Conference terri::cars_uk

When you're stuck in the mud:

If you have an ordinary diff, one wheel (the one in the mud) will spin like
crazy, while the one on solid ground sits still.

With an LSD, the difference in speed between the two wheels is limited (that's
why it's called a Limited Slip Diff), so you always have some traction on all
the driving wheels.

I believe the internals of an LSD are similar to a torque converter (ie it's
a viscous-coupled clutch).

But then again I'm probably totally wrong...

Scott

    Well I've got one on my new lease car, and I'm wondering if it's
    making any difference. I don't really want to bog it down in some
    mud just yet to find out though.
    
    One thing that I have noticed is that if I put power on coming out
    of a corner, the back end 'wiggles' from side to side slightly.
    I wondered if this was the diff 'doing its stuff', but this is the
    first rear wheel drive car I've had, so I don't really know what
    to expect. I'm used to torque steer in the same situation from the
    last car - a R5 GTT.
    
    Pete
                                           

If the rear-end "wiggles" as you press the loud pedal coming out of corners,
it could be that the rear suspension isn't seated properly, or loose, or the
bushes are "broken".

Maybe the wheels aren't balanced properly?

You should expect less understeer and no torque steer with RWD, but certainly
not a "wiggle" (I assume you mean side-to-side wobbling)

The LSD should be unnoticeable in normal operation.

I'd get the dealer to have a look at it...

Scott

    What car is it??????
    
    
    Martin

    Limited slip diffs were notorious on high power rwd rally cars for
    making the back "squiggle" on acceleration.
    
    We never worried about a "cure". It just seemed part of the fun.....
    
    The other "test (-: is to break a half-shaft and listen to the clunk
    from the ends rubbing together as you drive along with wheel providing
    the traction.......
    
    Eee lad, them were the days..... cardboard box in middle of 'tut
    road....................

    Oopps! -.1 should have been "with the *Other* wheel providing the
    traction."

isn't rear end 'squiggle' a "feature" of most BMWs ?




...art			:-)

    re .-1
    
    Only after closing time :-)
    
    Thinking about when this has happened, the road's been damp/wet.
    I wouldn't call the 318iS a powerful rally car by any stretch of
    the imagination, but p'raps it's the same effect scaled down onto
    a wet road.
    
    Hmmmm

    I don't know what sort of slip-limiting device is fitted to the BM.
    
    If it is anything like the 'plate-type' lsd that is often fitted to
    rally cars and the like, you will know it is there by the graunching noise
    it makes when going round sharp corners (junctions etc) on dry tarmac.
    
    Just because you could hear it would not mean it is working properly though.
    
    If you have a Torsen or a Viscous Coupling diff, I would start to worry
    if you hear any noise from it !
    
    If corner is particularly tight and grip is good, you may know that
    it is working by some tyre squeal being generated - depends on tyres,
    and on the ratio dialled in.
    
    
    Anyway, why worry ?  Have you no faith in your new BMW ?

    I'm not worried, just curious that's all. 
                                          
    I was wondering if I've benefitted at all by splashing out extra on 
    the LSD option.
                   
    Pete

    An LSD helps you achieve those aggressive rock-ape/boy-racer stances
    seen in magazines when going round wet roundabouts and so on !

The 'wiggle' would indicate the LSD is working.  If it was not the inside rear
wheel (unladen) would just start spinning and you would get no power to the 
outside wheel.  With the LSD, power is getting sent to both rear wheels and
(because of the wet roads) both are slipping a bit on the tarmac and
kicking the rear end out a bit.

I can get this to happen with my tow vehicle when empty (4.3 litre V6, 3.73 LSD
rear end) if pulling out 'abruptly' and turning a corner.

Dave

    My LSD in the Frogeye is the plate type, and it does indeed 'graunch'
    on tight corners like junctions. Worried me a lot until I was assured
    that it was supposed to do it. It bangs, and almost jerks slightly as
    the plates give. I can't say I've ever noticed any 'squiggle' at the
    rear end, but it is a much lighter car than the BM, and it has a far
    harder suspension set-up.
    
    I reckon it's just the extra traction kicking the back-end about as
    someone said earlier.
    
    Laurie.
    

For GM LSD they have an additive you put in when you change the diff fluid (you
have done that, haven't you?) that prevents the plates from sticking and
eliminates the noise.  For some reason they refuse to put it in at
the factory so after 7k miles or so you get the 'banging' when turning tight
corners.  Once you start using the additive with the fluid you only need
to change the fluid every 15k or 20k miles, depending on use and all that.

Dave

Aren't BMW 3-series FWD?

(I looked at one at lunchtime and couldn't see a diff between the rear wheels,
unless it's very high up; I didn't get down on hands and knees to look that
closely!)

Scott

    It's definitely RWD, with a transmission tunnel to prove it. I must
    admit I've never looked for the diff tho'.
    
    Pete

    re .17
    
    NO BMW's are Rear wheel drive not Front wheel drive.
    
    Grant

    
    There are 4WD BMW 3-series, although (as mentioned) the bulk are RWD.
    
    Mark

Humbly yours,

Scott

    re .20
    
    As a matter of interest, just why do you dislike BMs so much ??

    
    'Coz he had one!
    
    Mark

    To check your limited slip diff - get on to a road with a loose
    surface, ie possibly an unmade road, and do a clutch-drop start - if
    you leave two wheel tracks behind, your LSD is working, if one only,
    there is no limited slip. Another way is to drop the clutch on a wet
    day standing start. If you get wheel spin, but no sideways movement of
    the rear of the car, there is no LSD. (I am assuming that a BMW can
    spin the drive wheels under these circumstances.!)
    Regards, Ray.
    

    RE: A few back.
    
    I changed the diff oil after about 500 miles. The diff was initally
    filled with EP90, but after I mentioned that I was less than happy
    about the noises coming from it, I was advised by the supplier to put
    ordinary 20/50 in. This I did, but the noise was worse, and so I
    changed it after a few miles. I refilled with an oil especially
    designed for LSDs (Castrol something or other), and the noise lessened
    considerably. It still bangs and cracks under severe load though.
    
    RE: -1
    
    If I were to drop the clutch on a loose surface I would destroy the
    paintwork on the rear end of my car!
    
    Laurie.