Limited slip diff

Ken Mason · 05-19-04, 10:46 AM

I wonder if anyone could tell me whether I should bother with a limited slip diff for road use. I tried searching the forum but came up with no ideas.

It's just that I have been told a limited slip diff can make the car a bit 'squirrely' in normal road use and I might be better off without one.

The engine is a 350 chevy small block with no particular claim to huge horsepower. The current gearbox is a Renault 30 which I intend to change for a 21 turbo box, but should I go for the special diff as well or save £1000???

Ron Earp · 05-19-04, 10:51 AM

Well, with that Chevy engine in there you won't need a limited slip - you'll never generate enough power to break traction!! Just kidding [img]/ubbthreads/images/graemlins/smile.gif[/img]

There is no reason the LSD should make the car unsettled. I could see that if you were using a locker diff or spool, but to my knowledge folks aren't making these/using these in GT40s. I assume you're referring to a quaife type that a lot of us use and that shouldn't give you any problems.

Paul W · 05-19-04, 05:37 PM

I think the LSD problems you are on about are associated with front wheel drive cars as this affects steering considerably. On a rear wheel drive car theoretically it shouldn't affect the steering - just allow you to get more power down on those traffic light take offs. [img]/ubbthreads/images/graemlins/smile.gif[/img]

JP · 05-20-04, 04:58 AM

Good question.

Well since I use the road like a racetrack I would have to say that you are losing some handling ability without one - especially at the limit.

You need to speak to Kevin Jones of GTO Engineering. TEL 0118 940 1101. Should be about £650+VAT.

Regards,

J.P

P.S Why not phone Kevin and ask him what he thinks. He his very knowledgable.

Paul Thompson 'Hooligan' · 05-20-04, 05:25 AM

[ QUOTE ]

Well since I use the road like a racetrack I would have to say that you are losing some handling ability without one - especially at the limit.

[/ QUOTE ]

Hmmmmm.... Save it for the track James, its a whole lot safer and you won't get 'nicked'. [img]/ubbthreads/images/graemlins/frown.gif[/img]

However - Quaife ATB Diff transformed Roy's GTD40, the rear end has become more stable in corners (both tight and sweeping) - A big thumbs up from ME! [img]/ubbthreads/images/graemlins/grin.gif[/img]

ps - just added James's Profile to the club website. [img]/ubbthreads/images/graemlins/wink.gif[/img]

Malcolm · 05-20-04, 05:26 AM

Everyone I know who has an LSD really likes it. For road driving you should be fine. I advertised a Renault LSD in the for sale section a while back but its still in my garage. Therfore if you are interested am now open to offers.

Malcolm

Robert Logan · 05-20-04, 06:52 AM

I highly recommend LSD for all my cars. They make the car easier to drive in bad conditions such as rain and snow (we rarely get either here in Australia). The rear of the car is less likely to step out and when it does it is Limited.

If your car is very stiff as most race cars are than the LSD comes into its own; we have spun cars on circuits because the inside rear wheel was free spining as it is not in contact with the track. When that wheel come back down onto the track it was spinning much faster than the outside wheel and round the car went. That particular time the driver stopped the car at 90 degrees but the car still backed into a wall. The rear was damaged as were a few other things and the repair / replacement was MUCH greater than the "slippery diff" would have been.

For those reading this and a little sceptical about the wheel in the air thing, we had full MoTeC data logging on the car and a TOP test driver in the car. The engine rev spikes and other things recorded tell the full story.

In short I think the slippery diffs are simply the BEST THING MONEY CAN BUY for our cars. Give Malcome a call very quickly before someone else gets in before you.

