M32 / M20 gearbox - where is it and what to do with it?

The M32 marking is well known to users of Opel and Italian cars. This is the 6-speed manual transmission that has fallen from the sky in many workshops. There are even sites dedicated only to its repair. Widely recognized as one of the most problematic gearboxes, it can last a long time. Check what breaks, in which models and how to protect yourself from breakage.  

In fact, it is difficult to talk about the failure of this box, rather, about low durability. Failure is the result early bearing wear, which increases the temperature inside the gearboxby destroying interacting components, including mods.

How to recognize problems?

The noise of the gearbox should attract the attention of the user or mechanic. The next and by far the most important symptom is shift lever movement while driving. Sometimes it shakes, and sometimes it switches when the engine load changes. This indicates the appearance of backlash on the transmission shafts. This is the last call for a speedy repair. It will get worse later. However, before disassembling the gearbox, it is worth checking for damage to the engine and gearbox mounts - the symptoms are similar.

More serious damage occurs when the first symptoms described above are ignored. Damage to the gearbox housing (very common) requires replacement of the housing. In extreme cases, gears and hubs wear out, as well as the differential and shift forks.

It is also worth mentioning that The M32 transmission has a smaller counterpart called the M20. The gearbox was used on city models - Corsa, MiTo and Punto - and was combined with a 1.3 MultiJet/CDTi diesel engine. All of the above applies to the M20 transmission.

Which cars have M32 and M20 transmissions?

Below I list all car models in which you can find the M32 or M20 gearbox. To recognize it, just check how many gears it has - always 6, with the exception of 1,0 liter engines. The Vectra and Signum models are also an exception where the F40 transmission was used interchangeably.

• Adam Opel
• Opel Corsa D
• Opel Corsa E
• Opel Meriva A
• Opel Meriva B
• Opel Astra H
• Opel Astra J
• Opel Astra K
• Opel Mokka
• Opel Zafira B
• Opel Zafira Tourer
• Opel Waterfall
• Opel Vectra C/Signum - only in 1.9 CDTI and 2.2 Ecotec
• Opel Insignia
• Fiat Bravo II
• Fiat Croma II
• Fiat Grande Punto (M20 only)
• Alfa Romeo 159
• Alfa Romeo MiTo
• Alfa Romeo Giulietta
• Lyancha Delta III

You have an M32/M20 chest - what should you do?

Some car owners, having learned about the presence of such a gearbox in their car, begin to panic. No reason. If the transmission is working - i.e. there are no symptoms described above - do not be alarmed. However, I advise you to act.

With a high degree of probability, no one has changed the oil in the box yet. For the first such exchange, it is worth going to a site that is well versed in the topic. There's a mechanic not only there choose the right oil but also pours the right amount. Unfortunately, according to the recommendations of the Opel service, the amount of oil indicated at the factory is too small, and even worse, the manufacturer does not recommend replacing it. According to experts, even factory oil is not suitable for this transmission. Therefore, accelerated wear of the bearings in the gearbox occurs.

The fact that the problem is mainly related to low oil levels and the lack of replacement is evidenced by the following experience of mechanics:

• in tires it is not recommended to change the oil for decades, in other brands it is recommended
• in other brands, the problem with bearing wear is not as common as with tires
• in 2012 the transmission was improved by adding, among others, oil lines for bearing lubrication

If we suspect bearing wear, it's not worth the risk. You have to replace the bearings - every single one. It costs about 3000 PLN, depending on the model. Such prevention is combined with draining the old oil and replacing it with a new, serviceable one, as well as replacing it every 40-60 thousand. km, gives confidence that The M32/M20 gearbox will last a long time. Because, contrary to appearances, the transmission itself is not so faulty, only the service is inappropriate.

How else can you influence the durability of gear? Professionals recommend smooth gear shifting. In addition, on vehicles with more powerful diesel engines (torque above 300 Nm), it is not recommended to accelerate from low revs, with the gas pedal fully depressed, in 5 and 6 gears.