Transfer Box - How Does It Work ?

[pgp001]

I have been looking at a sectional view of the transfer box on my 4.2 2004 model.

I see it has both a front diff and a centre diff for the take off to the rear axle, so three diffs in all.

Just before the output to the rear prop shaft there is a bevel wheel and pinion to turn the drive through 90° and it says there is a viscous coupling in the bevel wheel.

Can someone please explain the exact function of this particular viscous coupling, it says it is for giving a "limited slip" effect.

I know some vehicles have this viscous coupling in the prop shaft (Freelander ?), is this one in the RAV doing exactly the same function, ie only giving drive to the rear wheels when the fronts start to slip.

I understood that the RAV 4.2 had 50/50 front and rear all the time.

Phil

[jedi134]

Do you have a link as to to this, sounds interseting

[pgp001]

Do you have a link as to to this, sounds interseting

Hope this works

Phil

2004 FRONT DIFF & TRANSFER BOX.pdf

[anchorman]

I need to just check when I'm at my desk top computer but I don't think yours has this transfer box.

[bothwell_buyer]

I seem to remember some 4.2s had a limited slip diff, but I couldn't be certain. There has been posts in the past on this subject.

[jedi134]

But just some and on the rear diff if I remember correctly, and I belive it was manually operated.

[pgp001]

I too have tried to find out if I have a Torsen rear diff, but no one can give a definitive answer on that one.

But it is the viscous coupling in centre diff that I was wondering about.

My exploded parts list calls it a "control coupling"

I have just found this on another website, that seems to confirm its existence.

http://www.samarins.com/reviews/rav4.html

I am interested to hear what Anchorman finds out for me.

Phil

[bothwell_buyer]

But just some and on the rear diff if I remember correctly, and I belive it was manually operated.

You might be getting mixed up by the 4.1 which was a diff lock between front to back and not a limited slip diff.

[jedi134]

Hmmmmmm interesting, maybe this was just on the auto boxs? I presume the manual box will be totally different? I never thought it had a vc inside, I thought rear drive was taken straight of the differential?

[bothwell_buyer]

Found this post on a search...

4.2 diff

[jedi134]

Good find, so vsc and tc took its place. But still interested whether there is a vc in the front box.

[pgp001]

I have managed to scan and copy the relevant exploded views of both the diff case and the transfer box.

The transfer box definately has a "control coupling" shown which sits in the crown wheel at the output end to the propshaft.

Phil

DIFF CASE.pdf

TRANSFER BOX.pdf

[jedi134]

The rear diff is known to have LSD on some models. Where is the coupling on the transfer box? Or Are calling the rear diff the transferbox.

[pgp001]

I think we are getting a bit confused here.........forget the rear axle diff altogether.

There are two diffs in the transaxle at the front of the car, one to split the drive between front and rear axle, and one to split the front axle drive between left and right wheels.

These are both shown on the "DIFF CASE" drawing, the drive from the gearbox gears is fed onto the "Differential Ring Gear" which is then split by the "N°2 Differential" the drive to the front wheels goes out on shafts at either side via the "Front Differential".

The other side of the "N°2 Differential" feeds the "Differential Side Gear Subassembly"

Now look at the "TRANSFER CASE" drawing.

The "Centre Differential Control Coupling" (or Viscous Coupling as we are calling it) picks up the drive from the "Differential Side Gear Subassembly" mentioned above, and then the drive goes out to the rear axle propshaft via the "Ring Gear" and the "Driven Pinion"

So to sum up, my original question was:-

Does the "Centre Differential Control Coupling" have a Viscous Coupling in it, and if it does how is it intended to operate.

Phil

[jedi134]

Hmmmmm Im confused, As I always thought the LSD was located in the rear diff?????????? do you have a PDF of the rear diff?

Is this VC coupling and LSD totally seperate things?

But according to your TRANSFER BOX PDF its says Central Differential Control Coupling (what ever that is?? is it like the VDU on freelanders?) , and also specifies the use of LSD type oil, sugesting the LSD is indeed in the front transfer box.

So is this coupling is going to the rear diff via the prop you say

I always thought LSD went in the center diff to stop the wheels spinning on opposite sides. either the front or back.

I really dont have a clue now??????????????????? Looks like it may have both? VC in the front and LSD on rear (only on some models)

SUSPENSION AND AXLE.bmp

[kipperwood]

Hi all. I can remember searching for details to find out how my old rav, a 2003 vx worked. I remember finding out that a rear axle limited slip diff was introduced in that year for the vx model only, to go along with the centre viscous type coupling fitted to all the 4.2 models. It did not have the traction control that was later introduced on the 2004 facelift model. The centre diff is to transmit the drive from front to back to give AWD and then the centre viscous coupling would lock if one set of wheels were slipping to take the drive to the other set, unlike the 4.1 and 4.3 there was no centre diff lock button. The rear limited slip diff is an addition to give a limited lock across left to right on the rear axle only. There is no lock from left to right on the front axle set up at any time. Traction control now does that function electronically. It took me ages to find out this information and of course I have forgotten now where I had it from in the first place. Hope this helps a confuse things further, Kipperwood.

