Differential change and speedometer reading

[Minibusman37]

I've got a 2010 Ford Transit which is currently running on a 5.3 diff ratio, this puts the rev counts at 3000rpm at 60mph. I'm looking to change it to a 3.73 ratio diff to lower the revs, does anyone have any experience or knowledge on having this done, would it be easier to change the whole rear axle and would it put the speedometer out? Not sure where the Mk7's take the speed reading from, if it's from the gearbox then the axle moving slower at 60mph would this cause the reading of the speedo be lower than it should? Also if you have any other info on possible issues on this, it would be appreciated

[knobby1]

Depends on what engine you have..if you plonk a 3.73 into a 100ps machine, she may struggle a bit.

Speed is taken from ABS sensors so speedo shouldn't be affected.

Lord Knobrot

[MK7 user]

Try the forum search tool buddy....the same topic has been covered 1001 times.

I'll maintain my stance that it depends on what you are using the van for & how much weight you carry....under geared is an arse - over geared is a pigs arse.

You need the engine torque to pull the higher gearing & a 6-speed box works much better with a 3.73 due to first gear being slightly lower & a better spread across the remaining gears.

Try another van with a 3.73 before changing yours would be the way to go.

[ake]

Diff ratio would need resetting in bcm using ids