dazzaTypeR

Hi Guys,

I'm new to this site but have owned my scoob for 18months now and I still am not entirely sure about the truth on the diff control. I must have spoken to half a dozen so called experts and have had probably 4-5 different answers. The consensus though was that you should'nt use it while road driving.

Then today I lick through a mag to find a piece on a 22B saying that you can have the car in rear wheel drive, 4wheel drive and finaly locked diffs.

I drive with it on the bottom position and it feels and drives almost like a rear wheel drive to my suprise on several occasions when me foots more aggressive than my brain.

Is the artical right and can I use 4W/D with the diff in central position and not break or over strain the drive train.

Also anyone know what suspension kit will be best for lowering coil overs etc, I'm running on 18's so handling is'nt best in world but it does look the muts.

Cheers thats all for now.

dazzaTypeR

johnfelstead

best use of the centre diff is all the way back (light in the green on the dash) when its dry and then when its wet you can move it forward a couple of positions. A lot depends on your driving style though.

dont drive at speed with the diff locked, it will overheat the centre diff and wont handle that well either.

dazzaTypeR

Thankgod someones talking to me, being new thought I might have to know some funny hand shake or signal like the Masons or summat.

I tend to keep it on green all the time and roll it on if I'm running at pace in the wet, the differance is unreal. It feels so much more sure footed. I really like it when it snows but how often do we get that to play in.

Cheers dazza

Bruiser.STi

I do exactly what is said, in the green for 90% of use and bump up for wet weather or go full lock for power launches down the 1/4 mile...
Had a local doctor who owned a type R bought back to dealer after a month wanting the car checked over...was a bitch to park and manuever, he had it in full lock always!!!

IanA

I've driven a type R with Leda suspension from Scoobysport, it was seriously good and I think Leda is generally considered to be one of the best suspension conversions available.

Fast Forester

I'd go for Weitec / KW coilovers. They are used widely for racing and is adjustable for bump, rebound and height. On the more 'dear' shocks you can set bump for high and low speed, and the shocks have linear bearings.....

MorayMackenzie

The car is permanent 4wd with a natural 65 rear / 35 front torque split and a driver adjustable viscous lsd centre differential. Adjusting the diff control varies the viscous coupling's locking characteristics, all the way back is fairly loose, all the way forward is pretty much fully locked. Tightening up the diff(moving dial forwards) will cause it to lock harder and faster when the shaft speeds differ. So, in the wet or slippery conditions, if you move the dial forwards a bit it will fight the cars natural 64/35 rearwards torque bias by transferring torque forwards more quickly when the rear wheels begin to loose traction.

Moray
bbs.22b.com (22b not required, honest)

Pete Croney

My mate Stephen Byers says its fine to drive with it all the way forward, no matter what the conditions.

He also says that if you can spin the rear wheels, with the front wheels stationary, then abuse of the centre diff lock hasn't already destroyed your centre viscous coupling.

Bruiser.STi

Pete- Makes incredibly heavy steering though....and the tyres don't like the extra load at slow speeds...But I have heard that it doesnt hurt the centre diff.

dazzaTypeR

You wanna check out the pic in Japanese performance mag of the gezzer with the 22B rear arches full of smoke and front nice and stationary, Best thing is I think it's for sale...

Nice one that should get you best price I dont think.

Cheers Moray that's cleared it up for us. And explains why I've lost the rear so many times....

Dave R

Moray is nearly there but it's not a viscous coupling but a set of friction plates running i oil. As the diff tightens up (green to red) the unit resists more and more the ability to allow the front and rear axles to run at different speeds, so reducing power on wheel spin and increasing off throttle understeer.

Cheers
Daver

johnfelstead

you can actually do donuts with the rears spinning and the inside front wheel stationary without any harm at all, it's not an indication of a knackered centre diff, its just the way the torque is transfered to the wheels that demand it when the centre diff is left open.

http://www.scoobynet.co.uk/video/22b...20Doughnut.mpg

[Edited by johnfelstead - 5/30/2002 1:23:00 AM]

Pete Croney

John

The picture in question is a 22B, stationary, with the rear wheels well lit up and smoke billiowing out.

