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Sierra Scorpio 7.5” 3.38 diff
GavMax - 13/8/19 at 08:39 PM

Hi all

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

Any leads gratefully received.

Thanks
Gavin

CosKev3 - 16/8/19 at 01:28 PM

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

GavMax - 16/8/19 at 05:12 PM

They did a 3.3(something) in 7.5" that I think was bolted onto a Scorpio

mcerd1 - 16/8/19 at 05:44 PM

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]

CosKev3 - 16/8/19 at 06:22 PM

Can't you fit spacers and use the much more common 7 inch diff?

GavMax - 16/8/19 at 07:46 PM

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?

CosKev3 - 16/8/19 at 08:14 PM

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.

GavMax - 16/8/19 at 08:25 PM

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 - I’m just trying to get my head around the best way of sourcing everything

Thanks
Gavin

CosKev3 - 16/8/19 at 08:44 PM

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

mcerd1 - 16/8/19 at 09:16 PM

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]