Danger in driving w/no driveshaft on AWD car?

[idosubaru]

what guinnea pig is needed? one with a failed diff or good diff? you're looking for someone with a good trans to disconnect the shaft and see what happens? interesting.....if i get a wild hair i'll try it.

 

(see all the people who made switches to force it on or off).

all? how about everyone that has used it properly is running fine...and some of us did it many years before anyone here even talked about it. there's no need to spread incorrect information or bring up the same thing that's been addressed over and over again in other threads.

[jamal]

all? how about everyone that has used it properly is running fine...and some of us did it many years before anyone here even talked about it. there's no need to spread incorrect information or bring up the same thing that's been addressed over and over again in other threads.

 

Oh, okay sorry, I edited it to say "some"

 

Anyway, more than one person has ruined a center diff/duty c with the switch.

[dave833]

Oh Boy! I can't wait...

 

I picked up a used 5 spd transaxle from a '96 Leg AWD today for when THAT happens.

 

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:

 

 

 

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.

[86BRATMAN]

I've seen it recommended here for somebody wanting to have a rwd wagon that they disceonect the front axles and fuse the vccd by overheating it. Why then wouldn't this work for the fwd route as well.

 

He's having torque bind. Ya know binding like a 4wd would in turns and such. This implies that the fried vccd HAS NOT turned into a open diff. But rather more like a welded diff.

 

You'll be fine as long as you want to drive the car like this IMHO.

[Skip]

Ill take this all

 

as

 

the link Nipper provided is not correct

 

or

 

my ill. has everyone corn-fused

 

or

 

is incorrect??

[jamal]

No, the link nipper posted was correct.

 

basically it has a regular center differential which distribute torque to front and rear under normal condition, an additional Viscous Coupling Differential Lock provides anti-slip function when needed.

 

But what people seem to be missing is the part that says "a regular center differential which distributes torque to the front and rear."

 

The viscous coupling acts to limit slip. So what you have is a VLSD transferring power front and rear.

 

The driven shaft (what the output/driven gears are connected to) does not directly drive the front differential, as nipper posted. It drives the center differential. The drive pinion shaft, as it's called, which goes to the front ring gear, is inside the driven shaft, and is connected to the front output of the center diff. The rear output goes through a transfer gear and then to the rear wheels.

[idosubaru]

seems like running a VLSD in 2WD would be bad news. running one that has failed (binding) sholudn't matter...like i said, i know someone running one like this right now. what exactly are we after/discussing?

 

Anyway, more than one person has ruined a center diff/duty c with the switch.

now that i agree with, the person ruins the solenoid, not the switch. the one failure we have documented from a reliable source admits he left it on...on the highway. i think i heard of another, but he was also offroading and abusing the vehicle, don't think that's considered normal either. so still no documented, reliable sources of failure due to the switch.

[Andyjo]

now that i agree with, the person ruins the solenoid, not the switch. the one failure we have documented from a reliable source admits he left it on...on the highway. i think i heard of another, but he was also offroading and abusing the vehicle, don't think that's considered normal either. so still no documented, reliable sources of failure due to the switch.

 

actually i think that was me in both cases :cool:

but yeah, my switch actually bridged, and locked it up... towing a trailer on the highway. and it may have been abused offroad.. .alot.

after i fried my awd :-\ i pulled the switch, and checked the resistance in both the on and off positions, got the same thing, so.. switch was fried.

now, i'm sure if you used a better switch that i did (we just used something we found in the barn), say something that could handle up to 20-50amps, then you'd be all set, or even use a relay... which would have been the smart thing to do but... then again i was young and stupid.. and have my te 4eat taken apart in my shop now

[Skip]

[jamal]

 

That is not a Subaru center diff/viscous coupling.

 

The VC is not off the back, only providing rear assist when the fronts spin.

 

If that were the case, it would have to lock it up before the car could even move, because initally the rear output would just spin.

 

The subaru unit is one combined part that will allow either the front or rear to spin faster to "lock up" the VC.

[Gloyale]

i pulled the switch, and checked the resistance in both the on and off positions, got the same thing, so.. switch was fried.

now, i'm sure if you used a better switch that i did (we just used something we found in the barn), say something that could handle up to 20-50amps

 

I used a 30 amp rated switch. But I wired in a 10 amp fuse into the line so I would think the fuse to go first. I also set up opposing male/femaleconnectors in an easily accessable place so that if the switch fries open I can easily eliminate the switch, returning it to stock operation.

