Im asking this as when i floor the pedle when its wet it seems to spin round like a rear wheel drive car. Im new to 4wd but would still expect the front end to have more drive.

Is there a problem ?

 

What model and age mate?

 

Its a wagon import on a 97 automatic.

 

What power mate?

 

standard at 280 i was told.

 

Seems a little odd to me as I have a forester TTB with 260bhp[auto] and it's the fronts that break loose first in the wet??

 

On 4EAT(automatic):

ALL 4EAT transmissions have the 90/10 split under "normal" driving conditions,The MAX distribution you can have with the 4EAT trans is 50/50

Some AUS or JDM models have split 60/40

Under normal conditions as result, the 4EAT has a bit more understeer in corners. Also, on very slippery roads you may feel the rear kick in every-so-often, rather
than being active all the time, which some drivers have described as unsettling

Jura

 

That's the EXACT same problem that i'm suffering from!
I have the 1996 JDM WRX Wagon Automatic (standard 237 bhp with it being the auto, but it's certainly had a bit of playing about done to it)
In the wet with a bit of right foot and the rear end is leary as hell, yet in the dry, i can floor it into and round bends and the car starts to try and move a little but the rest of the car doesn't allow it to.
When in the dry you can sort of feel the power 'move around' to maintain traction, whereas in the wet, a quick pulling out of a junction suddenly turns into donuts in the middle of the road ... LITERALLY!!
I was told that my centre diff has failed, however it's been in the garage this morning to check the center diff oil level and it turns out that i don't even have a centre diff!!!
I have a front transfer box and a rear diff, but no centre diff.
Can anyone help me here or is this normal?

 

The centre diff is integral to the transfer box. It does have one, because if it didn't your transmission would be in shards all over the road.

 

I was told that it sits at the back of the gearbox and there is simply nothing there, unless it's inside the gearbox or inside the transfer box?
I simply have no idea as i'm extremely new to scoobies, hence why i'm here trying to find these things out and learn something about my car.

 

Your centre diff isn't a separate unit. It's housed inside the gearbox at the back of the engine.

Here is how a Suabrus 4WD system looks in general:

You can see that behind the engine there's a big lump of a gearbox. In an automatic Subaru, this houses the torque converter, auto transmission, and the front and centre diffs. It's a bloody complex box:


The section on the left is mated to the engine, and you can see the torque converter in section (32), (30) (looks like a donut cut in half). That puts power back to the auto gearbox which is in itself a fiendishly complex thing. Parts (10)->(17) in the diagram are all the planetary gears and stuff that make an auto box do it's thing. The gearbox then puts power out to a plated clutch in the automatics (towards the right in the diagram)- manuals are different and use a viscous Limited Slip Differential to do this. Apparently they're 90% front wheel drive in 1997 legacys until conditions mean the front loses traction, when they shunt power to the rear but I have no real idea and you could research this yourself to find out what should be going on. The clutch pack - a series of plated clutches - can progressively lock up to allow more torque to the rear as the car senses one axle travelling faster than the other indicating that something somewhere is slipping. Under normal conditions there is a bit of difference in speed allowed, because if it was all run at the same spped you would get "wind up" because the front of the car actually travels further in bends than the rear, for example.

Anyway, that clutch-differential is what decides how much torque gets sent forwards and backwards. On the diagram, (23) is the clutch pack which surrounds the centre differential. The centre differntial is an essential part of any road 4WD system. The front and rear axles MUST be able to rotate at differnt speeds without mechanical damage. THey do it all the time - even a slightly different amount of wear on front and rear tyres can cause diffential speeds between individual wheels, or a mild bend in the road. Looking at the centre diff you can see it has two outputs - one goes along a shaft directly backwards: (21) towards the rear wheels. They have their own differential sat in between them, and that's what that prop shaft turns.
The power to the front wheels is drops down and is sent down and internal prop shaft. You can see it running between (24) and (28) in the diagram. (29) is the front differential itself and drive shafts come out each side of this, outside the gearbox and run to each front wheel. The centre of that circular unit is roughly lined up with the front axle of your car.

As for if there's a problem?

