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        General >> Give/Need advice to/from others >> Diffs
        
(Message started by: Highlander on Oct 20^th, 2006, 8:40am)

Title: Diffs
Post by Highlander on Oct 20^th, 2006, 8:40am

Anyone know if these diff ratios are definitely correct on this page?

http://www.fordscorpio.co.uk/manual/rearaxle/RAxleSpecs.pdf

reason being is ive just removed what looks like an original diff from a 97 2.3 estate and its a 3.9 instead of the 4.27 it says on here.

Past experience with Escorts/Capri's etc tells me usually the lower capacity engines have the highest ratio diffs so a 3.9 in a 2.3 would "seem" to be correct

Also the 4.09 in the 8v's seems not to fit the pattern either..

Anyone shed some light? ;D

Title: Re: Diffs
Post by martin_rowe on Oct 20^th, 2006, 8:53am

4.27 is higher ratio than 3.9.

Title: Re: Diffs
Post by martin_rowe on Oct 20^th, 2006, 8:56am

oops get brain in gear, wrong way round, 3.9 is higher than 4.27, the 'lower' diff gives lower top speed for same rpm, smaller engines dont have the power to pull the higher diff ratio. the 4.09 in the 8v is probably to suit the engines charicteristics, & provide higher cruising gear, for economy.

Title: Re: Diffs
Post by Highlander on Oct 20^th, 2006, 9:06am

Yep, i understand the principles of it but why have i got a 3.9 when it says 4.27? ;)

When the car is running the speedo seems to read correctly when tested alongside another car

Title: Re: Diffs
Post by howiedintheplace on Oct 20^th, 2006, 11:02am

I had a diff from a 2.0L 16v that was a 4.27:1.

People can help you out here.

If you select either 4th (manual) or 3rd (auto) & post what RPM exactly you have at say 50 mph + your tyre size then I can tell you what diff you have.

Title: Re: Diffs
Post by TiberiuS on Oct 20^th, 2006, 12:01pm

Slightly off topic but this may help ;).

On the Racer Scorpio model, the 2.0 and 2.3 16v have a 4.27 axle ratio giving 3050rpm@70mph in 5th, 24v has the 3.64 as does the automatic on all 16/24valves I believe giving 2650rpm@70mph. 16v auto has same diff ratio as the 24v which puzzles me as the manual one is shorter, gear ratios are similar in both auto and manual.

If it's of any use, I think these are the correct gear ratios for the A4LDE automatic, 1st:2.08 2nd:1.56 3rd:1.00 4th:0.76 Rev:-2.08, Final drive:3.64.

Worked these out from quoted top speeds@rpm, they seem to work ok in the sim, 60mph in 1st seems a bit tall though. Pitted two 2.3's against each other, one with each diff ratio and with all the weights/torque/drag coeff setup there wasn't a big difference in performance.

Regards, Bruce.

Title: Re: Diffs
Post by Highlander on Oct 20^th, 2006, 1:50pm

Ok, just took another diff off a facelift 2.3 auto saloon, same thing, I can read the tag on this one though and it says 3.91 which confirms my method of turning the prop end of the diff just short of four complete turns to get one complete turn on the driveshafts..

Was there a change in spec for these diffs on later cars??

I did take a diff off one of the very first 94 2.0 16v estates once and it was definitely a 4.27

all the later ones seem to have the double mount at the rear of the diff, the early one had a single mount.

any more ideas?

Title: Re: Diffs
Post by TiberiuS on Oct 20^th, 2006, 1:55pm

Manual had the 4.27 and auto the 3.91, overdrive on both auto and manual is the same ratio ;)

2650rpm@70mph in o/d for the 3.91

3060rpm (or thereabouts ;))@70mph in o/d for the 4.27

I'm curious myself...

Bruce.

Title: Re: Diffs
Post by Highlander on Oct 20^th, 2006, 2:31pm

So this page has the wrong data??

http://www.fordscorpio.co.uk/manual/rearaxle/RAxleSpecs.pdf

Thats a manual 2.3 Estate and an Auto 2.3 saloon I've seen both with a 3.9 diff

The estate had huge miles on it so possibly might have had a "wrong" diff from an auto at one time if they are indeed 3.9

Title: Re: Diffs
Post by mazzy_j on Oct 20^th, 2006, 2:32pm

Just noticed 3rd box from the bottom it says 2,9 V6 Cosworth (TCI Diesel), bit of a typo but i wouldn't mind a Cosworth v6 td lump in my car ;) ;D

Maybe your diff was from one of Ford's infamous friday afternoon built cars?

