BMW Manual Transmission and Clutch Guide
BMW manual transmissions can sometimes be complicated. Performing maintenance on them can be even more complicated as they have quite a few pieces but most of them can be replaced. This article will cover all the common BMW transmissions and their components.
One of the most well known BMW transmissions of the 80s, the G260 was placed behind the M20 engine in the E30. This transmission is extremely reliable in stock form. One of the only complaints users have with this transmission is the quality of the shift. Early G260s had a sheet metal shifter carrier that allowed a ton of play in and out of gear. Midway through the E30s production, BMW replaced the sheet metal shifter with something similar to what is used in today's manual trans. This offered a slightly better shift quality. In most cases, it is possible to upgrade to the updated shifter. After this has been done upgrading a few components in that system can make shifting a G260 a breeze.
Getrag 250 - 23001434410
With the release of the E36 and the M50 engine BMW also released a new transmission. The G250. This transmission improved upon the G260 and was known for having a much smoother shifting feel. These transmissions are known for being reliable behind stock power vehicles. But don't stand up well to high power NA or forced induction applications. As with the G260 pretty much all of the components in the shift linkage system can be replaced and improved.
ZF 5 Speed S5D - 23001434485
The ZF5 is one of the most popular BMW transmissions for high horsepower applications. Withstanding well over 500hp these transmissions are known for being extremely strong and affordable. However, they do have a common issue that can be frustrating for newer automotive enthusiasts. Over time the Detent pins for 5th and reverse can wear out and cause the shifter to lean towards 5th gear and be difficult to shift into reverse and 5th. Although this repair isn't too difficult it does require removal of the transmission.
ZF 6 Speed GS6 - 23007532498
The GS6 is one of, if not the best shifting BMW transmission of it's time. Mated to both the M54B30 and even the S54 in Z4s, this transmission can handle plenty of power and offers both a 6 gear and a buttery smooth shift. The biggest downsides to the GS6 are the price of the clutch and flywheel combos as the GS6 requires a specific item and the rarity of the transmission as it only came in Z4Ms and late model E46 330s.
Getrag 6 Speed G420 - 23002229721
The G420 is one of the strongest BMW transmissions to date. Able to handle 600+ HP these transmissions are unbelievably reliable in high horsepower applications. Prices are not unreasonable either as they were mated to the E46 M3 which was produced in mass quantities in the early 2000s. The biggest complaint about the G420 is the notchiness of the shift. This however can be improved with a few minor upgrades.
Transmission Hydraulic Components
In this next section, we will cover all the different Transmission components starting at the pedal and moving to the transmission and then the shifter. These components can sometimes become confusing and the goal of this portion of the article is to give you an understanding of all the components that make up a transmission and its shifting components.
Clutch Pedal and Bushings
In most BMWs the clutch pedal itself is plastic and over time it likes to bend. Most of the time to the left. It will eventually begin missing the clutch stop and hitting the floor. This can also be attributed to worn clutch pedal bushings. These bushings sit in the pivot point of the clutch pedal to help keep it centered. When replacing a bent clutch pedal or worn-out clutch bushings it is always a good idea to upgrade to brass or polyurethane clutch pedal bushings.
Clutch Master Cylinder #1
The clutch master cylinder is located just behind the clutch pedal and is used in conjunction with the clutch pedal to push hydraulic fluid from the fluid reservoir to the clutch slave which then actuates the clutch. The clutch slave cylinder is a common failure item in any BMW and it is recommended to replace these every time you do a clutch job to prevent being left stranded on the side of the road.
Rubber Clutch Line #10
In most BMWs, the slave cylinder will have a hard-line running from it through the cabin to the transmission tunnel. At the end of this line, you will find a rubber line. This line allows the clutch system to move with the engine and prevent cracking of the hard lines. However, being that the line is rubber it is prone to failure. Over time the rubber can break down and become brittle. This can lead to leaks or bursts if not replaced in a timely manner. Upgrading to a stainless steel brake line will prevent this ever happening and give the user a more precise clutch feel.
Clutch Delay Valve CDV #15
In the early 90s, BMW began installing a CDV or Clutch Delay Valve at the end of the rubber soft lines. These valves restricted fluid flow from the clutch slave to the master cylinder. This slowed the engagement of the clutch and although originally intended to help prolong the life of the clutch, only made the clutch feel more numb. Installing a stainless steel braided line will allow you to removed the CDV and give you the most consistent clutch feel possible.
Clutch Slave Cylinder #18
The slave cylinder is the end of the hydraulic clutch system. This is what the master cylinder controls. When you push your clutch pedal in the hydraulic system moves fluid to the slave and pushes a rod into the pressure plate disengaging the clutch and allowing you to shift gears. These items like the master cylinder can fail and leave you stranded. It's always a good idea to replace them when performing a clutch job.
Clutch and Associated Components
Clutch Disk #2
The clutch disk is like a giant circular brake pad that clamps down on the flywheel. This is what allows the engine to transfer power to the wheel. Clutches are made in a few different styles. Each is listed below with a brief description
- Sprung Disk with Solid Friction Plate: These are the most common types of clutches as they are used in almost all OEM configurations. These offer easy driveability and comfortable clutch travel and feel.
