VXT75 final drive swap?

[DG-Unit]

New year, new nonsense… I’ve got a VXT75 gearbox with a 4.54 final drive and thinking about changing it. Now I’ve split the gearbox it doesn’t feel too scary messing about inside. I know you can get a VXT75 with a 4.23 final drive. Can you just unbolt and swap over the ring gear (to avoid changing the driveshaft splines) or does it need the output shaft too? And if you can do this, can you theoretically bolt in a final drive ring gear from the Focus MTX75 for a 4.06 ratio (might be too tall) or do you need to also replace the output shaft? I think I’d be happy with the 4.23 ratio as it is but wondering if something like the 4.06 would be practical with a remap?

At 70mph the revs sit at 3250-3500 rpm which is higher than I’d like with plans for long-distance trips when mpg and cruising noise becomes an issue. It’s happy in 5th gear on the flat from 40mph and 1st/2nd are almost too jerky/short around town. It’s also happy in 4th for 30mph (these are all actual GPS speeds). I plan to get it mapped at some point this year and am keeping the camper conversion lightweight where I can so it won’t be carrying a lot of load.

[knobby1]

You'll need to change both the pinion and ring gear for the ratio you want as they'll be a matched ratio pair, you can't just change the ring gear.

I believe the ring gear of the 4.54 ratio has 59 teeth and the 4.23 ratio has 55.

Lord Knobrot

[DG-Unit]

You'll need to change both the pinion and ring gear for the ratio you want as they'll be a matched ratio pair, you can't just change the ring gear.

I believe the ring gear of the 4.54 ratio has 59 teeth and the 4.23 ratio has 55.

Lord Knobrot

Nice one. I’ll start looking into what I need to do to change the pinion/ output shaft.Hopefully someone here has some ideas about the comparability of MTX75 internals… and Mk7 VXT75 internals. I have to keep this case really because of the Mk6 speed sensor.