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Author: Subject: Sierra Scorpio 7.5 3.38 diff
GavMax

posted on 13/8/19 at 08:39 PM Reply With Quote
Sierra Scorpio 7.5 3.38 diff

Hi all

Looking to buy a 7 1/2 3.38 Sierra/ Scorpio diff (ideally limited slip)

Any leads gratefully received.

Thanks
Gavin

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CosKev3

posted on 16/8/19 at 01:28 PM Reply With Quote
Did they ever make a 3.38 ratio in 7.5 inch?

Deffo wont find a original one with LSD,as it was only cosworths that had a 7.5inch LSD,and they weren't 3.38 ratio

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GavMax

posted on 16/8/19 at 05:12 PM Reply With Quote
They did a 3.3(something) in 7.5" that I think was bolted onto a Scorpio
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mcerd1

posted on 16/8/19 at 05:44 PM Reply With Quote
quote:
Originally posted by GavMax
They did a 3.3(something) in 7.5" that I think was bolted onto a Scorpio



the 7.5" did come in a 3.36 ratio - I believe it was on the 2.5 Turbo Diesel Scorpio, so zero chance of it being a LSD from the donor



the 2wd sierra cossie used a 7.5" LSD with a 3.64 ratio and 108mm flanges for the CV's (same size CV's as some BMW's etc...)

the early granda/scorpio 24v cosworth's used a 7.5" LSD also with 3.64 ratio but with 100mm CV flanges (same size CV's as normal sierra's with read discs and the 4x4's ) - later cars with traction control don't have an LSD.

(in both cases the ford LSD's need bolt-on driveshafts, and the LSD flanges are different from open diff ones)



so you can mix and match all the above to get what you need but its a full rebuild of the diffs

[Edited on 16/8/2019 by mcerd1]





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CosKev3

posted on 16/8/19 at 06:22 PM Reply With Quote
Can't you fit spacers and use the much more common 7 inch diff?
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GavMax

posted on 16/8/19 at 07:46 PM Reply With Quote
I had new drive shafts made to suit my application and I don't really want to go through all that again - it wasn't cheap so I' rather stick with the 7.5" set up. The only problem is that I fitted a 3.92 which means that at 70 I'm around 3,500 revs. I want to use the car for longer journeys and the noise gets quite wearing. A 3.64 should drop 70 to around 3000. If i could find a 3.34, that would be better still but I don't know how many are around.

Is it possible to convert a 7.5" open diff to an LSD using the same ratio? - What needs to be changed?

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CosKev3

posted on 16/8/19 at 08:14 PM Reply With Quote
Yeah the crown wheel and pinion are the same,so you change the centre part of the diff,the crownwheel just bolts on and off.

But if it's the same as the 7 inch diffs you will need the LSD output shafts,open diff output shafts cant be used.

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GavMax

posted on 16/8/19 at 08:25 PM Reply With Quote
Thanks

So if I sourced an LSD unit from a different ratio 7.5 diff say a 4.27, could I switch it into a 3.64 non LSD 7.5 unit?

Sorry to be inept about this - Im just trying to get my head around the best way of sourcing everything

Thanks
Gavin

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CosKev3

posted on 16/8/19 at 08:44 PM Reply With Quote
Yeah,but you will need to find out if you need the output shafts too,pretty sure they will be needed.

With a 7 inch diff the LSD output shafts are unequal lengths,where as the open diff ones are equal length

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mcerd1

posted on 16/8/19 at 09:16 PM Reply With Quote
quote:
Originally posted by GavMax
I had new drive shafts made to suit my application and I don't really want to go through all that again - it wasn't cheap so I' rather stick with the 7.5" set up.


I've only got a couple of 7" diffs here, but I didn't think the input flange location was much different between a 7" and a 7.5" ?

My dax chassis is built for either size, but only comes with a single length of prop (although that is in a type 9 box so its got a little adjustment built in)
I can measure the distance from the 7" input flange to the mount / driveshafts for comparison if you like



[Edited on 16/8/2019 by mcerd1]





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