Best wishes,

Robert

Ross Nicol · 05-20-04, 09:29 AM

Ken
I've owned a rear wheel drive car fitted with a limited slip diff.On a wet road and a bit too much throttle the rear end would step out, which could be described as "squirrely".With an open diff this doesn't happen and the wheel with least traction will spin.The silly thing is as this wheel spins, more power is fed to it and more wheel spin occurs.I reckon if you do a lot of fast starts and get a lot of wheel spin that annoys you, get a lim slip, if not don't waste your money.
Regards Ross

Lynn · 05-20-04, 09:43 AM

Ken,

When I purchased my transaxle I didn't buy an LSD since I was building a road car. The more people I talked to, the more it became apparent that an LSD is a good thing to have and the more power you have the better it is. The choice then becomes do you get a true (clutches) LSD or a torque biasing unit. The LSD will give you control on acceleration and deceleration; whereas, the TBA style will only effect the handling on acceleration. But either will work to stabilize the car over the open diff. If you never plan to do any track days or high performance driving, I really think it is totally optional though. Also, remember that most of them can be adjusted as well. The way it was described to me, the only time you will notice any adverse behavior is if you do a very tight U-turn with the car.

Regards,
Lynn

roaldin · 05-20-04, 10:04 AM

As the owner of (past and present) several cars so equipped, I submit that there is a vast difference between various types of LSD. A plate diff' with too much preload will make a car "squirrely" in slippery conditions and can make the car tend towards understeer on dry surfaces (unless provoked [img]/ubbthreads/images/graemlins/cool.gif[/img]). This can of course be "driven around".
A well set up plate diff' should behave fairly well but getting a compromise that works wet and dry can be difficult.
A Quaife or Torsen type diff' should be well behaved under most conditions.
I don't particularly like locked type diff's although they are very predictable.
Lockers, as in either open or locked depending on situation, are awful and should be avoided.
I quite like viscous coupled diff's for the road but they can't take much of a beating and destroy themselves fairly quickly.
The behaviours of the above diff's (and the rest) are completely different to each other. It's up to the owner/driver/designer/whoever to decide what characteristics they want, eg what does the diff' do on overun as opposed to under power.
I would never have an open diff' in a light high powered car.

Tim.

Mark Worthington · 05-20-04, 11:15 AM

In my opinion a torque-biasing limited-slip differential is an absolute must in a GT40. For those who use Audi transaxles, the 016 boxes come from the factory with an open diff (I believe the 5000 Quattro center diff was lockable from inside the car via a pneumatic mechanism). The 01E boxes come from the factory with a Torsen-type torque-biasing LSD (the Quattro 01E boxes also have a Torsen unit on the tailshaft). My 016 box has a Quaife LSD supplied by Roaring Forties. I still haven't figured out if it can be used in the 01E box (Quaife lists two different part numbers for the 016 and 01E LSDs, and they both cost $1,500). I keep meaning to call Quaife but can never seem to get through. If possible, I'd like to adapt my 016 LSD to an 01E box, because some of the Audi guys say the Torsen will be one of the first things to fail under high-HP applications.

andys · 05-20-04, 02:24 PM

[ QUOTE ]
In my opinion a torque-biasing limited-slip differential is an absolute must in a GT40. For those who use Audi transaxles, the 016 boxes come from the factory with an open diff (I believe the 5000 Quattro center diff was lockable from inside the car via a pneumatic mechanism). The 01E boxes come from the factory with a Torsen-type torque-biasing LSD (the Quattro 01E boxes also have a Torsen unit on the tailshaft). My 016 box has a Quaife LSD supplied by Roaring Forties. I still haven't figured out if it can be used in the 01E box (Quaife lists two different part numbers for the 016 and 01E LSDs, and they both cost $1,500). I keep meaning to call Quaife but can never seem to get through. If possible, I'd like to adapt my 016 LSD to an 01E box, because some of the Audi guys say the Torsen will be one of the first things to fail under high-HP applications.

[/ QUOTE ]

Mark,

Do you have more info on the factory LSD for the 01E? I am not aware it was offered....Reading your post, I'm not sure about your reference to the Torsen, since it is only the Quattro (to my knowlege) that uses a Torsen for the front to rear drive torque biasing.

It is my experience that an open differential is somewhat easier to drive in wet conditions (or crossing a wet spot under accelleration) on the road. Light weight high HP cars can become exceedingly abrupt when wheelspin occurs in a turn on a street with limited run off area (read curbs or opposing traffic). This can be a frighteneing experience, even for an accomplished driver. Even when placidly driving my Ford Explorer with LSD in the wet, you must pay attention. The flip side is that it is difficult, even frustrating to get any power/traction whatsoever to the groung with an open diffferential in wet conditions.

