snow+donuts+low speed+high rpm= fun+stinky cabin..why??

[xt2005bonbon]

Is your car equiped with VDCS? (Vehicle Dynamic Control System)

 

^ no VDCS. no special button nothing. Just plain old subbie AWD.

[Power6]

Great topic. I too have noticed the clutch smell. In more than one AWD car. Not just doing donuts in the snow, but getting my WRX up a steep unplowed driveway as well. Whether VDC is off or on didn't matter. I got out once and smelled near the brakes, I am pretty sure it wasn't the VDC heating them up, the same experience with the VDC off.

 

I first noticed this years ago doing snow drifts in a huge parking lot in a friend's Eagle Talon TSi, and AWD car with a similar center and rear VLSD setup to a Subaru. Then again in that same friend's '05 LGT, and my own '09 WRX.

 

I have to say I did a ton of drifting in snow back in the day in my Mom's Audi 90 Quattro, and I never had the clutch smell. That car had a center Torsen and a vacuum locker rear so the setup was quite different, this might be a clue to what is going on.

 

First to the clutch naysayers...I think you have to open your mind. I have owned a car that burns damn near everything at one point. I have broken motors, transmissions, fried brakes etc. I know clutch/brake overheating when I smell it. Viscous units are sealed so we can't smell them, and we should all know what diff lube or tranny oil smells like, nothing like clutch, even if we could heat them up to flash point doing donuts in the snow. I know it goes against what you might think about the clutch and how it should operate in the snow, I always thought so too, that is why it has been a mystery to me for years.

 

I have learned, since a big part of my job as a computer systems engineer is troubleshooting big complex systems, that sometimes a really tough mystery, you have to throw out your notions if how it "should" work, otherwise you will never be able to figure it out. Seeming illogical is what makes something a mystery in the first place

 

I do have a couple theories:

 

1.) when you are on snow, you can't really judge the engagement of the clutch vs. wheelspin. It might be possible that you tend to slip the clutch upon take off, thinking you are regulating the speed of the slipping wheels when you are really just slipping the clutch.

 

2.)I have a theory based on the absence of this problem in a Torsen equipped Audi, which does not require wheel speed difference to transfer torque. That means as you let the clutch out, the biasing is already happening, even as you spin the tires. With the Subaru viscous, you are actually spinning one set of wheels, and the other axles are only moving as fast as the car is. As the speed difference transfers torque, you have to spin up the drivetrain at the other end of the car. Suddenly spinning it up might cause the clutch to slip a litle. Viscous diffs tend to do this repeatedly in very slippery conditions, which might be tough on the clutch.

 

Perhaps it is a combination of the two, or some different interaction that we are all not quite understanding yet.

 

One thing is clear, the 50% who say clutch say that because we know just what it smells like, the rest of you may be clouded by your belief that it can't be the clutch, enough to doubt your nose ;-)

[mwiener2]

A clutch is rated at, lets say, 300 ft lbs. In first gear, with a 200hp engine, you can get well over 800ft lbs of torque at the wheels due to the mechanical advantage of the gears. That means you would need over 1200 ft lbs of torque resisting the spinning of the tires to make the clutch slip. If even one wheel slips, a significant portion of the torque is lost, relieving the stress on the clutch.

 

IT"S NOT THE CLUTCH!!!!

[thestratomaster]

 

I have learned, since a big part of my job as a computer systems engineer is troubleshooting big complex systems, that sometimes a really tough mystery, you have to throw out your notions if how it "should" work, otherwise you will never be able to figure it out. Seeming illogical is what makes something a mystery in the first place

 

I do have a couple theories:

 

1.) when you are on snow, you can't really judge the engagement of the clutch vs. wheelspin. It might be possible that you tend to slip the clutch upon take off, thinking you are regulating the speed of the slipping wheels when you are really just slipping the clutch.

 

2.)I have a theory based on the absence of this problem in a Torsen equipped Audi, which does not require wheel speed difference to transfer torque. That means as you let the clutch out, the biasing is already happening, even as you spin the tires. With the Subaru viscous, you are actually spinning one set of wheels, and the other axles are only moving as fast as the car is. As the speed difference transfers torque, you have to spin up the drivetrain at the other end of the car. Suddenly spinning it up might cause the clutch to slip a litle. Viscous diffs tend to do this repeatedly in very slippery conditions, which might be tough on the clutch.

 

Perhaps it is a combination of the two, or some different interaction that we are all not quite understanding yet.

