Building an RX7 LSD diff

Technical info not specifically 1st gen RX7 related.
mc turbo

Re: Building an RX7 LSD diff

Post by mc turbo » Tue Jan 20, 2015 1:59 am

TOOL wrote:An ATB LSD is a type of Torsen diff. I think the original Torsen patent expired and then it's been copied over and over. Gleasman designed it.

Here's a Torsen LSD for MX5 at £615 plus VAT: http://shop.quaife.co.uk/catalogsearch/ ... del=416&q=

Kaaz LSD is $1000.
Here's a light hearted read for you about KAAZ LSDs: http://magnusmotorsports.com/tech-artic ... erentials/

Viscous are junk. OBX seem to be slated too.

I'm not sure what you're getting for £220 new. You've still got to add side bearings and assembly. They can't be any good at that price.

The clutch type is the original Mazdaspeed design. It's what they put in the JDM 12AT. It's what they put in the GSL-SE. You can rebuild them.
I think they went with the Torsen later on cos they don't need maintenance.
The ones I get and build have all been in great shape. They're easy to work with, so I use them. I'm happy to install Torsen's if that's what people want. I did it to show it could be done.

Bottom line, they are both a huge improvement over an open diff. They'll both take 250hp all day too.
I have a mazdaspeed selective diff on my fc3s which apparently is adjustable from 1, 1.5, & 2 way but mine is a bit harsh as its set on 2 way setting do u know how to adjust the setting? as 1.5 would b more than enough for street & track !

TOOL
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Re: Building an RX7 LSD diff

Post by TOOL » Sat Mar 07, 2015 6:14 pm

I figured it was time for an update on the diff front.

I've done a few LSDs for people now, which I personally think is great, because until I started doing them you really couldn't find one in Europe. I'm pleased I could help people out and I've enjoyed learning about them and working with them.

Anyway, the next thing is diff ratio changes. All the RX7 diffs I've had have been 3.9:1 ratio. It's a good all round ratio, but for getting off the line and for circuit racing and the like, you really want something a bit shorter, in the 4.3:1 to 4.5:1 ratios. This will mean you'll be revving higher on the motorway, but that's not where we want to spend a lot of time with our cars so who cares. What you will do is be able to spend more time in your preferred rev range, which we do want.

The trick is finding suitable gears........

18 months of hunting and searching and I finally tracked down a 4.3:1 ratio crown wheel/ring and pinion 43 teeth on the ring and 10 teeth on the pinion. Here it is:

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Here's the complete stack, with bearings, crush washer etc.

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Here's the single use crush washer, which maintains the tension on the bearings (new one on the right):

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Here's the new crush washer in place on the stack:

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Back in sunny France

TOOL
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Re: Building an RX7 LSD diff

Post by TOOL » Sat Mar 07, 2015 6:19 pm

And here is a 4.44:1 ratio set of gears I picked up late last year. 40 teeth on the ring and 9 teeth on the pinion:

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I'll share pics when I build them up as well.
Back in sunny France

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MelloYello
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Re: Building an RX7 LSD diff

Post by MelloYello » Sat Mar 07, 2015 6:27 pm

Spreading the love Tool. You are a good man. th:

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ian65
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Re: Building an RX7 LSD diff

Post by ian65 » Sat Mar 07, 2015 6:40 pm

Great stuff Tool, having fitted a lsd last week, I can testify just what a difference they make..... changing ratios for different applications is a good idea th:

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spirit r
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Re: Building an RX7 LSD diff

Post by spirit r » Sat Mar 07, 2015 7:16 pm

You have to change speedometer drive or wheel dimension sometimes.
Thomas

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ian65
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Re: Building an RX7 LSD diff

Post by ian65 » Sat Mar 07, 2015 7:50 pm

spirit r wrote:You have to change speedometer drive or wheel dimension sometimes.
Thomas
that's a good point Thomas th: Can't just change the speed drive though because the pitch of the gear teeth are different on the s1 / s2 / s3 gear boxes so the drives aren't interchangeable.

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Re: Building an RX7 LSD diff

Post by TOOL » Sat Mar 07, 2015 9:14 pm

You just get it re calibrated if it concerns you.
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Re: Building an RX7 LSD diff

Post by TOOL » Mon Mar 09, 2015 10:29 am

If anyone else is interested in a lower ratio ring and pinion for their diff, let me know and I will keep searching. It's been a lot of research and some trial and error, but I'm starting to get results.

Let me know what ratios you want.
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Re: Building an RX7 LSD diff

Post by TOOL » Mon Mar 09, 2015 8:51 pm

Come to think of it, if I take the 43 tooth crown wheel and put it with the 9 tooth pinion, I've also got a 4.78 set of gears.

There could be lots of interchangeability here. I might have to put a table together.
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