Matt

Title: Re: Diffs
Post by TiberiuS on Oct 20^th, 2006, 5:16pm

Quite sure the 3.91 is correct, seems odd to me that Ford dropped a 4.27 into the manual, wouldn't it be the other way around with the auto having less gears i.e more load on the engine?

Thats the figures I got from this site and I looked elsewhere and got the same, did a lot of drivetrain research for that bleedin' model...

The physics of the drivetrain should be good, the chap who makes Racer also does a commercial version for a company, plonked the auto/final drive ratios I had for the 3.91 24v above and speeds/engine revs are the same as my 2.3...

3.91 diff on a 4.27 speedo setup would surely reduce the mileage, engine doing less revs etc.

Just off to put my anorak back on ;)

Bruce.

Title: Re: Diffs
Post by Highlander on Oct 20^th, 2006, 6:29pm

Did you find the info on this site Bruce? can you remember where?

Title: Re: Diffs
Post by TiberiuS on Oct 20^th, 2006, 6:49pm

Took me ages to find the page on this site, it's here (http://www.fordscorpio.co.uk/mt75.htm). Scroll down and there's a final drive/tyre profile reference, no mention of the 3.91 on the 16v manual.

I found the same info on another site, can't remember what one, I'll have a search around.

Bruce.

Title: Re: Diffs
Post by Octavian_P on Oct 22^nd, 2006, 1:16am

There was a TSB (thenical service bulletin) from ford regarding clutch uder-rating for the new diff fited cars....i belive it was stated that in '97 the 2.3 got the 3.9 diff instead of the 4.27. I'll search and try to find the info again.... ::)

Title: Re: Diffs
Post by howiedintheplace on Oct 22^nd, 2006, 10:01am

I think Octavian may be right, I seem to remember something about when the manual box got the higher top gear the diff was changed also on all 2.3 cars.

What build dates are these 2.3 cars highlander?

Title: Re: Diffs
Post by Highlander on Oct 22^nd, 2006, 10:12am

Magic ;D Thats what i was thinking Octavian, some change in spec for later models..

Dave, would have to check but both were R Reg so 97 likely, one was a facelift.

Title: Re: Diffs
Post by howiedintheplace on Oct 22^nd, 2006, 10:39am

I don't think it was a TSB thou but a revised mpg figure/performance sheet.

Also you should be able to tell what diff it has from the plate.
There is a axle code which relates to the different ratio's.

Title: Re: Diffs
Post by Highlander on Oct 22^nd, 2006, 11:18pm

http://www.fordscorpio.co.uk/images/vin.gif

3.91 is shown on the vin plate as an option ;)

getting there slowly :)

Title: Re: Diffs
Post by Octavian_P on Oct 23^rd, 2006, 3:15pm

TECHNICAL SERVICE BULLETIN No.28/1999
Car and Light/Medium Commercial 08.04.1999
Section: 16
Model: Scorpio '97 with 2.3 DOHC 16V engine, manual transmission and tow bar, built from 07.96 to
06.98 (build code TD to WU)
Markets: All
Subject: Clutch failure / overheated clutch disc when towing
Summary
Should a customer express concern about clutch failure and/or an overheated clutch disc when towing, this
could be caused by excessive clutch operation resulting from theoverall ratio of the drive train being too high.
To resolve the concern, the manual transmission should be removed and a revised clutch disc installed.
NOTE:
The revised clutch disc must only be installed in vehicles with overheated clutch discs. If the revised clutch
disc is installed in vehicles with less load on the clutch, this can lead to clutch judder and increased clutch
wear.
Remove the manual transmission (refer to the Scorpio Service Microfiche, Operation Number 16 114 0) and
Install a revised clutch disc (see Parts Required) (refer to the Scorpio Service Microfiche, Operation Number
16 724 4).

Title: Re: Diffs
Post by howiedintheplace on Oct 24^th, 2006, 12:35pm

Hmm but it don't actually say the ratio ???

I know what your thinking it hints at a higher gear fitted.

I seem to remember they issued new performance figures & on there it say for cars fitted with the higher top gear & diff. But was a while ago I saw it.

Maybe in a revised owner manual for the car ;)

Title: Re: Diffs
Post by Octavian_P on Oct 24^th, 2006, 7:27pm

I'll dig some more, maybe i'll find more details, but for now this is all i had found.....it's more of a hunch, but i think that is the year of the change.

Title: Re: Diffs
Post by Highlander on Oct 24^th, 2006, 8:20pm

Can some of you 2.3 guys have a look for me?
Its on the VIN plate beside the bonnet catch.