[anchorman]

OK, I believe the viscous coupling is for the US/Canadian models as this European version only has one front diff and no viscous coupling. This is from the UK Toyota Manual;

352 UK gearbox.pdf

It is a clever design and the transfer box picks up on the front diff so there is no centre or third diff. As stated, on models with square fog lights there was a limited slip diff (LSD) on the REAR axle;

Torque sensing LSD.pdf

[pgp001]

Hi Anchorman

I appreciate you taking the time to look that up for us.

The document you have found states it is a model 352F trans-axle, is that not the same as the one in the earlier PDF I linked showing the drive path through centre and front diffs and a viscous coupling, or do the US models have the same number ?

I wonder why they would make different variants for the UK and the US markets, if what you say is correct then the UK 4.2 is truly "Permanent" All Wheel Drive, but it is possible to get some transmission wind up between front and rear axles if tyre sizes were mismatched as there is no viscous coupling.

But on the US model, it must surely be front wheel drive only until the viscous coupling detects front slippage and locks up to provide drive to the rear axle, much the same as the Freelander system only the viscous coupling is enclosed on the RAV.

Do you also have the relevant exploded views showing the internals of both the transfer box and the diff carrier form the UK version so I can compare them to the ones I have which are US versions please, it does appear that the page you have linked is the same as the one in my manual for the US version ?

Thanks

Phil

[mnl]

It is rather difficult to figure out how it is supposed to work from what little information we have available.

I suggest checking to see if you have a viscous unit, and that it works, the same way we used to check Range Rovers.

Gearbox in neutral, ignition off.

jack up a front wheel.

Put the wheel brace on it horizontal, and stand on it.

If you are now on the floor, there is no viscous unit, and there is an open centre differential, or one of these on demand drive units like a CRV.

If you are in the same place after 30 seconds, the viscous unit is seized, and likely you will be getting steering issues, and chirping from the front tyres on corners.

If the wheel oh so slowly turns round, there is a viscous coupler, and it is working.

The viscous unit should be across the centre diff, providing a great deal of friction between front and back axles. If you remove the propshaft (don't oil will come out) it should drive happily on the front axle.

My 4.1 auto has the hydraulic diff lock, and I've driven it round the block with no rear propshaft, so it works.

[jedi134]

I dunno but mine is definatly truly "Permanent" All Wheel Drive with no transmission wind up.

with knobs on

[pgp001]

So what would happen with the set-up that Anchorman has described where there is no centre diff and no viscous coupling ?

I have to admit that I am still not convinced by Anchormans diagram, I have compared the one in which he has stated the lack of diff and vc, with the diagram in my US manual, and unless I am very much mistaken they are identical. (see attached copies of each and make your own mind up.)

The thing is all the information in my manual points to this particular transaxle being the same regardless of it being UK or US bound.

The next few pages in the manual describe in great detail how to dismantle the diff casing, this looks to be just a single diff from the outside but in fact it houses both the front and centre diff in the one combined unit.

I am really hoping Anchorman is looking at this, and will go and have another look to see what is inside the diff housing and the transfer box in his UK manual. The drawing he posted earlier just made it more uncertain for me.

Don't get me wrong here, I not trying to do a points scoring exercise against anyone, I just don't fully understand it yet, and really want to get to the bottom of with absolutely no doubt left in my mind.

Phil

Anchormans Diagram (No Centre Diff or V.C.).pdf

Phils Diagram (With Centre Diff & V.C.).pdf

[jedi134]

I`ve got the same manual I presume? US version only for petrol 4.2 ravs.

I just know that the prop comes off the front diff and with some gearing magic acts like there is a center diff in there.....Seen a diagram for it some where a long time ago...

So defo no wind up like you get on freelanders and old audi quattros thats used VC`s

[pgp001]

Quote

"and with some gearing magic acts like there is a center diff in there"

As a mechanical design engineer I learnt many years ago that there is no such thing as gearing magic, neither do gearboxes have any acting skills as far as I am aware.

So it either has a centre diff or it hasn't.

Hopefully we will get to the bottom of it soon.

Phil

[mnl]

I would love to know how they work, but as no-one has one for me to take apart, and I can't figure out the diagrams* we are back to testing the cars, and reverse engineering what must be inside.

jack up one side, and leave it in gear/park with the handbrake off (chock the other wheels)

Turn a back wheel by hand.

Results:

a) it rotates like billy o and the front wheel goes the other way = open centre differential. (my 4.1 does this with the engine off)

B) it rotates very slowly and stffly (might need a spanner applied to one of the nuts and held with some pressure on it) and the front goes the other way = differential with viscous coupler

c) it just rotates and the front does nothing = on demand 4wd like a CRV

d) (I can't believe this one) it rotates and the front goes the same way = no centre diff

*looks to me as if the front diff actually has a double set of spider gears, the RH outer set gear the front diff carrier (actually the bevel gear taking the drive from the gearbox) to the second large bevel gear that drives the rear prop. The drive to the RH front wheel just goes straight through the middle of the second bevel gear. This viscous unit appears to lock the RH driveshaft to the second bevel gear, which will impose a friction between the front diff and the second bevel gear all right, but seems a bit odd design wise.

Edit how come bee right bracket is giving me an emoticon? how odd.

[mnl]

Does a 4.2 have any warning stickers about testing the brakes on a 2 wheel roller brake tester?

With a viscous unit you wont be able to.