Opinions on LSD's

[Russwhitehouse]

Gents, I would value your opinions. I am looking to fit a LSD to my historic tarmac rally car to be. It is a 1969 2litre 911 and nearing the end of its conversion from track car to rally car.
There seem to be various options. My Indy Porsche specialist who is doing the work swears by ZF units, but they are seemingly impossible to locate these days ( unless you know something I don't) I can't find one online, but plenty of repair kits for them
Drexler Motorsport do a nice unit that can be fine tuned and adjusted in situ, sadly with a price tag to suit.
Kaaz don't seem to make a unit for a car that old, although I may be wrong.
Quaife make a unit which uses helical gears instead of friction plates which looks OK and not too dear, but is it any good?
If you were in my shoes, what would you fit and why?

[Trev450]

In your position I would have a chat with Richard Tuthill. http://www.tuthillporsche.com/
What he doesn't know about preparing 911's for rallying is not worth mentioning.

[NJH]

The american Porsche forums tend to swear by these guys;
http://www.guardtransmissionllc.com/products/limit...

It seems pretty common over here though to just rebuild an original ZF unit with new disks and belleville washers selected to suit.

[woof]

The obvious choice is Quaife. The geared LSD is service free. It's a no brainer.
I've run them in various cars. Classic Porsches to Corvettes - road and race. Great customer service. Just give them a call and see what they can do for you.

Re Guard - I believe they ripped off the Quaife diff - but don't quote me on that.

[anonymous-user]

Gear based diffs don't work when you have one wheel off the ground, which happens a lot on a rally car, so a quaife is not what I would be using for that application.

You would be best off with a plated diff, any will do so long as you can select the appropriate ramp angles and plate config. Getting that setup right is key, which is why its worth talking to specialists on that particular car in that particular environment.

[Russwhitehouse]

NJH said:

The american Porsche forums tend to swear by these guys;
http://www.guardtransmissionllc.com/products/limit...

It seems pretty common over here though to just rebuild an original ZF unit with new disks and belleville washers selected to suit.

Do Guard have a european distributor or is it a case of buying from the states. Import duty in France is horrific!!

[NJH]

I have never seen one in Europe. I have bought from the states before, fast delivery 2 out of 3 times but getting stung on import duty, customs handling fee and delivery tends to make it an expensive way to buy Porsche parts. I am in a different situation in that my flavour of Pork has the engine in the front and therefore we don't really need or want to much the lockup on deceleration which helps stabilise the rear engined cars, our cars tend to understeer enough already IMHE. If I was buying an LSD or ATB for a 944 I would probably buy a Wavetrac unit as its like an ATB but has ramps in it to stop an unloaded inside wheel from spinning the power away, this is really the only problem my own car has and I have found it really frustrating this last year in medium speed corners. 911s are different though and everyone seems to run a traditional plate type LSD with loads of lockup on deceleration, I have no idea about the rally cars though but as previous poster said nobody in the world knows more about rallying 911s than Tuthill's.
http://www.tuthillporsche.com/about-tuthill/histor...

[Willhire89]

Anything except the Quaife ATB - there is no comparison to a proper plate differential

[woof]

Willhire89 said:

Anything except the Quaife ATB - there is no comparison to a proper plate differential

I can only disagree with this.
I have both plate and geared LSDs and there's a lot of positives for a Quaife differential.

[Dollyman1850]

woof said:

Willhire89 said:

Anything except the Quaife ATB - there is no comparison to a proper plate differential

I can only disagree with this.
I have both plate and geared LSDs and there's a lot of positives for a Quaife differential.

The quaff ATB is what I have fitted in the back of my Griff. It is a very good unit for a short wheelbase race car which has enough suspension movement to keep the rear wheels both in contact with the ground. It is a very safe choice for a ltd slip diff and a little more controllable. It also tends to be a little more " A man for all seasons". I do tend to feel a little power loss and spin up out of tight hairpins such as Crofts complex etc…The benefits for me and my car however outweigh its limited disadvantages on a few corners on a few circuits..

A plate diff needs careful setting up to work on a race car especially if the car is light. In my opinion they are still better suited to stage rally cars where the severity of lock up is almost preferred. Horses for courses….. As an ATB user however I would probably be looking to something with a bit more lock up on a stage car…tarmac rallying a slightly different matter again and something which the ATB could be suited…The ATB is a very reliable unit.

I would be speaking to a good 911 rally specialist who no doubt will have tried all variants. An ATB will work out of the box. A Plate diff has many possibilities of making the car worse but when properly set up could be miles better for a specific application.

N.

