RE: Born slippy: All about limited-slip differentials

[s m]

anything fast said:

Am I being thick here, but if he first started working on LSD systems in 1988 with the ford escort rs turbo, what exactly did he do?

As far as I know the Escort RS Turbo was on sale in 1985 and ford had been working on it for 2 years already. That car was the first FWD roadcar ever to have LSD with a viscous coupling system.

The later S2 RS came out in in 1986 and also had the LSD, so what am I missing here?

Wasn't it Ford who put in quite a bit of investment into the German Viscodrive factory in the early/mid 80s as Ferguson couldn't supply viscous couplings in great enough quantities for their road cars. I think up till then they'd got their VCs from Ferguson for stuff like the rally Fiestas etc as they only needed small quantities. I think it was something like GKN saying they could supply as long as they got large orders which Ferguson declined to fill?

[urquattro]

This is one of the key mechanical components that I just about know where it is and what it does, my main concerns with an old E Type is not to wreck the lsd and always remember the small amount of special oil needed to top it up. After 47 years and two rebuilds it is important to keep the fluid in the diff casing and not on the garage floor. Fantastic piece of engineering the lsd, whoever saw the need, did the design and converted it to hardware reality.

Edited by urquattro on Wednesday 29th February 11:09

[s m]

urquattro said:

This is one of the key mechanical components that I just about know where it is and what it does, my mine concerns with an old E Type is not to wreck the lsd and always remember the small amount of special oil needed to top it up. After 47 years and two rebuilds it is important to keep the fluid in the diff casing and not on the garage floor. Fantastic piece of engineering the lsd, whoever saw the need, did the design and converted it to hardware reality.

Yes, a lot of MOT places don't realize unless you mention it and not many places seem to have a Tapley

[loomx]

sege said:

I thought that a Torsen diff couldn't really wear, only break as the worm gears distributed the torque? ...And a torsen is just a type of branded torque-sensing diff?

So this part of the article seems to contradict that:

"PistonHeads:
Wouldn't a mechanical system be more reliable than an electronic one?

Joerg:
I don't think so. In particular the torque-sensing differential's reliability was a big issue. Because they create friction, they create noise and they have wear.

Heinrich:
With old-fashioned torque-sensing plate differentials, depending on driving style, after 60,000-80,000km the effect is just gone. Years ago we had an Opel Omega with a ZF differential, we bought it with 80,000km on the clock and measured the torque bias ratio. In one direction it was 18 per cent and in the other direction it was 13 per cent. Even an open differential, a new one which is a little bit sticky, has similar figures to this."

Heinrich does quote a 'torque-sensing plate differential': is this different to a Torsen? That sounds like he might be talking about a clutch type diff?
I have a DC2 Honda Integra Type-R (that has a Torsen) that is probably going to require a gearbox rebuild (boohoo) and after reading that I'm considering getting the Diff rebuilt/replaced at the same time to make it feel like new.
Can anyone clarify?
Confused....

The friction in a Torsen diff is due to basically a set of friction washers, I guess as these wear out the bias the diff gives will change. Theres quite alot of info on the interwebs about people changing the washers to those of different thickness' to increase the bais the differential can give. Some of the B5 Audi guys have done modifications that change it from a 60/40 split to an 80/20 split.

Having said that, IIRC the washers used to increase the bias are actually less thick, so surely as the wear the bias would increase.

[juansolo]

Excellent article. More of this please!

[pilchardthecat]

Nice article

[Mark Benson]

450Nick said:

Great to see some technical articles from PH, more of this please on other vehicle systems - very interesting read!

This, PHers are a broad church and this is the sort of thing that helps broaden it more.

[s m]

loomx said:

sege said:

I thought that a Torsen diff couldn't really wear, only break as the worm gears distributed the torque? ...And a torsen is just a type of branded torque-sensing diff?

So this part of the article seems to contradict that:

"PistonHeads:
Wouldn't a mechanical system be more reliable than an electronic one?

Joerg:
I don't think so. In particular the torque-sensing differential's reliability was a big issue. Because they create friction, they create noise and they have wear.

Heinrich:
With old-fashioned torque-sensing plate differentials, depending on driving style, after 60,000-80,000km the effect is just gone. Years ago we had an Opel Omega with a ZF differential, we bought it with 80,000km on the clock and measured the torque bias ratio. In one direction it was 18 per cent and in the other direction it was 13 per cent. Even an open differential, a new one which is a little bit sticky, has similar figures to this."

Heinrich does quote a 'torque-sensing plate differential': is this different to a Torsen? That sounds like he might be talking about a clutch type diff?
I have a DC2 Honda Integra Type-R (that has a Torsen) that is probably going to require a gearbox rebuild (boohoo) and after reading that I'm considering getting the Diff rebuilt/replaced at the same time to make it feel like new.
Can anyone clarify?
Confused....

The friction in a Torsen diff is due to basically a set of friction washers, I guess as these wear out the bias the diff gives will change. Theres quite alot of info on the interwebs about people changing the washers to those of different thickness' to increase the bais the differential can give. Some of the B5 Audi guys have done modifications that change it from a 60/40 split to an 80/20 split.

Having said that, IIRC the washers used to increase the bias are actually less thick, so surely as the wear the bias would increase.

Amazing the difference the bias ratio can make though when the diff is in action. My friend had a K-reg 220 Turbo Coupe and the gearbox went west. That had the early Torsen diff that Rover used. The bias ratio was much higher than on the later types they ( and most other manufacturers with Torsen type diffs ) used and it was much more 'friendly' in the bends with the later box and diff fitted.
The early types are something like a 4:1 ratio whereas later oners are around 2.2ish:1

If you've got a Rover 220 Turbo coupe with the early diff I'd recommend the swap to the later type!

