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The first choice you must make when selecting a gearbox is between automatic and manual. There is a range of selections for both, each with their advantages and disadvantages.

The second decision you have to make is whether to keep the stock gearbox from your vehicle (Land Rover/Mitsubishi etc) or whether to use a BMW gearbox. Again there are advantages and disadvantages of both routes so it is an individual decision about what is right for you.

Whichever gearbox you decide on it is important to consider gear ratios so that you can match your transfer and diff ratios.

BMW Gearboxes

The main advantage of using a BMW gearbox is that the connection between the engine and gearbox has no flaws. The bellhousing pattern is correct and you can use a standard clutch/flywheel and slave cylinder setup. In many cases the BMW gearboxes are stronger than the recipient vehicle’s gearbox and better suited to the higher torque engine.

There are two main disadvantages, both can be worked around but must be considered in advance. 

The first is that to retain 4wd you must couple the gearbox to your vehicle’s transfer case. We offer a range of adapter plates in our web shop depending on your gearbox choice and transfer case. This adds to the cost of the build and in some cases can mean custom mountings and propshaft length may need changing.

The other consideration you must make is gear selector location. In the case of a manual transmission this will involve custom gear linkages. We do have these available for some setups in our shop. Automatic gear selection is arguably easier, you will just have to mount the BMW transmission shifter (either with a cable linkage or fly-by wire canbus).

GS6x-37

The GS6x-37 is a 6 speed 4wd box so has a flat mating surface at the output shaft end, which makes it ideal for mating to a transfer case. Although this gearbox is only strictly rated for 370Nm, it is commonly used up to 500Nm without issues.

The main advantage of this gearbox is its price; it can be found very cheaply second hand. It has the smaller bellhousing so mates to the 184, 193 and 204 engines from an E46. We have adapters available in our shop to mate this gearbox to both Land Rover LT230 transfer cases and Mitsubishi Pajero 2.8 transfer cases.

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GS6-53/GS6x-53

These 6 speed manual gearboxes are available in both 2wd variants and 4wd variants (denoted by the x). Whilst rated for 530Nm, they are known for putting up with much more. One to watch here is that they are available in both bellhousing sizes. The GS6-53 HGA is the smaller bellhousing size. Most other variants are for the larger bellhousing size. Check also that you are buying a gearbox with the starter in the right location.

We currently have adapters from the 2wd (GS6-53) to the Land Rover LT230 available in our shop.

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Automatic

The 5 speed GM 540LE 5 speed gearbox found is a known weak gearbox, therefore we don’t recommend using it for a conversion.

6hp26/6hp26x

The 6hp26 (2wd gearbox) is found in E60 530d models. The 6hp26x (4wd gearbox) is found in the e53 218hp X5. Both are the large bellhousing size. It is important to get a matching engine to make this gearbox work as the gearbox will not work with earlier generation engines. We would recommend buying a gearbox and engine combination so that you are sure.

The gearbox has an internal speed signal so as long as the canbus connection is made properly between the gearbox and engine ecu then gear changes will be made properly. It is also possible to wire up the tiptronic function of the shifter.

For high torque applications, this automatic gearbox is better suited than the manual, as there isn’t a clutch to worry about, and it is officially rated for 600Nm. It is important that the engine is tuned properly to ensure that the engine calculated torque is accurate, which ensures that the gearbox will apply enough pressure to the clutch packs so that they don’t slip and fail prematurely.

The gearbox is cable operated. It is usually easiest to use the BMW shifter.

Due to the abundance of 6hp26x gearboxes and their flat mating face, we would recommend fitting this gearbox if you are mating to a transfer box. We have adapters for this gearbox available in our web shop.

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 6hp28/6hp28x

The 6hp28 is a refreshed version of the 6hp26 with a higher official torque rating of 700Nm. This transmission is found in the facelift e70 X5’s and the LCI 5 series and 3 series cars. In the 3 series it is cable operated, whereas the 5 series and x5 it is fly-by-wire shifting. In the wiring section you will find a guide on how to connect this shifter.

Again, we recommend fitting the x5 box for its suitability mating to a transmission adapter. However, one thing to consider is that the x5 box was the first to have the EWS 4 immobiliser. Therefore, it would be necessary to use a mechatronic unit from a 5 series or send the mechatronic unit to us for immobiliser removal. 

Stock gearbox

Rather than use the BMW gearbox, it is often possible to use your original vehicle transmission. For example, we currently provide solutions for the Land Rover R380 and the Mitsubishi v5m31 transmissions.

The options for R380 are as follows:

  • Adapter plate from engine to gearbox along with custom clutch (we don’t currently support this route).
  • P38 bellhousing along with a spacer, custom clutch and clutch fork modification.
  • P38 bellhousing, p38 input shaft, custom clutch.

As you can see, these routes are definitely cheaper than the BMW gearbox route, however you have more work and are left with an inferior gearbox.

The Mitsubishi V5m31 adapters use a standard flywheel, custom clutch and release bearing modification. Again, this is more work, however the transmission is much stronger than the Land Rover option, so if you are converting a Shogun/Pajero then the standard transmission is a viable option.

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