 

One thing is clear, the 50% who say clutch say that because we know just what it smells like, the rest of you may be clouded by your belief that it can't be the clutch, enough to doubt your nose ;-)

 

he does have a valid point. i can almost guarantee i slip the clutch when doing long drifts, not donuts, but long drifts, which is mainly when I get the smell. Diffs are still my first choice, but I think some of the scent could be me slipping the clutch

[Dutch Eagle]

He has the best point.

 

The winning point actually.

 

 

1.) when you are on snow, you can't really judge the engagement of the clutch vs. wheelspin. It might be possible that you tend to slip the clutch upon take off, thinking you are regulating the speed of the slipping wheels when you are really just slipping the clutch.

It's hard to say whát is actually slipping in the beginning when you try to create wheelspin. The feeling is almost simmilar, have in mind you are not driving fast and the rev's go up all time without getting speed when slipping the tyres on snow/ice.

The rev's going up on snow/ice, often without gaining speed is a familair feeling, and therefor very easely mistaken with clutch-slip.

 

 

@'mwiener2': 800ft lbs is the holding capacity, but this figure only counts once the clutch is sticking to the flywheel.

Before it grabbes the flywheel, in the first 'grey area' it is very easy to let it slip and keep letting it slip.

(Even with the handbrake pulled a little, one can create continues slip in first gear very easely, standing still.)

When you put your pedal to the metal, and try to let your clutch grab the flywheel, it is VERY easy to let it slip like hell if you do it to carefull, even on snow.

 

Cause you are not hanging out of the car looking at the wheels, you cannot allways tell what is slipping on a slippery surface.

 

 

And as someone allready said, diff's are sealed and don't smell.

If they would be open however, the smell would be very strange and very different from clutch burn.

 

 

It's your clutch 100%.

 

I tried yesterday having some driftingfun on snow, cause I was convinced of my VDCS story. No smelling brakes however.

What I did smell a few times was the clutch, definitely.

[mwiener2]

The LSD part of the diff is sealed.... by an o-ring. If you get it hot enough, it will blow past that seal. The rest of the diff is not sealed. You can smell your diffs getting hot. Now I'm not saying getting it hot will blow the seals and kill the diff. If you get it hot enough, some vapor will make it's way past and that's what you smell, but your diff is not dead.

 

Now if the driver is slipping the clutch, then yeah, that can cause a stink. But if you are clutch out in snow, it's nearly impossible to make the clutch slip on its own.

 

 

 

The breathers on the diffs seep oil onto the case. It smells like ass when it gets hot. That is mostly what people smell.

 

 

 

But can it also come from the clutch? If so, why since the latter is indeed engaged? Is it because that sucker is slipping even though it is engaged? That'd mean that the engine is too strong for it??

 

This was the original question, and the answer is no, it's not the clutch.

[kaz98gt]

For starting off though from a dead stop, you can only slip the clutch so much, right? And it's not like you're going to be starting alot of times when you're doing donuts; usually when I go, I keep my speed up/rpms up (even though mine's an auto), and hardly ever stop except to see videos from my friends watching.

 

And yet...I could still see the clutch cooking just a little bit if you're not careful with the launches. But this still brings me back to my point: why do I get the "post donut smell" and I'm a 4EAT? It's acrid, burning, clutch-like smell, but no clutch. Can we get a 5EAT guy to chime in who has done some donuts? And how similar are these two smells? Maybe we're muddling them; anyone cook their diffs before and know that smell? And how does it compare to clutch cooking?

[thestratomaster]

 

The breathers on the diffs seep oil onto the case. It smells like ass when it gets hot. That is mostly what people smell.

 

 

 

 

 

This was the original question, and the answer is no, it's not the clutch.

 

i think we've all been saying the same thing here hah. the clutch is almost impossible to slip when engaged on snow. If you're coming from a stand still to get into a donut or drift, it is very likely you slip your clutch. It is possible for the diffs to smell, but likely it's the clutch burning from slipping on take off that is the majority of the smell that lingers

[mwiener2]

but likely it's the clutch burning from slipping on take off that is the majority of the smell that lingers

 

No, it's not. Go launch your car hard on dry pavement, if you slip the clutch too much you'll get stink. Now go do the same launch on snow... wait you can't, or you'll just spin the tires and not go anywhere. Due to the limited traction, the clutch is under less load. It becomes harder, not easier to slip the clutch. Because of the limited traction, the wheels could spin in the snow when the clutch is only 75% engaged.

 

The clutch will still slip when being engaged/disengaged, but because of the limited traction at the wheels, it doesn't generate the heat it would on pavement.

 

So unless the driver is doing the slipping, and it's excessive, it's not the clutch.

