Author |
Topic: Diff Swap (Read 3482 times) |
|
Highlander
Moderator
Expert
13 Scorpios, XR4x4, Suzuki SJ413 for off road :)
 
Posts: 8244
|
 |
Diff Swap
« on: Jul 3rd, 2009, 11:44pm » |
|
Been meaning to do this for ages as quite a few people have shown an interest in doing it...
The Scorpio uses a 7.5 inch (crownwheel diameter) Differential
The diff transfers the drive from the propshaft to the rear wheels, the diff "ratio" is the number of complete revolutions the propshaft makes to turn the rear wheels once.
eg.
on the 2.0 16v the propshaft will turn 4.27 times to rotate the wheels one complete revolution.
on the diesel the prop will turn 3.36 times to rotate the wheels once.
The Scorpio diffs have different ratios for each specific engine type:
ENGINE RATIO
2.0 8v 4.09
2.0 16v 4.27
2.3 16v 3.91
2.9 12v 3.64
2.9 24v 3.64
2.5 TD 3.36
http://www.fordscorpio.co.uk/manual/rearaxle/RAxleSpecs.pdf
(the spec for the 2.3 is wrong on the above link, they have a 3.91 ratio)
There are aftermarket diff ratios available (usually marketed for the 2WD Sierra Cosworth which uses the 7.5 inch diff but they are expensive!!)
http://www.kamdiffs.com/cosworth.htm
or you could fit a ratio from another make/model as long it has a compatible crownwheel and pinion, I've seen these range from 3.0 to 5.1
The reason for the different ratios is because of the power output of each specific engine, the lower BHP/Torque the lower the ratio on the diff.
The ratios are calculated for each specific engine size to give an optimum balance of performance (acceleration) and economy (engine revs at cruising speed)
I always try and explain it in terms of a pushbike..
If you start peddling in 1st gear its easy to get moving initially but before long you will be peddling flat out and not making much progress.. (fast acceleration, low top speed)
However if you start off in 5th gear you will find it really hard going to begin with but when you're eventually peddling flat out you will be doing a much higher top speed than your did in 1st gear (slower acceleration, higher top speed)
now transferring that thinking to our Scorpios...
the lower powered 2.0 starts off with its lower diff gearing to enable it to accelerate faster/easier while the larger V6's and the diesel with more BHP and torque can quite happily lay down enough power to move off fast under a higher gearing which allows them top speed at lower revs.
Now the reason for changing the diff ratio..
I have done it for two different reasons.
Firstly I swapped the standard 3.64 diff on a 24v for the 4.27 diff from the 2.0 16v
What this did was allow the 24v to accelerate a lot faster (nearly two seconds off the 0-60 time)
The downside is that the engine sits 1000 RPM higher for the same speed so will use a lot more fuel at motorway cruising speeds compared to the stock diff.
Although this would reduce the potential top speed it would still hit the limiter at 140mph.
Secondly I fitted the 3.34 Diesel diff to a 2.3 replacing the 3.91 diff.
What this achieived was to reduce the acceleration but allow me to cruise at motorway speeds at lower RPM, losing performance for economy (I do nearly all motorway driving with this car).
|
|
 IP Logged |
on Oct 17th, 2011, 12:35pm, Simmo wrote:I give up !  Too much for an old boy!  |
|
|
|
|
Highlander
Moderator
Expert
13 Scorpios, XR4x4, Suzuki SJ413 for off road :)
Posts: 8244
|
|
Re: Diff Swap
« Reply #1 on: Jul 3rd, 2009, 11:45pm » |
|
The range of Scorpio diff's look almost identical from the outside, indeed the main diff bodies are identical, the difference is internally with the number of teeth on the crown wheel / pinion.
There are two different types of backplate/diff mounting, both of which are interchangeable with each other, the older standard Ford mount on the left (picture above) and the newer double mount on the right (found on later model cars)
The only other difference is the drive pinions (The round parts the driveshafts bolt onto)
The Diesel and 2.9's have 108mm diameter drive pinions (for bigger CV joints) the others have 100mm. again they are interchangeable as the internal shafts are the same size.
