The Sierra 4×4 Front Differential was fitted to the following models:
- 2.0lt DOHC 4×4 Sierra (1982-1993) – some were 3.92:1
- 2.9V6 4×4 Sierra (xr4x4i) – 3.62:1
- Cosworth Sierra 4×4 – 3.62:1
- Cosworth Escort YB 4×4 – 3.62:1
- Granada Scorpio 4×4 (1985-1991) – 3.62:1
Most diffs are 3.62:1, however it was available in 3.92:1 (now a rare beast)
Obviously, the ratio of the front differential has to match that of the rear.
The numbers I have on my 3.62:1 differential are :
The Sierra 3.92:1 tag reads:
The FINIS number for the 3.92:1 is 1661121
The front diff is somewhat smaller than the rear and has been the point of failure for several rally cars. To this end several manufacturers offer strengthening plates. For a relatively small outlay they offer good piece of mind. They fit between the removable bottom cover and the casing. This plate increases rigidity of the original front diff case which has a tendency to flex and eventually crack under high torque loads.
Normally, the front differential mounts to the side of the sump. A central drive-shaft passes through the sump, to where the nearside drive-shaft mounts. If it is used in another set-up then the central shaft and cover will need to be replaced. See the CAD drawings on the left.
For the 3.92:1 I have FINIS 1661122 for the crown and pinion wheel.
In case you are wondering (I did!), if you turn the input shaft clockwise, the output shafts also turn clockwise.This is exactly the same as the Sierra Rear Differential. So if you are building a ‘special’ and were seriously worried about strength then you could use 2 rear diffs.
UPDATE – loads more info uploaded!
Sierra Front Diff exploded diagrams and part numbers can be found on my blog.
Ford Sierra Cosworth / Xr4x4 CAD