ZF LSD Plates

[chris_seven]

As we are planning to make some upgrades for ZF Plate Diffs I have have been trying to measure the spline on the friction plate and side gear.

Does anyone have any detail of this spline because an near as I can tell it is a Module 2 Involute to DIN 5482 and it would be good to confirm this measurement.

The plan is to make some sintered bronze plates and uprated cross pins.

[Geary]

OMG, Chris .. why would you bother? Porsche has proven that bronze plates are a joke, and Guard arrived at the ultimate in plate material & finish over 5 years ago ..



.. even going so far as to make half-thickness plates and discs, allowing double the number.

[HawgRyder]

Chris...if you ae looking for alternatives to the plates now available...how about examining the ones used by Barnett for motorcycle clutches.
They have been upgraded for decades...work like a charm either wet or dry...and give total control over friction.
I would pursue them to see if they could make you some discs in the correct size with their coatings for a test.
Bob

[chris_seven]

Bronze plates seem to be used in a number of diffs now and have some properties that seem interesting.

Limited Slip Differentials

I also believe that they are used in the new Maybach Hydraulically controlled diff.

I understand that sintered plates have more 'grab' and I like the idea of reducing preload.

The Barnett Plates look interesting but the distance and shipping costs will probably get in the way.

I guess I will just have to send a side gear to a colleague that can measure the profile.

[Matt Monson]

GKN already makes clutches that are similar to what Barnett is doing. They are found in the OEM Boxster/Cayman 987 LSD:

They have also shown themselves to be about as effective as GKN's bronze clutches that are in the GT3 OEM LSD (not very effective at all).

The sintered plates generally have less grab and the way that a hydraulically controlled diff works is by having no or low preload and then applying an external force to the plates when bite is needed. Without that external force (as Porsche is doing on their PTV+ equiped cars like the Turbo S and 991 GT3) the LSD and it's plates have almost no bite. It is the best of both worlds since it's open when it's open and locks when you need it locked. But it is a very expensive technology, is banned by most motorsports sanctioning bodies, and if you take away the external actuation, it doesn't work on just the clutches alone.

[chris_seven]

It is interesting that you say that sintered plates have less grab.

Every other discussion I have seen claims that they have more grab.

Sintered plates are also used in a significant quantity in situations where high 'grab' is needed such as ships winches and many earth movers and are normally specified for any 'heavy duty' application.

The common claims made by their manufacturers is improved thermal performance and higher friction with reduced wear.

Quote from Rennlist re 993 unit

I had a set of sintered plates put in my LSD (which, like most of them out there, was having no effect) and the change was well worthwhile, plus the plates are still holding up just fine approx 20,000 miles later. Get amazing drive out of slow corners. Work was done by G-Force Motorsports and the whole lot, parts, labour and 17.5% VAT, came to the equivalent of about $500.

This is a basic comment from a Transmission disc manufacturer.

Sintered Bronze Discs

The term ‘Bronze’ is used due to the appearance of the material; this is due to the high copper content of the composite. Also present in the composite are a number of raw materials such as copper powder, various metal powders and friction material. The production process involves the mixture of the powders, then moulding it into a mass using heat & pressure also know as sintering. Once the material is sintered to the steel core plate it’s then machined for the final thicknesses & groove patterns. Bronze materials are suitable for use in both wet & dry applications. The following are properties that are associated with this type of material:

> Good thermal stability
> Good wear resistance
> High and stable coefficient of friction
> High mechanical strength

Moly Coated Discs

Molybdenum friction materials are commonly used in low speed applications. The steel core plate is coated with pure molybdenum at a thickness ranging between 0.045 – 0.070mm per face. The process used is thermal spraying also known as flame spraying. Once this process is finished the final thicknesses & groove patterns are then machined to the surface to guarantee reliable friction behaviour. The following are properties that are associated with this type of material:

> Good oil compatibility
> Good wear resistance
> Stable friction Coefficient


They are confident that the Bronze plates will out perform the Moly Coatings and as they can supply both I have tended to believe their comments.