Driveshafts use internal T40 Torx bolts to bolt onto the pinions.
This is a diesel (3.36 ratio) on the left and a 2.0 16v (4.27 ratio) on the right (note the drive pinion sizes)
The diffs are secured to the subframe by 19mm bolts (usually) one large bolt running right through the bottom centre of the diff/subframe, one either side towards the prop and one either side top rear.
There are 4 x 15mm prop bolts, these are arranged in a rectangular pattern, they are not equidistant so if its on wrong you cant line the holes up (been there got the T-Shirt) 
The older single mount backplate is secured to the body by 4 x 13mm bolts
The newer style is bolted through the two mounts then
the subframe secured to the body by a single 15mm bolt
|
|
IP Logged |
on Oct 17th, 2011, 12:35pm, Simmo wrote:| I give up ! Too much for an old boy! |
|
|
|
|
Highlander
Moderator
Expert
13 Scorpios, XR4x4, Suzuki SJ413 for off road :)
Posts: 8244
|
|
Re: Diff Swap
« Reply #2 on: Jul 3rd, 2009, 11:46pm » |
|
The backplate is held on by internal T50 torx bolts.
when removing these soak them in in WD40 and scrape out the inside of the bolt head then hammer the bit in before trying to turn it, they are very soft and if the bit isnt in right they round very easily. (T-Shirt 2) 
Remember and point them front down before slackening the backplate or the oil runs out (T-Shirt 3)
A handy friend
There is no gasket for the backplates, just a very smooth machined finish, I usually smear a light coating of oil on the faces before I reassemble them.
Its worth checking the condition of the oil fill plug at this stage and making sure it can be removed. (the diff on the left above had very little oil in it)
If you are changing the drive pinions over they are held on with circlips right on the inner edge of the shaft (circled on picture) be careful removing them, they can disappear into the depths of the diff (T-Shirt 4)
If you change the diff ratio the speedo will read incorrectly (lower ratio diff = higher speedo reading and vice versa) it takes its reading from the Vehicle Speed Sensor (VSS) on the gearbox output shaft and the rear wheels will now be turning at a different rate compared to what they did with the old diff.
Automatic Gearbox VSS circled below
Or if its raining you can reach it by removing the gear selector
The VSS has a specific number of teeth to match it to the diff (21 teeth for 4.27 diff) (19 for 3.91 etc)
The way around this is to fit the correct VSS drive pinion (bit with the teeth) for the new diff.
There are TWO different Autobox VSS that I know of (only found that out recently) and they are interchangeable.
The MT75 Manual gearbox has a different VSS.
It may be possible to interchange the drive pinions between the manual and auto VSS but I dont know, will investigate.
The clips that hold the different VSS types are different, and not interchangeable, you will need the correct clip.
These are the two Automatic VSS types, the left one is the most common, the right one seems to be the one Ford supply now as a replacent
I have found one of these on a Scorpio but it may not have been the original one
Note : The Scorpio speedo reads higher than actual speed (approximately 10%)
If you fit the VSS from the next lower ratio diff the speedo will read almost exact speed.
eg
fit the 3.64 VSS from the 24v to the Auto Diesel
fit the 3.91 VSS from the 2.3 to the 24v
fit the 4.27 VSS from the 2.0 16v to the 2.3
Obviously you cannot do this for the 4.27 diff as there are no higher ratios
The following MT75 manual gearbox info may be of use
Not been able to track down similar info for the A4LDE box yet.
Changing the wheel size or more specifically the tyre size (diameter) will also affect acceleration and speed readings in a similar way to swapping the diff.
eg
smaller tyre diameter = faster acceleration and vice versa
but thats a whole other story 
If I remember anything else or anyone else can think of anything let me know and I'll add it in
|
|
IP Logged |
on Oct 17th, 2011, 12:35pm, Simmo wrote:| I give up ! Too much for an old boy! |
|
|
|
|
martin_rowe
Full Member
I love YaBB 1G - SP1!
