Automatic transmission judders when changing gear: identify the causes and take the right action
When the automatic transmission judders during gear changes and shifting becomes increasingly sluggish, there can be various underlying causes. The most common is degraded transmission oil with depleted additives and reduced viscosity. Less frequently, the cause lies with the torque converter, mechatronics unit or worn clutches. Automatic transmission oil is often the last thing people think of. Yet a professional oil change can resolve many symptoms at an early stage. If maintenance is delayed for too long, costly transmission damage may be the result.
Why does the automatic transmission judder when changing gear?
The automatic transmission judders during gear changes when power is no longer transferred smoothly and consistently between gears. The most common cause is a change in the friction characteristics of the clutches due to degraded oil, or deposits that have accumulated in the oil channels of the mechatronics unit. These deposits can prevent the correct oil pressure from reaching the individual clutch plates.
Less commonly, the cause is a fault with the torque converter, mechatronics unit or valves. However, if servicing intervals are not observed, mechanical components can also suffer considerable damage. The key is to service the transmission at an early stage and at the prescribed intervals to prevent juddering during gear changes in the first place.
Typical symptoms at a glance
Not all juddering is the same. Depending on the driving situation, the behaviour can indicate different underlying causes. The following symptoms are among those most frequently encountered in practice.
Automatic transmission judders when pulling away
Juddering as soon as the vehicle pulls away often indicates that the friction plates are slipping. There can be various reasons for this, including worn plates, insufficient hydraulic pressure, or restricted oil flow caused by blocked channels or faulty solenoid valves. Contaminated oil that has lost its original properties can also prevent the clutch from engaging smoothly.
Automatic transmission changes gear harshly
Harsh, noticeable gear changes occur when hydraulic pressure or shift points are no longer controlled correctly. Possible causes include worn solenoid valves, incorrect adaptation values or degraded oil. If maintenance has been neglected, clutch wear debris may also clog or restrict the oil channels throughout the mechatronics unit. As a result, the correct pressure is no longer supplied to the individual clutch packs.
Automatic transmission changes gear with a delay
If the transmission changes gear with a delay or appears to ‘hunt for’ the right gear, the cause is often low oil pressure, a blocked hydraulic filter or incorrect adaptation values in the mechatronics unit. Many modern automatic transmissions automatically adapt their shifting behaviour to the driver’s driving style. If the driver tends to drive in a very sporty manner, for example, the engine may rev to higher speeds before the actual gear change takes place. In such cases, resetting the driver adaptation values may be worth considering.
What causes the automatic transmission to judder?
Juddering in an automatic transmission can have several possible causes. The main ones range from degraded transmission oil to faults with the torque converter and mechatronics unit, as explained in more detail below.
What role does degraded transmission oil play?
Degraded transmission oil is the most common cause and, at the same time, one of the easiest to address. The background is simple: even today, many manufacturers promote so-called ‘filled for life’ and use terms such as ‘maintenance-free’. However, no such condition exists for vehicle components subjected to mechanical and thermal loads. Any component expected to operate reliably over the long term requires regular, professional servicing. This includes the automatic transmission oil: it performs several important functions that can deteriorate over time without proper maintenance.
Simply checking the fluid level and looking for leaks, as many manufacturers recommend, is not sufficient. As the oil ages, its viscosity decreases and its additives become depleted. When the system’s specified friction characteristics deteriorate, the clutches can slip even when they are still mechanically sound. As a result, the oil can no longer perform its functions reliably. This condition cannot be identified by checking the fluid level alone.
Why are wet clutches particularly affected?
Changing the transmission oil is particularly important in automatic transmissions with wet clutches. The friction material operates immersed in the transmission oil, which can accumulate wear debris over time. The hydraulic filter captures some of this debris and helps prevent deposits from forming, but only for a limited period. Even the best filter medium will eventually become clogged. This can affect surrounding components, including the gear tooth flanks and running surfaces. Deposits can also accumulate in the oil channels, preventing the correct oil pressure from reaching the individual clutch packs.
Torque converter and torque converter lock-up clutch
Juddering at a constant speed or under part-load conditions often indicates a worn torque converter lock-up clutch. Its purpose is to establish a direct mechanical connection, but as it wears, it can slip, causing vibrations or juddering. A typical sign of a faulty torque converter lock-up clutch is slight engine speed fluctuation when driving at a constant speed under part load.
Mechatronics, solenoid valves and adaptation values
The control unit uses the mechatronics components to control shift points and regulate oil pressure. Worn solenoid valves or incorrect adaptation values can lead to harsh or delayed gear changes. In many cases, the adaptation values can be reset and the system can relearn them following an oil change. However, not all manufacturers require adaptation values to be reset during a routine oil change. Many modern transmissions automatically adapt their clutch fill times and pressures over the service life of the transmission to maintain smooth gear changes despite wear. Unless a reset is explicitly specified, an extended test drive should initially be carried out after the oil change.
How dangerous is it to continue driving?
Persistent juddering should not be ignored. With every additional kilometre, more wear debris enters the transmission oil, accelerating wear on clutches, gears and the mechatronics unit. What could initially have been resolved with a relatively inexpensive oil service can develop into a costly transmission overhaul.
At this stage, an oil change or transmission flush is necessary to help prevent transmission damage. However, once mechanical components have been damaged, a simple oil change or flush will no longer be sufficient to resolve the problem fully.
What solutions are available?
Depending on the cause and condition of the transmission, various measures may be appropriate, ranging from routine maintenance to repairs. The following three options are the most relevant in workshop practice.
Transmission oil change
During a conventional oil change, the oil is drained through the drain plug and replaced, usually together with the filter and seal. In automatic transmissions with a torque converter, some of the old oil remains in the converter.
Transmission flushing
A transmission flush replaces almost all the oil, including the old oil and residues in the torque converter. Although it is more involved, it can provide a more thorough solution when the oil is heavily contaminated.
Repair or overhaul
If the clutches, torque converter or mechatronics unit have already been damaged, an oil change will no longer resolve the problem. Repairs or an overhaul at a specialist workshop will then be required.
MEYLE recommendation: Change the transmission oil every 80,000–120,000 kilometres, or earlier if the vehicle manufacturer’s specifications call for a shorter interval.
Why do the right parts matter?
Precisely fitting components are essential for a reliably performing drivetrain over the long term. MEYLE parts – from drive shafts and flex discs to the practical MEYLE KITs – are manufactured with an OE-compliant fit in full accordance with MEYLE specifications and fit just like the original in every detail.
Frequently asked questions (FAQ)
Why does my automatic transmission judder when changing gear?
The most common cause is degraded transmission oil with altered friction characteristics. Faults involving the torque converter or mechatronics unit are less common.
Can an oil change resolve juddering?
Yes, if the problem is caused by degraded transmission oil. Mechanical damage will require repairs.
How often should automatic transmission oil be changed?
MEYLE recommends changing it every 80,000–120,000 kilometres, or earlier if the vehicle manufacturer’s specifications require a shorter interval.
Transmission oil change or flush: which is better?
An oil change is sufficient when the oil has deteriorated moderately. A flush provides a more thorough solution when the oil is heavily contaminated.
Is it dangerous to continue driving?
Yes. Persistent juddering can lead to consequential damage. Early diagnosis is advisable