SOOBAAROO

Hi guys,

completely new to the whole subaru thing just wanted to know a few things about the gearboxs

on the SPDA chart what are these things

Define:
Rev.
T.R.
F.D
Center Diff (IE. Viscous 4kgf) - what does that all mean
Front Diff type (IE. A.P suretrac) - what does that all mean?

And for example, if a gearbox has the same F.D ratio can i put it in without changing the Diff or in anyway stuff up my car

IE

TY752VB3AA is the same as TY752VB3BA

Fat Boy

Rev = Reverse gear ratio
T.R. = Transfer gear ratio- either 1:1 or 1.1:1 . If 1.1 you need equal ratio front and rear diffs if 1.1:1 then the rear diff needs to have a diff ratio to the front e.g. 3.9 front, 3.54 rear
FD = Front Diff
Centrediff = type - either dccd (controllable split - either when open older diffs 35 Front /65 Rear drive or 41F / 59R newer types open) or viscous 50:50 F:R with varying degrees of viscosity in the fluid providing varying levels of lock up. 4 kgf = normal gentle lock up, 20kgf (grp N) giving much more aggressive diff action. Dccd allows you to progressively lock up the diff from the open state to 50/50 but in open state makes the car more like a RWD car.

Front diff types - various different front diffs were fitted as standard and as options - ranges from open (i.e. no LSD effect) to AP Suretrac (viscous) and various torsen type diffs. Helix LSD probably preference for road / track.

VB3AA might be a different set up to VB3BA - but if all the diff ratios are the same including transfer gears then it would be interchangeable and might, for instance, have a differnt set of 1-5 gear ratios i.e. longer or whatever.

SOOBAAROO

Hi mate,

Thanks a lot for that

APIDavid

iTrader: (4)

Fat Boy is nearly word perfect, but has fallen into the trap of exactly what happens with a dccd.

The gear set inside a dccd variable rate LSD is and always will be: 65% rear / 35% front. That cannot be altered by the driver as it is a planetary reduction gear set.

What happens when you adjust the potentiometer [ the thumb wheel ] is to increase voltage to an electromagnet that exerts pressure on the plated part of the centre diff.

That reduces slip in the friction plates and makes the drive to the front wheels more aggressive. So at full lock ALL wheels are trying to drive / rotate at the same speed, hence the scrubbing you get on full lock turns and parking .

You can never create a 50 / 50 situation from a dccd without changing the gear set inside the dccd [ there is no such part in the Subaru parts list ]

Otherwise well done fat boy.

David APi

PS VB3AA and VB3BA are in fact quite a bit different.

VB3AA has ratios VB3BA has:

3.454 1st 3.454
2.062 2nd 2.333
1.448 3rd 1.750
1.088 4th 1.354
0.825 5th 0.972

Both have viscous centre diffs and both have open front diff - both are 4.1 final drive ratio front and rear

VB3BA is the first that is generally known as the Group N rally ratios and is very short geared, for maximum acceleration - but low top speed

It is not at all good on motorway cruise, as you will most likely be doing 5000 rpm where you used to be doing nearer 4000 rpm.

Parts to repair VB3BA are fairly thin on the ground these days, if you break one it may well be scrap depending upon which gear you break.

Our new rolling road is being installed MOnday 30th November - nearly there guys.


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dunx

iTrader: (3)

And an AP Suretrac isn't viscous it uses "nuggets" IIRC

dunx

APIDavid

iTrader: (4)

Possibly thinking about the Suretrack that is fitted standard to the Vers 7, 8, 9, STI types in the rear diffs. Just a fancy name for a viscous in that case.

I don't know of AP making LSd's - any info? Or just a slip of the tongue ?

By " nuggets" l guess you mean interlockers that are about the size if a Fox's Glacier mint? If you've ever seen one?

This type if diff is quite old fashioned and aggressive. In the US it is known as a locker. It consists of two cylinders with serrated interiors and a cylinder rotating with the ' nuggets ' in it by applying power the nuggets get forced out by centrifugal [ centripedal maybe - I can never remember the difference ] force and jam the two serrated cylinders.

It will remain locked as long as power is kept on. Lift off and it unlocks with quite exciting circumstances most times. NOT for the faint hearted

David APi

dunx

iTrader: (3)

Quite !



dunx

APIDavid

iTrader: (4)

Oh! sorry mate - l thought l'd simplified it. You get the drift though?

David

dunx

iTrader: (3)

quite old fashioned and aggressive.

Mine was a bit scary when new, but seems a bit tired now, is there a service kit available ?

TIA

dunx

P1SWRT

iTrader: (2)

A bit off topic but picking up on Guru Mr APi...

VB3BA is the first that is generally known as the Group N rally ratios and is very short geared, for maximum acceleration - but low top speed

VB3AA has ratios VB3BA has:

3.454 1st 3.454
2.062 2nd 2.333
1.448 3rd 1.750
1.088 4th 1.354
0.825 5th 0.972

These were the ratios in my Group N box .... the gear ratio is created by the teeth count on each part of the gear as each gear consists of 2 'gears'

12 - 35 2.916 : 1 1st
11 - 23 2.090 : 1 2nd
18 - 28 1.555 : 1 3rd
17 - 20 1.176 ; 1 4th
20 - 18 0.900 : 1 5th

1 : 1 drop gears.
4.444 crown wheel + pinion

brisk acceleration.

Cheers
Rob

APIDavid

iTrader: (4)

If it is a locker with 'nuggets' in, then the nuggets will have no sides on them anymore and the slip to lock ratio will be rather more comfortable. IE probably not working.

The problem is usually that the high spots on the serrated inner and outer rings get the tops knocked off too and at that point it becomes a throwaway. If you've got to buy all the insides to repair it, then you might as well buy a new one.....

It is really a ciruit racing type of diff that gets a lock on in corners where the car is committed to a line and the line remains constant.[ hopefully ] In rallying or road use there is so much change of direction that the locker is in and out all the time and that accelerates the wear.

Actually, buy a better one........ like a proper plated set up

IF that is what you have. If you pull it out the I'd appreciate a look at it to see if I was close......

Those Gp N ratios? were they original Subaru road gears or a Sportpart set that were competition use only ? As I have no paperwork for those being ever in a road car. Any info is always helpful.

They would be VERY short geared on 4.4 final drives...............

David

APIDavid

iTrader: (4)

The nearest to those as road gears are: Vers 3/ 4 RA gears [ VB5ba or 5CA, 6EA or 6SZ [ 22B ]. 754 VB1BA, 754VB1CA, 754VB1EA, are similar on Vers 5 / 6

2.916 : 1 1st 3.083
2.090 : 1 2nd 2.062
1.555 : 1 3rd 1.545
1.176 ; 1 4th 1.151
0.900 : 1 5th 0.825

I remember now Rob, yours were Modena gears weren't they? But I think you were on 4.1's if I recall??

David

David

P1SWRT

iTrader: (2)

The ratios above were the correct homologated ratios for GC8 cars and you are correct they were Modena (don't get me started on that one!)
But I was running the 'forest' dog box with 4.444 final drive... the std RA 'tarmac' box was on 4.1's but I never went on tarmac as that is a crime in rallying

Cheers
Rob