I've read that the MKII XR's will have a shorter diff ratio, now pardon my stupidity but can someone please explain what the numbers actually mean? They say dropping the ratio from 3.46 to 3.73 will help with better acceleration.

2 things... why do the numbers go up for a lower ratio?

and will these diffs be used for owners of MKI XR's who have problems?

The numbers mean:- how many turns does the tailshaft turn per axle turn. If the diff ratio is 3.45:1 then the tailshaft revolves 3.45 times for every 1 time that the rear wheels revolve. If the ratio is 3.73:1 then the tailshaft turns 3.73 times for every .... etc etc.

The ratio represent the mechanical advantage that the engine has over the rear wheels. The higher (numerically) the ratio is then the more easy it is for the engine to turn the wheels. The engine revs higher for every kph of road speed. On the other hand the more engine revs you have then the more fuel you use. The lower (numerically) the ratio is then the higher the potential top speed of the vehicle. The engine revs lower for any given road speed. This gives better economy but is offset by the engine being under undue load if the gearing is not matched to the torque/power characteristics of the engine and having regard to the weight and aerodynamics of the vehicle.

To what problems with the MkI BA are you referring?

Thankyou for clearing that up T6man.

The issue I was talking about was the all the members on this forum having diffs replaced under warranty.

Ah yes, that problem. Well that has to do with build quality of the diff and other driveline components and sadly will continue whether there is a ratio change or not.

Correct me if I am wrong but I think this backlash problem occurred when they first released the AU 1 back on 98.I remember all these people complaining about this issue and there fix was to add some diff treatment additive that was supposed to eliminate the backlash?.The same way people used to put bannana skins inside to do the same thing.Funny thing is when I go to visit clients at Expensive Daewoo dealerships there warranty sections are full of diffs going back for warranty,Not small amounts but 30-40 at a time so makes you wonder what is going on with the manufacture of these things.

Never happened to the trusty old 9 inch diff that was fitted years ago to all the V8 fords

ASNU> The first of what you might call recent models to suffer backlash to any degree was the XF Falcon range. It was driveline shunt originating in the first of the T5 gearboxes and was only really prevalent in first gear.

You are correct about the AU having it also - mainly Series II models in the XR8 range as they used a beefed up box from the earlier models.

With the current crop of cars, both Expensive Daewoo and Ford, it seems to be manifested in the diff and half-shafts but I also believe that even if the "back end" was sorted perfectly, some gearbox shunt would also then become evident. What I'm saying is that the problem seems to be through the entire driveline from the clutch back and fixing one area will expose shortcoming in another because at the moment the diff seems to be the biggest problem and is to some extent masking the rest of the driveline problems.

The answer is not a 9" diff I can assure you. They had problems too. The major one was internal balance - the centres are so big and heavy that any imbalance becomes exaggerrated and, in XCs for example, the whole car would shake at about 110kph just as if the rear wheels were out of balance. The 9" is also very difficult to set up the clutches - too tight and they give you a very clunky ride and chop out, and too loose the (limited slip) diff just doesn't work. They are good for drag racing in straight lines but for a road car I'll have the Borg Warner 8.5" 4 pinion diff in a Watts link rear end thanks very much

You are correct about the AU having it also - mainly Series II models in the XR8 range as they used a beefed up box from the earlier models.

With the current crop of cars, both Expensive Daewoo and Ford, it seems to be manifested in the diff and half-shafts but I also believe that even if the "back end" was sorted perfectly, some gearbox shunt would also then become evident. What I'm saying is that the problem seems to be through the entire driveline from the clutch back and fixing one area will expose shortcoming in another because at the moment the diff seems to be the biggest problem and is to some extent masking the rest of the driveline problems.

The answer is not a 9" diff I can assure you. They had problems too. The major one was internal balance - the centres are so big and heavy that any imbalance becomes exaggerrated and, in XCs for example, the whole car would shake at about 110kph just as if the rear wheels were out of balance. The 9" is also very difficult to set up the clutches - too tight and they give you a very clunky ride and chop out, and too loose the (limited slip) diff just doesn't work. They are good for drag racing in straight lines but for a road car I'll have the Borg Warner 8.5" 4 pinion diff in a Watts link rear end thanks very much

Turbo6man.

I just first noticed it in numbers concerning the AU with IRS.Dont know if this was a option for these cars only on the XR6/8 and T cars but all the problems started then,Same time when Expensive Daewoo introduced there IRS.I would just like to know why for say a example Mercedes can get it right with bascilly the same setup?.I realise manufacurers want to keep costs down but in reality they have had 6/7 years to sort.

I agree with you concerning the 8.5 diff as seems to handle alot of power without breaking as seen in many cortinas with either the 289 or 302 fitted.I think the 9 inch has alot better aftermarket gearing available and when set up properly will out proform any diff as used by many a different racing applications over the years,Ford and Holden.