Volkswagen 01M transmission
The Volkswagen 01M transmission is an electronic/ hydraulic four-speed automatic transmission, developed in-house by Volkswagen, and deployed in Cabrio, Jetta, Golf, GTI, New Beetle manufactured between 1995 through 2005, and transverse engine Passats manufactured between 1995 through 1997.
It is an electronically controlled transmission with a lockup torque converter, using planetary gears, clutch packs, and a gear-driven final drive with an open-differential. There is no chain inside this transmission. It does not have provision for a dipstick. VW determined that a dipstick and fill might invite owners to introduce incorrect or inferior fluid. More information on design and function can be found in VW's publications, mechanic's Self Study Programs SSP112 for early versions for the 92-94 096 (predecessor to the O1M), or SSP172 for 01M from 95-06. Better to find one in your language on ebay or an online pdf file.
Some areas of failure on this transmission include damage to plastic internals due to fluid over-temperature conditions, internal fluid pressure leaks from torn piston diaphragms, worn piston bores for solenoids in aluminum valve body, and the resulting worn clutches and bands. Occasionally, the plastic speedometer drive gear will break and fall off of the differential carrier and the speedometer will stop working. To repair this, the transmission must be removed and the differential disassembled far enough to replace the plastic gear. With age, the resistance in the wiring and/or electrical terminals between the valve body and transmission controller can increase. The additional resistance may prevent the computer from reading the faint pulses from the transmission speed sensors. Any missing sensor signal causes the transmission to go to "fail safe" mode. This mode keeps the transmission in third gear and the gear indicator in the instrument panel indicates all gears are selected simultaneously.
If replacing this transmission with a new or used transmission, pay special attention to the transmission code. The code is a three character code stamped in a pad just above the starter flange. This transmission was available in several gear ratios for different engines and vehicles, so it's important to get a transmission with the same code or another code KNOWN to be the same gear ratios. If the gear ratios are not the same the transmission controller will assume the transmission is slipping and go into fail safe mode. To find which transmission codes share gear ratios with your transmission, use this link zelek.com
The 01M transmission is a specialized transmission used only on Volkswagen vehicles. As a result, most local transmission shops or national chains won't have specific training, knowledge and equipment to test and re-machine vital parts of this transmission. This may result in several teardowns under warranty to get an acceptable result, if possible at all.
There are specialists who rebuild many 01M transmissions and can stand behind their work. Two such regional rebuilders are European Transmissions located North of Atlanta, GA, and German Transaxle located in Bend, OR. Both are capable shops with excellent reputations. Always check with The Better Business Bureau to be sure a company is maintaining their reputation. European Transmissions in Georgia also provides parts for rebuilders and limited tech support for experienced rebuilders.
Checking / Filling Oil Levels
The correct fluid is a synthetic mineral oil, such as Pentosin ATF-1 or Volkswagen G 052 162 A2. The transmission fluid is checked from underneath the vehicle while running and must be completed before the transmission warms up beyond 85 degrees Fahrenheit. Once running, the fill screw on the bottom of the transmission oil pan is removed with a 5mm allen wrench. Some fluid will drip out whether oil level is full or low. There is a plastic stack in the hole, similar to a chimney, which keeps all the fluid from running out. This stack maintains the proper level at the proper temperature. The stack can be removed with a 6mm allen wrench to drain all the fluid from the pan, if so desired. If a steady stream of fluid does not run out the bottom hole when the temperature of the transmission is very near 85 degr F, fill the transmission with specified fluid through the filler neck located on the front of the transmission just above the oil pan. Fill until fluid is observed running out the hole in the bottom. Install drain and fill plugs and the transmission is filled.
This transmission has a separate oil for the differential in the transmission, so there are two fluid levels to check. The differential fluid is checked by unscrewing the speed sensor gear assembly and use it as a dipstick. The speed sensor gear assembly is located on top of the transmission just above the right inner CV joint. Differential is emptied by removing the steel plate on the rear of the transmission or by vacuum extraction through the speed sensor hole. Vacuum extraction is the more attractive option since a paper gasket seals the steel cover and access is very difficult. Filling is through the speed sensor hole. Differential oil capacity is about 1 liter. An acceptable differential oil is Redline synthetic MT-90 75W90 gear oil. Be very careful not to introduce sand or dust into the differential, as the differential has no way to filter its' oil.
The shifting of this transmission is controlled by the Transmission Control Module, or TCM. This computer uses "fuzzy logic" to learn the driving habits of the driver in order to anticipate what to do next.
If two or more drivers with different driving styles have been driving the car, the TCM may become "confused" and start acting goofy. Such goofy behavior may manifest in hard shifting, slipping, trouble getting in gear at idle, etc.
A quick fix is to reset the "fuzzy logic" by performing the following: Sitting in the driver's seat turn the ignition on without starting the car. Immediately put the accelerator to the floor. Count to five seconds. Release the pedal. Turn the key off then immediately start the engine.
If your problem is from a confused TCM, this will solve the problem. This will not reset trouble codes in the computer. That must be done with the proper OBDII scan tool such as http://ross-tech.com or the VAG 5052 tool at the VW dealer.
The transmission computer is located under the back seat on Volkswagen Golf Mk3 /Jetta/Passat models, under the right side dashboard cover on Volkswagen New Beetle models, and in the wiper area plenum on other Volkswagen Golf Mk4/Jetta models.
Before the 01M transmission, VW produced the 096 four-speed for Mk3 Golf/Jetta cars from 1992-1994. These cars will have a SPORT/ECONOMY switch near the shifter or on the dashboard to alter the shift points. Some of the 096 parts were held over for the 01M transmission, such as oil filter, oil pan, filler tube, gaskets, speedometer gears, skid plate, etc. These transmissions have different torque converters and many other internal parts that are not interchangeable.
The 01M production ended with the last of the Mk4 body style Golf in 2006. It was succeeded by an Aisin designed 5-speed automatic (09A) Tiptronic, and later 6-speed automatic (09G) Tiptronic transmission in New Beetle Convertibles, as well as a Direct-Shift Gearbox (DSG) based dual clutch transmission in recent models of the above cars. The DSG does not have a torque converter, and is more akin to a pair of manual transmissions within a single housing.