There is no drive at all going to the front wheels

That's a poorly centre diff in my book.

Adam M

john, inside front wheel staionery confuses me a bit, as the 22b has a limited slip front diff.

I could believe you if it were a type r as the other wheel could be spinning perfectly happily.

to anyone interested in that 22B, please email me first, not cos I am selling mine but because all is not as it seems.

btw. that is the same 22B that rc developments have worked on that produces 380bhp on a standard intercooler, turbo and injectors.

It also manages to do 175mph apparently in top gear, despiter the fact that the redline and gearing on a jap 22B (which have not been changed on that car) prevent it exceeding 158mph!

Dave R,

If Moray is partially wrong, can you please explain what other nomenclature you would use for a diff where the in output shaft and input shaft are coupled together by the viscosity of the oil in between the drive plates?

That to me suggest they are viscous coupled.

The seaparation of the plates is determined byt the position of the switch and so when locked they are practically touching. Ie int he front and rear axles are driven by a locked diff, preventing them from turning relative to one another and making turning difficult. This is no problem at all in a straight line but not great if cornering on a flat surface.

In short leave it fully open unless you are driving in rain or heavy rain, in which case, one or maybe two notches forwards.

Dave R

Viscous coupling meaning VCU/silicon filled plate pack that stiffens when the fluid is sheared by plates attached alternately
to the inner and outer splined shaft/housing.

The Type R uses a set of plates running in normal trans oil, that need the roller switch to be moved to give the locking, although some locking is available in the lowest position, ie. some drag between the plates.

Hope this clears it up a bit. Difficult getting it over to the layman without the bits infront of you.

Cheers
Daver

MorayMackenzie

Dave R,

Interesting. Confusing.

If these plates are actually friction plates, that would imply that:

A) The plates will wear over time and require replacement
B) As they wear, they will polute the transmission oil, thus requiring frequent replacement for safe running.

I am also interested to know how the LSD locking works? are you saying that it is just a clutch type diff with an electronic preload adjustment?

Regards,

Moray

pat

Dave,

your reference to "friction plates" suggests that it is a clutch type diff. Both clutch and VC diffs have plates that generate friction, in the former case directly and in the latter by means of recesses that allow one to utilise the shear strength of a fluid between the plates to limit the slip. You not not have to use a silicone fluid for this, it is possible to use normal gearbox or diff fluid. If you think about it, the rear diff on a normal scooby is a standard VC LSD and this most certainly uses diff fluid.

With regard to the centre diff with electronic control, it is a planetary diff with a natural 36:64 front:rear torque bias (by nature of being planetary). There is also a viscous coupling between the front and rear output shafts, whereby the plates are kept apart by a spring. There is, round the outside of the diff, a coil which is energised by the centre diff controller using PWM drive. This creates a magnetic field within the diff assembly which causes the plates to move closer together. As they do so, the oil film thickness reduces, thereby increasing the amount of resistance to slip. As the current in the armature is progressively increased, the plates move closer and closer together, until they become locked.

Driving with the diff control fully unlocked, the centre diff is pretty much an open diff, because the spacing is large enough to allow the plates to spin relative to eachother without significant viscous drag. One or two notches forward and you have a centre VC LSD as you would in a normal scooby, and as you keep going forward it begins to lock up (great for gravel ).

With regard to damaging the diff, it is very unlikely to get damaged by being one or two notches forward during normal asphalt driving, especially in the wet. Any more and you should really be on the loose, or putting down so much power that you're lighting up all four.

