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Sierra Diff 7" 3.92 LSD I think


samfransisco

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This has been sitting in my garage for ages now as was bought for a upgrade to a westie that never happened.

Looks clean inside.

Desirable 3.92. Now this acts as an LSD when I turn the input shaft and try and hold onto one of the output shafts. However, I'm not 100% sure. If someone has an idea of what to look for. Maybe it's obvious off the part number in the pictures.

Shafts turn smoothly and cogs look in good shape.

Any inspection welcome.

Collection only please from CV37 8RJ

 £250 ono

Thanks

 

Mark

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I may be interested if it can be confirmed as a LSD. The numbers don't seem to appear on a database that I'm looking at super7thheaven: http://www.super7thheaven.co.uk/components/sierra_rear_differential/ but that's not to say that this is entirely correct. Mark, are you able to brush some of the crud off to better read the part nos, please.

TBH, I may also be interested if it's non-LSD as I currently have a 3.62 LSD fitted and I'm pretty sure that the LSD unit is transferable .. I await the diff gurus to confirm or correct me! :)

 

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Found some more info here: http://www.super7thheaven.co.uk/components/sierra_rear_differential/granada_microfiche_2/ that would appear to suggest that it's a 3.62 however, unless we know the history, it is likely that someone has maybe put a 3.92 cwp into a 3.62 casing?? Does anyone know of a foolproof way in which Mark can confirm the ratio?

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The only foolproof way is to either count teeth or to mark the input and output flanges and count the turns.

Its been so long since many of these diff stuff left their original fitments that many have indeed had ratios swapped over the years. Not everyone tries to keep the tags with the right crown wheel and pinions.

Its not the clearest of pictures on an iPad, but the casing at the back of the crown wheel does just about look thick enough to be a viscous lsd module. Would want a clearer shot to be sure though.

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I thought you could tell if it is an LSD if you look through where the output flanges go?

If you look through and see a bar, it's not LSD - if you see straight through it is - but there's also an ATB that has an "X" (I think) - will find pics...

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Looks open to me as you can see the planet gear cluster

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you can see the planet wheels on both open and viscous LSD diffs, it's ATB's etc where you can't.

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In my experience for what its worth.

It looks like an LSD due to the fact that the drive shafts are of unequal length.

Proof though will be to turn one output shaft and the other output shaft will turn the same way for it to be an LSD. Don't turn the input shaft, its not relevant.

The codes on the casting are a bit difficult to trace, ideally you need the small metal tag that would have been on the top bolt but these get lost easily.

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Heres a video I just took of the output shafts turning as they should for an LSD.

This is why I am pretty sure. However, I can't remember buying the thing it was so long ago. Feels smooth though.

 

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12 minutes ago, samfransisco said:

Secondly, do you think I can make it as a hand model?

Mark, you'd make a great hand model! :laugh: Okay, so let me PM you shortly. 

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I'll contact you again tomorrow re payment, etc. 

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Hold on a sec. I put some bars on the ends last night to try and make sure (I fear my hand modelling is simply not torquey enough) and managed to get them to turn like an open diff.

Pretty sure I should not be able to do this with such a relatively small amount of torque.

I'll do a bit more investigation today and if so I will reduce the price and change the description.

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36 minutes ago, samfransisco said:

Hold on a sec. I put some bars on the ends last night to try and make sure (I fear my hand modelling is simply not torquey enough) and managed to get them to turn like an open diff.

 

Pretty sure I should not be able to do this with such a relatively small amount of torque.

 

I'll do a bit more investigation today and if so I will reduce the price and change the description.

 

Ah, I've heard that diffs do need to have some 'load' put on them when identifying open or LSD.. :oops: I'm pretty sure you shouldn't be able to either. Again, I think I recall that it's different testing it on a bench compared to on a car but I may be wrong. Hoping someone will be along shortly to assist further in confirming whether it is open or LSD :)

 

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