[Matt Monson]

So your proof is that someone with a worn LSD had it rebuilt and it worked better afterwards?

The proof is in the pudding, so to speak. Make them. And then we will see how they perform against the other options that are available.

Though it is curious that if the sintered brass plates are so superior to the moly ones, why did Porsche use the sintered plates on the GT3 street cars but the moly version on the GT3 Cup? Just something to consider.

[Geary]

Your 993 disc comparison was against carbon discs, which after 1000 miles have about the same friction as plain steel-on-steel. Anything would be an improvement over carbon (or brass), and there are literally hundreds of 993 & GT3 owners who know this first hand.

I've seen every claim under the sun from various manufacturers. Quoting them sounds wonderful, but isn't the same as actual testing in ZF LSDs. I'm confident that your new brass discs will underperform against OE ZF or GT discs (unless it's slippage that you're after).

[chris_seven]

I don't think I have any proof as I have never tried alternative plates. I only have the opinions of various manufacturers.

I have discussed the Sintrak plates with the guys who make them and they are convinced that they offer better performance than steel or moly coated.

I have also discussed the material choice with an industrial friction disc manufacturer that has been in the business for 40 years and makes friction discs in all of the above materials and he recommends bronze for the most arduous conditions.

Originally Posted by Geary

Your 993 disc comparison was against carbon disc
I've seen every claim under the sun from various manufacturers. Quoting them sounds wonderful, but isn't the same as actual testing in ZF LSDs. I'm confident that your new brass discs will underperform against OE ZF or GT discs (unless it's slippage that you're after).

Every claim made is,of course, subject to a vested interest and some good reliable data would certainly help to make selection more straightforward.

I also thought that at some predetermined torque value the idea was that the unit would slip, surely the debate is how much and when and the repeatability of these characteristics.

[Matt Monson]

Originally Posted by chris_seven

Every claim made is,of course, subject to a vested interest and some good reliable data would certainly help to make selection more straightforward.

Are you aware that Paul is retired and has no vested interest in the company that bears his name? His only "vested interest" is well deserved pride in what he helped to create and any endorsements or recommendations he makes have zero financial benefit to him at this point.

[Geary]

Chris wasn't referring to me, Matt .. but rather the various manufacturers he's spoken to.

Chris, the correct path with the 911 is to start with a good durable disc & plate combo (with a predictable and long-lasting friction coefficient), and do any fine tuning with the Bellevilles and ramps. This is WAY more important in a rear-engined 911 than with just about any other type of track car.

Bonded pads are a joke, as those pads come unglued all the time .. and any research in the Porsche world will confirm that carbon, bronze, etched steel, and coated discs are all inferior to what's readily available.

[chris_seven]

I don't think I said that Paul had a vested interest.

I was simply agreeing that in all cases manufacturers always claim to have the best product so the only way to make some judgements and try new ideas is to try to canvass a broad opinion and come to a conclusion.


When I started this thread it was to try to find the spline information not to debate the merits/weaknesses of any particular system or particular plate, the background study I made does seem to suggest Sintered bronze may be a good idea and quite clearly you disagree.

If the plates we make work I will be pleased, if not I will simply waste a little money - what's the harm.

I do agree that glueing anything onto this type of disc just seems too risky and that a thermal/plasma coating is much better.

Many diffs made in the UK have steel plates which are just phosphated and run with huge preload and on gravel are just a misery.

If you back them off they just won't develop any lock and just add weight.

I have some colleagues that are using the Titan diffs with Bronze Sintrak plates in Alfa Romeos and they tell me that they are a great improvement on the standard ZF diff and the lower cost UK manufactured units with steel/steel plates.

I agree that this isn't 'proof' but is an interesting opinion as they have used quite a few of these diffs.

As we are going to cut steel plates we will try bronze, if it doesn't work we can always moly coat. One of my old pals from University is Tech Director of a Plasma Spraying Company (another damned Metallurgist)and is quite local so we have a fall back position.