but you are putting a ton of stress on the coupling. You must be experiencing some sort of slippage and eventually you won't go anywhere. Quote Link to comment Share on other sites More sharing options...
nipper Posted June 13, 2007 Share Posted June 13, 2007 http://www.autozine.org/technical_school/traction/tech_traction_4wd_2.htm that should help. The viscous coupling wont really care either wzay, and others have doen it before . Redmeber these are FWD cars (look at the transmission power flow some time, direct connection to the front diff) with the AWD control section connected to the reare wheels. No matter what happens the front wheels will always spin. In both cases we are talking about transmissions with fried clutch packs and a fried VSS, so it wont mae anything any worse. Thos eunits have already lost there ability to vary the torque to the rear wheels. nipper Quote Link to comment Share on other sites More sharing options...
idosubaru Posted June 13, 2007 Share Posted June 13, 2007 As far as the 5mt, the center diff and clutch pack are not capable of transferring all the power to the front or rear. So driving and accelerating slowly it might handle it, but you are putting a ton of stress on the coupling. You must be experiencing some sort of slippage and eventually you won't go anywhere. technicalities aside, it's being done right now and can be done in FWD or RWD....so far i've yet to hear of it "not working", but obviously the sample size is tiny. in cases where the viscous coupling has failed such that it's "locked", i don't know what that means or exactly what is happening inside that unit, but it does work to run in 2WD. i've done it myself for many thousands of miles as well on a diff lock equipped manual trans, on multiple vehicles. no problems, but those certainly aren't viscous couplings and are better for this than the viscous units. i would think you would be fine. in a perfectly working 4EAT, stock config, i had bad luck running with front axles. i did not have the duty C switch then i don't think. it really confused the TCU. but running with the rear driveshaft disconnected it would run fine...but i'm guessing i probably used the duty C switch to do that, it was awhile ago and i did not drive it very long like that. also, this is all on first generation 4EAT stuff in an XT6, so differences are possible. Quote Link to comment Share on other sites More sharing options...
Skip Posted June 13, 2007 Share Posted June 13, 2007 Nip, good link (poor edit?) this is the Subaru system so they say If so and if the diff section is the connection between the tranny input shaft (a.k.a. engine output) and the drive to the front and rear diffs.. I doubt this is true?? Would this not act like an open rear diff with one rear wheel off the ground and only spin the wheel in the air? i.e. the rear non connected driveshaft I think I'm seeing this all wrong?? Quote Link to comment Share on other sites More sharing options...
nipper Posted June 13, 2007 Share Posted June 13, 2007 Nip, good link (poor edit?) this is the Subaru system so they say If so and if the diff section is the connection between the tranny input shaft (a.k.a. engine output) and the drive to the front and rear diffs.. I doubt this is true?? Would this not act like an open rear diff with one rear wheel off the ground and only spin the wheel in the air? i.e. the rear non connected driveshaft I think I'm seeing this all wrong?? No, think more like a limited slip diff, which is exaclty what it is. If the VC wasnt there then yes it would nipper Quote Link to comment Share on other sites More sharing options...
Skip Posted June 13, 2007 Share Posted June 13, 2007 no yes maybe Corn-fused If the following is correct??? The front and rear diff outputs become the two rear axles in an open diff car. The VC will lock up with the free wheeling rear driveshaft as it is ment to. The rear output will spin like the wheel in the air. Hot darn, I is one corn-fused country bumkin. Quote Link to comment Share on other sites More sharing options...
Hocrest Posted June 13, 2007 Share Posted June 13, 2007 I'm thinking about doing this w/ my OBS until i get new parts, but it has a 4eat, anyone think there'd be a problem with that? My 97 Leg with the 4EAT has been like that for about a month, I have the FWD fuse in. But I'm not really concerned if I fry the trans the rest of the way. It's given me 265,000 miles and it's getting replaced with a 5-spd. Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted June 13, 2007 Share Posted June 13, 2007 maybe. The car might be limited to 50mph by the TCU/ECU. Its the same as driving with a bad VSS sensor. The car will try to correct the the speed difference between axles. In the past when somone with an auto has driven with a blown front axle the car limits itself to 50 mph. On the other hand, the car may just spin the rear driveshaft ( 90/10 split) and not really care. You wont hurt anything by trying. nipper in my opinion, as long as the rear output shaft on the 4eat is spinninig and the speed sensor on the rear of the trans 'sees' it, the car will be happy as a FWD car. no binding, no undue wear and tear, no more damage to the AWD/trans. as nipper suggested, the weak link will be the support bearing for the front section of the drive shaft. long term, it may not be happy and start to vibrate at high speed.?? but i don't know. Quote Link to comment Share on other sites More sharing options...
