Diff

[JNC]

Quick question ?, While underneath my car tonight I looked at the diff to my surprise it's a BMW in all the time I've owned my car I thought it was a Ford diff . Now here's the question is it an LSD  ? I ask this because I've never had the back out or wheel spin from junctions ! But it's very quiet all my experience of LSD's are very noisy ,  do BMW supply CC with open diff's as well as LSD's ?

[Jonathan Kay]

Did you try the turning one wheel by hand trick?

Jonathan

[JNC]

No it never occurred to me until after !  

[Mucus72]

How can you not have got the back end out? That's saintly driving. Well done sir. To give you more of a clue if both wheel rotate in the same direction when spinning one by hand, you have a LSD installed. In open diffs, the wheels spin in opposite directions. 

[JNC]

The jack will be out tomorrow after work. I know it sounds daft but I often hit the limiter when pulling away from junctions and hand on hart I can say I can't remember any time I've span out.

[Roadsport06]

Empty car park. Try to doughnut the car. More enjoyable that jacking up the car.

[JNC]

Had the car up at the rear tonight to fit the extra earth wire for the speedo , While it was off the ground I span the offside wheel and now I know it's a open diff. Thanks JK 

[martyn]

Dont be too sure.   My experience is that the wheels-off-the-ground spinning check isn't at all conclusive.  Caterham supply several different types of LSDs, the main two being plate and ATB. An ATB diff will behave exactly like an open diff in this test.

You'll also find that both an ATB and an open diff can behave in both ways, with a very gentle rotation causing the wheels to turn in the same direction and a more firm push causing them to reverse.

I believe that Caterham mostly only supply the quaife ATB LSD now, so it is possible you could have one of those.

Short of removing the drive shafts to check or calling Caterham and asking - an empty carpark is the best option.

[Mankee]

Nail it down a fairly flat and straight road and see if you get one tyre fire/one wheel squeal or you paint a nice black number 11 up the road.

[Geoff Brown]

LSD will be engraved on the bottom of the casing along with the final drive ratio.

[Titanium7]

To add to the above, I had one of the early BMW doffs with an LSD. It was a carbon plate diff (I think TItan) and the wheel turning test does not work with this type. There was LSD letter stamped on the underside of the diff.

[JNC]

Why is owning a Caterham so awkward from rollbar's to coil overs to extra earth wires clear or coloured tail  lights ! Carbon or not RBTB's or Jenveys the list is endless . Aargh cant help myself  Tillets  and half hoods  Avon's or toyo's . Flat floor,  remap . And not a straight forward answer anywhere.   

Is the stamped LSD in the cast iron or the Ali cover ? .

Thanks for your reply .

 

[Roadsport06]

Doughnut - Job done

[7 wonders of the world]

If it running a Titan the the wheel test will work assuming the bellevelle springs in the Titan have not already snapped and lost all the preload !!  - which is quite common due to a design flaw

[The_ASH]

That's interesting, I've seen Seven suitable diffs on eBay for sale previously both just the Titan internals without cwp and complete whole unit inc casing & backplate, obviously no guarantee of what state the things are in. Should the springs 'go' then presumably its rebuild time as the all important preload has gone. How long do they last roughly? Is there an upgrade fix available or are you constantly stuck in a reciprocal loop twixt preload and no preload.

[7 wonders of the world]

Well Titan certainly know of the problem but seem happy just to sell you new springs.

It's not merely the constant flexing that causes the issue, more flexing them outside there designed limit as in this case, since the permissible movement of the clutch pack inside the casing is quite significant this not only takes the springs through their entire range - which there not design to do, but also submits them to shock loadings.

Are you looking for an LSD at the moment?

[Jonathan Kay]

Is the following correct for the wheel test, please?

If the wheels turn the same way you know it's an LSD. If they don't you don't know what it is.

Can it be refined by doing anything with the brakes and/ or prop shaft?

Thanks

Jonathan

[The_ASH]

Not directly looking for one but had surveyed it as a possible future upgrade, I've only got a 120hp K in this car so it's not really necessary at the moment but the relative ease of the BMW diff removal (not that the Ford one is hard) means 'some bolts' and it's out. As there seem to be a few different types available, which is the best or most desirable in your opinion (or do they all have specific drawbacks).

As an aside the BMW unit is although more compact quite a bit heavier than the Sierra one I believe but to retrofit one would need driveshafts etc etc.

[martyn]

There are too many complicating factors to create any rules.  However, I think that by having the wheels off the ground and observing you can get a good feel for what you likely have.  Keep the following in mind..

A plate LSD will satisfy this test if it has enough pre-load. If it doesn't then it may appear to be an open diff.

A Quaife ATB will appear to behave like an open diff in this test.

To complicate all that further a simple open diff can appear to behave in both ways depending on many factors such as how aggressively you spin the wheel and varying levels of friction at different points in the diff.  You can observe this by playing with a simple lego technics diff.  This alone probably makes the whole test invalid.

To be correct I think it could be re-written as..

If the wheels turn the same way no matter what you do, its probably an LSD (likely a plate type). If they don't, or they behave unpredictably then you might have an LSD or you might not.

The whole matter of whether you have an LSD or not is academic.  Either the car drives how you want it to or it doesn't.  If you can't tell the difference then having one or not is probably irrelevant.   This is why the car park test is the best, because you're observing the behavior of the car as you will feel it from the drivers seat.

Edit to add..   This is also a matter of terminology.  The Quaife is actually a torque biasing diff, it cant technically be called a 'limited slip diff'

[JNC]

I will take you back to my original question ? I am pleased with how my car preforms but as I first stated to my surprise to find a BMW diff as I thought it was a Ford and could it be a LSD due to he lack of wheel spin   .I have phoned CC to ask the archivist what was supplied from new 

[aerobod - near CYYC]

Caterham shipped an upgrade for the Titan LSD to the previous owner of my 2012 R400D in 2014. It contained a couple of shims about 2mm thick to go under the belleville washers, plus a couple of new driveshaft seals. This also got rid of the clunk in the diff under load reversal and hard cornering.

[7 wonders of the world]

2mm !!!! that is MASSIVE

So CC expected you to remove the final drive strip it then strip and rebulid the LSD to add the shims?

[aerobod - near CYYC]

I could have taken the car to the only Canadian service centre for it to be done under warranty, but it is an 1100km drive plus a 95 minute ferry crossing, each way - 2 very long travel days in a 7, or preferably a 5 day trip if the car is fixed in a day. It took me a day to do it myself at home, I combined the job with the diff cover replacement (the redesigned cover that doesn't hit the dedion tube), parts also sent to me as a upgrade from Caterham. We have to improvise here in the Colonies!