[Dale Lomas]

Great read!

[Dagnut]

good stuff!

[FlavaDave]

The best way to learn how these things work is with a technic lego kit - should be made part of the Nat Curriculum for ALL boys to have this at primary school. I might write to the PM, give me a minute...

[Cheburator mk2]

I would disagree with them about reliability of the electronically controlled diffs vs. normal LSDs. E-diffs are nothing new - Porsche was the first to introduce them in the 959 and then in the 928. Granted, today's system takes a few more inputs, but the basic principles and action are the same. The E-diffs still have friction plates inside the clutch pack, which wear out, thus I think I am right to question their rather bold statement. Although I would agree with them that E-diffs are much better than standard LSDs...

[anonymous-user]

Cheburator mk2 said:

I would disagree with them about reliability of the electronically controlled diffs vs. normal LSDs. E-diffs are nothing new - Porsche was the first to introduce them in the 959 and then in the 928. Granted, today's system takes a few more inputs, but the basic principles and action are the same. The E-diffs still have friction plates inside the clutch pack, which wear out, thus I think I am right to question their rather bold statement. Although I would agree with them that E-diffs are much better than standard LSDs...

However an E-diff operating in closed loop speed control can "adapt" to the wear, and return a constant output status even as the mechanical wear occurs. In fact, you can simply put nice thick clutch discs in, and extend the life significantly. A mech diff that relies on preload can't adapt as that preload reduces through wear.

Further to which, the Electronic system can diagnose its own health. It's up to the driver to spot the mech diff is cream crackered.......

[jhayward1980]

Just a fantastic article - thanks - more please!

[NickGibbs]

s m said:

anything fast said:

Am I being thick here, but if he first started working on LSD systems in 1988 with the ford escort rs turbo, what exactly did he do?

As far as I know the Escort RS Turbo was on sale in 1985 and ford had been working on it for 2 years already. That car was the first FWD roadcar ever to have LSD with a viscous coupling system.

The later S2 RS came out in in 1986 and also had the LSD, so what am I missing here?

Wasn't it Ford who put in quite a bit of investment into the German Viscodrive factory in the early/mid 80s as Ferguson couldn't supply viscous couplings in great enough quantities for their road cars. I think up till then they'd got their VCs from Ferguson for stuff like the rally Fiestas etc as they only needed small quantities. I think it was something like GKN saying they could supply as long as they got large orders which Ferguson declined to fill?

Heinrich first worked for Viscodrive, which was part of GKN (or became part of) and they did lots for Ford, as you say. As well as the Escort front LSD they did the four wheel drive system for the 4x4 Sierra and Scorpio (both had essentially the same drivetrain with two viscous couplings).

[Gorbyrev]

Thanks Nick - superb article, really interesting, more please! Wonder how many XR4x4's are left out there! Not many I would wager.
Love the idea that the Beemer test pilots are all chuffed with the predictable shift to oversteer in an E60 while the rest of us mere mortals are laying down with the rear tyres. Heres to the guys who make sure we don't kill ourselves unnecessarily !

Edited by Gorbyrev on Wednesday 29th February 13:33

[wst]

legalknievel said:

I am surprised at how much I understood of that. I'm off to hit my head with a hammer until the clarity has worn off.

Here is also a pretty handy guide to how the basic open diff works, if you're still feeling intelligent. Though really this one puts it in such pleasant terms that everyone can follow it.

[s m]

NickGibbs said:

s m said:

anything fast said:

Am I being thick here, but if he first started working on LSD systems in 1988 with the ford escort rs turbo, what exactly did he do?

As far as I know the Escort RS Turbo was on sale in 1985 and ford had been working on it for 2 years already. That car was the first FWD roadcar ever to have LSD with a viscous coupling system.

The later S2 RS came out in in 1986 and also had the LSD, so what am I missing here?

Wasn't it Ford who put in quite a bit of investment into the German Viscodrive factory in the early/mid 80s as Ferguson couldn't supply viscous couplings in great enough quantities for their road cars. I think up till then they'd got their VCs from Ferguson for stuff like the rally Fiestas etc as they only needed small quantities. I think it was something like GKN saying they could supply as long as they got large orders which Ferguson declined to fill?

Heinrich first worked for Viscodrive, which was part of GKN (or became part of) and they did lots for Ford, as you say. As well as the Escort front LSD they did the four wheel drive system for the 4x4 Sierra and Scorpio (both had essentially the same drivetrain with two viscous couplings).

That's right, the XR4x4 used a centre VC as well as one in the rear diff. Ford made a 'big play' of it when the car was launched with ads showing the undercarriage of the car. They also used a VC on the S1 RS Turbo but softened up the settings for the S2 RS Turbo as it came in for quite a bit of press criticism initially.
I think Ford continued to use Ferguson Developments for their competition hardware even though the road cars were supplied by GKN-Viscodrive

Edited by s m on Wednesday 29th February 15:04

[The Black Flash]

Gorbyrev said:

Thanks Nick - superb article, really interesting, more please! Wonder how many XR4x4's are left out there! Not many I would wager.

Most of the ones which are left get turned into kitcars, the xr4 rear LSD is highly sought after.

[s m]

The Black Flash said:

Gorbyrev said:

Thanks Nick - superb article, really interesting, more please! Wonder how many XR4x4's are left out there! Not many I would wager.

Most of the ones which are left get turned into kitcars, the xr4 rear LSD is highly sought after.

I should imagine a lot of them are approaching 'open' operation after 25 years usage!