Modified Front Sierra Differential

Unlike the Rear Sierra Differential, the front differential is not located along the vehicles’ centre-line. The prop-shaft driving the front diff exits the side of the MT75 gearbox and travels forward to the front differential bolted to the side of the sump. The front differential mounts only to the engine’s sump and is therefore subject to twist as the engine is loaded or revved.

The central shaft passes through a tube, exiting on the opposite side, where the nearside drive-shaft mounts.

In this application, the central drive-shaft passes in front of the engine (no longer a Cosworth 2lt or Cologne V6). As a result, a custom drive-shaft cover assembly would be needed to replace the Cosworth sump.

Locost Sierra Front Diff Locost 7 Cosworth SumpLocost 7 with MT75 4x4 gearbox and Sierra Front Diff

This assembly would also incorporate a strengthening plate between the diff and bottom cover. This plate, will be welded and brace to the plate at the side. In theory this should drastically increase the rigidity of the case.

Locost Sierra Front Diff Strength Plate

Unlike in the original set-up, the whole assembly will be mounted directly to the chassis via urethane mounts. Hopefully, this should increase the rigidity and strength of the front axle even more.

The reason I chose to modify the standard axle was because I was struggling to find a 4×4 front diff with a ratio that tied up the Sierra Rear diff. I looked at Ford Rangers, Freelanders, various Japanese cars etc. I needed a diff that I was confident could cope with 300+bhp. After much research I went with the 3.62:1 ratio Ford Sierra set-up. Maybe, one day I’ll find a suitable combo – I probably need to start data-basing all possible front and rear diffs and cross referencing them.

Click here for more info on the Sierra Front Differential