Chippy
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| posted on 14/12/06 at 11:40 PM |
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Sierra LSD question ?
Hi All, trying to find out what exactly happens when/if your LSD stops working. Do you just end up with basicaly an open diff, or does something else
happen. Just interested, mines working fine, (at the moment). 
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smart51
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| posted on 15/12/06 at 08:19 AM |
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The sierra LSD is an open diff with a limited slip device bolted on. The limited slip device does nothing normally but when slip occurs, a special
fluid becomes viscous, increasing friction between the wheels, limiting slip.
I can see 2 failure modes. The more likely is that you need more slip before it starts to limit, upto the point where it never limits. the other is
that it might stick in limited slip mode for ever.
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mookaloid
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| posted on 15/12/06 at 09:22 AM |
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I think I read somewhere that the special viscous fluid which locks up under slip conditions can overheat and 'wear out'
I guess this would mean that the diff would remain as an open diff in the event of failure.
Cheers
Mark
"That thing you're thinking - it wont be that."
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mcerd1
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| posted on 15/12/06 at 09:44 AM |
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There is a rough way to test these on the car in the haynes manuals (in the V6/ 4x4 manual anyway)
you jack the back of the car (so both wheels are off the ground)
put it in gear so the propshaft can't turn
and give the axle a short fast turn (1/2 a turn in ~1 sec or something) with a torque wrench (or something that can measure the torque you reach)
if the torque is in the range your LSD is supposed to be working
I did this with my sierra, and it seamed to work, but I think there must be a better way ??
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goodall
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| posted on 15/12/06 at 05:10 PM |
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the seals in the viscous coupling can get worn allowing leakage of the viscous fluid and the fluid can get contanintated by capillary action with
would cause a can in the shear value if the fluid
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mark chandler
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| posted on 15/12/06 at 05:36 PM |
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In range rovers the LSD's tend to lock solid when knackered in the secondary gearbox.
Not an issue with a locost for straight line performance !
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Chippy
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| posted on 15/12/06 at 11:23 PM |
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Hi, and thanks. So it would seem that in the event of the LSD failing then you would just have an open diff, which was really what I wanted to find
out. Rather than being left parked on the verg, if it decided to pack it in, you could continue on your merry way, but with no LS. Regards, Ray
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NS Dev
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| posted on 18/12/06 at 11:29 AM |
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quote:
Originally posted by mark chandler
In range rovers the LSD's tend to lock solid when knackered in the secondary gearbox.
Not an issue with a locost for straight line performance !
now this is what I have heard about sierra 4x4 centre diffs too, but then others have said otherwise????
its a VC just like the rear one
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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Liam
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| posted on 18/12/06 at 06:19 PM |
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When a diff locks solid, maybe it's a failure of the mechanical diff mechanism seizing, and not necessarily the viscous limited slip coupling?
Maybe planetary centre diffs are prone to siezing solid?
Whatever, i'd definately expect a sierra LSD to get looser and looser as it wears out. I've had high mileage 2.8 4x4 LSDs on which
it's been quite easy to turn the output flanges in opposite directions. My 3.92 LSD, by comparison, which is low mileage and has only had a
weedy 2 litre DOHC to bother it, is still nice and tight - almost impossible to turn the output flanges in opposite directions by hand.
Liam
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