The race track is an entirely different enviornment where a car is driven nothing like it is on the road (well at least in my case). The debate will surely continue, though.

Andy

jimbo · 05-20-04, 07:53 PM

Don't the ZF transaxles have a limited-slip rear axle in them; I think it is the clutch type but I am not sure. I don't know if Torsen rear sections were available at that time. I have a 5DS25-2 unit. Would like to know, if anyone is up on this...

Robert Logan · 05-20-04, 07:59 PM

AJS and Mark,

We have just had a ATB style LSD built for the 6 speed Audi OIE box for a car we are building at the moment. I contacted Quaife a number of times and got no response regarding their LSD for the 6 speed. This is not to say that they do not make them only that they did not respond to my calls and e-mails.

The 6 speed LSD's will be available from us shortly and the price should be close to our 5 speed LSD.

Mark,

Our machinists could not convert the LSD's and I am happy to exchange LSD's if you would like.

Best wishes,

Robert

andys · 05-21-04, 12:49 AM

[ QUOTE ]
AJS and Mark,

We have just had a ATB style LSD built for the 6 speed Audi OIE box for a car we are building at the moment.
The 6 speed LSD's will be available from us shortly and the price should be close to our 5 speed LSD.

Best wishes,

Robert

[/ QUOTE ]

Robert,

Are the units you will be offering for the 01E a modified version of an existing ATB type, or a custom made unit to your specifications? What price range will it be?

Thank you,

Andy

JP · 05-21-04, 05:07 AM

Quaife make a bloody good product. But. Their customer service has to be the worst I have ever come across in any industry.

It seems as if they are only interested in the big deals .i.e Ford.

It's a pity there is not an alternative.

Ross Nicol · 05-21-04, 05:09 AM

Jim R
The ZF 5DS25-2 certainly does have a limited slip diff of the clutch pack type.I know the internals of mine intimately. By the way during my last race meeting at Sandown it got very wet and I found myself on some very worn out and hard Yokohama AO32r tyres.There is a tight corner coming onto the straight and when I gave it a boot full I nearly sideswiped a Ferrari 360(yes they clapped in the pits).Now as I managed to hold it together, each time I applied power going down the straight it stepped out and frightened the crap out of me.Now this is what a car with a lim slip will do because both wheels are driving at the rear.When I'm cornering the lim slip also pushes the car and tends to make it understeer.Only racers will have experienced this.Oh BTW I went out and purchased some wet slicks Cost $1800 instead of writing off the $100k car and boy do those tyres make a difference.They are so soft your finger nail disappears into the rubber.
Regards Ross

Chris_K · 05-21-04, 03:40 PM

Ross-

Take a look at roaldin's post up above. Based on my (albeit limited) knowledge of LSD's, it sounds like either your clutch pack may be too tight, or if it's that tight on purpose some restraint may be required when the going gets wet.

If it's as tight as it sounds, I'd bet both your rear wheels shake loose and the rear end slides. If more slip were allowed, maybe one could hold on a little longer...

If you're finding your car is also pushing through corners in dry race conditions, it sounds like it may be time to loosen your clutchpack. Your dif may be NSD (no slip dif).

FWIW, I had a spooled RX7 which I rallied. To "break it in" I got it out on road courses and autocrosses. It flat out refused to turn in without large amounts of persuasion. Once out on the dirt though it was money!

Your mileage and opinions may vary though...

Cheers,

Ron Earp · 05-21-04, 03:48 PM

Here is what I can tell you about no LSD in a mid engine car. When I run my Lotus hard in corners, hard enough to unload the inside wheel, it starts to light up the inside tire. And, when on the power it keeps lighting it up with no end in sight except to reduce throttle. Now, if one has already got the rear end stepped out a bit dropping the throttle will give you some other issues to deal with, that is for damn sure.

Basically, I don't get too much on the juice in that car while hard in a corner, it does no good. Plus, I'm on the street as my first track day in it isn't until July. However, I imagine the same thing will be found on the track as others have indicated.