Well, it depnds what you mean by "Spins round like a rWD car".
The transmission on the auto cars is very differnet from the transmission on the Manual cars. The normal Manual WRX layout is an open diff at the front, a viscous locking centre differntial, and a viscous Limited Slip rear differential, but there's even ambiguity as to exactly what is fitted where even though it's one of the most produced AWD systems in the world! There are subtle but important differences to the way a viscous locking diff and a viscous limited slip differential operate as a centre diff, and to this day I can't work out exactly which a normal WRX has. I think it's a viscous locker, but I could well be wrong.

The clutch packs in the centre diff on an auto box are wear items and can fail if the car has been abused or driven in tough conditions. Viscous differentials lose their magic over time, as the in them geats heated and overheated, it transfers less torque and so the differntial becomes more open with time. VIscous differntials actually rely on one wheel spinning before they begin to transfer torque to the non-spinning wheel anyway which is why there are also clutched or "plated" diffs, and mechanical "torsen" (Torque/sensing) differntials to do the job of a limited slip diff.

It's really complex. WIthout more information, and perhaps driving a similar model car to your own, it's impossible to know whether your car is behaving as it should. It will behave very differently to a manual impreza under hard driving in any even, because it's entire transmission is differently set up and arranged, and has different components.

I hope that helps a bit. Perhaps if you can lift your car (safely) or get it on a ramp you can havea poke about underneath it and find all the differnt bits - engine block ,gearbox, prop shafts and rear diff.

 

Wow, that's some reply Dave. My car seems to handle differently to singledad's motor. In the dry pushing as hard as i can, the car sticks to the road with just a slight hint of under-steer. In the wet, traction is very good even with cheap branded tyres. It doesn't slip slide all over. just seems to kick out dropping down from 2nd to 1st and booting it at 30 mph. I may just have to find a decent bit of space and film what the wheels are doing.

 

Many thanks Dave, that is a fantastic reply ... :-)
I understand all of the basics of modern(ish) day motors, it was just the understanding of the 4WD system more than anything ... Oh .. and finding out why i couldn't find the centre diff in the position where I was told it should be ... lol

You say they are wear items, have you any idea of what the costing would be to pay someone to do the repair?
Or would it be cheraper and less hassle to get a reconditioned box fitted?

With regard to how the car reacts, in the wet if i try to pull away, not fast, but quickish, with close to lock either left or right then i move away, but then the turbo belts in at about 2500 revs and sends the **** end flying out and literally spins the car round!
This ALMOST happened to me on the road once, since then i've only checked it on a private road for obvious reasons.
The same happens if i'm turning a corner and i'm maybe a shade heavy on the gas, again i've tried it on the private road ;-)

However, in the dry... That's a different story altogether, boot it into a turn and then floor it half way round and... NOTHING!!!!
It's like i can feel the power being moved from wheel to wheel and the car just grabs hold and says 'Is that all you've got???' ... lol

 

Sounds to me like you might need better tyres

Also well worth checking that your shocks and suspension are in good order as this can lead to handling issues, however that would normally be worse i nthe dry than the wet because of the higher forces involved.

I'm sorry, without any experience of an auto legacy or impreza, I have no idea what could be going on. It appears that the centre clutch is actually computer controlled - a computer monitors wheel speeds and tells the clutch how much power to send front and rear. In the manual a viscous differential does that job.

IT appears that the clutch shunts power backwards when needed (car is somthing like 80% torque to the front in normal driving) - yours appears to be working being as it can turn the car rear wheel drive at will! If it had failed, it would fail open and the car would become front wheel drive.

 

Cheers for that Dave.

The car came with brand new Toyo's on the front (I usually use these anyway) and it had brand new Bridgstones on the rear for some reason?!?!?!
When they wear down some then i'll put Toyo's on the rear too.

Thanks for your help, it's appreciated

 

Or, jdm, uk and benelux countries have had vtd awd, with a rear bias, since the auto SVX split 36/64.
Other countries had the 90/10 split, shifting to max 50% rear bias.
The TCU/auto transmission in the '95 wrx, is essentially the same as an svx. Apart from the SVX having differing shift maps, depending on shifter position.
Looking up under the steering wheel, end on to you, like the spine of a book, will be the TCU. Should have 2 letters written on the cover. I'm guessing 'MW', if '95/96.
Later versions of 4eat vtd, (not the active awd 90/10 version) post '02, were a 45/55 split. they allowed more than 50% to the rear wheels. This system uses axle speed sensors within the transmission unit itself, not the ABS sensors, the ABS and AWD are two completely independent systems.
HTH

