DCT Bible, Chapter 2- Transmission Hardware

Updated: Apr 21, 2021

So now that we went over how capable the DCT is, let's go over how you're going to get it in your car!

Transmission Versions

The BMW 7-Speed DCT, aka the GS7D36SG, comes in four versions. They are essentially the same except for gear ratio and bell-housing combinations. They all feature the same input spline, filters, oil pan and weigh about 175 pounds. For reference, the bell-housing is the part of the transmission where it bolts to the engine.

The first version of the GS7D36SG came in the 2009-2013 135i, 2008-2013 E9X, and 2008-2016 Z4 E89. The bell-housing is the standard for BMW straight 6 engines, and has the starter off to the side to fit in the area created by the BMW slant-6 engines leaning to one side. At this time this is the most common and inexpensive DCT option. They can usually be found for between $750-1100 on eBay and even less from from certain scrap yards if you haggle a bit. This version features a 1:1 top gear ratio, similar to the popular ZF 5-speed used in E36 and E46 models for years, so it makes for a great swap. It also features a 105mm bolt circle output flange tripod, while all the rest feature a 110mm bolt circle tripod. The full gear ratio chart can be seen below.

The next most common DCT is also the slant-6 style with the starter off to the side. It came in the 2012-2018 F80 M3, 2013-2019 F82/F83 M4, and the 2014-2019 F87 M2. These look the same as the earlier 135i/335i model and have the same bell-housing bolt pattern. However, they feature a longer gear ratio set. The top gear ratio is .671:1. These units are usually more expensive, ranging from $1300 to $2000 on eBay. As mentioned before, it's usually best to haggle a scrap yard for the best price and not go through eBay.

The next two options feature a different bell housing as they came standard on BMW V8 engines instead of the slant-6 options.

The first iteration comes from the 2006-2013 E9X M3 models and has a 1:1 top gear, like the 135i/335i DCT transmission. There stand out by the starter portion which is positioned right at the top. These usually range from $1100-1500.

Its cousin comes from the 2010-2016 F10 M5 and 2011-2018 F06/F12/F13 6-Series. This DCT version features a .671:1 top gear ratio like the F80 M3 transmission and are usually priced between $1600-2000. The bell housing is the most large on this one, so they are not desirable for swaps that have tight transmission tunnels and engine bays.

Full Gear Ratio Chart

Attaching It To Your Engine

At this time, people are making all sorts of adapter plates and flywheels to match their chosen engine and transmission combination. Most of these manufacturers are smaller shops, build in small quantities and make the adapter plate and flywheel together to match and have correct input spline depth. It is important to choose your adapter setup before you decide on a transmission type as there is a wide selection of adapters for almost all popular engines.

If you have a BMW engine and it's a straight 6, you're in luck because chances are with a little grinding and welding, the DCT box can bolt on and all you need is a flywheel. The grinding required is to slightly open up the two top mounting holes. The welding is required to add a bolt hole for the original starter to bolt on. You can either build up welded material and then drill a hole, or cut off a section and then weld on a section from an older transmission.

Another option for older BMW 6 cylinder engines is to run a N5X 8 bolt flywheel and a starter spacer with the N55 style starter. The reason you need a spacer is because the N55 block spaced the starter back, and you use it to re-align the starter gear with the teeth on the flywheel like factory. Note: The flywheel teeth style is different between the older S5X/M5X engines and newer N5X style engines. They are not compatible and you cannot mix-and-match their starters and flywheels.

For non-BMW engines it is common practice to bolt a spline adapter to a standard flex plate from an automatic transmission of the engine you're using. This works great, is usually low cost and light-weight. However, you must make sure you stay compatible with the adapter plate if one is used, and be wary if you use a inline-4. The 4 cylinder engine harmonics are very hard on the transmission clutch baskets and can lead to cracks and eventual failure. It is best in these cases to use a flywheel with some mass to it so you don't have any issues. This is also why the original DCT flywheels from BMW are pretty dang heavy and not the same as an automatic flex plate. If you have an Inline-6 or V8 it's much easier to get away with this though, as these engines run much smoother.

If you have any questions about adapting a DCT to your engine, BMW or not, please shoot us a message and we would be happy to support you with the best options currently available.

DCT Driveshafts

So now that your DCT is attached to your engine, you have to get the power to the differential. The DCT comes with an odd tripod output flange. This originally went to a rubber guibo and then to a BMW 2-piece driveshaft. We found the best way to create strong and affordable driveshaft setup is to use one of our DCT flange adapters which bolt to the tripod and then lets you attach a standard 1350 style U-Joint yolk. Then, we can easily make you a single piece driveshaft with a slip-shaft (since there is no slip yoke) to suit whatever rear end you are using like a BMW M3 or Ford 8.8 differential, for example. We have the adapters and yolks for many differentials in stock. Please contact us with any questions about making the perfect driveshaft setup.

Parking Brake Options

The BMW DCT features a small parking brake lever that locks the transmission when the engine is off. When the engine is idling/running the transmission has oil pressure and this lever automatically lifts itself up, taking itself out of "Park" and into Neutral. This is great in a perfect world, however, if you ever break down, get towed or need to push your car on a trailer you are out of luck. The good news is that the aftermarket controllers may be able to control the stock parking brake module soon, but in