Edited by Dollyman1850 on Sunday 11th January 14:18

Edited by Dollyman1850 on Sunday 11th January 14:22

[Willhire89]

woof said:

Willhire89 said:

Anything except the Quaife ATB - there is no comparison to a proper plate differential

I can only disagree with this.
I have both plate and geared LSDs and there's a lot of positives for a Quaife differential.

A proper differential could save you tens of thousands of pounds.


Try breaking a shaft off the start - thankfully I managed to get enough drive to get off towards the outside of the circuit.

With the Quaife I'd have been a sitting duck

[Marcus R]

Go for a plate diff!

Do Gripper or 3J Driveline do one that's suitable?

[stevieturbo]

Willhire89 said:

A proper differential could save you tens of thousands of pounds.


Try breaking a shaft off the start - thankfully I managed to get enough drive to get off towards the outside of the circuit.

With the Quaife I'd have been a sitting duck

Then get stronger shafts ?

How could a "proper" diff save tens of thousands ? And what defines a proper diff ?

I'd agree that for most hard driving a plate diff will be better. But also in my experience...any diff with a diff pin, it's only a matter of time before they break. Torsen style diffs tend to be stronger design from the outset.
I'd presume tight corner grip on something like a 911 should be pretty good anyway, so any downside of a torsen there would be much less than a live axle car.

But it would depend on application, power/grip levels, usage etc.

[Trev450]

stevieturbo said:

Willhire89 said:

A proper differential could save you tens of thousands of pounds.


Try breaking a shaft off the start - thankfully I managed to get enough drive to get off towards the outside of the circuit.

With the Quaife I'd have been a sitting duck

Then get stronger shafts ?

How could a "proper" diff save tens of thousands ? And what defines a proper diff ?

I think willhirew89 was referring to the fact that getting stranded on the startline is likely to result in getting rear-ended.

Edited by Trev450 on Tuesday 13th January 08:55

[woof]

I think Quaife do a decent drive shaft as well

Willhire89 said:

woof said:

Willhire89 said:

Anything except the Quaife ATB - there is no comparison to a proper plate differential

I can only disagree with this.
I have both plate and geared LSDs and there's a lot of positives for a Quaife differential.

A proper differential could save you tens of thousands of pounds.


Try breaking a shaft off the start - thankfully I managed to get enough drive to get off towards the outside of the circuit.

With the Quaife I'd have been a sitting duck

[Willhire89]

woof said:

I think Quaife do a decent drive shaft as well

Willhire89 said:

woof said:

Willhire89 said:

Anything except the Quaife ATB - there is no comparison to a proper plate differential

I can only disagree with this.
I have both plate and geared LSDs and there's a lot of positives for a Quaife differential.

A proper differential could save you tens of thousands of pounds.


Try breaking a shaft off the start - thankfully I managed to get enough drive to get off towards the outside of the circuit.

With the Quaife I'd have been a sitting duck

Happy to have their halfshafts....

So what are the positives of an ATB in a race car??

[NJH]

If one follows the Carroll Smith school of race car engineering absolutely no point. He said it clear in black and white that the only purpose of an LSD is to stop an unloaded inside wheel from spinning up.

[woof]

Valid points
Really you should all 4 wheels in contact with the tarmac ? Especially on a rear wheel drive car.
The big advantage to me is that they are maintenance free. A plate diff needs readjusting. Mine needs to be checked probably 4 times a season

Willhire89 said:

woof said:

I think Quaife do a decent drive shaft as well

Willhire89 said:

woof said:

Willhire89 said:

Anything except the Quaife ATB - there is no comparison to a proper plate differential

I can only disagree with this.
I have both plate and geared LSDs and there's a lot of positives for a Quaife differential.

A proper differential could save you tens of thousands of pounds.


Try breaking a shaft off the start - thankfully I managed to get enough drive to get off towards the outside of the circuit.

With the Quaife I'd have been a sitting duck

Happy to have their halfshafts....

So what are the positives of an ATB in a race car??

[anonymous-user]

stevieturbo said:

I'd agree that for most hard driving a plate diff will be better. But also in my experience...any diff with a diff pin, it's only a matter of time before they break. Torsen style diffs tend to be stronger design from the outset.

Race spec plated LSD units don't have a pin, they have floating gear assemblies.

[Willhire89]

woof said:

Mine needs to be checked probably 4 times a season

Its rare that a cost implication is important to a racer ahead of outright overall performance.

The leading Mk1 Cortinas have a fresh engine every other meeting and indeed one of the entrants for the Silverstone Classic stated to me that his lack of pace (he was off the podium) was due to it being his second meeting