Stihl MM55 Gearbox Problems- Common Problems With Symptoms & Easy Solutions

by Jason Ryffe
Reading time: 13 min Prefer to listen?

What is the common Stihl MM55 gearbox problem? Whining noise is the most common problem of the Stihl mm55 gearbox. Every user will agree with that.

The noise can be induced by many reasons like excessive load, temperature effect as well as faulty design.

Like the whining noise issue, there are many other problems with the Stihl MM55 gearbox that you may face at the time of using the Stihl MM55.

In this context, we will focus on the 5 irritating problems of Stihl MM55. You will also know the symptoms of the problems to identify the exact issue within a short time.

Therefore to get the complete guidelines on mm55 gearbox difficulties read this informative article till the end.

Stihl MM55 Gearbox Problems

a quick overview for-stihl-mm55-gearbox-problems
A Quick Overview for Stihl Mm55 Gearbox Problems

Problems with the Stihl MM55 gearbox are very familiar for those who use the Yard Boss for their yard cleaning. 

Here we will show a table of Stihl MM55 troubleshooting where we will introduce the 5 most complicated issues of the Stihl MM55 gearbox with short solutions.

After the table, we will elaborate on the symptoms and the reasons for the issues. So! Stay tuned.

Major Or Minor ProblemsSolution
Transmission fluid leakageTighten the fuel tank or replace the damaged tank  
Slow responseUse sufficient and contamination-free fuel  
Whining noiseReduce the load  
Burning smellAvoid shortage of fuel or avoid using an old machine  
Slipping gearSolve solenoid or clutch or torque issues and fuel properly  

1. Transmission Fluid Leakage

Transmission fluid leakage is a common problem for any other tools like the Stihl MM55 gearbox. The transmission fluid comes out from the tank or the tube.


  1. Grinding gears
  2. Odd sounds come out
  3. Discontinue accelerator
  4. Strange vibration
  5. Wet and soggy conditions

If you observe these symptoms while running the Stihl MM55, you may be sure that your Stihl MM55 transmission fluid is leaking.


There are some reasons behind the transmission fluid leakage case. Here are the most widespread reasons.

  1. Damaged Gasket: If the transmission gasket is damaged or cracked, fluid will be leaked.
  2. Damage Torque Converter: Torque is related to gear, to increase speed; you need to decree the torque. If the torque converter is damaged, the transmission fluid will leak.
  3. Cracked Fluid Line: If the transmission fluid pipe is damaged or broken down, fluid will seep.
  4. Loosen Knob: The loose knob allows the transmission fluid which is the basic reason for most of the time we face the issue.


We will suggest tightening the knob and replacing the damaged gasket, transmission tubes, and torque converter.

2. Slow Response

Slow response is a secondary problem of the Stihl mm55 gearbox. When the Stihl MM55 gear head cannot function properly, a slow response occurs.


  1. Cannot increase speed instantly.
  2. Troubles during acceleration.
  3. Takes time to gear shifting.


The reason is very clear. We can understand the fuel problem is creating the slow response problem of the Stihl MM55 gearbox.

  1. Using Contaminant Fuel: If you are using fuel for your Stihl MM55, which is not pure and filtered, then you will face the slow response problem.
  2. Using Insufficient Fuel: It is the main reason to slow down your gear trimming. When your tank does not have sufficient fuel, gear response will slow down.


Use a mixture of gasoline and Stihl two-stroke oil for the fuel of Stihl MM55. The gasoline should not contain more than 10% ethanol.

And always keep in mind to use an adequate amount of fuel. 

Also Read: Stihl ms 661 problems with Symptoms, Reasons, and Solution

3. Whining noise

This is the most common use for the users. Often people complain about the whining noise of the Stihl MM55 gearbox.


  1. Harsh or odd sounds coming from the machine. 
  2. Strange vibrations are common.
  3. The crackly sound came during shifting the gear.


There are some manufacturing reasons for the whining noise issue. Such as;

  1. Faulty Design: Sometimes the design of the Stihl MM55 gearbox is responsible for the whining sounds.
  2. Excessive Load: If you force the Stihl MM55 to deliver an excessive load that it cannot pursue, the noise can come out.
  3. Low Fuel Level: The noise also can come if the fuel level is very low. It indicates you should refill the fuel.


Make sure you are buying the correct one which is not faulty. And resist giving too much load that it cannot take. 

4. Burning Smell

A burning smell is a problem with the Stihl MM55 gearbox, which is a vital reason for a damaged fuel gearbox.


  1. An unpleasant smell comes out when you run the Stihl MM55.
  2. You can observe smoke over the machine at running time.
  3. Fuel leakage is a symptom of releasing a burning smell.
  4. The poor physical condition of the gearbox.


A burning smell is related to the fuel and the physical condition of the gearbox that you are using.

  1. Using Inadequate Oil: When you run the Stihl MM55 with inadequate oil, incomplete compassion occurs which generates a burning smell issue.
  2. Using Contaminated Oil: Like the amount, the quality of the fuel also matters. If the oil is not pure and burned to generate energy, then the burning smell will appear.
  3. Bad Physical Condition Of The Gearbox: A burning smell is generally generated with the old gearbox. If you are using a gearbox that is older than 5 years, emitting a burning smell is very common.


Stop using impure and insufficient fuel. And you should replace the Stihl MM55 if you are using it for more than 5 years.

5. Slipping Gear

Slipping gear refers to facing problems while shifting the gear. You cannot shift from one gear to another smoothly.


  1. Stihl MM55 tines won’t turn.
  2. Troubling during a gear change.
  3. You can hear an odd sound when you want to change the gear.
  4. Unsatisfying experience during shifting gear.


The common reasons for slipping gear include;

  • Fuel Issue: Using inadequate and inappropriate fuel is also responsible for the slipping gear problem. When the gearbox does not get proper fuel, it is obvious that it cannot function correctly.
  • Damage Gearbox: If the gearbox is damaged or cracked, you will encounter problems shifting from one gear to another. 


According to the gearbox repairers, “You should use the mixture of gasoline with Stihl 2-stroke oil in the ratio of 50:1” for your Stihl MM55.

And immediately replace the broken or damaged gearbox.

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Frequently Asked Questions (FAQs)

What fuel does Stihl MM55 use?

Stihl MM55 uses a mixture of gasoline and the Stihl two-stroke oil as the fuel.

How do you start a Stihl MM55?

After filling up the fuel, you have to depress the throttle trigger lockout button first, then only the throttle trigger controller.u003cbru003eAnd hold them down until you can shift to the start direction. Now you are ready to use the Stihl MM55. 

What is the oil ratio for a Stihl Tiller?

The oil ratio for a Stihl tiller is 50:1 that indicates if you use gasoline 50%, then you can mix 1% Stihl two-stroke oil to produce the fuel of the Stihl tiller.


Before using any tool, we should know about the related problems that we can face at the time of use.

There are two effective reasons behind this fact. One is we can avoid the problems, and the other is that if we go through the problem, we can get relief easily.

Hence the article on the Stihl MM55 gearbox problem is important content for those who use the Stihl mm55.

After getting the information, we hope you will easily identify your problems, and fixing time and efforts will be reduced.

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