 

 

 

Also, as kaz98gt pointed out, Auto Tranny's get the same stink

[thestratomaster]

^^i literally just did it two nights ago...you still get the smell when launching on snow. if the rpms are up high and your disengaging the clutch, you get the clutch burning smell. it doesn't matter what the road condition is.

[mwiener2]

then you are slipping your clutch too much and that is driver error

[thestratomaster]

yeah...we've been over this i thought. the original posters question asked if it slips when it is engaged, answer: no it does not. can the smell be coming from the clutch, absolutely, if you are slipping it

[Power6]

The LSD part of the diff is sealed.... by an o-ring. If you get it hot enough, it will blow past that seal. The breathers on the diffs seep oil onto the case. It smells like ass when it gets hot. That is mostly what people smell.

 

This was the original question, and the answer is no, it's not the clutch.

 

Not feeling you yet mwiener, but great discussion. I am still coming from the point that those of us that have experience with donuts and other sort of extreme wheelspin events smell clutch. I am not saying it makes any sense at all, just that my nose is well calibrated.

 

But on the other hand, why would viscous fluid smell?? As it heats up the viscosity goes up, the LSD starts to "hump" and turn as one unit, not sure what the flash point of the fluid is or if it would ever get there. And what is the chance that it would smell just like burning clutch material? Those of us with some experience know gear oil and the rear diff fluid don't smell like that when burned.

 

The leap of logic you make is just as hard to swallow.I'm sticking with clutch, I just haven't figured out the WHY yet.

 

Also, as kaz98gt pointed out, Auto Tranny's get the same stink

 

Hmm this may be the one that proves you are right! If we could get some others to confirm, it would eliminate the clutch theory in my mind...

[thestratomaster]

k, so literally just got back from about an hours worth of drifting and donuts. I made a conscious effort to stay off the clutch in every situation. no smell at all. putting my money on user error causing clutch slippage

[kaz98gt]

k, so literally just got back from about an hours worth of drifting and donuts. I made a conscious effort to stay off the clutch in every situation. no smell at all. putting my money on user error causing clutch slippage

 

 

Ok, so some good progress is made! Any more test subjects? If I pick up a standard legacy, I'll try this out and see if I can't find out anything more.

[mwiener2]

I've had my car for 5 or 6 winters. I get the smell and I know it's not my clutch slipping. I've driven for hours on snow covered roads under normal driving with the clutch engaged with my foot on the dead pedal, and would occasionally get the smell. Under certain conditions, the awd system gets really hot and makes a stink. Stupid human tricks force those conditions.

[Dutch Eagle]

^^i literally just did it two nights ago...you still get the smell when launching on snow. if the rpms are up high and your disengaging the clutch, you get the clutch burning smell. it doesn't matter what the road condition is.

so literally just got back from about an hours worth of drifting and donuts. I made a conscious effort to stay off the clutch in every situation. no smell at all. putting my money on user error causing clutch slippage

See?

 

For the last time, it is the clutch.

 

NOT a diff.

 

then you are slipping your clutch too much and that is driver error

Error or not, this is what I and 'power6' say what is happening in practice.

On snow 'clucthfeeling' versus 'tyrefeeling' is somtimes very alike.

Don't forget you are used to dry tarmac most of the time.

 

Some people here seem to forget what is actually happening in practice when you let the clutchplate grab the flywheel.

What is 'clutch feeling'?

Why drive away with some amount of slip, or for instance a clutchdump?

Where is the feeling based upon?

 

The 'clutch feeling' (The way you let the cluchtplate grab the flywheel) is the feeling that is produced between engine and wheels.

When the wheels have good grip, your left foot can feel exactly what's happening between plate and flywheel (or engine and wheels if you like.)

When the wheels loose allmost all of there grip and spin very easy, the feedback from the wheels you get on your left foot is very much gone.

In other words, your left foot is allmost completely in the dark, compared to what it is used to feel in dry conditions.

When of course you rev up high too, it is no surprise you'll slip the clutch even more easy.

Engaging or dis-engaging your clutch, same thing.

 

More slip than usual cause of the lack of feedback from the wheels, and thus clutch smell in the cabin

 

There it is.

 

 

 

Call it driver error, in practice it is a very common fenomenon on snow, and the reason you smell your slipping cluctchplate revving high.

 

 

Only with very grippy snowtires, or better, spiked ice tyres it is very feelable what is happening, and clutchslip can be easely avoided on snow and ice.

[mwiener2]

 

 

Also, as kaz98gt pointed out, Auto Tranny's get the same stink

 

so get your 'fenomenon' outta here

[Max Capacity]

Can't believe you guy's are still talking about this.

 

Get over it.

