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OK boys and girls, I've spent a good part of the afternoon looking for the LSD fluid
that the most knowledgeable group on the net says is the right one for a 1974 spider.
I've had my first "hot Toddy" of the evening so I'm done looking. What do the experts say???
 

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The real question is do you want a gear oil with a limited slip additive or one without for the differential? And do you want to run a synthetic or conventional gear oil?

I've always had great luck with Redline gear oils, and that's what we sell. Their 75W90 gear oil has the limited slip additive, and their 75W90NS doesn't.

Conventional wisdom says you would want the 75W90 for a rear end, and for most people it is the best choice. The limited slip additive eliminates the "chatter" you can get with a LSD diff going around tight corners.

BUT - some people advocate for the 75W90NS in a limited slip differential as well - the thinking being that without the limited slip additive the differential can lock up a little quicker. I have run the 75W90NS in my GTV and didn't notice much "chatter". Keeping in mind that the Alfa LSD is a relatively mild 25% locking factor.
 

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Joe,
please elaborate on the "chatter". Are you more or less likely to hear it in tight turns and could it be mistaken for a tire rubbing a fender?
Thanks.
 

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Joe,
please elaborate on the "chatter". Are you more or less likely to hear it in tight turns and could it be mistaken for a tire rubbing a fender?
Thanks.
You are most likely to hear the chatter in tight turns. It is the clutch plates binding on each other and then releasing. As I said, with a 25% locking factor in a stock Alfa differential if you do feel it it will generally be mild.

Using a gear oil with limited slip additive (or adding some to a gear oil without it) will make it go away, at the expense of some traction.

This video explains it from a very basic standpoint:

 
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