Fourth box down on the left

http://i13.tinypic.com/2hpn4vl.gif

Title: Re: Diffs
Post by Octavian_P on Oct 24^th, 2006, 9:41pm

Just took a small brake from work, nice ideea to go and check the VIN ;D anyway mine is 9 = 3.91. It is a manual 2.3 made in december 96, if i remeber corectly, to dark to note the whole vin in the parkinglot, and my registration papers....well...i forgot them home ;D

Title: Re: Diffs
Post by Highlander on Oct 24^th, 2006, 10:48pm

Late 96? I wonder if its a mistake on the spec sheet then, as the 2.3 was introduced mid 96

Title: Re: Diffs
Post by howiedintheplace on Oct 24^th, 2006, 11:10pm

I think you may be right, I just done some digging & the 2.3 has always had the same diff. What I can remember seeing maybe from when it got the better top gear.

You need some owners to check their plates to be sure.

Title: Re: Diffs
Post by DazRSK on Oct 26^th, 2006, 6:45pm

Guys - I realise that I have come into this topic really late - so apologies if I restate something already mentioned or provide answers to the bleeding obvious.

I took an interest in this whole aspect about 15 years back when I owned a 2.8i Capri. Reason - I could not work out why the 0-60 figure of a 2.8 Sierra XR4i was a quicker car. Roughly same weight, same size car, yet quicker.

The reason for this - the Capri inherited the very tall 3.09 diff from the torquey/4 speed 3.0L Capri - which gave that car a good acceleration, yet good top end in 4th (top) gear at still a relatively low rpm - something like 125mph at about 5000rpm. I realise nothing today with 5 & 6 speeds around but now take a look at your car in 4th (or 3rd in auto) and work out what 125mph would be. To save Ford the cost of redesigning a whole new diff/live axle, they lumped it into the 2.8i Capri.

The Sierra's diff was 3.44 - much better for the 2.8 engine, which wasn't torquey low down. Peak torque on the 3.0L was about 2,800rpm vs 4,300rpm on the 2.8. So there is my interest and a quick swap over to a 2.0L Capri diff from a breakers - which I think was about 3.40 - and the 2.8 Capri's acceleration and general manner at 70 in 5th was so much better.

So this should answer some of the questions why Ford have placed this diff / this gearbox ratio against different power plants. Mech Engineer will tell you that an engine is at its most efficient at peak torque. Therefore, ideally, for motorway cruising, your car's peak torque would be ideal at that point intop gear - this will give the compromise of best economy yet best acceleration in that gear - notwithstanding drag, of course.

It also explains where they may enhance ratios - like the gearbox ratio in the 2.3 from 1997 on - makes it a better car to drive.

The other point - you can change the diff on one of these cars and still settle the speedo down. This is what I had to do with the Capri otherwise the usual 10% inaccuarcy tolerance is blown out of the water. One of you mentioned you thought you had the "wrong" diff but the speedo was accurate - a different speedo drive has been placed in the 'box.

Finally, here is the speed per rpm in 4th / 5th (3rd/4th auto) with the facts given on this site. Also - I have had to choose a wheel/tyre so gone for the Ultima 215/55/16. Hope this comes out OK. If it doesn't, have a look at this link and plug your car's figures in.

http://www.geocities.com/z_design_studio/transmission_z28_6.html

3rd rpm 4th rpm 5th rpm
2.0 8V - 70mph 3,802 3,118
2.0 16V -70mph 3,969 3,295
2.3 16V (1997-) - 70mph 3,969 3,295
-'97 2.3 16V - 70mph 3,969 3,017
2.5 TD - 70mph 3,124 2,374
2.9 24V - 70mph 3,394 2,579

You can see possibly why Ford changed the 2.3 - that is a monster of a gap for that type of BHP if you accelerated in 4th then changed up.

Title: Re: Diffs
Post by howiedintheplace on Oct 26^th, 2006, 11:00pm

;D ;D

You have probably confused alot of people with that last post.

Basically the gearing has to be matched to the engine power curve.
There is always a balance between performance & mpg.

A 2.0L 8v has more low down power & less in the upper revs so has a 4.09 diff.

A 2.0L 16v because it's multivalve it's power is higher up the rev range hence a 4.27 diff.

The 2.3 has a bigger capacity so more low down power so it makes sense to have a 3.91 diff.

24V has even more low down grunt hence 3.64 diff.

The diesel can't rev as high as the others & makes all it's power low down in the rev range hence 3.36.

The top gear or overdrive is mainly aimed towards a good mpg figure.

A 24v with a 4.27 diff is over 1 sec quicker too 60mph but you wouldn't be able to live with the mpg you would get ;D