With regard to allowing the rear to spin with the front stationary, this is a normal function of this centre diff. Because it is essentially an open diff with a heavy rearward bias with the control fully back, the torque will go to the wheels with the least resistance, which would be the back as they have lost traction. They are more likely to lose traction than the front because of the torque split. Simple. In fact, the centre diff controller has an input from the handbrake... yes, this type of diff *IS* designed to allow you to handbrake turn the car

If memory serves correctly, there is one other "trick" bit in the centre diff, but sadly I cannot remember exactly what it is. Anyone interested in exact details should go to an Subaru dealer which services 22B Type UK cars, as they should have the 22B supplement to the normal workshop manuals, which describes in great detail, the operation of the centre diff.

Hope this helps,

Pat.

Pete Croney

If Tony hadn't buggered off to the USA with my digital camera, I'd take a picture of the internals for you all.

Pat's description is spot on, but I don't agree that the car should be able to sit stationary with the rear wheels billowing smoke and the fronts not moving, unless the centre diff was damaged.

Where has the 36% of 300lbft torque (that should be driving the front wheels) gone?

Pete Croney

Pat

The other trick is to map the centre diff to go onto full lock up when the brake pedal is pressed or when using WOT. It then acts like an abs system and traction control system combined.

Commonly used in group A, but possible and legal in group N.

MorayMackenzie

It would be an idea to add a steering angle input to the brake/wot lock system... i would be ok with full diff lock if i was braking in a straight line, but i am not so sure it would be as helpful if i were steering at the time.

Pete Croney

Moray

If you stand on a big set of tarmac brakes, whilst turning, no diff is going to save you

Adam M

agree with pete, but it is a nice idea.

I am wondering if a pwm output from an ecu with lots of pwm outputs could be rigged to do such a thing.

hhmmmm

ian/555

I have uploaded the following image which explains a bit about when to use the diff lock.



That's correct about being able to do handbrake turns on Imprezas with the centre Diff control, but this should only be done when the diff lights are in the green positions. I will have a look today or tomorrow to see if I have any more info on using the Diff lock.
ian

Adam M

Ian, I was under the impression, as was pat having fitted it that the handbraking ability was regardless of diff lock position as it has an input from the handbrake which frees the diff when the handbrake is applied.


also with this info in mind, is there a recommended postion for when in use on a rolling road?

ian/555

Adam, I can't remember if it mentions rolling roads at all. I'm as sure as I can be without the book, that it says only to use the handbrake when in the green positions, maybe this was different for cars produced before the STi VI type R's.
I have moved house twice since I last saw the book this info is in, so it might take a while for me to track it down and check.
ian

Bruiser.STi

Im pretty sure that the handbrake is safe to use as both my V4 Type R and a V6 Type R use them frequently in our car club events to negotiate hairpins and they work fine, the speed is not great when using, 20kph maybe...so the stresses would be minimal. Its only pulled on for a moment (wrc style) to get the car sideways then powerslide round the bend.

ian/555

Adam you are correct, I was only going from my memory as I had not seen the book in some time.

What it said was, that with the indicator in the green positions if you pull the hand brake so that the brake warning light on the dash comes on, this will put the diff into a diff free situation and it will be possible to do rear wheel braking.

If I have understood that right it is saying that you can isolate the front braking circuit by using the handbrake as a sort of brake bias switch! when the indicator is green.

It then goes on to say that with the indicator set to orange when swerving or parking due to the front and rear rotation difference you will get some noise/vibration and the dial should be changed to diff free or the handbrake pulled up a little so that the warning light on the dash comes on.

So if I understood that bit correctly, you can select which percentage of orange diff lock you want for straight stretches of road and then when going round corners, pull the hand brake up slightly and this will put the diff into free mode, and as such will stop it from making noises and vibrating. Then once round the bend release the handbrake and the diff will go back to the pre selected setting

Here is all the info it gives on operating the Diff, which I got from a handbook which from the looks of it came from Australia, which was originally translated from I believe the Japanese owners manual.






ian
edited to resize pic


[Edited by ian/555 - 6/2/2002 6:38:30 PM]

Hol

iTrader: (1)

I got a knock from the front driveshafts when reversing with the dial in halfway mode.

Is this normal? as I stopped doing it straight away.

PeteC, I might come up to Basildon later this week and have my car given the 'twice' over.

Andy