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Old 07-11-2005, 12:02   #1 (permalink)
stuart adair
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Powerlock Diff Question

I've got a query with a powerlock diff that I need some help with please
folks.

I had a problem with my XJS where the diff locked up, so when you turned a
corner both wheels tried to turn at the same speed and the tyres scuffed
along the floor. I stripped the diff down and found a couple of the clutch
disks were stuck together as it had run dry of oil.
I have freed up and cleaned the disks down so they are nice and smooth
again. When I put the diff back together though its impossible to turn one
output shaft without the other turning in the same direction. On a "normal"
diff I would expect the other output shaft to turn in the opposite direction
if there is no load.

Looking at the detail of the diff, the last friction disk to be installed is
cone shaped that when bolted up puts a lot of pressure on the planet gears
and seems to be preventing them from turning in opposite directions.

My question is to ask is this normal behaviour for a powerlock diff off the
car ?

Thanks

Stu


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Old 07-11-2005, 21:02   #2 (permalink)
Don Young
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Re: Powerlock Diff Question

Yes, this is how you identify a limited slip differential, both wheels turn
the same way when one is turned. With some types it takes a fairly high
torque to cause the clutches to slip. This is one reason for the special
"friction modifiers" used in the oil and why they will sometimes "groan"
when going around a corner. Sounds normal and good to me, Though I am not a
specialist in this.
Don Young
"stuart adair" <stuartadair@btopenworld.com> wrote in message
news:dau6mm$d7a$1@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com...
> I've got a query with a powerlock diff that I need some help with please
> folks.
>
> I had a problem with my XJS where the diff locked up, so when you turned a
> corner both wheels tried to turn at the same speed and the tyres scuffed
> along the floor. I stripped the diff down and found a couple of the clutch
> disks were stuck together as it had run dry of oil.
> I have freed up and cleaned the disks down so they are nice and smooth
> again. When I put the diff back together though its impossible to turn one
> output shaft without the other turning in the same direction. On a
> "normal" diff I would expect the other output shaft to turn in the
> opposite direction if there is no load.
>
> Looking at the detail of the diff, the last friction disk to be installed
> is cone shaped that when bolted up puts a lot of pressure on the planet
> gears and seems to be preventing them from turning in opposite directions.
>
> My question is to ask is this normal behaviour for a powerlock diff off
> the car ?
>
> Thanks
>
> Stu
>
>



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Old 07-12-2005, 02:02   #3 (permalink)
Blake Dodson
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Re: Powerlock Diff Question

Ta da! =)

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Old 07-12-2005, 02:02   #4 (permalink)
stuart adair
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Re: Powerlock Diff Question

Now does that mean that everything Don has said is accurate - Or are we
missing something ?

Stu


"Blake Dodson" <dieinterim@comcast.net> wrote in message
news:1121147666.437582.123130@z14g2000cwz.googlegroups.com...
> Ta da! =)
>



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Old 07-12-2005, 23:02   #5 (permalink)
jk
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Re: Powerlock Diff Question

I think they work like this:
The lions share of the locking torque come from the spider gears trying to
push themselves apart when they are transmitting torque and consequently
load the clutches. The more torque, the more locking; so when you are going
up that mountain road and poke that V12 a bit the inside tire will tend to
chirp and hop a bit more than if you were coasting thru a corner. However,
they need some pre-load. Take the case where one wheel is on glare ice; if
there is no initial load the clutches would not lock up (unless you give it
a little parking brake). So there are springs, or in your case, a curved
disk, to provide this.

I thought friction modifiers increased the friction on the disks, not the
other way around, but I'm not sure.

-jk

"stuart adair" <stuartadair@btopenworld.com> wrote in message
news:davq8j$p02$1@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com...
> Now does that mean that everything Don has said is accurate - Or are we
> missing something ?
>
> Stu
>
>
> "Blake Dodson" <dieinterim@comcast.net> wrote in message
> news:1121147666.437582.123130@z14g2000cwz.googlegroups.com...
>> Ta da! =)
>>

>
>



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Old 07-13-2005, 11:02   #6 (permalink)
Blake Dodson
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Re: Powerlock Diff Question

I am in agreement with Mr. Young. The other wheel will slip when a
preset torque is achieved.

Blake

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Old 07-14-2005, 03:02   #7 (permalink)
stuart adair
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Re: Powerlock Diff Question

Righto - I'll put it back on the car then and see what happens.

Stu


"Blake Dodson" <dieinterim@comcast.net> wrote in message
news:1121267171.201391.263780@g43g2000cwa.googlegroups.com...
>I am in agreement with Mr. Young. The other wheel will slip when a
> preset torque is achieved.
>
> Blake
>



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