SeanStone
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| posted on 22/4/10 at 11:41 AM |
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Changing 7" diff for 7.5"
What is involved in this? Am I able to use the existing drive shafts?
There are far more ratios that I need (4.2+) in the 7.5" form than with the 7" form so it might be more cost effective to change the diff
rather than go for a new crownwheel and pinion which is 500 +vat +fitting
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mcerd1
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| posted on 22/4/10 at 12:06 PM |
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it'll depend how much room you've got around the diff at the moment - the 7.5" is a fair bit wider across the mounts....
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SeanStone
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| posted on 22/4/10 at 12:32 PM |
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Presumably half an inch?
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Lars
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| posted on 22/4/10 at 01:26 PM |
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quote:
Originally posted by SeanStone
Presumably half an inch?
I believe that is the case, but that is not what the 7" refers to
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SeanStone
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| posted on 22/4/10 at 01:34 PM |
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Okay, so apart from the difference in top mount width, what other things are effecting the swapping of the different diffs?
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Paul (Notts)
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| posted on 22/4/10 at 02:57 PM |
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swapped my 7 1/2 inch bolt on for a 7 inch bolt on by just dropping out one and putting a spacer on the top mount of the 7 inch to make it 7 1/2 .
shafts just fitted back on.
Paul
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jacko
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| posted on 22/4/10 at 03:38 PM |
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diffs
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t16turbotone
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| posted on 22/4/10 at 03:46 PM |
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Be carefull to get the right size output flanges. There is 108mm (2wd cosworth), and 100mm Flanges.
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SeanStone
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| posted on 22/4/10 at 04:53 PM |
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the differing output shaft wont be a problem if the prop hasnt been made yet will it? Or is the output shaft where the driveshafts join?
I'd be using the 4.27 ratio which i believe is on the 2 litre 16v scorpio
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jacko
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| posted on 22/4/10 at 05:22 PM |
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Its the drive shafts that are different
cozzy shaft bolts are 10mm were sierra 's are 8mm
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SeanStone
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| posted on 22/4/10 at 05:32 PM |
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Hmm. Well from the chart on here http://www.fordscorpio.co.uk/mt75.htm
it would seem that the only car the 4.27 is from would be the 2 litre 16v, which isn't the cossie cariant. Whether or not the scorpios have
cossie sizes as standard, I don't know
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mcerd1
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| posted on 22/4/10 at 05:40 PM |
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the 2.0 scorpio's they have the same size CV joints as the 7" bolt-on sierra ones 
I guess you'll have to watch the driveshaft lengths (there are a few different lengths) and the mounting bolts are 6 short ones instead of 2
long and 2 short.
btw some cars (inc. dax rush's) are designed to fit both types of diff, you just use different bolts and spacers to make them fit 
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SeanStone
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| posted on 22/4/10 at 05:46 PM |
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Well I'm going from a 7 to a 7.5, so Hopefuly it's already needed spacing!
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nike5
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| posted on 22/4/10 at 08:08 PM |
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Why are you changing - most people I heard go the other direction - to save weight.
Just curious.
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SeanStone
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| posted on 22/4/10 at 09:18 PM |
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Because to change my 7" diff to a ratio above 4.1 will cost me the best part of £750.
To change to a used 7.5" 4.27 will probably cost around £200 or less.
The S2000 has a final drive of 4.1 and I wanted a ratio either the same or bigger.
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mcerd1
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| posted on 23/4/10 at 07:48 AM |
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^^
do you know that a higher numbered ratio is actuall a lower gear ?
(sorry - just asking the obvious question)
have you had a go with one of the gear calc. programs yet ?
http://locost7.info/gearcalc.php
I know that some of the S2000 dax's use 4.1 / 4.4 ratio diffs and are very happy with them - but tyre size comes into it too and folk tend to
use bigger wheels/ tyres on the dax's
[Edited on 23/4/10 by mcerd1]
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MikeRJ
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| posted on 23/4/10 at 08:42 AM |
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quote:
Originally posted by mcerd1
^^
do you know that a higher numbered ratio is actuall a lower gear ?
Do you know the S2000 engine revs to 9000RPM? 
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SeanStone
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| posted on 23/4/10 at 09:11 AM |
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yea i'm aware of how the ratios work, and that 4.44 ratio will cost me a lot of money to fit into my existing diff.
I'm not so bothered about going past 140, i know there is a westfield with an s2000 engine that topped 150 at spa but i wont achieve that on the
british race tracks that i'll be going on.
And yea, as is correctly pointed out, it revs to 9000 rpm which effectively lengthens the gearing
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mcerd1
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| posted on 23/4/10 at 10:06 AM |
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I didn't think you were wrong - its confused alot of people on here in the past so its normally worth asking
I've actually looked at the same diff's before - my 3.92 should do for now
but if I ever get round to my head upgrades then 9000 rpm is a posability for me too 
assuming I had limitles power the 3.92 would give me a top speed of 196mph 
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SeanStone
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| posted on 23/4/10 at 11:08 AM |
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What engine are you running?
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mcerd1
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| posted on 23/4/10 at 11:13 AM |
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well its not running yet - but it will be a 2.1 pinto :lol:
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