cannonball Posted September 27, 2004 Share Posted September 27, 2004 Yesterday I was out cruising the back roads of the SC Blue Ridge Mtns with my wife and boy. I decided to take them on a lightly used gravel road that is used primarily by hunters. I have a 2000 OBW limited MT BTW. At one point the road makes a switchback to the right and up a short hill. My guess would be a slope of approx 8-10%. Due to all the rain from the hurricanes a gully had formed crossing the road diagonally from one side to the other. It wasn't too deep or wide (so I thought) just at an odd angle. It may have been 3' wide by 12 to 18" deep. Well of course I decided to test the OB. This car has proven itself by driving up a sheet of ice before. I pulled the front wheels down into the ditch slowly then proceed to gas it up the other side. It was deep enough that the front bumper grazed the other side. No luck. The wheels start to spin. I think to myself... Hmmm. I back up and go to the right a hair and same thing this time. Wheels start spinning. At this point I'm like what the hell. I decided to not push my luck and turned around since the family was with me. Well of course I start wondering what was going on. I remember seeing the spin out marks from the front wheel but like a big dummy I didn't look to see if there were ruts from the rear wheels. Now the only thing I can come up with is that the gravel was so loose that none of the wheels could get traction. Please correct me if I'm wrong but since I have a LSD in the rear doesn't that mean 3 wheels would have had to be spinning. As you can imagine I can't stop thinking about going back sans my family. I want to a) see if there are any rear wheel marks and try it again. I don't however want to destroy my car. This road is normally driveable. I've done it in my S-10 4x2. But the road of coures was in better shape. I guess what I'm getting at is I found a situation that gave my OB a fit. Anybody else have any stories where there Subie couldn't make it? Charles Quote Link to comment Share on other sites More sharing options...
rweddy Posted September 27, 2004 Share Posted September 27, 2004 correct me if I'm wrong but since I have a LSD in the rear doesn't that mean 3 wheels would have had to be spinning. Charles You are wrong!! Just kidding. But you are. Sorry but with AWD only one wheel will spin, you do not have a lockable center diff in your Subaru so it is least path of resistance. IE one wheel will spin on the entire car, front or rear. Quote Link to comment Share on other sites More sharing options...
cannonball Posted September 27, 2004 Author Share Posted September 27, 2004 You are wrong!! Just kidding. But you are. Sorry but with AWD only one wheel will spin, you do not have a lockable center diff in your Subaru so it is least path of resistance. IE one wheel will spin on the entire car, front or rear. True, I understand this concept but power should be transfered to the wheel/s with the most grip. Since I was going no where and torque split is 50/50 at least 2 tires should have been spinning. Correct? Quote Link to comment Share on other sites More sharing options...
Guest lothar34 Posted September 27, 2004 Share Posted September 27, 2004 You are wrong!! Just kidding. But you are. Sorry but with AWD only one wheel will spin, you do not have a lockable center diff in your Subaru so it is least path of resistance. IE one wheel will spin on the entire car, front or rear. The center diff does "lock". He's got a manual tranny, so it doesn't do it mechanically, but the silicone in the diff should gel up and keep the front and rear outputs spinning at the same speed. From there, the rear LSD should try to keep the rear wheels spinning the same speed, and the front open diff will transfer it's power to the wheel with the least resistance. So to get stuck like that, one front wheel and both rears would have to have no traction. Quote Link to comment Share on other sites More sharing options...
Setright Posted September 27, 2004 Share Posted September 27, 2004 I suspect that all four wheels spun due to a total loss of traction. The center diff divides torque 50/50 under all circumstances. The front wheels ARE free to spin alone, but the rears will still get half the torque. If one front wheel has no traction and the other one does, the one without traction is free to spin 50% of the entire torque away. Even in that situation, the rears are still getting 50%, so they will push the car forward. This why an MT Sube is hard to steer as you enter a snow filled road. The fronts hit the snow and spin, and the rears still on tarmac push the car in a straight line. Howver, once all four are on the slippery stuff, it's tail-out galore ;-) Quote Link to comment Share on other sites More sharing options...
cannonball Posted September 27, 2004 Author Share Posted September 27, 2004 The center diff does "lock". He's got a manual tranny, so it doesn't do it mechanically, but the silicone in the diff should gel up and keep the front and rear outputs spinning at the same speed. From there, the rear LSD should try to keep the rear wheels spinning the same speed, and the front open diff will transfer it's power to the wheel with the least resistance. So to get stuck like that, one front wheel and both rears would have to have no traction. You know. Something just dawned on me. I could smell the clutch burning after I was through playing. Could there have been a possibility that the clutch was slipping as well. The car does have 95,000 miles on it. A few months back I was playing around on another gravel road pointed up hill. From a stand still I was trying to make the wheels slip. Couldn't make it happen but I did it to the point where the clutch overheated and was slipping like an SOB. I quickly decided not to do that again. This could be the same scenario. I have enough clutch to drive day to day, but it's days are numbered. Quote Link to comment Share on other sites More sharing options...
