nstrug
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| posted on 11/10/09 at 09:59 PM |
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Open diff vs LSD
I need to get my diff rebuilt as it's started to leak through the front seal. My question is whether I should fit an LSD or ATB diff while
it's being rebuilt - it would be cheaper to do it at the same time as the rebuild.
What are the advantages/disadvantages of an LSD or ATB vs an open diff? I know about the technical advantages, but would really like to know about the
downsides - e.g. does it actually increase the chance of over/understeer under particular conditions?
Finally, what do people recommend as the best type of LSD for a 7 for road driving with the occasional track day - Quaife ATB? viscous type? ramp type
like a Suretrac?
Cheers,
Nick
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turbodisplay
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| posted on 11/10/09 at 10:11 PM |
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ATB is best because it "senses" a loos of torque and transferes power, so the wheel losing tourque does not spin, a viscous type is speed
dependant so the wheel losing tourque has to spn faster than the road speed to transfer torque accros.
Just look how well the focus rs handels as a result of an ATB.
Darren
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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MikeRJ
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| posted on 11/10/09 at 10:26 PM |
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quote:
Originally posted by turbodisplay
ATB is best because it "senses" a loos of torque and transferes power, so the wheel losing tourque does not spin
"Best" for some applications certainly, but a torque biasing diff is useless if one wheel has no grip at all.
On a FWD car any form of diff that gives unequal torque distribution between the wheels will increase torque steer, torque biasing being one of the
better solutions in this respect but it didn't stop the RS gaining a bad rep for torque steer.
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mark chandler
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| posted on 11/10/09 at 10:33 PM |
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Pushed hard on bends an open diff will spin up the light wheel, with an LSD both will go together so you can corner faster and harder but the rear
will let go very quickly, the breakaway with an open diff is much slower.
The Sierra viscous LSD in mine feels great as you can induce and control opposite lock with a bit of track practice, never had a posh LSD, however
have had plated LSD's in the past, these clonk in and throw you off if badly set up.
However spend lots of care and attention on corner weighting, springs, dampers and ride height first, this is the trick to being fast, the diff is the
icing on the cake unless you aretrying to push loads of power through the rear wheels.
Regards Mark
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blakep82
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| posted on 11/10/09 at 11:53 PM |
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if its slippery out, a LSD (any type) can lock up if one wheel slips, making both wheels spin up. an open diff will still keep sideways grip on 3 out
of 4 wheels.
for a road car, i can't really see the point in an LSD really. in saying that though, i still want a atb for the truck 
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mad4x4
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| posted on 12/10/09 at 06:51 AM |
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Point of an LSD is to tranfere the power of the engine to the road with out wheels spin.
If you car is prone to spining wheels on tkae off. I would go LSD as this would force both rears to spin. (well try)
Scot's do it better in Kilts.
MK INDY's Don't Self Centre Regardless of MK Setting !
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turbodisplay
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| posted on 12/10/09 at 07:07 AM |
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I agree if one wheel completly loses grip with an ATB you will loose torque transfere, but how common is that, only in deep snow, but how many people
will take a seven out in those conditions.
Darren
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Dusty
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| posted on 12/10/09 at 10:15 AM |
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I fitted a viscous lsd two years back having had an open one for the previous 5 years in the seven. Track performance is transformed. Just so much
more planted and I now feel I have control of the backend of the car when pushing hard. Second best thing I have done to improve track times. (Best
was a set of 888's) As it's done 100,000 miles in a sierra the LSD bit is probably a bit tired and gentle in operation, idealy suited to a
light car? Brand new or a posh LSD might be less well suited.
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MikeRJ
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| posted on 12/10/09 at 01:56 PM |
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quote:
Originally posted by turbodisplay
I agree if one wheel completly loses grip with an ATB you will loose torque transfere, but how common is that
Common enough if you get the car to lift a wheel. e.g. the earlier Sylvas had enough roll stiffness in the rear suspension that ATB's
aren't the best solution for this reason.
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