MickeyG

Sorry if this is obvious to you all, but I was wondering if they do, since my last spell in the snow. My wife would not stand outside and check for me!!!

Regards,

MickeyG

logiclee

Yes,

Centre with 50/50 torque split and rear.
Front is a standard diff

Lee

MickeyG

Cheers Lee,

MickeyG

scoobyboy

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by logiclee:
<B>Yes,

Centre with 50/50 torque split and rear.
Front is a standard diff

Lee[/quote]

sorry to contradict you but they don't have a lsd in the back coz on a 30,000 ml service we put ep90 oil in the back not lsd oil. and it's a 60 40 split with most to the back wheels.

logiclee

MikeyG,

The full info for you.

"Transmission All wheel drive. Center and rear viscous coupler.
Epicyclical center differential with 50/50 F/R torque distribution. Five speed synchronized gear box.
Gear ratios:
1:3.55:1 58 Km/h
2:1.95:1 102 Km/h
3:1.37:1 146 Km/h
4:0.97:1 205Km/h
5:0.74:1 234 Km/h
Final drive ratio:
3.9:1
Single dry plate clutch hydraulically actuated."

Sorry about the km/h, taken from a European site.

Lee



[This message has been edited by logiclee (edited 15 February 2001).]

SCOTTY

I understand that it has 60/40 with 60 to the front.

I am positive I am right. But who cares anyway. I'm not a techy and the car drives like a dream

Scotty.

Chris p

[ Sorry but these are the Facts....

All legacy turbo have LSD rear diffs

NO impreza has LSD. The only imp with LSD is 22B.
I can only speak for UK spec cars.As these are all I have worked on exclusively for the past 7 years .

[This message has been edited by Chris p (edited 28 February 2001).]

logiclee

I am an electrical engineer (HND) who is also a fully trained mechanic (HND) and have been involved with motorsport for years. Six years at College and Uni means you learn about more than 3 wires.

All the web site's list the rear as LSD, so do Scoobysport and TSL

And the UK Subaru Impreza Owners Manual has Full info on the 4X4 system as well as a section warning of the do's and don'ts on the Rear Viscous Limited Slip Differential (Turbo Models Only)

Lee

[This message has been edited by logiclee (edited 15 February 2001).]

scoobyboy

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by logiclee:
<B>I am an electrical engineer (HND) who is also a fully trained mechanic (HND) and have been involved with motorsport for years. Six years at College and Uni means you learn about more than 3 wires.

All the web site's list the rear as LSD, so do Scoobysport and TSL

And the UK Subaru Impreza Owners Manual has Full info on the 4X4 system as well as a section warning of the do's and don'ts on the Rear Viscous Limited Slip Differential (Turbo Models Only)

Lee

[This message has been edited by logiclee (edited 15 February 2001).][/quote]

can you tell me where on scooby sport they list the diff as ls because i can't find anything to do with transmission at all

logiclee

I was refering to one of Pete's posts. I'll do a search and see if I can find it.

logiclee

A bit more info for MickeyG

If I'm wrong, which I am from time to time , so is the Impreza owners manual and 90% of the web.

4X4 Turbo road cars

Most implementations use the classic Ferguson layout which consists of 3 differentials 2 of which (the central and rear) are coupled to the wheels they drive through "free" differentials which use viscous couplers as locking devices. A viscous coupler can be seen as a tube containing a pressurized viscous fluid in which discs are rotating. Half of the discs are attached to the incoming axle and the other half to the outgoing one to the tube's walls. The discs are pierced and the viscous fluid completely surrounds them. Minor speed differences are allowed between discs. Increased slip (i.e. rotational speed difference between discs) leads to a rapid increase in the viscosity of the fluid which, in turn, locks up the coupling.

Schematic view of a Viscous Coupler


Viscous Coupler mounted on a differential




Viscous couplers are convenient devices mainly because they are not very expensive and do not require extensive maintenance. Their major drawbacks are:

An exponential increase of their locking to speed difference curve (their are not very progressive)

A delay in their locking ability induced by the time the viscous fluid needs to increase its viscosity

Are difficult to handle under braking (they lock in braking situations)

The close relation of their locking abilities to that of the viscous fluid temperature (its viscosity decreases as temperature increases)

Some of the more known examples of this 4WD layout are:

The Ford Escort (and Sierra) RS Cosworth

The Subaru Impreza (and Legacy)


Cheers
Lee

MickeyG

Bloomin heck!!!

I just thought I would have a look into this thread, as there seemed to be an awful lot of replies etc...