cannonball Posted September 27, 2004 Author Share Posted September 27, 2004 I suspect that all four wheels spun due to a total loss of traction. The center diff divides torque 50/50 under all circumstances. The front wheels ARE free to spin alone, but the rears will still get half the torque. If one front wheel has no traction and the other one does, the one without traction is free to spin 50% of the entire torque away. Even in that situation, the rears are still getting 50%, so they will push the car forward. This why an MT Sube is hard to steer as you enter a snow filled road. The fronts hit the snow and spin, and the rears still on tarmac push the car in a straight line. Howver, once all four are on the slippery stuff, it's tail-out galore ;-) Interesting concept. I have noticed when driving in the rain that when going through a turn with a puddle, the front of the car will push straight momentarily. Feels like it is slipping. The first time it happened it caught me off gaurd, but now I know what's happening. Quote Link to comment Share on other sites More sharing options...
99obw Posted September 27, 2004 Share Posted September 27, 2004 AFAIK no modern sube sold in the USA has a center diff lock. Viscous coupler or computer controlled clutch pack. No locking transfer case. I think the VC can be overwhelmed, allowing the front wheels to spin while the rears don't. I haven't seen this on subes, but I know the jeeps with a VC in the transfer case exhibit this behaviour (respective axles swapped) when punished on the trail. These systems may be more different than I am aware of so take this into account. My crappy old toyota tercel with a center diff lock would run circles around our outback with the computer controlled clutch pack. In 12"+ of snow the computer doesn't know what to do, so it cycles power front to rear constantly. I wish subes had a TC with some options for power transmission, like FWD, AWD via VC, 4H (locked) and 4L. It would be cool if they sold a version of the 4EAT with the VC as well. Quote Link to comment Share on other sites More sharing options...
rweddy Posted September 27, 2004 Share Posted September 27, 2004 AFAIK no modern sube sold in the USA has a center diff lock. Viscous coupler or computer controlled clutch pack. No locking transfer case. I think the VC can be overwhelmed, allowing the front wheels to spin while the rears don't. I haven't seen this on subes, but I know the jeeps with a VC in the transfer case exhibit this behaviour (respective axles swapped) when punished on the trail. These systems may be more different than I am aware of so take this into account. This is correct. What you are seeing is the VC is being overwhelmed. There is not way to lock it 50/50. That is why AWD wo diff lock in no use off road, or in really deep snow. All power will only goto one wheel. Get your Subaru high centered in snow some time and check this out. Only one wheel will spin. And it will always be one of the front wheels. I think last Subaru with center diff lock was the late 80’s RX. Quote Link to comment Share on other sites More sharing options...
cannonball Posted September 28, 2004 Author Share Posted September 28, 2004 This is correct. What you are seeing is the VC is being overwhelmed. There is not way to lock it 50/50. That is why AWD wo diff lock in no use off road, or in really deep snow. All power will only goto one wheel. Get your Subaru high centered in snow some time and check this out. Only one wheel will spin. And it will always be one of the front wheels. I think last Subaru with center diff lock was the late 80’s RX. I would tend to think it takes a lot to overwhelm a VC. I really wasn't pushing the limit here. I would hope that the sube could do better than that. What do you think of my clutch theory. If a VC does overheat what would it smell like? What I smelled was definitely a clutch. Quote Link to comment Share on other sites More sharing options...
rweddy Posted September 28, 2004 Share Posted September 28, 2004 I would tend to think it takes a lot to overwhelm a VC. I really wasn't pushing the limit here. I would hope that the sube could do better than that. What do you think of my clutch theory. If a VC does overheat what would it smell like? What I smelled was definitely a clutch. It does not take much to overpower the VC or a Limit Slip Diff. It is just fluid. I am sure if you had it on a steep angle you are not geared for such a climb so you might have smoked the clutch a bit, but this has nothing to do with the fact that only one wheel will spin on a AWD vehicle without a Locking Center Diff. Quote Link to comment Share on other sites More sharing options...
powderhound Posted September 28, 2004 Share Posted September 28, 2004 I would suspect the VC is on the way out and not the clutch or a combo. I to like to spin the tires on our gravel driveway...hey its the only chance we get. Anyway I can barely lay four patches with my 98 whereas the 01 OBW will go crazy fishtailing and all. Quote Link to comment Share on other sites More sharing options...