- Sprung Disk with Pucked Friction Material: Most commonly found in entry-level performance clutches. They can come in a 4, 6, or 8 puck configuration. The more pucks the more aggressive the engagement. These are great upgrades over a stock clutch and will still retain decent driveability.
- Unsprung Disk With Pucked Friction Material: Common in a lot of high-performance street and entry race applications, unsprung clutches provide great feedback and can handle a lot of power. This however comes at the cost of driveability. Engagement can be very aggressive and can make street driving difficult.
- Unsprung Disk with Solid Friction Plate: This is the most aggressive single disk clutch offering available. These types of clutches are meant only for dedicated racecars and are not meant to be driven on the street. They have very aggressive engagement and aren't designed to be slipped like other clutches.
- Multi-Disk Clutch: A multi-disk clutch is used in ultra-high horsepower configurations and like the Unsprung above is not easy to street drive. These tend to be extremely expensive and are only meant to be used on a racetrack.
Pressure Plate #1
The pressure plate is what is used to disengage the clutch from the flywheel. It has teeth that the clutch slave applies pressure to. This works to release the clutch from the flywheel and allow you to shift gears. Pressure plates can have different clamping forces. Then higher the clamping force the stiffer the clutch pedal will feel as it will require more effort to release the clutch from the flywheel. More clamping force however means more effectiveness in the clutch and its friction material.
Throw Out Bearing #3
The throwout bearing is used to allow the pressure plate to spin while the clutch is engaged by the driver. It is what allows the pressure plate teeth to be engaged by the rod on the slave cylinder.
Clutch Fork #5
The Clutch for is what the throwout bearing mounts to. It is used as a lever for the clutch slave to press. This in turn applies pressure to the throwout bearing and the pressure plate. This then releases the clutch from the flywheel.
Pivot Pin #6
The pivot pin in its stock form is made of plastic. It is what the clutch fork rests on and can fail over time as it gets brittle. In general it is common practice to replace these with a brass or aluminum pin to prevent failure.
Flywheels are like giant brake rotors. They give the clutch a surface to grab on to. There are two types of flywheels. Most common in newer BMWs is a dual-mass flywheel. These are very heavy and use a set of springs in between the main disk that the friction surface to allow dampening this is intended to give the user a clean and comfortable clutch engagement. Most car enthusiasts feel this makes the clutch imprecise and numb. Some older BMWs came with single mass flywheels. These are ideal for the enthusiast as they offer direct clutch engagement and weigh significantly less taking some load off of the engine. Single mass flywheel conversions are available for almost all BMW transmissions that did not originally come with them. These are an awesome upgrade for any enthusiast.
BMW Shifters and Shift Linkage
Unlike some transmissions BMWs have external shift linkage. This means that there are items outside of the transmission that connects the transmission to the shifter. These items tend to degrade over time and tend to need replacing. Below we will go over each one of these items and what they do.
Shifter Rod #6
The shifter rod is that thing that sticks up inside the car that you use to shift gears. This is what is used to create your shifters throw length. BMWs have a pivot ball and a pick-up point under it. This connects the shifter rod to the chassis and to the shift linkage. Changing the length of the lower portion of the shifter rod is what creates a shorter shift.
Shifter Cup #7
A shifter cup is what holds the pivot ball on the shifter rod to the shifter carrier. These are made of plastic on all updated shift linkage BMWs and are known to fail. When the do shifting can become very difficult as the shifter rod will be able to move up and down. When installing a new shifter or doing shifter maintenance it is essential to replace these.
Shifter Carrier #1
The shifter carrier is what gives the shifter rigidity and what holds it in place inside the car. The shifter cup installs into the shifter carrier which then connects to the body of the car through a bushing. These don't often have failures. But older model BMWs use a sloppy sheet metal style shifter carrier that is less than ideal for an enthusiast.
Selector Rod #9
The selector rod is one of the most well known and modified pieces of any BMWs shifting system. The factory single shear selector rod or SSSR only connects the shifter rod to the transmission using one rod on one side of the shifter and transmission. This can cause shifters to feel loose or floppy. It is very common for enthusiasts to replace these with a DSSR or dual shear selector rod. These connect to the shifter rod and transmission on both sides and help tighten up the shifter and make shifting more precise.
Oval Shifter Bushings #2
The oval shifter bushings connect the shifter carrier to the transmission and are what help give the shifter carrier its side to side rigidity. Over time these can wear down and create a play in the shifter. Replacing them with polyurethane bushings will restore shifter feel and prevent them from having to be replaced again.
Shifter Carrier Bushing #5
The shifter carrier bushing is located at the back of the shift carrier. It is where the shifter carrier connects to the chassis. These are originally made from rubber and over time will degrade allowing movement in the shifter. Replacing this item with a polyurethane variant will help secure the shifter carrier and give a very rigid and consistent shifter feel.
Selector Rod Joint #12
The selector rod joint is what connects the selector rod to the transmission. Although these aren't too common of a failure item it is good practice to replace them when replacing shifter components.