Vito rear diff ratio. Manual gearbox

[Shep75]

Hi does anyone have any info about changing the rear differential on a 109DCI manual gearbox.
I have read loads of different forums and all I can really see is for an automatic box.
If I change ratio from 41.11 to 36.11
Will the ECU pick up fault.
I did read that someone did it with a CClass W203 and didn't have any issues as it was a manual box.
Any help would be appreciated.
Cheers

 

[m80]

I believe the issue will be that the traction control is programmed to a particular diff ratio and would kick in as it sees a fault. This can be reprogrammed with Star I believe.

If you learn how and where to do this please update us, as I would have interest to change from the 115 (auto) 36:11 (3.273) to the V6 38:13 (2.923),
for me that would represent a drop in revs of nearly 11% so I anticipate a remap to compensate.

 

[BTB 500]

I assume the speedo signal comes from the transmission (rather than the wheels), so that would also need reprogramming for a different back axle ratio?

There were actually four different ratios for the W639:

3.727 (109)
3.455 (low ratio option for 111 and 115)
3.273 (standard for 111 and 115)
2.923 (120)

 

[Shep75]

Thank you for a response I will look into the star diagnostic.
Cheers

 

[Shep75]

Hi just to let you all know I changed the rear diff on my manual gear box vito 41.11 to 36.11 and drove 5 mile with no fault codes.
17" wheels 75mph and 2600rpm
That's if the Speedo is correct.
Cheers Alan

 

[m80]

Thanks for the update.
Are you feeling the improvement from lower revs and engine noise?

I've upped my tyre size to 205 / 75 / 16 for a slightly softer ride (and lower revs). That's a rolling circumference increase of about 6%
Tire Size Comparison
Against GPS the speedo is now spot on up to 65mph, but the odometer under reads by about 3.5%

 

[BTB 500]

Hi just to let you all know I changed the rear diff on my manual gear box vito 41.11 to 36.11 and drove 5 mile with no fault codes.
17" wheels 75mph and 2600rpm
That's if the Speedo is correct.
Cheers Alan

I would check the speedo against GPS speed to be on the safe side. It could be under-reading now, depending on where the speed signal comes from.