Tech Question - ATB Central Diff

[Karlheinz]

Hi guys,
anyone know who produce (Quaife, Bara, R&D)
a good ATB central diff?
Thanks.

[Karlheinz]

Anyone know something?!?!?

[Gatecrasher]

Contact mike rainbird he will steer you in the right direction... Sure quaife do one!

[Karlheinz]

Contact mike rainbird he will steer you in the right direction... Sure quaife do one!

Thanks a lot!!!

[Sunnysidebb]

Hi guys,
anyone know who produce (Quaife, Bara, R&D)
a good ATB central diff?
Thanks.

Personally ( if they did go one) I would be very cautious, as these cars are 66R:33F torque split. which means the rears are more likely to break loose before the front when on full power on bad surfaces. If your centre VC ( ATB) is too strong you will transfer more power/torque to the front whilst the rears are spinning and hence possibly overload the front diff/shafts and they aren't that strong in the first place.
You would be better just to send your standard Centre VC off and have the torque rating upped a little. you might find it has gone soft and needs an overhaul anyway.

[Karlheinz]

Personally ( if they did go one) I would be very cautious, as these cars are 66R:33F torque split. which means the rears are more likely to break loose before the front when on full power on bad surfaces. If your centre VC ( ATB) is too strong you will transfer more power/torque to the front whilst the rears are spinning and hence possibly overload the front diff/shafts and they aren't that strong in the first place.
You would be better just to send your standard Centre VC off and have the torque rating upped a little. you might find it has gone soft and needs an overhaul anyway.

Well,
I have a Quaife front diff in Quaife case and I will want (I hope early)
to change the rear diff with a Quaife.
Then, I have upgrade the gearbox with strong gears...

[Gatecrasher]

Do the rear diff and box and just do as frank said have it checked as its not a common fault for the centre to need replacing

[grcossie]

When oe center became wear, you loose torque to front wheel, it`s easy to see. My mates have broken a few, then his car is like a rwd.

[Sunnysidebb]

When oe center became wear, you loose torque to front wheel, it`s easy to see. My mates have broken a few, then his car is like a rwd.

not strictly true but sort of near the point....

The centre VC works in conjunction with the centre differential.
The torque split of 66:33 is all the time and not just when you get wheel spin. Even with no centre VC you will always see the torque split front and rear. However once either the front or the rear wheels/axle spin, then the centre diff, like any other free diff, will spin out power/torque to the wheels / axle that are spinning. The VC controls /diverts that torque/power from the spinning wheels/axle to the axle/wheels that are not spinning. Front to back or back to front. In the case of a 66:33 Cosworth it normally works by diverting torque to the front when the rears spin out.
One last point all Land Rover 200 and 300 TDI's do not come with a centre VC. They only have a Diff lock which is completely different......and they are still " 4x4" until you go off road or until you engage the diff lock.

FF who used to do my rally car VC's said its very common for a 4x4 Cosworth to spend many years on the road with a defective centre VC and the owner never suspects a thing.

[grcossie]

You can have a full burn out on a 4x4 whit only rear wheel spinning, have don it and seen it many times. Change center visco, and it`s works ok. When you have a worn center visco, you can see it`s blue from heat, and the it`s burnt inside

[Sunnysidebb]

You can have a full burn out on a 4x4 whit only rear wheel spinning, have don it and seen it many times. Change center visco, and it`s works ok. When you have a worn center visco, you can see it`s blue from heat, and the it`s burnt inside

Correct they do go blue although not always. They can be burnt in side but again not always. The best ways to fook up a brand new VC are.

a. Do burnouts
b. Do long distance high speed driving with the wrong wheel sizes front to rear. ie Miss match input /out put speeds. IIRC FF recommend no more than 18 rpm* per 1000 rpm's miss match. This allows for minor tyre height differences such as new tyres on front and worn on rear for eg Or differences in tyre pressures etc.

* 18 rmp/1000 was my recollection from FF it could very well have been a little less for a standard VC

[Boostjunky]

This is all interesting stuff

I was lead to believe that mine has a 1:1 vc..?
Its extremely hard to get it to let go. But when it does it more of a slide like evos do rather than a sideways drift.....

Does that make sense?

[grcossie]

Correct they do go blue although not always. They can be burnt in side but again not always. The best ways to fook up a brand new VC are.

a. Do burnouts
b. Do long distance high speed driving with the wrong wheel sizes front to rear. ie Miss match input /out put speeds. IIRC FF recommend no more than 18 rpm* per 1000 rpm's miss match. This allows for minor tyre height differences such as new tyres on front and worn on rear for eg Or differences in tyre pressures etc.

* 18 rmp/1000 was my recollection from FF it could very well have been a little less for a standard VC

Agree one your point how to break a center visco. My mate used rally winter tyres on his 4x4 Sapphire, and whit one of the worn visco, his front wheel don`t have any torque at all. One of mine gearbox, have a worn visco, and it`s easy to feel the different, on how you loose drive on the front wheels

[Sunnysidebb]

Agree one your point how to break a center visco. My mate used rally winter tyres on his 4x4 Sapphire, and whit one of the worn visco, his front wheel don`t have any torque at all. One of mine gearbox, have a worn visco, and it`s easy to feel the different, on how you loose drive on the front wheels

You will definitely notice the loss of the centre VC on loose surfaces but on Tarmac, not so easy. So long as you don't loose traction then the torque is always been split front to rear in the ratio of 66:33 . You might not thing the front is getting any torque but if the wheels don't spin you will be.
If your used to these cars you might notice that manoeuvring on full lock at slow speeds becomes a little easier with a duff VC. When you manoeuvre in an arc not only do the inner and outer wheels turn at different speeds but the axles/ front & rear diffs turn at a slightly different speed. The stronger the Centre VC the more you can feel the judder as the wheels skip a little.