Posts: 879
|
|
Re: Diff Swap
« Reply #3 on: Jul 4th, 2009, 9:57am » |
|
Tooooo much spare time.
how about fitting the LSD diff from the MKIII 24v granada ?.
|
|
IP Logged |
Rally Drivers Do It Sideways
|
|
|
Highlander
Moderator
Expert
13 Scorpios, XR4x4, Suzuki SJ413 for off road :)
Posts: 8244
|
|
Re: Diff Swap
« Reply #4 on: Jul 4th, 2009, 10:09am » |
|
lol yes I do
would imagine the Granada LSD diff would be the same principle although only really of benefit to cars without traction control I would think
|
|
IP Logged |
on Oct 17th, 2011, 12:35pm, Simmo wrote:| I give up ! Too much for an old boy! |
|
|
|
|
tlundkvi
Full Member
Ex. Scorpio 2.9 24V -95
Posts: 909
|
|
Re: Diff Swap
« Reply #5 on: Jul 5th, 2009, 10:30am » |
|
on Jul 3rd, 2009, 11:46pm, Highlander wrote:
These are the two Automatic VSS types, the left one is the most common, the right one seems to be the one Ford supply now as a replacent
I have found one of these on a Scorpio but it may not have been the original one
|
|
I had the one on the left in my 24V (manufactured nov. -94). I got the feeling the one on the right was the standard one and the one on the left the odd "Scorpio I" one. The one on the right I got as a replacement.
All service pictures in charts I've seen feature the one on the right. The clip for the VSS pinion seem different too. What do you think, is the driver pinion and it's clip interchangable as well, as I've as a precaution ordered a new pinion to eliminate wear factor of my VSS problem?
Thank you for the new guide, nice piece of work!
|
|
IP Logged |
|
|
|
tlundkvi
Full Member
Ex. Scorpio 2.9 24V -95
Posts: 909
|
|
Re: Diff Swap
« Reply #6 on: Jul 5th, 2009, 1:07pm » |
|
on Jul 3rd, 2009, 11:46pm, Highlander wrote:
The VSS has a specific number of teeth to match it to the diff (21 teeth for 4.27 diff) (19 for 3.91 etc)
|
|
I got to check this too, the guy at ford said 21 teeth for 24V. It was ordered based on VIN, so hopefully he read the info from the wrong place.
With logic:
(diff ratio / teeth) is approx. 0.2033 the V6 would have 18 teeth, the 8V would have 20, the diesel would have 16 or 17. Can anyone confirm this?
The pinion and clip was at FMD available for approx. 25 euros, suspect around £20 in UK inc. VAT.
|
|
IP Logged |
|
|
|
Highlander
Moderator
Expert
13 Scorpios, XR4x4, Suzuki SJ413 for off road :)
Posts: 8244
|
|
Re: Diff Swap
« Reply #7 on: Jul 5th, 2009, 2:37pm » |
|
Interesting tlundkvi,
I seem to have found the opposite to you, all the VSS I have removed have looked like the one on the left apart from one.
Will have a look at a 24v VSS today and post the number of teeth, the diesel one might be harder to find as it would need to be an auto and i've never even seen one in the flesh
The MT75 VSS is different so we cant compare, however it does seem to follow the lower diff ratio = lower VSS teeth pattern.
I have posted new info on these above.
|
|
IP Logged |
on Oct 17th, 2011, 12:35pm, Simmo wrote:| I give up ! Too much for an old boy! |
|
|
|
|
tlundkvi
Full Member
Ex. Scorpio 2.9 24V -95
Posts: 909
|
|
Re: Diff Swap
« Reply #8 on: Jul 5th, 2009, 4:30pm » |
|
on Jul 5th, 2009, 2:37pm, Highlander wrote:Interesting tlundkvi,
I seem to have found the opposite to you, all the VSS I have removed have looked like the one on the left apart from one.