jamal Posted June 13, 2007 Share Posted June 13, 2007 Redmeber these are FWD cars (look at the transmission power flow some time, direct connection to the front diff) with the AWD control section connected to the reare wheels. No matter what happens the front wheels will always spin.nipper Nope. In a Subaru Manual transmission, the output shaft is directly connected to the center diff. Power has to go through it to get to the front or rear wheels. Quote Link to comment Share on other sites More sharing options...
nipper Posted June 13, 2007 Share Posted June 13, 2007 As long as we are on the subject, does anyone have a blow up of the variable center diff? Been curious about that, as i cant find a good drawing of it. nipper Quote Link to comment Share on other sites More sharing options...
jamal Posted June 13, 2007 Share Posted June 13, 2007 looking. There are some great tech docs about how dccd works floating around (this pretty much covers it). MRT has a few pictures of the standard center diff/VC. http://www.mrtrally.com.au/performance/viscous_coupling.htm Their drawing is just a generic viscous coupling and not was is really in a subaru Quote Link to comment Share on other sites More sharing options...
nipper Posted June 13, 2007 Share Posted June 13, 2007 So we need a guinia pig. Somone with a manual remover thier driveshaft and let us know if the car goes. nipper Quote Link to comment Share on other sites More sharing options...
northgeorgiaroo Posted June 13, 2007 Share Posted June 13, 2007 Been driving the car all day with NO rear section of the driveshaft. Front section is in place from the tranny to the carrier bearing, as is the rear diff and axles. I'm not sure what the VC is doing, but sufficient power is definitely getting to the front wheels. Umm....... The "Guinea Pig" is the one who started this thread:-p Sounds like it will at least move the car, so we can close that debate. If my torque bind gets worse (I suppose it would be wishful thinking to hope it would get better:rolleyes: ), I'll try it on my 4EAT, and be another guinea pig for the autos. When that happens, I vow to do it until the tranny grenades, and I'll report back. Quote Link to comment Share on other sites More sharing options...
jamal Posted June 13, 2007 Share Posted June 13, 2007 If my torque bind gets worse (I suppose it would be wishful thinking to hope it would get better:rolleyes: ), I'll try it on my 4EAT, and be another guinea pig for the autos. When that happens, I vow to do it until the tranny grenades, and I'll report back. Like I said earlier, your 4eat will be fine in FWD. The 4eat is FWD based and uses a clutch to transfer power rearward. Putting a fuse in a holder under the hood disables power transfer to the rear, but will cause damage to the duty solenoid C after extended periods of time (see some the people who made switches to force it on or off). The manuals don't just use a viscous coupling off the rear to transfer power, they actually have a center differential. Found an interesting piece of info about the viscous coupling in an old nasioc thread: 2. The standard center viscous diff. is a 4kgf unit. This rating is an indication of the viscous resistance force when there is a 100rpm difference in axle speeds. Heavy duty STi competition units are built with more plates and different oil to air ratios to provide more viscous action. Early (pre-1999) units were available in 12kgf and 20kgf ratings while later units are available only in the 20kgf rating. I believe the Subaru viscous center diffs are designed with hump phenomenon. The hump phenomenon occurrs when the viscous oil heats dramatically and expands to the point where the pressure inside the diff. causes the viscous plates to actually contact each other and lock solid. This attempts to prevent overheating of the viscous oil during high wheel slip conditions. 3. The rear viscous LSD used on the Subaru WRX and some RS and Legacy models is very small. Disassemble a differential with one in it and you will be hardpressed to even notice it. There are probably only a couple of plates inside of it. --Dave RalliSpec http://www.rallispec.com post 54 here How much power can transfer to the front and for how long is not something I'd be inclined to experiment with. I guess we'll find out when Dave833 gets stranded somewhere. Quote Link to comment Share on other sites More sharing options...
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