cannonball Posted September 28, 2004 Author Share Posted September 28, 2004 It does not take much to overpower the VC or a Limit Slip Diff. It is just fluid. but this has nothing to do with the fact that only one wheel will spin on a AWD vehicle without a Locking Center Diff. I don't disagree with this statement. I just need to go back to the same spot and try it again. I'm curious to see if at least one of the rear wheels was spinning as well. If so then I will know that the pitch was to much for the AWD system. If not then I may have a more serious problem or as in the header I pushed the limit. Oh well. Thanx for the replies. Quote Link to comment Share on other sites More sharing options...
ron917 Posted September 28, 2004 Share Posted September 28, 2004 <stuff deleted> My crappy old toyota tercel with a center diff lock would run circles around our outback with the computer controlled clutch pack. In 12"+ of snow the computer doesn't know what to do, so it cycles power front to rear constantly. I wish subes had a TC with some options for power transmission, like FWD, AWD via VC, 4H (locked) and 4L. It would be cool if they sold a version of the 4EAT with the VC as well. As I understand it, if power is removed from the the solenoid that controls the clutch pack, it will lock in 50/50 mode. Should be a simple matter of splicing a switch in the appropriate wire.... Hmmm..... Still no 4L, but you would have a locked center. A manual locker for the rear would be nice, too...anyone know if one is available for Subies? (I don't have a rear LSD). Quote Link to comment Share on other sites More sharing options...
friendly_jacek Posted September 28, 2004 Share Posted September 28, 2004 As I understand it, if power is removed from the the solenoid that controls the clutch pack, it will lock in 50/50 mode. Should be a simple matter of splicing a switch in the appropriate wire.... Hmmm..... Still no 4L, but you would have a locked center. A manual locker for the rear would be nice, too...anyone know if one is available for Subies? (I don't have a rear LSD). I thought that 1st gear selection on AT gave you fixed 50/50 split. I use it when I pull my boat in my backyard (moderade grade and slippery wet grass). If I forget to use "1", and start in "D" or "3", the front wheels spin before the computer tranfers the power to rear. I presume same would happen in snow/ice. People on various other forums confirmed this feature in 4EAT, but it is not mentioned in the manual for the car. Have no idea why not. Quote Link to comment Share on other sites More sharing options...
cannonball Posted September 28, 2004 Author Share Posted September 28, 2004 I would suspect the VC is on the way out and not the clutch or a combo. I to like to spin the tires on our gravel driveway...hey its the only chance we get. Anyway I can barely lay four patches with my 98 whereas the 01 OBW will go crazy fishtailing and all. Dear allah I hope it's not the VC. When I was playing on the gravel road trying to spin out, and the car decided to go nowhere it resembled the clutch going because the front tires weren't spinning either. The rpm's were just revving way high. As soon as I let off and resumed normal driving habits it seemed to be fine. I don't notice slippage from day to day use. I still however have the infamous clutch judder from time to time. Makes me wonder if the clutch is very sensitive to heat build up, and if it's late in its life then maybe this scenario can happen. JOT Quote Link to comment Share on other sites More sharing options...
99obw Posted September 28, 2004 Share Posted September 28, 2004 I thought that 1st gear selection on AT gave you fixed 50/50 split. I use it when I pull my boat in my backyard (moderade grade and slippery wet grass). If I forget to use "1", and start in "D" or "3", the front wheels spin before the computer tranfers the power to rear. I presume same would happen in snow/ice. People on various other forums confirmed this feature in 4EAT, but it is not mentioned in the manual for the car. Have no idea why not. Who wants to drive around in 1st gear, even if there is a foot of snow. Quote Link to comment Share on other sites More sharing options...
Setright Posted September 28, 2004 Share Posted September 28, 2004 Erm, the VC will take some punishment to "overwhelm". For sure it would be easier to spin the rear wheels, on gravel remember, than to trash the VC. VC overload is more likely on a two-wheel brake test stand. Quote Link to comment Share on other sites More sharing options...
dashton Posted September 28, 2004 Share Posted September 28, 2004 Just wanted to add my two cents here. I have a '90 legacy w/ auto trans where the AWD has been broken since I bought it. Something's wrong with the electrical connections to the tranny, and the computer won't lock up the rear wheels. So I spliced a switch in to force the transfer case to lock it up. It works great - with the switch connected I have front wheel drive, and disconnected it's four wheel drive. And yes, it does lock up the transfer case. I will only get stuck if one front wheel and one rear wheel lose traction at the same time. And by the way - it's a blast offroad and in the snow. Always locked up and goes like crazy. Dave Quote Link to comment Share on other sites More sharing options...
