This creates a problem in so far as the top gear on the 2.9 XR4x4 is not high enough, with top gear ratio of 0.83 to 1.
Over the last few years the slower revving diesel engines have become more commonplace and due to this ford has made a new high gear for this application, by good luck and in true ford style, the MT75 gearbox has been modified with a higher top gear to allow the diesel cars to reach reasonable top speeds yet still retains the MT75 Gear box.
Here is where our good fortune comes in to place, if you could use the top gear from one of these gear box’s you would have a top gear ratio of 0.75 to 1. But will the parts fit?
To my surprise we found that when ford redesigned the MT75 they keep all the same ratios for 1st, 2nd 3rd and 4th but changed 5th gear only.
With this in mind we investigated the part numbers for the countershaft bearings, (same as 4x4) then the syncro’s (same as 4x4) to check compatibility, all compatible. Below you can see the similarities between the gear ratios.
| Sierra 2.9XR4x4 | Scorpio 2.3DOHC 16v 97+ | Scorpio 2.5 TDI Diesel 98+ | |
| 1st | 3.61 to 1 | 3.61 to 1 | 3.61 to 1 |
| 2nd | 2.08 to 1 | 2.08 to 1 | 2.08 to 1 |
| 3rd | 1.36 to 1 | 1.36 to 1 | 1.36 to 1 |
| 4th | 1.0 to 1 | 1.0 to 1 | 1.0 to 1 |
| 5th | 0.83 to 1 | 0.75 to 1 | 0.75 to 1 |
Dojj and i are using ours, they do present us with a small problem,,,, how to keep at the legal speed limit.
To modify your standard MT75 gearbox to the new gear ratio you would only have to change the countershaft (orange) and the 5th gear (yellow), the remaining parts would all be standard and compatible.
From here we spent some time at a ford parts center finding correct parts/numbers, after our picking up the parts from our local ford shop a day later and checking them we made a note of the part numbers for you.
Countershaft part number P F 1058879 cost £127.35+vat
5th gear part number P F 1058870 cost £30.35+vat