Will have a look at a 24v VSS today and post the number of teeth, the diesel one might be harder to find as it would need to be an auto and i've never even seen one in the flesh
The MT75 VSS is different so we cant compare, however it does seem to follow the lower diff ratio = lower VSS teeth pattern.
I have posted new info on these above. |
|
Or it was me that misinterpreted your reply om my post on the different VSS. I thought you referred to the metallic one when saying you never saw one of these before on a mk2 scorpio. I sourced a 2.9i Scorpio I from 1994 in Sweden that had the left style VSS. If you look at the guide I gave the link to in that very post, it is clearly the newer plastic frame model in the picture. Have seen plasic ones when browsing through bildelsbasen.se for mk2 scorpio parts. One is here: http://www.bildelsbasen.se/122-W533190.html
This post: http://www.fordscorpio.co.uk/cgi-bin/yabb/YaBB.pl?board=Advice;action=di splay;num=1245684243
But good that these kind of things get documented. The erratic behaviour of my VSS is really interesting. It works when cold, but quits working when the car gets hot after 6-8 minutes. If the car cools down for 1-2 hours the VSS works again for 6-8 minutes. Rarely, it will work again during the same run. If the pinion would be too worn, it would "jump" i'd say. It seems related to heat, but close to the VSS is only the front silencer, not the cat as I first thought. The rear heatshield foil is still in place. Maybe the plastic one is less sensitive to heat?
|
|
IP Logged |
|
|
|
Tekno
Full Member
Tenho Ruohoranta
Posts: 599
|
|
Re: Diff Swap
« Reply #9 on: Jul 6th, 2009, 10:57am » |
|
Does the (little bit different as stated above?) VSS from Granada III + A4LD still fit Scorpio ?
I'd like to put VSS from Granada III (3.64 diff) to my Scorp (3.91 diff) to correct speedo
|
|
IP Logged |
1998 Ford Scorpio Ultima Estate 2.3i 16V
|
|
|
tlundkvi
Full Member
Ex. Scorpio 2.9 24V -95
Posts: 909
|
|
Re: Diff Swap
« Reply #10 on: Jul 6th, 2009, 11:50am » |
|
on Jul 6th, 2009, 10:57am, Tekno wrote:Does the (little bit different as stated above?) VSS from Granada III + A4LD still fit Scorpio ?
I'd like to put VSS from Granada III (3.64 diff) to my Scorp (3.91 diff) to correct speedo |
|
Probably no difference, I'm not sure. But the pinion (the tip) can be ordered separately from Ford, you don't need to replace the whole VSS for that. Or just take the pinion from it if you already have it in your hands.
If you don't Tekno, I can detach the pinion from mine (3.64, 24V) and send it to you (mine is like the left one, I'm putting in a new like the one on the right). The VSS on mine is probably broken, but not the pinion. I can't reuse it when putting a new one in.
|
|
IP Logged |
|
|
|
Tekno
Full Member
Tenho Ruohoranta
Posts: 599
|
|
Re: Diff Swap
« Reply #11 on: Jul 6th, 2009, 12:40pm » |
|
on Jul 6th, 2009, 11:50am, tlundkvi wrote:
Probably no difference, I'm not sure. But the pinion (the tip) can be ordered separately from Ford, you don't need to replace the whole VSS for that. Or just take the pinion from it if you already have it in your hands.
If you don't Tekno, I can detach the pinion from mine (3.64, 24V) and send it to you (mine is like the left one, I'm putting in a new like the one on the right). The VSS on mine is probably broken, but not the pinion. I can't reuse it when putting a new one in. |
|
pm sent.
|
|
IP Logged |
1998 Ford Scorpio Ultima Estate 2.3i 16V
|
|
|
Highlander
Moderator
Expert
13 Scorpios, XR4x4, Suzuki SJ413 for off road :)
Posts: 8244
|
|
Re: Diff Swap
« Reply #12 on: Jul 6th, 2009, 4:47pm » |
|
on Jul 6th, 2009, 10:57am, Tekno wrote:Does the (little bit different as stated above?) VSS from Granada III + A4LD still fit Scorpio ?