[kaz98gt]

^^ This.

 

Look, I'll go do donuts when I get home. I'll see if I can't smell the clutch-type smell. If not, it's whatever. We've already got a few people testing with clutch-related results. Donuts are supposed to be good, clean fun, so let's all go do donuts and relax

 

/subscription

[xt2005bonbon]

^^ This.

 

Look, I'll go do donuts when I get home. I'll see if I can't smell the clutch-type smell. If not, it's whatever. We've already got a few people testing with clutch-related results. Donuts are supposed to be good, clean fun, so let's all go do donuts and relax

 

/subscription

 

Hey dude, when you go do some donuts, try to do the following. I think this would be a fair test to run:

1-Engage the clutch before entering "snow playground". Try to do so with minimum slippage (i.e. start with revs as low as possible just before engine starts bogging).

2-Then, once the clutch is engaged, no disengagement for a while if possible.

3-Just maintain high revs.

4-Have a bit of fun.

5-Then, as soon as you get to a full stop or the car gets stuck in the snow, stop driving.

6-Go smell.

 

I'd be interested to hear what you have to say. Once I have a chance, I'll go try.

BTW, where I live, roads are snow covered all the time and icy as well (above arctic circle). Sometimes, it is literally PURE ice (3 inch thick and slick). They never put any salt; they can't keep up. So we always have slippery conditions 24/7. Studded tires are a must up here.

But in any case, no smell while driving on the roads, though I don't drive for very long periods of time. Still, though lots of stop and go traffic but no smell..

[kaz98gt]

Hey dude, when you go do some donuts, try to do the following. I think this would be a fair test to run:

1-Engage the clutch before entering "snow playground". Try to do so with minimum slippage (i.e. start with revs as low as possible just before engine starts bogging).

2-Then, once the clutch is engaged, no disengagement for a while if possible.

3-Just maintain high revs.

4-Have a bit of fun.

5-Then, as soon as you get to a full stop or the car gets stuck in the snow, stop driving.

6-Go smell.

 

I'd be interested to hear what you have to say. Once I have a chance, I'll go try.

BTW, where I live, roads are snow covered all the time and icy as well (above arctic circle). Sometimes, it is literally PURE ice (3 inch thick and slick). They never put any salt; they can't keep up. So we always have slippery conditions 24/7. Studded tires are a must up here.

But in any case, no smell while driving on the roads, though I don't drive for very long periods of time. Still, though lots of stop and go traffic but no smell..

 

 

Keep in mind, I have the 4EAT out of the bunch but, I'll try and get a hold of my dad's audi (5 speed) and see if I can't find the same symptoms that you guys are dealing with. VDC off, TCS off, the works. To be honest, I think the older subaru AWD system ousts his (I think) 4th gen quattro AWD on his '02 A4, but that's just my opinion.

 

Or, I might pick up a standard transmission subie over break if the guy who's looking at mine gives me the right amount of coin for it. Then I can do this test for real!

[Power6]

I've had my car for 5 or 6 winters. I get the smell and I know it's not my clutch slipping. I've driven for hours on snow covered roads under normal driving with the clutch engaged with my foot on the dead pedal, and would occasionally get the smell. Under certain conditions, the awd system gets really hot and makes a stink. Stupid human tricks force those conditions.

 

You must be talking about something different than the rest of us here then. I've never noticed this phenomenon when driving normally on snowy roads. It only occurs after working through deep snow like an unplowed driveway, or parking lot hi-jinks, events where there is lots of wheelspin.

 

You really blew it with the "under certain conditions..." stuff, now we know you don't understand how the system works. I know my AWD system doesn't get "really hot" when I am driving normal with the clutch engaged!

 

I'm not normally the grammar police, but after you correct the spelling of phenomenon, you might want to look up the definition ;-)

[Power6]

Keep in mind, I have the 4EAT out of the bunch but, I'll try and get a hold of my dad's audi (5 speed) and see if I can't find the same symptoms that you guys are dealing with. VDC off, TCS off, the works. To be honest, I think the older subaru AWD system ousts his (I think) 4th gen quattro AWD on his '02 A4, but that's just my opinion.

 

Or, I might pick up a standard transmission subie over break if the guy who's looking at mine gives me the right amount of coin for it. Then I can do this test for real!

 

Hey I thought you didn't care!

 

Just FYI, I mentioned it before, I never did get this behavior in a torsen equipped Audi. It is a slightly different system than the viscous, and I am not sure what that has to do with it.

 

You are saying you cannot reproduce this with your 4EAT or you can?

[thestratomaster]

went out again tonight. only smell i got was tire smell when i hit a pavement patch