 

Hi 2pot

Thanks for getting involved, just been out and had a look at the TCU, it says:
RT
4WDAT

Just as i have written/typed it.
What does that mean? ... (I aint stupid, just new to scoobs and want to learn what i can about them :-) )

 

Hi
I suppose what I'm getting at is this. I've got a '95 wrx auto wagon. It's rear wheel biased in its normal state. When you accelerate hard, it's programmed to transfer even more power to the rear. You can't be surprised it loses traction, and tries to swap ends, in poor road conditions.
It's not clever enough system to send power forward, when all the weight is traveling backwards, due to acceleration.
Don't forget it's only awd when your on the throttle. Beware lifting off mid corner - look up snap oversteer.
Slow in, fast out.
Get some cold weather tyres - Dunlop winter sports, Nov - April, it's more fun, if your going to drive, lets say, progressively.
You could use the snowflake setting. It starts you off in 2nd gear, might tame things down a bit.
There is a solenoid that controls the transfer clutch pack. Try doing some figure of eights or very tight turns. Is the transmission noisy/binding? If the duty 'C' solenoid has failed, you'd get a rear bias continuously.

 

Hahaha ... I usually approach slow and accelerate out anyway, p****s off the s***ty Saxo boy racers when they choose to sit on my **** end ... lol

I am aware of snap oversteer, hence why i don't lift off in a corner. I only go mad when i'm trying it out on a private road or industrial estate.

So would it be safe to say that my motor is also running a rear wheel bias too? ... It certainly feels like it does ... lol

 

Ive been told my 2005 Blob STi has a split drive of 65% power to the rear and 35% to the front.

How true this is I don't know, but its what I've been told.

 

As above better tyres will help you counter this with good alignment setup,we are run before on our 4EAT with sport shift 350bhp and has been great in any conditions...

But main problem of the UK and US 4EAT is absence of manual shifting like(Sport shift/Tiptronic) is on the JDM,we have this before and has been just pleasure to drive


Jura

 

JDM auto WRXs have VTD-AWD which is 33:66 rear biased - very different to the 'Active' system that is fitted to the Forester XT. VTD-AWD gives the feel of a rear wheel drive and as a result the VTD autos handle far superior to the non-STI manuals out of the crate - but you have to watch them in the wet if you are expecting push.

 

Thanks Rexguy,

all this info is great. Glad to know we have an advantage over the manuals somewhere for the lack of power we have.

Terry

 

Thanks from me too Rexguy, now i have a better understanding of my car (which is the main reason for coming into the forum).

2pot, my transmission is fine, changing up and down without any strains or noise or binding etc etc.
Just out of curiosity, where is the Duty 'C' Solenoid situated? And is there any way for me to check it/test it myself?

 

The driving in figure of 8's and tight turns, is the test. If the transmission binds in these situations, the duty c solenoid needs changing - its in the tail housing of the transmission, where it applies pressure, or not, to the multi-plate clutch.
To confirm this: you should have a fwd fuse holder under the bonnet. If the binding goes away, with a fuse inserted, this would confirm duty C solenoid, or the power to it.

 

Therein lies the probelm .... There is NOT any fuse holder to change from AWD to FWD fitted to my car!
I have literally had so called specialists telling me that it is there, but when i send them a picture of exactly where it's supposed to be ... It isn't there, nor are there any signs that it has even been there.

In tight turns, the only noise i get is the sound of the power steering belt slipping slightly, but that's only at the complete end of the turning circle (complete full lock either way).

 

Some variations, but normally:
Under bonnet fuse box , '98 on, phase 2 transmission - spin on atf filter ON transmission
or
drivers side bulk head, pre '98, phase 1 transmission, no spin on atf filter.


http://img516.imageshack.us/img516/9...234013bes1.jpg

or

http://i680.photobucket.com/albums/v...G_1059copy.jpg

 

Right then, if the above is the case, then i simply do not have the AWD/FWD fuse at all.

 

'RT' tcu's were used on '96- '99 Legacy - non turbo. Has your transmission got a spin on atf filter
All the 95 -96 wrx' I've seen are 'MW' tcu's

 

I really haven't got a clue 2pot - All i know is that i wrote exactly what I saw ... lol