 

I used it a whole bunch in the snow crossing the country on I-94 last year. No problems, no blown fse or switch. I actually measured the load of the circuit and got only about 3 amps. It may use more under heavy load?

[Skip]

Quote the Skip

" the link Nipper provided is not correct"

 

Quote the Jamal

"No, the link nipper posted was correct."

 

Quote the Jamal

"That is not a Subaru center diff/viscous coupling."

 

Now sayth the Skip once again as it is the link

Nipper posted

" my ill. has everyone corn-fused"

 

 

 

 

 

 

 

 

 

 

 

My brain is decidedly lame but I thought (operative word)

this is a post/thread on the

manual AWD tranny

(read - 5 speed - ya know the kind with a clutch pedal? )

 

not the 4EAT AWD tranny.

 

 

But hellfire I am gittin' way to old for all this thnkin' stuff!!

[nipper]

i just dropped SOA an email. They are usually pretty good about answering our geeky questions, so lets see what happens.

 

nipper

[Skip]

Thanks Nipper, lets hope they shed some light in the

form of ill. of the diff

 

I do not need rhetoric that tells us this and that

with no more than obscure concepts that

expect us to understand their meaning.

 

I.E.

The subaru unit is one combined part that will allow either the front or rear to spin faster to "lock up" the VC.

 

The viscous coupling acts to limit slip. So what you have is a VLSD transferring power front and rear.

 

The driven shaft (what the output/driven gears are connected to) does not directly drive the front differential, as nipper posted. It drives the center differential. The drive pinion shaft, as it's called, which goes to the front ring gear, is inside the driven shaft, and is connected to the front output of the center diff. The rear output goes through a transfer gear and then to the rear wheels.

 

 

 

I am sorry, as I used all of these definitions to come up with the ill.

 

Now Jamal says they are not correct ???

 

Please Jamal, your understanding of this system is far

superior than most of us here.

We (I) need to see what's in your mind's eye.

 

I beg of you to show what you are talking about.

My appreciation will be apparent.

[Andyjo]

sorry i brought up the 4eat

i still love you guys though :-p

ok... back to breaking the new car...

[jamal]

Skip, the error in your illustration is where the viscous coupling is hanging off the back of the center differential. The VC is actually inside the center differential, between the front and rear driveshafts.

 

Picture time.

 

From the motor, power goes through the clutch to the the main shaft, which has all the drive gears. The drive gears are meshed with the driven gears, which are on the driven shaft, which is hollow.

 

Here is the transmission:

 

 

The main shaft, which is connected to the clutch, is blue. The driven shaft is yellow and the front diff is green.

 

Here is the driven shaft:

 

 

The part highlighted in red is the drive pinion. It is inside the driven shaft. Here is an exploded view:

 

 

Once again the red part is the drive pinion. The little part highlighted in yellow is where the driven shaft connects to the center differential. All those other things are the driven gears, dogs, collars, and syncros, etc. Here is the center differential:

 

 

The red is where the drive pinion connect to the differential. The yellow is where the driven shaft connects to the center differential. The viscous coupling is purple. As you can see, it's part of the center diff and is connected to both the front and rear output. The red part labeled "10" connects to the rear transfer drive gear.

 

Here is the transfer case:

 

 

Yellow, once again, is where the driven shaft connects. Blue are the transfer gears to send power to the rear. Red is where the transfer driven shaft connects to the center differential (item 10 in the previous picture).

 

How does this all work?

 

Power goes from the clutch to the main shaft, through the selected gear to the driven shaft which turns the center diff. From there it is split to the front diff and through the transfer gear to the rear diff. When there is a speed difference between the front and rear, the viscous coupling heats up and tries to speed up the slower moving end.

 

Now, the viscous coupling is not supposed to be able to transfer all of the power to one end. The stock unit is rated at 4 kg-m/100rpm. What that means is that for a 100 rpm speed difference in the coupling, it will provide 4 kg-m, or about 28 lb-ft, of resistance. However, this relationship is not linear (one of the downsides to a vc), and there is a limit to how much power can actually be transferred. 200 rpm difference does not mean 56 lb-ft is transferred. How much the vc can actually lock up, I'm not sure. For all I know it's proprietary information that Subaru doesn't release. What I can say is that it is much less than the full power of a car. Some guy on nasioc jacked up the rear of a WRX, put a 2x4 on the ground in front of the front wheels, and put the car in gear. The car was unable to pull itself over the wood by the front wheels and the rears just sat there spinning in the air, even after revving it to over 4k rpm.