I did not realise that I had started WW3 with what I thought was an "innocent" question.

Thanks to everyone (especilly logiclee, scoobyboy and chris p) who contributed, I have found the information very interesting. I hope you are all still pals .

See you all later,

MickeyG

AndyMc

Scoobyboy

Logiclee is 100% correct
Just to back him up a bit more the reason the Impreza rear diff does not use LSD oil is because the viscous coupling, ie the bit that provides the lsd function, is self contained and full of silicon oil.
The oil thats replaced on a service just lubricates the crown wheel and pinion / bearings and does not come into contact with the working part of the viscous coupling at all.The viscous coupling is a sealed for life unit.

The torque split is also 50:50 (uk cars)unless there is wheel slip when it can move in either direction depending on wether the front or rear is slipping.

Andy (no credentials what-so-ever)

Darren Thompson

I have just spoken to a mate of mine who works for Subaru and was trained by IM and he confirmed what I thought the UK Impreza does have an LSD in the back as described above.

Darren.

[This message has been edited by Darren Thompson (edited 16 February 2001).]

MikeWood

Just to clarify

The UK Turbo has viscous couplings in the centre and rear differentials.
These are sealed units and therefore do not need lsd oil unlike a plate type differential.

The torque split is biased to the front by 10%. Not being a transmission engineer I can't explain in detail why, but it is partly due to the fact that the front and rear have different final drive ratios (3.54 & 3.9) although the effective ratio is 3.9.

Normally aspirated cars have 50:50 torque splits and no rear lsd

Hope this helps!

Mike

logiclee

Thanks Guys

So Scoobyboy I don't have a clue then!!

Which dealers do you work at?

Lee

Darren Thompson

Some of the comments on this thread are more than likely why some people just read and don’t add to the threads in fear of being slated by someone who has got there facts wrong.

Darren.


[This message has been edited by Darren Thompson (edited 16 February 2001).]

logiclee

Darren,

I have to agree with you, I have posted things on the bbs which have turned out to be wrong, I dont mind being corrected.

I do not like abuse from those who think they know better but obviously do not. We take our cars to be seviced by these guys and pay Subaru a fortune, they don't even know what they are servicing. TSL for me I think.

I develop and oversee the installation of multimillion pound systems that are life dependant. I have to make sure I know my Job inside out.

Lee

jack

The export WRX in Singapore has a torque split of 55:45 (or thereabouts). The final drive is 3.9:3.5 (or thereabouts). AFAIK, it should be the same specs as the UK WRX.

Kurt R

Forgive this rather empirical test, but in the recent icy weather, I could sit my car (94MY UK Turbo)half way up my drive with 3 wheels spinning - both rear and one front. Conclusion - splippy diffs of some kind centre and rear. Which seems to support most of what has gone before. I seen it wiv my own eyes....

logiclee

MickeyG

You see it wasn't obvious to us all.

You even got a reply from Prodrive themselves!! Thanks Mike.

Been trying to find more info today.
The viscous diffs centre and rear are sealed units as said earlier so don't use LSD oil. The centre diff is epicyclic with an effective 50/50 torque split, however due to different front and rear final drive ratio's the drive is slightly front biased. Opinions differ as on this thread from between 5 and 10 percent front.

Don't be put off asking questions even if they appear simple and never be afraid to post a reply the majority of Scooby owners will not slate you if you are wrong.

Cheers
Lee


[This message has been edited by logiclee (edited 16 February 2001).]

scoobyboy

what has your job got to do with ls diffs.
nothing thats what.
a lsd is different to a viscous coupling because a lsd has plates in it that when 1 wheel spins it forces the oil out that is in between them and the plates connect making it a solid drive. a viscous coupling doesn't have these plates therefore cannot be a lsd .
and another reason if a viscous coupling is a lsd why does the centre diff not lock when the rear wheels turn at different speeds to the front i.e cornering because the rear diff is the same type as the centre diff
also as centre diff also has a viscous coupling

logiclee

A Viscous Coupling is a type of Limited Slip Differential of which there are many.

A viscous coupler can be seen as a tube containing a pressurized viscous fluid in which discs are rotating. Half of the discs are attached to the incoming axle and the other half to the outgoing one to the tube's walls. The discs are pierced and the viscous fluid completely surrounds them. Minor speed differences are allowed between discs. Increased slip (i.e. rotational speed difference between discs) leads to a rapid increase in the viscosity of the fluid which, in turn, locks up the coupling. All this is in a sealed unit inside the diff.

