F30 318d gearbox issues

[Jaybmw]

Hi lads. I have a 2014 318d and it appears it has a box issue.. no reverse or 2nd gear. Not going to repair it just going to swap it out. I have a stop start box from an e90 320d. Bar ratios maybe been off are they roughly the same box, same n47 engine basically both 6 speed etc ? Thanks

[BFleming]

Jaybmw said:

Hi lads. I have a 2014 318d and it appears it has a box issue.. no reverse or 2nd gear. Not going to repair it just going to swap it out. I have a stop start box from an e90 320d. Bar ratios maybe been off are they roughly the same box, same n47 engine basically both 6 speed etc ? Thanks

Be very careful here. I've been there and it took a lot to sort it out. My story...
Had a 2010 E90 320d efficientdynamics. These have the GS6 45DZ gearbox, which is known in the industry as chocolate. Reverse gear goes, and BMW nor the gearbox manufacturer will sell the internals - so you're in for a new or secondhand box. Sound familiar already?
My car's previous keeper put a gearbox in from a slightly older 320d (which still had start stop) but things like cruise control wouldn't work, and the gear indicator (gear you're in / gear you should be in) never worked properly. It said 4th when I was in 5th, so I did a lot of homework here on BMW ratios etc. Sure enough the ratios in the donor gearbox were wrong, and the car was never happy as a result. I sorted mine out (not straightforward at all) and got there in the end. But my best advice is to get a like-for-like gearbox with some kind of warranty.
Your 2014 318d's gearbox is a GS6 17DG. You haven't given enough info to say what the donor box is from, however this is my research:

GS6 17DG (2014 F30 318d):
1st: 4.002
2nd: 2.108
3rd: 1.380
4th: 1.000
5th: 0.781
6th: 0.645

Diff ratio: 3.231

GS6 45DZ (2010 E90 320d):
1st: 4.11
2nd: 2.248
3rd: 1.403
4th: 1.000
5th: 0.802
6th: 0.659

Diff ratio: 3.15 (2.79 in the efficientdynamics model)

GS6 37DZ (2007/8 E90 320d):
1st: 5.14
2nd: 2.83
3rd: 1.804
4th: 1.257
5th: 1
6th: 0.831

Diff ratio: 3.15

In summary, bar ratios they'll physically fit, but ignore the ratios at your peril.

[The Conflated Outlier]

Indeed.

Stop start gearboxes have a speed sensor on top to measure the output/mainshaft speed. If you fit a lower ratio diff for example this sensor will argue with the ABS sensors as something isn't right - it can even put the car into limp home mode with restricted performance. A similar story with incorrect gearboxes.

The 17 'box is generally a bit better than the 45 but it still needs to be the right one.