Danger in driving w/no driveshaft on AWD car?

[WoodsWagon]

I've done the test with a 1995 legacy, manual tranny. Put the front up on jackstands, put the e-brake on full, and let out the clutch. The engine spun the front wheels without much effort, however, if held at a constant throttle position, it would start to slow the engine, which meant the coupler was heating up and locking down. The viscous coupler has it's limitations.

 

The viscous coupler is only on one of the spider gears because it only needs to be on one. For one output to be spinning faster than the other, the case of the differential, which is what half the plates are attached to, has to be moving at a different speed than the output shaft that the other half of the viscous coupler's plates are attached to.

 

The center differential is no different than your average rear differential in operating principals.

 

 

Some people say that the center diff becomes an open diff when the VC is overheated. However, I disagree with this because the diff always seems to go to torqe bind (which is full locked) after it's been towed with 2 wheels on the ground, driven with an undersized tire, or otherwise abused. If you overheat it to a point, it must either change the composition of the viscous fluid, or warp the plates to the point they bind, much like what happens when you cook the clutch pack in the auto's.

[jomo12]

It can always be the tranny, but hard to tell via the web. The whine is unusual. Whine is usually a hint of something more hidous wrong.

If somone drives with Torque bind (without caring), it is very possible to damage the transmission. Dealers arent big fans of selling transmissions, so i would pay head to what they have to say.

On the bright side, a used one is much cheaper. The whine can be the front diff, or an internal bearing or three. Driving with TB can beat up the bearings, which in turn can destroy the case. Its possible, rare but possible.

 

What condition is the tranny lube and front diff lube in?

nipper

No idea. Right now, this is the problem of the dealer (Chev) I bought it from. They had me take it to a Subaru dealer, who AFAIK checked neither. I moved from Washington state recently where every third person has a Subaru, and I've never heard of this.

 

That whine at speed, again, it sounds exactly like a part-time 4wd vehicle when you run it in 4x4 on a dry road -- you get a little scrubbing because the front and back are locked. It only starts after some incubation period of driving, that's why I'm hoping it's just the differential I hear. Is the front diff contained in the transmission housing too?

 

The Chev dealer is going to bring in another transmission guy tomorrow morning to look at it. The Sub service manager warned me that Subaru transmissions aren't like other transmissions. Huh, I don't know about that.

 

If they decide it's too expensive to repair, they'll may try to buy me out of that car (or really, give me DealerBux for another car on their lot ) I'd really rather have the Legacy since I went looking for it. Although, it sounds like the head gasket is a time bomb waiting to happen...87k and counting.

[86BRATMAN]

Some people say that the center diff becomes an open diff when the VC is overheated. However, I disagree with this because the diff always seems to go to torqe bind (which is full locked) after it's been towed with 2 wheels on the ground, driven with an undersized tire, or otherwise abused. If you overheat it to a point, it must either change the composition of the viscous fluid, or warp the plates to the point they bind, much like what happens when you cook the clutch pack in the auto's.

 

This is my stand piont on the issue at hand as well...

[nipper]

This is my stand piont on the issue at hand as well...

 

When you over heat the VC, the silicon fluid inside it bakes and becomes a glue. i have never seen anyone here say it becomes an open diff when the VC goes bad, but there is always a first time.

 

nipper

[WoodsWagon]

When you over heat the VC, the silicon fluid inside it bakes and becomes a glue. i have never seen anyone here say it becomes an open diff when the VC goes bad, but there is always a first time.

 

nipper

 

http://www.ultimatesubaru.org/forum/showthread.php?t=73996

There's one.

[Skip]

????

Nipper says

"When you over heat the VC, the silicon fluid inside it bakes and becomes a glue. i have never seen anyone here say it becomes an open diff when the VC goes bad"

 

Jamal says

"No that's not how it works. When the viscous coupling overheats, the fluid loses it's ability to resist shear, meaning no power transfer."

 

 

Are these guys both saying the same thing or??

[nipper]

????

Nipper says

"When you over heat the VC, the silicon fluid inside it bakes and becomes a glue. i have never seen anyone here say it becomes an open diff when the VC goes bad"

 

Jamal says

"No that's not how it works. When the viscous coupling overheats, the fluid loses it's ability to resist shear, meaning no power transfer."

 

 

Are these guys both saying the same thing or??

 

This is from a VW synchro site but its the best explination out there as to why they fail.

 

http://syncro.org/VCTest.html

 

nipper

[bulwnkl]

????

Nipper says

"When you over heat the VC, the silicon fluid inside it bakes and becomes a glue. i have never seen anyone here say it becomes an open diff when the VC goes bad"

 

Jamal says

"No that's not how it works. When the viscous coupling overheats, the fluid loses it's ability to resist shear, meaning no power transfer."