Other types of LSD use a type of clutch plate to limit slip, then there is the fully mechanical Torsen LSD which uses gearing as fitted to the celica GT4 and Lancia Integrale. The WRC cars now have fully electronic LSD so the drive characteristics can be changed by laptop.

So you can see there are more LSD than the one you described.

Perhaps you think Mike Wood of Prodrive is wrong too. Makes you wonder how they won the world championship when they don't know whats fitted to Impreza's. Perhaps they need to go on an IM course.

Lee

scoobyboy

sarcasm is the lowest form of wit.
i don't think mike wood is wrong and i believe what he says i have spoke to him at prodrive on various subjects before.

so why does the centre diff not lock then?

scoobyboy

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by scoobyboy:
<B>sarcasm is the lowest form of wit.
i don't think mike wood is wrong and i believe what he says i have spoke to him at prodrive on various subjects before.

so why does the centre diff not lock then?[/quote]

prodrive will up rate the diffs anyway so of course they know whats fitted to their imps

AndyMc

Hi Logiclee and anybody else that may know

I don't understand this torque split malarky and have a few theories I would like to try out on you.

It has been suggested above that the front and rear final drive ratios are different.If they are then would this not mean that the centre diff has to absorb this speed difference and the viscous coupling would be turning all the time.I wouldn't have thought Subaru would have designed it like this because it would be bad for fuel economy and would cause unnecessary wear.

What I do know is that the center diff is in the lower part of the rear gearbox housing and the rear propshaft exits from the top.This means the drive has to get there somehow.I reckon there must be a pair of gears that transfer the drive.If these gears have different numbers of teeth then that might account for the different final drive ratios eg if the rear is 3.54:1 then when the transfer gears are taken into account it might be 3.9:1 the same as the front.
Hows that for a theory.I have another one too!!

I have seen a picture of a 4x4 Cossy gearbox and this has a torqe split of around 65:35 this is acomplished using an epicyclic gear train for the center diff.(The drive from the engine is fed to the planet gears,the rear drive is fed from the anulus and the front drive from the sun wheel).It also has a viscous coupling just like an Impreza.In this design the viscous coupling does nothing when the car is driving in a straight line as you would expect.

Looking at the picture I also noticed that if the centre diff cage is held still eg by putting the car in gear and one of the axles is turned then the other axle will turn by a different amount due to the anulus and sun wheel having different numbers of teeth.If the car had a 50:50 split then they would turn by the same amount.

I tried this yesterday on my car.I jacked up both wheels on the drivers side and wedged a rag into the alternator drive belt to stop the engine from turning.Then I put the car in first gear and turned the front wheel one complete turn.The rear wheel turned exactly one turn as well in the oposite direction(I checked it very carefully).This suggests to me that the torque split is 50:50

Based on the above and the limited info I have I don't see how it can be anything else other than 50:50

Anybody else got any info that might help me understand better

Andy

PS who started this anyway,I think my head is going to explode

scoobyboy

correct the autos do have a fuse to disable the 4wd systembut you dont really need to use it for servicing.

the centre diff is lower than the prop but there is a small shaft that fits in to the diff with a gear on it to transfer the power uphill to the prop

logiclee

LOL @ AndyMc, you are a sad man.

Scoobyboy,
Thanks for the reply, any ideas why Subaru fitted the disengage facility to the Auto's?

Lee

logiclee

Limited Slip Diffs can be set up to suit the application. They do not have to lock solid only prevent torque from being spun away by a wheel with little traction.

The 22b and STI's have a more visous set up than the UK cars, ask Simon De Bank who runs scoobynet and is an advanced circuit driving instructor, the rear diff on a 22b has been known to lock solid on wheel spin and cause hairy oversteer moments. The idea of LSD is to limit slip not lock solid or any car fitted with them would be undriveable

If the centre diff was totally free with no form of limited slip diff one front wheel with no traction on snow or ice would spin away all the torque and the car would be stranded. A Landrover has a free centre diff and its easy to get in that situation, thats why they have diff locks. The Range Rover has Electronic Limited Slip Diffs that prevents the driver having to do this.

Look at Mikes post again.
"The UK Turbo has viscous couplings in the centre and rear differentials.
These are sealed units and therefore do not need lsd oil unlike a plate type differential"

Lee.

simes

I'm sorry to interrupt your argument, but a quick question...

I understood that power distribution on saloon turbo was 60/40 front/rear (although Mike Wood says there is a 10% difference which would mean 55/45), however on a 5 door I believe the split is 50/50, can anyone confirm this and explain the rationale on the difference?

Cheers

Simon