 

Subaru does, however, make stronger center viscous couplings, in 10, 12, and 20 kg-m/100rpm varieties. Everything I have heard about the 20 is that you should not use it driving around on the street, and that it will bind up and cause hopping etc as if the 4wd was engaged in a truck. Seems to be good in rally cars, though.

 

Now, in Dan's case, the VC has somehow bound up and is fused together. Can he rely on this to get him around? I'd say no, and I guess that answers the original question.

[Skip]

Jamal,

Many many thanks for the time and

the most excellent explanation.

 

I now see the link Nip provided was just for basic reference.

 

Very well done and I agree with your speculation that

Subaru holds some of their cards close to their vest.

 

Also very interesting the 2x4 test.

 

I have a 2.5 RS 5 speed. I may try and dupilcate

his findings.

 

Once again thank you.

[jamal]

Well, it would be easy enough to plot some points to get an idea of the torque/rpm curve for the vc, especially if you had a really big torque wrench. MRT sticks them on a lathe, attaches a torque wrench to the other end, and turns it at 100 rpm to measure the resistance. Finding the upper limit might be difficult, though.

 

And you're welcome, but if I didn't want to do this I wouldn't post.

[Gloyale]

Some guy on nasioc jacked up the rear of a WRX, put a 2x4 on the ground in front of the front wheels, and put the car in gear. The car was unable to pull itself over the wood by the front wheels and the rears just sat there spinning in the air, even after revving it to over 4k rpm.

 

 

Wow, This is another reason why I like the 4EAT. I just tried this and was able to go over like nothin in my 93 Legacy with 4eat. no slip or nothin.

[jamal]

yeah, the older 4eat cars are front biased. Unless the fronts slip or the tcu has reason to send more power rearward with a clutch pack, you basically have a fwd car. I would still prefer to have a 5-speed with a stronger center diff (well, after the dccd sti), because it operates at 50:50 during normal driving.

 

The new automatics with VTD are much better, have a rear bias, and can transfer much more power to the front or rear. Instead of a clutch pack that just sends some power to the rear or a VC, they have a planetary gearset in a system similar to the STi. The sti uses clutches in the center differential instead of a viscous coupling, and a computer that takes inputs from a lot of sensors to determine how much the center diff should lock. It also provides even more rear bias, and has way better front and rear differentials.

 

I guess I'll try to dig up a newer service manual to learn more about vtd one of these days.

[nipper]

SOA says hi.

 

They will have more informtaion for us later, as they have to go wake somone up on a friday to do it :-p

 

 

nipper

[Gloyale]

double post, see below

[Gloyale]

Tried it with the front jacked up and a board in front of the rear and it worked fine too. I think it was only the really early 4eats(*fulltime*xt6, GL/Loyale turbos) that where so heavily front biased. My Legacy seems to be pretty solidly 50/50. No slip required before the rears get power. And with a C solenoid switch you can make it a full locked diff(Clutch pack). But again, I haven't found a need to install a switch in my legacy. My 89 GL turbo needed it to handle deep snow however.

[jomo12]

I hate to start a new thread on my first day so I thought I'd jump in here. I read through this and I'm in a similar situation as Dave. i bought a 2002 Legacy wagon, 5-speed last weekend, and right after I drove it off the lot for about ten miles, the problem starts.

 

You can hear a low (not too loud) howl, like gear whine, that goes as vehicle speed, and then this binding phenomenon at low speed and turning, right or left, forwards or backwards. Sounds exactly like the problem that is described as viscous coupling failure. This car has been to a subaru dealer, and they drove the vehicle and put it on the lift. They describe it like this:

 

"found noise coming from rear of the transmission, noise is coming from transfer case and extention, will have to remove rear part of the transmission to determine what we have to replace. explained that the transmission may need replaced if it cannot be rebuilt"

 

Basically, the service advisor told me that it's the transmission, not just the diff. And, it's a $5500 transmission (!). Is this crazy? Could that whole transmission be bad?

[nipper]

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