 

 

Are these guys both saying the same thing or??

 

 

No, those guys are saying the opposite thing. Jamal's assertion there would indicate that the viscous coupling would fail in a way that the center differential reverts to purely open (i.e. the car would not move and the rear propeller (drive) shaft would just spin). Jamal does say in the thread here that the viscous coupling may be designed such that it will lock up tight and the car will drive.

[jamal]

This is from a VW synchro site but its the best explination out there as to why they fail.

 

http://syncro.org/VCTest.html

 

nipper

 

Cool. My understanding was that when the fluid overheats it loses some ability to resist shear (i.e. lock the diff).

 

Obviously this isn't the case here, but whether it is due to the fluid or the "hump effect" I mentioned earlier I can't say.

 

http://www.ultimatesubaru.org/forum/showthread.php?t=73996

There's one.

 

Well, it is the same person...

Here's an example of a vc not working, though:

http://forums.nasioc.com/forums/showthread.php?t=325909

[idosubaru]

to all the "open" and what not discussion and other comments, there are people driving around in 2WD right now due to a locked/failed torque bind equipped trans. i don't think that's characteristic of an open diff. i don't know the technicalities but i know it works. that may help those with real world problems and would certainly reduce stress on other components once it's "completely failed", whatever that means!

[edoutback]

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.

 

Jamal is correct. I removed the drive shaft to the rear wheels and my Outback will not move easily. The engine makes a lot of effort and after few seconds I can hear weird noises coming from the tranmission/ transaxle area.

 

BTW, I have a 1999 Outback with manual transmission that has been developing torque binding problems lately. I wanted to run the vehicle in FWD to prevent more damage until I am ready to replace the VC.

 

Some people were able to do it without any problems. It seems that this temporary fix may not work in all the Subarus. Any comments?

[jamal]

did you read the whole thread?

[idosubaru]

Any comments?

like ive already mentioned in this thread:

i know a guy with an EJ trans just like yours, with torque bind and he's running it in 2WD (RWD actually).

there are people driving around in 2WD right now due to a locked/failed torque bind equipped trans.

there's not much info out there because not many people do this. so you hear a few stories about people doing it and discussion from those that have never tried. there are people out there doing it right now, i just spoke yesterday with someone i know doing it and all is well, he's running in RWD.

[WoodsWagon]

Jamal is correct. I removed the drive shaft to the rear wheels and my Outback will not move easily. The engine makes a lot of effort and after few seconds I can hear weird noises coming from the tranmission/ transaxle area.

 

BTW, I have a 1999 Outback with manual transmission that has been developing torque binding problems lately. I wanted to run the vehicle in FWD to prevent more damage until I am ready to replace the VC.

 

Some people were able to do it without any problems. It seems that this temporary fix may not work in all the Subarus. Any comments?

 

Your VC hasn't failed completely yet. This makes you a good test case. Leave the driveshaft out, and keep trying to drive it with it out. The wierd noises from the tranny is probably the VC slipping, so push it till it siezes and you should be fine. If it cooks open, then hook the drive shaft back up and you will have AWD again, just only one wheel will spin in low traction.

 

Put it in gear with the shaft out, and lay into that mother! time how long it takes to seize.

[SueB4life]

I have a 1997 outback manual 2.5L DOHC. Recently I was driving and noticed a clunk common to CV joints. It became worse until I was on the HW in cruise control when a wind up noise came from the gear shifter. As soon as I looked down the shifter POPPED up about 1/2in and the car was coasting to a stop. I didnt hear any metal grinding and I reved the RPM before I came to a complete stop to see if there was engine noise (non noticed). The cv joint was broke at the front of the rear drive shaft. I disconnected the drive shaft in the rear hoping to at least move it around by FWD. The car didnt move. I Jacked the front end up and put it in all 5 gears. The tires rotate freely but I can stop them with my hand. It feels as though the gears are not fully engaged. Is there something I am missing?

 

Thanks 

[Fairtax4me]

Because of the way the center diff works in the manual trans, the car has to have the rear driveshaft connected in order for the car to move.

 

Replace the driveshaft and you should be OK.

[wally]

i realize this is an old thread, with lots of confusing information.

 

for a manual transmission, with a working center diff, removing the driveshaft will result in the car not moving, or moving with limited ability, until the center diff heats up enough to lock, and then the car will drive.

 

if, however, the center diff has already failed (and they fail by locking up), a manual transmission car can be driven in fwd with the rear driveshaft removed, with no problems. i drove mine in this condition for 2 years, and never had an instance where the front wheels lacked drive effort/power. i put nearly 50K miles on it in that condition, and only replaced the transmission once it started popping out of gear in 3rd and 5th.