I'd like to put VSS from Granada III (3.64 diff) to my Scorp (3.91 diff) to correct speedo |
|
Tekno, you'll need a VSS from a 4.27 diff to show an accurate reading on a 2.3
If you fit the 3.64 one your speedo will read 20% higher than actual speed
|
|
IP Logged |
on Oct 17th, 2011, 12:35pm, Simmo wrote:| I give up ! Too much for an old boy! |
|
|
|
|
Tekno
Full Member
Tenho Ruohoranta
Posts: 599
|
|
Re: Diff Swap
« Reply #13 on: Jul 6th, 2009, 5:57pm » |
|
Humm... that's not what I want
|
|
IP Logged |
1998 Ford Scorpio Ultima Estate 2.3i 16V
|
|
|
tlundkvi
Full Member
Ex. Scorpio 2.9 24V -95
Posts: 909
|
|
Re: Diff Swap
« Reply #14 on: Jul 6th, 2009, 9:44pm » |
|
If you enter the in-dash diagnostics (press trip reset etc.) I believe the speed that is shown live digitally is much closer to the truth than the analogue one.
|
|
IP Logged |
|
|
|
Highlander
Moderator
Expert
13 Scorpios, XR4x4, Suzuki SJ413 for off road :)
Posts: 8244
|
|
Re: Diff Swap
« Reply #15 on: Jul 6th, 2009, 10:44pm » |
|
I think they both use the VSS dont they?
They always seemed very similar when i've tried it
|
|
IP Logged |
on Oct 17th, 2011, 12:35pm, Simmo wrote:| I give up ! Too much for an old boy! |
|
|
|
|
tlundkvi
Full Member
Ex. Scorpio 2.9 24V -95
Posts: 909
|
|
Re: Diff Swap
« Reply #16 on: Jul 7th, 2009, 9:03am » |
|
on Jul 6th, 2009, 10:44pm, Highlander wrote:I think they both use the VSS dont they?
They always seemed very similar when i've tried it |
|
They do use the same VSS, but I think the error is induced slightly to the "needle". Not ofcourse saying the VSS is perfect, but I've used the diagnostics quite a lot when monitoring fuel levels (I have a 12.5 liter error at all levels). It has always shown a little less than the needle. Then again, the trip meter is pretty accurate which speaks for that the scorp knows the real value but shows something else. It uses the VSS signal too.
|
|
IP Logged |
|
|
|
pinto
Full Member
TD04 on a galaxy manifold ? whooooooosh !
Posts: 474
|
|
Re: Diff Swap
« Reply #17 on: Jul 7th, 2009, 8:30pm » |
|
viscous LSD unit from the Granada III can be assembled inside the scorp case AFAIK - benefits would mainly be a REAL locking action over the traction control on the later models
|
|
IP Logged |
|
|
|
Tekno
Full Member
Tenho Ruohoranta
Posts: 599
|
|
Re: Diff Swap
« Reply #18 on: Jul 7th, 2009, 10:00pm » |
|
Would be nice traction in winter with LSD diff + traction control hitting also
|
|
IP Logged |
1998 Ford Scorpio Ultima Estate 2.3i 16V
|
|
|
Highlander
Moderator
Expert
13 Scorpios, XR4x4, Suzuki SJ413 for off road :)
Posts: 8244
|
|
Re: Diff Swap
« Reply #19 on: Jul 8th, 2009, 5:25pm » |
|
I'm guessing here but I think your traction control would cut in before your LSD would, making the LSD redundant when used with a TC system
I dont think they work as a combination do they?
I would have thought either one or the other with the TC being the better option of the two?
Anyone know for sure?
|
|
IP Logged |
on Oct 17th, 2011, 12:35pm, Simmo wrote:| I give up ! Too much for an old boy! |
|
|
|
|
|
Home
Help
Search
Members
Login
Send Topic
Print