WoodsWagon Posted September 30, 2004 Share Posted September 30, 2004 EJ manual transmissions have a viscous center differential. The more it slips (wheels spinning), the hotter the fluid gets and the thicker it becomes. Saying its overloaded w/ the origional wheels is bs. Most failures of the V/C in the subies are from towing w/ the front wheels locked and result in the fluid being burned and fusing the diff together. I've tested the offroad abilities of this system. The fronts will slip w/ the backs, usually diagonaly, or nobody will slip at all. In mud it will spin all four. My car doesn't have a rear lsd, but if it did, it would have to have all 3 spinning to stop the car. He has a burnt clutch, he's confessed it multiple times. Its not the V/C. I have limited knowledge of the automatic clutch pack, but it sounds like a stupid system. Subaru should have just used the V/C on all their trannies. The statement that only one wheel will spin even if the car is AWD is untrue for the subarus. In an old RX or GL-10, this would be true, hence they were labled "full time 4wd". They had a vacuum operated locking center differential for the tough stuff. The AWD SUBARU cars all have some sort of limited slip devise in the middle differential. This claim cannot be made for all other manufacturers, some of whom masquerade full time 4wd cars as AWD. Quote Link to comment Share on other sites More sharing options...
wrxsubaru Posted September 30, 2004 Share Posted September 30, 2004 I have to aggre the VC is not being over whelemed it needs more wheel spin to cause the VC to heat up enough to thicken up enough to spin the rear tires, along with the front. When i was really offroading a 1st gen legacy 5spd AWD it would spin 1 front 1 rear, it takes some time for the center diff to really harden up. The center diff was strong enough to back the car out up a 20 deggre hill, while 1 tire was in the air so its not weak, it just takes 1sec or 2 to heat up. The center diff never went out either and this car was abused before i got it, and it already had 220,000 miles on it. Driving a car with a VC diffs requires a diffrent dring style to use them you need to either spin your tires fairly fastly or not at all. Driving a auto sube is complety diffrent than a manule, it acts like a regualr locked center diff, which i prefer to the VC diff. Quote Link to comment Share on other sites More sharing options...
rweddy Posted October 1, 2004 Share Posted October 1, 2004 EJ manual transmissions have a viscous center differential. The more it slips (wheels spinning), the hotter the fluid gets and the thicker it becomes. Saying its overloaded w/ the origional wheels is bs. Most failures of the V/C in the subies are from towing w/ the front wheels locked and result in the fluid being burned and fusing the diff together. I've tested the offroad abilities of this system. The fronts will slip w/ the backs, usually diagonaly, or nobody will slip at all. In mud it will spin all four. My car doesn't have a rear lsd, but if it did, it would have to have all 3 spinning to stop the car. He has a burnt clutch, he's confessed it multiple times. Its not the V/C. I have limited knowledge of the automatic clutch pack, but it sounds like a stupid system. Subaru should have just used the V/C on all their trannies. The statement that only one wheel will spin even if the car is AWD is untrue for the subarus. In an old RX or GL-10, this would be true, hence they were labled "full time 4wd". They had a vacuum operated locking center differential for the tough stuff. The AWD SUBARU cars all have some sort of limited slip devise in the middle differential. This claim cannot be made for all other manufacturers, some of whom masquerade full time 4wd cars as AWD.I have a lot of experience off-roading vehicles. Jeeps, Landcruiser, etc. AWD vehicles are not made for this use. It is not a failure of the VC is is the way it works period. You will not be able to get three wheels spinning on a Subaru in a off-road situation. You live where it snows. Get your AWD subaru High centered and only one wheel front left or right will spin. Without a center diff lock this is a matter of physics. Quote Link to comment Share on other sites More sharing options...
Setright Posted October 1, 2004 Share Posted October 1, 2004 The oil doesn't thicken, it expands. It gets "thinner" as it heats up. The VC will see to it that BOTH ends of the car get drive. Open diffs on both ends, mean that it only takes one wheel at either end, simultaneously to lose traction. That will see TWO wheels spinning away the torque. How on earth could one wheel spin it all away? Quote Link to comment Share on other sites More sharing options...
rweddy Posted October 1, 2004 Share Posted October 1, 2004 The oil doesn't thicken, it expands. It gets "thinner" as it heats up. The VC will see to it that BOTH ends of the car get drive. Open diffs on both ends, mean that it only takes one wheel at either end, simultaneously to lose traction. That will see TWO wheels spinning away the torque. How on earth could one wheel spin it all away? Since there is not locking mechanism in the VC it will become over powered. IE only one tire will spin. AWD is great for on road conditions but if you get high centered or try very steep dirt roads you have one wheel drive. When it snows a good amount next time in Colorado I will high center my car and take a video so show this. Quote Link to comment Share on other sites More sharing options...
cannonball Posted October 1, 2004 Author Share Posted October 1, 2004 Since there is not locking mechanism in the VC it will become over powered. IE only one tire will spin. AWD is great for on road conditions but if you get high centered or try very steep dirt roads you have one wheel drive. When it snows a good amount next time in Colorado I will high center my car and take a video so show this. Excuse my ignorance, but what do you mean by high centered? Charles Quote Link to comment Share on other sites More sharing options...
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