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x250 gearbox


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The details I have for the 3litre fiat are as follows


1 4.167


2 2,350


3 1.462


4 1.047 /0.995*



5 0.786 /0.659*



6 0.652/0.552*



rev. 4.083




axle ratio 3.950 - 4.222 - 4.563*



* different versions




if this info is correct and it comes from an official Fiat source then they are not all the same ratio ie;diff


this applies to 3litre do not know about any others

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These are the gearing data for the Ducato 3.0litre motor as shown on the 2006 Italiaspeed website:


Reduction ratios 1st 4.167:1; 2nd 3.350:1; 3rd 1.462:1; 4th 0.955:1; 5th 0.695:1; 6th 0.552:1; Reverse 4.083:1; Final drive ratio; 4.222:1 (76/18); 4.563:1 (73/16) Max


It's interesting that your figures include alternative ratios for 4th, 5th and 6th gears, but it was always going to be the case that different final-drive ratios would be fitted according to whether or not the chassis was "Light" or "Heavy".

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For the mechanically minded.. something I have put together from a Fiat drawing I have adapted.

This is the box in the 3 litre. I have coloured in and numbered the gears and tried to explain how it is shown flattened out for clarity.


From looking at 1st and reverse gears ( 1 and R) which mesh, it can be seen there is no room to alter the ratios without modifying the casing and design of box extensively. The reverse gear meshes with the 1st gear on the lower secondary shaft.


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So as I see it, reverse gear can be made lower if the 1st gear is made larger to suit?


This would increase the 1st gear ratio so might introduce another problem.


Things look tight in there, but a slight modification to the case would be a fairly easy job for such a large volume producer.



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1st gear on the input shaft has to be made smaller, 1st driven gear on the lower secondary shaft larger , and also the reverse gear smaller.

Ideally the alteration should be the reverse gear is made larger only but as the pitch of the shafts is fixed this cannot be done without a complete box redesign.

So all three gears have to be altered and 1st gear ratios will also be affected.

By making the both the input shaft gear and reverse gear diameters smaller by the same amount, only option without altering the shaft positions, the ratio is improved slightly. The 1st driven gear has to also be made larger to match and keep in mesh but actual size is irelavent to reverse as it acts as an idler gear when reversing.


Now some will immediately say making reverse gear smaller is totally wrong and will have the opposite effect to what is required.

This is not so.

Both gears are altered by the same diameter change. Imagine if you will making the iput shaft gear tiny, say 1mm diameter by taking 30 mm off the diameter. The reverse gear reduces by 30mm also. making it say 20mm diameter. We now have 1m dia driving via the idler a 20 mm diameter and you can instantly see the ratio is no longer say 1:4 but 1: 25. My figures are ony to demonstate the explanation. So by making the reverse gear smaller we have improved the ratio.

(bet many where not expecting a smaller diameter reverse gear mod actually helps!!!)




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